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-rw-r--r--tools/plink/sshbn.c3919
1 files changed, 2001 insertions, 1918 deletions
diff --git a/tools/plink/sshbn.c b/tools/plink/sshbn.c
index 51cecdf2b..a5e0552ff 100644
--- a/tools/plink/sshbn.c
+++ b/tools/plink/sshbn.c
@@ -1,1918 +1,2001 @@
-/*
- * Bignum routines for RSA and DH and stuff.
- */
-
-#include <stdio.h>
-#include <assert.h>
-#include <stdlib.h>
-#include <string.h>
-
-#include "misc.h"
-
-/*
- * Usage notes:
- * * Do not call the DIVMOD_WORD macro with expressions such as array
- * subscripts, as some implementations object to this (see below).
- * * Note that none of the division methods below will cope if the
- * quotient won't fit into BIGNUM_INT_BITS. Callers should be careful
- * to avoid this case.
- * If this condition occurs, in the case of the x86 DIV instruction,
- * an overflow exception will occur, which (according to a correspondent)
- * will manifest on Windows as something like
- * 0xC0000095: Integer overflow
- * The C variant won't give the right answer, either.
- */
-
-#if defined __GNUC__ && defined __i386__
-typedef unsigned long BignumInt;
-typedef unsigned long long BignumDblInt;
-#define BIGNUM_INT_MASK 0xFFFFFFFFUL
-#define BIGNUM_TOP_BIT 0x80000000UL
-#define BIGNUM_INT_BITS 32
-#define MUL_WORD(w1, w2) ((BignumDblInt)w1 * w2)
-#define DIVMOD_WORD(q, r, hi, lo, w) \
- __asm__("div %2" : \
- "=d" (r), "=a" (q) : \
- "r" (w), "d" (hi), "a" (lo))
-#elif defined _MSC_VER && defined _M_IX86
-typedef unsigned __int32 BignumInt;
-typedef unsigned __int64 BignumDblInt;
-#define BIGNUM_INT_MASK 0xFFFFFFFFUL
-#define BIGNUM_TOP_BIT 0x80000000UL
-#define BIGNUM_INT_BITS 32
-#define MUL_WORD(w1, w2) ((BignumDblInt)w1 * w2)
-/* Note: MASM interprets array subscripts in the macro arguments as
- * assembler syntax, which gives the wrong answer. Don't supply them.
- * <http://msdn2.microsoft.com/en-us/library/bf1dw62z.aspx> */
-#define DIVMOD_WORD(q, r, hi, lo, w) do { \
- __asm mov edx, hi \
- __asm mov eax, lo \
- __asm div w \
- __asm mov r, edx \
- __asm mov q, eax \
-} while(0)
-#elif defined _LP64
-/* 64-bit architectures can do 32x32->64 chunks at a time */
-typedef unsigned int BignumInt;
-typedef unsigned long BignumDblInt;
-#define BIGNUM_INT_MASK 0xFFFFFFFFU
-#define BIGNUM_TOP_BIT 0x80000000U
-#define BIGNUM_INT_BITS 32
-#define MUL_WORD(w1, w2) ((BignumDblInt)w1 * w2)
-#define DIVMOD_WORD(q, r, hi, lo, w) do { \
- BignumDblInt n = (((BignumDblInt)hi) << BIGNUM_INT_BITS) | lo; \
- q = n / w; \
- r = n % w; \
-} while (0)
-#elif defined _LLP64
-/* 64-bit architectures in which unsigned long is 32 bits, not 64 */
-typedef unsigned long BignumInt;
-typedef unsigned long long BignumDblInt;
-#define BIGNUM_INT_MASK 0xFFFFFFFFUL
-#define BIGNUM_TOP_BIT 0x80000000UL
-#define BIGNUM_INT_BITS 32
-#define MUL_WORD(w1, w2) ((BignumDblInt)w1 * w2)
-#define DIVMOD_WORD(q, r, hi, lo, w) do { \
- BignumDblInt n = (((BignumDblInt)hi) << BIGNUM_INT_BITS) | lo; \
- q = n / w; \
- r = n % w; \
-} while (0)
-#else
-/* Fallback for all other cases */
-typedef unsigned short BignumInt;
-typedef unsigned long BignumDblInt;
-#define BIGNUM_INT_MASK 0xFFFFU
-#define BIGNUM_TOP_BIT 0x8000U
-#define BIGNUM_INT_BITS 16
-#define MUL_WORD(w1, w2) ((BignumDblInt)w1 * w2)
-#define DIVMOD_WORD(q, r, hi, lo, w) do { \
- BignumDblInt n = (((BignumDblInt)hi) << BIGNUM_INT_BITS) | lo; \
- q = n / w; \
- r = n % w; \
-} while (0)
-#endif
-
-#define BIGNUM_INT_BYTES (BIGNUM_INT_BITS / 8)
-
-#define BIGNUM_INTERNAL
-typedef BignumInt *Bignum;
-
-#include "ssh.h"
-
-BignumInt bnZero[1] = { 0 };
-BignumInt bnOne[2] = { 1, 1 };
-
-/*
- * The Bignum format is an array of `BignumInt'. The first
- * element of the array counts the remaining elements. The
- * remaining elements express the actual number, base 2^BIGNUM_INT_BITS, _least_
- * significant digit first. (So it's trivial to extract the bit
- * with value 2^n for any n.)
- *
- * All Bignums in this module are positive. Negative numbers must
- * be dealt with outside it.
- *
- * INVARIANT: the most significant word of any Bignum must be
- * nonzero.
- */
-
-Bignum Zero = bnZero, One = bnOne;
-
-static Bignum newbn(int length)
-{
- Bignum b = snewn(length + 1, BignumInt);
- if (!b)
- abort(); /* FIXME */
- memset(b, 0, (length + 1) * sizeof(*b));
- b[0] = length;
- return b;
-}
-
-void bn_restore_invariant(Bignum b)
-{
- while (b[0] > 1 && b[b[0]] == 0)
- b[0]--;
-}
-
-Bignum copybn(Bignum orig)
-{
- Bignum b = snewn(orig[0] + 1, BignumInt);
- if (!b)
- abort(); /* FIXME */
- memcpy(b, orig, (orig[0] + 1) * sizeof(*b));
- return b;
-}
-
-void freebn(Bignum b)
-{
- /*
- * Burn the evidence, just in case.
- */
- memset(b, 0, sizeof(b[0]) * (b[0] + 1));
- sfree(b);
-}
-
-Bignum bn_power_2(int n)
-{
- Bignum ret = newbn(n / BIGNUM_INT_BITS + 1);
- bignum_set_bit(ret, n, 1);
- return ret;
-}
-
-/*
- * Internal addition. Sets c = a - b, where 'a', 'b' and 'c' are all
- * big-endian arrays of 'len' BignumInts. Returns a BignumInt carried
- * off the top.
- */
-static BignumInt internal_add(const BignumInt *a, const BignumInt *b,
- BignumInt *c, int len)
-{
- int i;
- BignumDblInt carry = 0;
-
- for (i = len-1; i >= 0; i--) {
- carry += (BignumDblInt)a[i] + b[i];
- c[i] = (BignumInt)carry;
- carry >>= BIGNUM_INT_BITS;
- }
-
- return (BignumInt)carry;
-}
-
-/*
- * Internal subtraction. Sets c = a - b, where 'a', 'b' and 'c' are
- * all big-endian arrays of 'len' BignumInts. Any borrow from the top
- * is ignored.
- */
-static void internal_sub(const BignumInt *a, const BignumInt *b,
- BignumInt *c, int len)
-{
- int i;
- BignumDblInt carry = 1;
-
- for (i = len-1; i >= 0; i--) {
- carry += (BignumDblInt)a[i] + (b[i] ^ BIGNUM_INT_MASK);
- c[i] = (BignumInt)carry;
- carry >>= BIGNUM_INT_BITS;
- }
-}
-
-/*
- * Compute c = a * b.
- * Input is in the first len words of a and b.
- * Result is returned in the first 2*len words of c.
- *
- * 'scratch' must point to an array of BignumInt of size at least
- * mul_compute_scratch(len). (This covers the needs of internal_mul
- * and all its recursive calls to itself.)
- */
-#define KARATSUBA_THRESHOLD 50
-static int mul_compute_scratch(int len)
-{
- int ret = 0;
- while (len > KARATSUBA_THRESHOLD) {
- int toplen = len/2, botlen = len - toplen; /* botlen is the bigger */
- int midlen = botlen + 1;
- ret += 4*midlen;
- len = midlen;
- }
- return ret;
-}
-static void internal_mul(const BignumInt *a, const BignumInt *b,
- BignumInt *c, int len, BignumInt *scratch)
-{
- if (len > KARATSUBA_THRESHOLD) {
- int i;
-
- /*
- * Karatsuba divide-and-conquer algorithm. Cut each input in
- * half, so that it's expressed as two big 'digits' in a giant
- * base D:
- *
- * a = a_1 D + a_0
- * b = b_1 D + b_0
- *
- * Then the product is of course
- *
- * ab = a_1 b_1 D^2 + (a_1 b_0 + a_0 b_1) D + a_0 b_0
- *
- * and we compute the three coefficients by recursively
- * calling ourself to do half-length multiplications.
- *
- * The clever bit that makes this worth doing is that we only
- * need _one_ half-length multiplication for the central
- * coefficient rather than the two that it obviouly looks
- * like, because we can use a single multiplication to compute
- *
- * (a_1 + a_0) (b_1 + b_0) = a_1 b_1 + a_1 b_0 + a_0 b_1 + a_0 b_0
- *
- * and then we subtract the other two coefficients (a_1 b_1
- * and a_0 b_0) which we were computing anyway.
- *
- * Hence we get to multiply two numbers of length N in about
- * three times as much work as it takes to multiply numbers of
- * length N/2, which is obviously better than the four times
- * as much work it would take if we just did a long
- * conventional multiply.
- */
-
- int toplen = len/2, botlen = len - toplen; /* botlen is the bigger */
- int midlen = botlen + 1;
- BignumDblInt carry;
-#ifdef KARA_DEBUG
- int i;
-#endif
-
- /*
- * The coefficients a_1 b_1 and a_0 b_0 just avoid overlapping
- * in the output array, so we can compute them immediately in
- * place.
- */
-
-#ifdef KARA_DEBUG
- printf("a1,a0 = 0x");
- for (i = 0; i < len; i++) {
- if (i == toplen) printf(", 0x");
- printf("%0*x", BIGNUM_INT_BITS/4, a[i]);
- }
- printf("\n");
- printf("b1,b0 = 0x");
- for (i = 0; i < len; i++) {
- if (i == toplen) printf(", 0x");
- printf("%0*x", BIGNUM_INT_BITS/4, b[i]);
- }
- printf("\n");
-#endif
-
- /* a_1 b_1 */
- internal_mul(a, b, c, toplen, scratch);
-#ifdef KARA_DEBUG
- printf("a1b1 = 0x");
- for (i = 0; i < 2*toplen; i++) {
- printf("%0*x", BIGNUM_INT_BITS/4, c[i]);
- }
- printf("\n");
-#endif
-
- /* a_0 b_0 */
- internal_mul(a + toplen, b + toplen, c + 2*toplen, botlen, scratch);
-#ifdef KARA_DEBUG
- printf("a0b0 = 0x");
- for (i = 0; i < 2*botlen; i++) {
- printf("%0*x", BIGNUM_INT_BITS/4, c[2*toplen+i]);
- }
- printf("\n");
-#endif
-
- /* Zero padding. midlen exceeds toplen by at most 2, so just
- * zero the first two words of each input and the rest will be
- * copied over. */
- scratch[0] = scratch[1] = scratch[midlen] = scratch[midlen+1] = 0;
-
- for (i = 0; i < toplen; i++) {
- scratch[midlen - toplen + i] = a[i]; /* a_1 */
- scratch[2*midlen - toplen + i] = b[i]; /* b_1 */
- }
-
- /* compute a_1 + a_0 */
- scratch[0] = internal_add(scratch+1, a+toplen, scratch+1, botlen);
-#ifdef KARA_DEBUG
- printf("a1plusa0 = 0x");
- for (i = 0; i < midlen; i++) {
- printf("%0*x", BIGNUM_INT_BITS/4, scratch[i]);
- }
- printf("\n");
-#endif
- /* compute b_1 + b_0 */
- scratch[midlen] = internal_add(scratch+midlen+1, b+toplen,
- scratch+midlen+1, botlen);
-#ifdef KARA_DEBUG
- printf("b1plusb0 = 0x");
- for (i = 0; i < midlen; i++) {
- printf("%0*x", BIGNUM_INT_BITS/4, scratch[midlen+i]);
- }
- printf("\n");
-#endif
-
- /*
- * Now we can do the third multiplication.
- */
- internal_mul(scratch, scratch + midlen, scratch + 2*midlen, midlen,
- scratch + 4*midlen);
-#ifdef KARA_DEBUG
- printf("a1plusa0timesb1plusb0 = 0x");
- for (i = 0; i < 2*midlen; i++) {
- printf("%0*x", BIGNUM_INT_BITS/4, scratch[2*midlen+i]);
- }
- printf("\n");
-#endif
-
- /*
- * Now we can reuse the first half of 'scratch' to compute the
- * sum of the outer two coefficients, to subtract from that
- * product to obtain the middle one.
- */
- scratch[0] = scratch[1] = scratch[2] = scratch[3] = 0;
- for (i = 0; i < 2*toplen; i++)
- scratch[2*midlen - 2*toplen + i] = c[i];
- scratch[1] = internal_add(scratch+2, c + 2*toplen,
- scratch+2, 2*botlen);
-#ifdef KARA_DEBUG
- printf("a1b1plusa0b0 = 0x");
- for (i = 0; i < 2*midlen; i++) {
- printf("%0*x", BIGNUM_INT_BITS/4, scratch[i]);
- }
- printf("\n");
-#endif
-
- internal_sub(scratch + 2*midlen, scratch,
- scratch + 2*midlen, 2*midlen);
-#ifdef KARA_DEBUG
- printf("a1b0plusa0b1 = 0x");
- for (i = 0; i < 2*midlen; i++) {
- printf("%0*x", BIGNUM_INT_BITS/4, scratch[2*midlen+i]);
- }
- printf("\n");
-#endif
-
- /*
- * And now all we need to do is to add that middle coefficient
- * back into the output. We may have to propagate a carry
- * further up the output, but we can be sure it won't
- * propagate right the way off the top.
- */
- carry = internal_add(c + 2*len - botlen - 2*midlen,
- scratch + 2*midlen,
- c + 2*len - botlen - 2*midlen, 2*midlen);
- i = 2*len - botlen - 2*midlen - 1;
- while (carry) {
- assert(i >= 0);
- carry += c[i];
- c[i] = (BignumInt)carry;
- carry >>= BIGNUM_INT_BITS;
- i--;
- }
-#ifdef KARA_DEBUG
- printf("ab = 0x");
- for (i = 0; i < 2*len; i++) {
- printf("%0*x", BIGNUM_INT_BITS/4, c[i]);
- }
- printf("\n");
-#endif
-
- } else {
- int i;
- BignumInt carry;
- BignumDblInt t;
- const BignumInt *ap, *bp;
- BignumInt *cp, *cps;
-
- /*
- * Multiply in the ordinary O(N^2) way.
- */
-
- for (i = 0; i < 2 * len; i++)
- c[i] = 0;
-
- for (cps = c + 2*len, ap = a + len; ap-- > a; cps--) {
- carry = 0;
- for (cp = cps, bp = b + len; cp--, bp-- > b ;) {
- t = (MUL_WORD(*ap, *bp) + carry) + *cp;
- *cp = (BignumInt) t;
- carry = (BignumInt)(t >> BIGNUM_INT_BITS);
- }
- *cp = carry;
- }
- }
-}
-
-/*
- * Variant form of internal_mul used for the initial step of
- * Montgomery reduction. Only bothers outputting 'len' words
- * (everything above that is thrown away).
- */
-static void internal_mul_low(const BignumInt *a, const BignumInt *b,
- BignumInt *c, int len, BignumInt *scratch)
-{
- if (len > KARATSUBA_THRESHOLD) {
- int i;
-
- /*
- * Karatsuba-aware version of internal_mul_low. As before, we
- * express each input value as a shifted combination of two
- * halves:
- *
- * a = a_1 D + a_0
- * b = b_1 D + b_0
- *
- * Then the full product is, as before,
- *
- * ab = a_1 b_1 D^2 + (a_1 b_0 + a_0 b_1) D + a_0 b_0
- *
- * Provided we choose D on the large side (so that a_0 and b_0
- * are _at least_ as long as a_1 and b_1), we don't need the
- * topmost term at all, and we only need half of the middle
- * term. So there's no point in doing the proper Karatsuba
- * optimisation which computes the middle term using the top
- * one, because we'd take as long computing the top one as
- * just computing the middle one directly.
- *
- * So instead, we do a much more obvious thing: we call the
- * fully optimised internal_mul to compute a_0 b_0, and we
- * recursively call ourself to compute the _bottom halves_ of
- * a_1 b_0 and a_0 b_1, each of which we add into the result
- * in the obvious way.
- *
- * In other words, there's no actual Karatsuba _optimisation_
- * in this function; the only benefit in doing it this way is
- * that we call internal_mul proper for a large part of the
- * work, and _that_ can optimise its operation.
- */
-
- int toplen = len/2, botlen = len - toplen; /* botlen is the bigger */
-
- /*
- * Scratch space for the various bits and pieces we're going
- * to be adding together: we need botlen*2 words for a_0 b_0
- * (though we may end up throwing away its topmost word), and
- * toplen words for each of a_1 b_0 and a_0 b_1. That adds up
- * to exactly 2*len.
- */
-
- /* a_0 b_0 */
- internal_mul(a + toplen, b + toplen, scratch + 2*toplen, botlen,
- scratch + 2*len);
-
- /* a_1 b_0 */
- internal_mul_low(a, b + len - toplen, scratch + toplen, toplen,
- scratch + 2*len);
-
- /* a_0 b_1 */
- internal_mul_low(a + len - toplen, b, scratch, toplen,
- scratch + 2*len);
-
- /* Copy the bottom half of the big coefficient into place */
- for (i = 0; i < botlen; i++)
- c[toplen + i] = scratch[2*toplen + botlen + i];
-
- /* Add the two small coefficients, throwing away the returned carry */
- internal_add(scratch, scratch + toplen, scratch, toplen);
-
- /* And add that to the large coefficient, leaving the result in c. */
- internal_add(scratch, scratch + 2*toplen + botlen - toplen,
- c, toplen);
-
- } else {
- int i;
- BignumInt carry;
- BignumDblInt t;
- const BignumInt *ap, *bp;
- BignumInt *cp, *cps;
-
- /*
- * Multiply in the ordinary O(N^2) way.
- */
-
- for (i = 0; i < len; i++)
- c[i] = 0;
-
- for (cps = c + len, ap = a + len; ap-- > a; cps--) {
- carry = 0;
- for (cp = cps, bp = b + len; bp--, cp-- > c ;) {
- t = (MUL_WORD(*ap, *bp) + carry) + *cp;
- *cp = (BignumInt) t;
- carry = (BignumInt)(t >> BIGNUM_INT_BITS);
- }
- }
- }
-}
-
-/*
- * Montgomery reduction. Expects x to be a big-endian array of 2*len
- * BignumInts whose value satisfies 0 <= x < rn (where r = 2^(len *
- * BIGNUM_INT_BITS) is the Montgomery base). Returns in the same array
- * a value x' which is congruent to xr^{-1} mod n, and satisfies 0 <=
- * x' < n.
- *
- * 'n' and 'mninv' should be big-endian arrays of 'len' BignumInts
- * each, containing respectively n and the multiplicative inverse of
- * -n mod r.
- *
- * 'tmp' is an array of BignumInt used as scratch space, of length at
- * least 3*len + mul_compute_scratch(len).
- */
-static void monty_reduce(BignumInt *x, const BignumInt *n,
- const BignumInt *mninv, BignumInt *tmp, int len)
-{
- int i;
- BignumInt carry;
-
- /*
- * Multiply x by (-n)^{-1} mod r. This gives us a value m such
- * that mn is congruent to -x mod r. Hence, mn+x is an exact
- * multiple of r, and is also (obviously) congruent to x mod n.
- */
- internal_mul_low(x + len, mninv, tmp, len, tmp + 3*len);
-
- /*
- * Compute t = (mn+x)/r in ordinary, non-modular, integer
- * arithmetic. By construction this is exact, and is congruent mod
- * n to x * r^{-1}, i.e. the answer we want.
- *
- * The following multiply leaves that answer in the _most_
- * significant half of the 'x' array, so then we must shift it
- * down.
- */
- internal_mul(tmp, n, tmp+len, len, tmp + 3*len);
- carry = internal_add(x, tmp+len, x, 2*len);
- for (i = 0; i < len; i++)
- x[len + i] = x[i], x[i] = 0;
-
- /*
- * Reduce t mod n. This doesn't require a full-on division by n,
- * but merely a test and single optional subtraction, since we can
- * show that 0 <= t < 2n.
- *
- * Proof:
- * + we computed m mod r, so 0 <= m < r.
- * + so 0 <= mn < rn, obviously
- * + hence we only need 0 <= x < rn to guarantee that 0 <= mn+x < 2rn
- * + yielding 0 <= (mn+x)/r < 2n as required.
- */
- if (!carry) {
- for (i = 0; i < len; i++)
- if (x[len + i] != n[i])
- break;
- }
- if (carry || i >= len || x[len + i] > n[i])
- internal_sub(x+len, n, x+len, len);
-}
-
-static void internal_add_shifted(BignumInt *number,
- unsigned n, int shift)
-{
- int word = 1 + (shift / BIGNUM_INT_BITS);
- int bshift = shift % BIGNUM_INT_BITS;
- BignumDblInt addend;
-
- addend = (BignumDblInt)n << bshift;
-
- while (addend) {
- addend += number[word];
- number[word] = (BignumInt) addend & BIGNUM_INT_MASK;
- addend >>= BIGNUM_INT_BITS;
- word++;
- }
-}
-
-/*
- * Compute a = a % m.
- * Input in first alen words of a and first mlen words of m.
- * Output in first alen words of a
- * (of which first alen-mlen words will be zero).
- * The MSW of m MUST have its high bit set.
- * Quotient is accumulated in the `quotient' array, which is a Bignum
- * rather than the internal bigendian format. Quotient parts are shifted
- * left by `qshift' before adding into quot.
- */
-static void internal_mod(BignumInt *a, int alen,
- BignumInt *m, int mlen,
- BignumInt *quot, int qshift)
-{
- BignumInt m0, m1;
- unsigned int h;
- int i, k;
-
- m0 = m[0];
- if (mlen > 1)
- m1 = m[1];
- else
- m1 = 0;
-
- for (i = 0; i <= alen - mlen; i++) {
- BignumDblInt t;
- unsigned int q, r, c, ai1;
-
- if (i == 0) {
- h = 0;
- } else {
- h = a[i - 1];
- a[i - 1] = 0;
- }
-
- if (i == alen - 1)
- ai1 = 0;
- else
- ai1 = a[i + 1];
-
- /* Find q = h:a[i] / m0 */
- if (h >= m0) {
- /*
- * Special case.
- *
- * To illustrate it, suppose a BignumInt is 8 bits, and
- * we are dividing (say) A1:23:45:67 by A1:B2:C3. Then
- * our initial division will be 0xA123 / 0xA1, which
- * will give a quotient of 0x100 and a divide overflow.
- * However, the invariants in this division algorithm
- * are not violated, since the full number A1:23:... is
- * _less_ than the quotient prefix A1:B2:... and so the
- * following correction loop would have sorted it out.
- *
- * In this situation we set q to be the largest
- * quotient we _can_ stomach (0xFF, of course).
- */
- q = BIGNUM_INT_MASK;
- } else {
- /* Macro doesn't want an array subscript expression passed
- * into it (see definition), so use a temporary. */
- BignumInt tmplo = a[i];
- DIVMOD_WORD(q, r, h, tmplo, m0);
-
- /* Refine our estimate of q by looking at
- h:a[i]:a[i+1] / m0:m1 */
- t = MUL_WORD(m1, q);
- if (t > ((BignumDblInt) r << BIGNUM_INT_BITS) + ai1) {
- q--;
- t -= m1;
- r = (r + m0) & BIGNUM_INT_MASK; /* overflow? */
- if (r >= (BignumDblInt) m0 &&
- t > ((BignumDblInt) r << BIGNUM_INT_BITS) + ai1) q--;
- }
- }
-
- /* Subtract q * m from a[i...] */
- c = 0;
- for (k = mlen - 1; k >= 0; k--) {
- t = MUL_WORD(q, m[k]);
- t += c;
- c = (unsigned)(t >> BIGNUM_INT_BITS);
- if ((BignumInt) t > a[i + k])
- c++;
- a[i + k] -= (BignumInt) t;
- }
-
- /* Add back m in case of borrow */
- if (c != h) {
- t = 0;
- for (k = mlen - 1; k >= 0; k--) {
- t += m[k];
- t += a[i + k];
- a[i + k] = (BignumInt) t;
- t = t >> BIGNUM_INT_BITS;
- }
- q--;
- }
- if (quot)
- internal_add_shifted(quot, q, qshift + BIGNUM_INT_BITS * (alen - mlen - i));
- }
-}
-
-/*
- * Compute (base ^ exp) % mod, the pedestrian way.
- */
-Bignum modpow_simple(Bignum base_in, Bignum exp, Bignum mod)
-{
- BignumInt *a, *b, *n, *m, *scratch;
- int mshift;
- int mlen, scratchlen, i, j;
- Bignum base, result;
-
- /*
- * The most significant word of mod needs to be non-zero. It
- * should already be, but let's make sure.
- */
- assert(mod[mod[0]] != 0);
-
- /*
- * Make sure the base is smaller than the modulus, by reducing
- * it modulo the modulus if not.
- */
- base = bigmod(base_in, mod);
-
- /* Allocate m of size mlen, copy mod to m */
- /* We use big endian internally */
- mlen = mod[0];
- m = snewn(mlen, BignumInt);
- for (j = 0; j < mlen; j++)
- m[j] = mod[mod[0] - j];
-
- /* Shift m left to make msb bit set */
- for (mshift = 0; mshift < BIGNUM_INT_BITS-1; mshift++)
- if ((m[0] << mshift) & BIGNUM_TOP_BIT)
- break;
- if (mshift) {
- for (i = 0; i < mlen - 1; i++)
- m[i] = (m[i] << mshift) | (m[i + 1] >> (BIGNUM_INT_BITS - mshift));
- m[mlen - 1] = m[mlen - 1] << mshift;
- }
-
- /* Allocate n of size mlen, copy base to n */
- n = snewn(mlen, BignumInt);
- i = mlen - base[0];
- for (j = 0; j < i; j++)
- n[j] = 0;
- for (j = 0; j < (int)base[0]; j++)
- n[i + j] = base[base[0] - j];
-
- /* Allocate a and b of size 2*mlen. Set a = 1 */
- a = snewn(2 * mlen, BignumInt);
- b = snewn(2 * mlen, BignumInt);
- for (i = 0; i < 2 * mlen; i++)
- a[i] = 0;
- a[2 * mlen - 1] = 1;
-
- /* Scratch space for multiplies */
- scratchlen = mul_compute_scratch(mlen);
- scratch = snewn(scratchlen, BignumInt);
-
- /* Skip leading zero bits of exp. */
- i = 0;
- j = BIGNUM_INT_BITS-1;
- while (i < (int)exp[0] && (exp[exp[0] - i] & (1 << j)) == 0) {
- j--;
- if (j < 0) {
- i++;
- j = BIGNUM_INT_BITS-1;
- }
- }
-
- /* Main computation */
- while (i < (int)exp[0]) {
- while (j >= 0) {
- internal_mul(a + mlen, a + mlen, b, mlen, scratch);
- internal_mod(b, mlen * 2, m, mlen, NULL, 0);
- if ((exp[exp[0] - i] & (1 << j)) != 0) {
- internal_mul(b + mlen, n, a, mlen, scratch);
- internal_mod(a, mlen * 2, m, mlen, NULL, 0);
- } else {
- BignumInt *t;
- t = a;
- a = b;
- b = t;
- }
- j--;
- }
- i++;
- j = BIGNUM_INT_BITS-1;
- }
-
- /* Fixup result in case the modulus was shifted */
- if (mshift) {
- for (i = mlen - 1; i < 2 * mlen - 1; i++)
- a[i] = (a[i] << mshift) | (a[i + 1] >> (BIGNUM_INT_BITS - mshift));
- a[2 * mlen - 1] = a[2 * mlen - 1] << mshift;
- internal_mod(a, mlen * 2, m, mlen, NULL, 0);
- for (i = 2 * mlen - 1; i >= mlen; i--)
- a[i] = (a[i] >> mshift) | (a[i - 1] << (BIGNUM_INT_BITS - mshift));
- }
-
- /* Copy result to buffer */
- result = newbn(mod[0]);
- for (i = 0; i < mlen; i++)
- result[result[0] - i] = a[i + mlen];
- while (result[0] > 1 && result[result[0]] == 0)
- result[0]--;
-
- /* Free temporary arrays */
- for (i = 0; i < 2 * mlen; i++)
- a[i] = 0;
- sfree(a);
- for (i = 0; i < scratchlen; i++)
- scratch[i] = 0;
- sfree(scratch);
- for (i = 0; i < 2 * mlen; i++)
- b[i] = 0;
- sfree(b);
- for (i = 0; i < mlen; i++)
- m[i] = 0;
- sfree(m);
- for (i = 0; i < mlen; i++)
- n[i] = 0;
- sfree(n);
-
- freebn(base);
-
- return result;
-}
-
-/*
- * Compute (base ^ exp) % mod. Uses the Montgomery multiplication
- * technique where possible, falling back to modpow_simple otherwise.
- */
-Bignum modpow(Bignum base_in, Bignum exp, Bignum mod)
-{
- BignumInt *a, *b, *x, *n, *mninv, *scratch;
- int len, scratchlen, i, j;
- Bignum base, base2, r, rn, inv, result;
-
- /*
- * The most significant word of mod needs to be non-zero. It
- * should already be, but let's make sure.
- */
- assert(mod[mod[0]] != 0);
-
- /*
- * mod had better be odd, or we can't do Montgomery multiplication
- * using a power of two at all.
- */
- if (!(mod[1] & 1))
- return modpow_simple(base_in, exp, mod);
-
- /*
- * Make sure the base is smaller than the modulus, by reducing
- * it modulo the modulus if not.
- */
- base = bigmod(base_in, mod);
-
- /*
- * Compute the inverse of n mod r, for monty_reduce. (In fact we
- * want the inverse of _minus_ n mod r, but we'll sort that out
- * below.)
- */
- len = mod[0];
- r = bn_power_2(BIGNUM_INT_BITS * len);
- inv = modinv(mod, r);
-
- /*
- * Multiply the base by r mod n, to get it into Montgomery
- * representation.
- */
- base2 = modmul(base, r, mod);
- freebn(base);
- base = base2;
-
- rn = bigmod(r, mod); /* r mod n, i.e. Montgomerified 1 */
-
- freebn(r); /* won't need this any more */
-
- /*
- * Set up internal arrays of the right lengths, in big-endian
- * format, containing the base, the modulus, and the modulus's
- * inverse.
- */
- n = snewn(len, BignumInt);
- for (j = 0; j < len; j++)
- n[len - 1 - j] = mod[j + 1];
-
- mninv = snewn(len, BignumInt);
- for (j = 0; j < len; j++)
- mninv[len - 1 - j] = (j < (int)inv[0] ? inv[j + 1] : 0);
- freebn(inv); /* we don't need this copy of it any more */
- /* Now negate mninv mod r, so it's the inverse of -n rather than +n. */
- x = snewn(len, BignumInt);
- for (j = 0; j < len; j++)
- x[j] = 0;
- internal_sub(x, mninv, mninv, len);
-
- /* x = snewn(len, BignumInt); */ /* already done above */
- for (j = 0; j < len; j++)
- x[len - 1 - j] = (j < (int)base[0] ? base[j + 1] : 0);
- freebn(base); /* we don't need this copy of it any more */
-
- a = snewn(2*len, BignumInt);
- b = snewn(2*len, BignumInt);
- for (j = 0; j < len; j++)
- a[2*len - 1 - j] = (j < (int)rn[0] ? rn[j + 1] : 0);
- freebn(rn);
-
- /* Scratch space for multiplies */
- scratchlen = 3*len + mul_compute_scratch(len);
- scratch = snewn(scratchlen, BignumInt);
-
- /* Skip leading zero bits of exp. */
- i = 0;
- j = BIGNUM_INT_BITS-1;
- while (i < (int)exp[0] && (exp[exp[0] - i] & (1 << j)) == 0) {
- j--;
- if (j < 0) {
- i++;
- j = BIGNUM_INT_BITS-1;
- }
- }
-
- /* Main computation */
- while (i < (int)exp[0]) {
- while (j >= 0) {
- internal_mul(a + len, a + len, b, len, scratch);
- monty_reduce(b, n, mninv, scratch, len);
- if ((exp[exp[0] - i] & (1 << j)) != 0) {
- internal_mul(b + len, x, a, len, scratch);
- monty_reduce(a, n, mninv, scratch, len);
- } else {
- BignumInt *t;
- t = a;
- a = b;
- b = t;
- }
- j--;
- }
- i++;
- j = BIGNUM_INT_BITS-1;
- }
-
- /*
- * Final monty_reduce to get back from the adjusted Montgomery
- * representation.
- */
- monty_reduce(a, n, mninv, scratch, len);
-
- /* Copy result to buffer */
- result = newbn(mod[0]);
- for (i = 0; i < len; i++)
- result[result[0] - i] = a[i + len];
- while (result[0] > 1 && result[result[0]] == 0)
- result[0]--;
-
- /* Free temporary arrays */
- for (i = 0; i < scratchlen; i++)
- scratch[i] = 0;
- sfree(scratch);
- for (i = 0; i < 2 * len; i++)
- a[i] = 0;
- sfree(a);
- for (i = 0; i < 2 * len; i++)
- b[i] = 0;
- sfree(b);
- for (i = 0; i < len; i++)
- mninv[i] = 0;
- sfree(mninv);
- for (i = 0; i < len; i++)
- n[i] = 0;
- sfree(n);
- for (i = 0; i < len; i++)
- x[i] = 0;
- sfree(x);
-
- return result;
-}
-
-/*
- * Compute (p * q) % mod.
- * The most significant word of mod MUST be non-zero.
- * We assume that the result array is the same size as the mod array.
- */
-Bignum modmul(Bignum p, Bignum q, Bignum mod)
-{
- BignumInt *a, *n, *m, *o, *scratch;
- int mshift, scratchlen;
- int pqlen, mlen, rlen, i, j;
- Bignum result;
-
- /* Allocate m of size mlen, copy mod to m */
- /* We use big endian internally */
- mlen = mod[0];
- m = snewn(mlen, BignumInt);
- for (j = 0; j < mlen; j++)
- m[j] = mod[mod[0] - j];
-
- /* Shift m left to make msb bit set */
- for (mshift = 0; mshift < BIGNUM_INT_BITS-1; mshift++)
- if ((m[0] << mshift) & BIGNUM_TOP_BIT)
- break;
- if (mshift) {
- for (i = 0; i < mlen - 1; i++)
- m[i] = (m[i] << mshift) | (m[i + 1] >> (BIGNUM_INT_BITS - mshift));
- m[mlen - 1] = m[mlen - 1] << mshift;
- }
-
- pqlen = (p[0] > q[0] ? p[0] : q[0]);
-
- /* Allocate n of size pqlen, copy p to n */
- n = snewn(pqlen, BignumInt);
- i = pqlen - p[0];
- for (j = 0; j < i; j++)
- n[j] = 0;
- for (j = 0; j < (int)p[0]; j++)
- n[i + j] = p[p[0] - j];
-
- /* Allocate o of size pqlen, copy q to o */
- o = snewn(pqlen, BignumInt);
- i = pqlen - q[0];
- for (j = 0; j < i; j++)
- o[j] = 0;
- for (j = 0; j < (int)q[0]; j++)
- o[i + j] = q[q[0] - j];
-
- /* Allocate a of size 2*pqlen for result */
- a = snewn(2 * pqlen, BignumInt);
-
- /* Scratch space for multiplies */
- scratchlen = mul_compute_scratch(pqlen);
- scratch = snewn(scratchlen, BignumInt);
-
- /* Main computation */
- internal_mul(n, o, a, pqlen, scratch);
- internal_mod(a, pqlen * 2, m, mlen, NULL, 0);
-
- /* Fixup result in case the modulus was shifted */
- if (mshift) {
- for (i = 2 * pqlen - mlen - 1; i < 2 * pqlen - 1; i++)
- a[i] = (a[i] << mshift) | (a[i + 1] >> (BIGNUM_INT_BITS - mshift));
- a[2 * pqlen - 1] = a[2 * pqlen - 1] << mshift;
- internal_mod(a, pqlen * 2, m, mlen, NULL, 0);
- for (i = 2 * pqlen - 1; i >= 2 * pqlen - mlen; i--)
- a[i] = (a[i] >> mshift) | (a[i - 1] << (BIGNUM_INT_BITS - mshift));
- }
-
- /* Copy result to buffer */
- rlen = (mlen < pqlen * 2 ? mlen : pqlen * 2);
- result = newbn(rlen);
- for (i = 0; i < rlen; i++)
- result[result[0] - i] = a[i + 2 * pqlen - rlen];
- while (result[0] > 1 && result[result[0]] == 0)
- result[0]--;
-
- /* Free temporary arrays */
- for (i = 0; i < scratchlen; i++)
- scratch[i] = 0;
- sfree(scratch);
- for (i = 0; i < 2 * pqlen; i++)
- a[i] = 0;
- sfree(a);
- for (i = 0; i < mlen; i++)
- m[i] = 0;
- sfree(m);
- for (i = 0; i < pqlen; i++)
- n[i] = 0;
- sfree(n);
- for (i = 0; i < pqlen; i++)
- o[i] = 0;
- sfree(o);
-
- return result;
-}
-
-/*
- * Compute p % mod.
- * The most significant word of mod MUST be non-zero.
- * We assume that the result array is the same size as the mod array.
- * We optionally write out a quotient if `quotient' is non-NULL.
- * We can avoid writing out the result if `result' is NULL.
- */
-static void bigdivmod(Bignum p, Bignum mod, Bignum result, Bignum quotient)
-{
- BignumInt *n, *m;
- int mshift;
- int plen, mlen, i, j;
-
- /* Allocate m of size mlen, copy mod to m */
- /* We use big endian internally */
- mlen = mod[0];
- m = snewn(mlen, BignumInt);
- for (j = 0; j < mlen; j++)
- m[j] = mod[mod[0] - j];
-
- /* Shift m left to make msb bit set */
- for (mshift = 0; mshift < BIGNUM_INT_BITS-1; mshift++)
- if ((m[0] << mshift) & BIGNUM_TOP_BIT)
- break;
- if (mshift) {
- for (i = 0; i < mlen - 1; i++)
- m[i] = (m[i] << mshift) | (m[i + 1] >> (BIGNUM_INT_BITS - mshift));
- m[mlen - 1] = m[mlen - 1] << mshift;
- }
-
- plen = p[0];
- /* Ensure plen > mlen */
- if (plen <= mlen)
- plen = mlen + 1;
-
- /* Allocate n of size plen, copy p to n */
- n = snewn(plen, BignumInt);
- for (j = 0; j < plen; j++)
- n[j] = 0;
- for (j = 1; j <= (int)p[0]; j++)
- n[plen - j] = p[j];
-
- /* Main computation */
- internal_mod(n, plen, m, mlen, quotient, mshift);
-
- /* Fixup result in case the modulus was shifted */
- if (mshift) {
- for (i = plen - mlen - 1; i < plen - 1; i++)
- n[i] = (n[i] << mshift) | (n[i + 1] >> (BIGNUM_INT_BITS - mshift));
- n[plen - 1] = n[plen - 1] << mshift;
- internal_mod(n, plen, m, mlen, quotient, 0);
- for (i = plen - 1; i >= plen - mlen; i--)
- n[i] = (n[i] >> mshift) | (n[i - 1] << (BIGNUM_INT_BITS - mshift));
- }
-
- /* Copy result to buffer */
- if (result) {
- for (i = 1; i <= (int)result[0]; i++) {
- int j = plen - i;
- result[i] = j >= 0 ? n[j] : 0;
- }
- }
-
- /* Free temporary arrays */
- for (i = 0; i < mlen; i++)
- m[i] = 0;
- sfree(m);
- for (i = 0; i < plen; i++)
- n[i] = 0;
- sfree(n);
-}
-
-/*
- * Decrement a number.
- */
-void decbn(Bignum bn)
-{
- int i = 1;
- while (i < (int)bn[0] && bn[i] == 0)
- bn[i++] = BIGNUM_INT_MASK;
- bn[i]--;
-}
-
-Bignum bignum_from_bytes(const unsigned char *data, int nbytes)
-{
- Bignum result;
- int w, i;
-
- w = (nbytes + BIGNUM_INT_BYTES - 1) / BIGNUM_INT_BYTES; /* bytes->words */
-
- result = newbn(w);
- for (i = 1; i <= w; i++)
- result[i] = 0;
- for (i = nbytes; i--;) {
- unsigned char byte = *data++;
- result[1 + i / BIGNUM_INT_BYTES] |= byte << (8*i % BIGNUM_INT_BITS);
- }
-
- while (result[0] > 1 && result[result[0]] == 0)
- result[0]--;
- return result;
-}
-
-/*
- * Read an SSH-1-format bignum from a data buffer. Return the number
- * of bytes consumed, or -1 if there wasn't enough data.
- */
-int ssh1_read_bignum(const unsigned char *data, int len, Bignum * result)
-{
- const unsigned char *p = data;
- int i;
- int w, b;
-
- if (len < 2)
- return -1;
-
- w = 0;
- for (i = 0; i < 2; i++)
- w = (w << 8) + *p++;
- b = (w + 7) / 8; /* bits -> bytes */
-
- if (len < b+2)
- return -1;
-
- if (!result) /* just return length */
- return b + 2;
-
- *result = bignum_from_bytes(p, b);
-
- return p + b - data;
-}
-
-/*
- * Return the bit count of a bignum, for SSH-1 encoding.
- */
-int bignum_bitcount(Bignum bn)
-{
- int bitcount = bn[0] * BIGNUM_INT_BITS - 1;
- while (bitcount >= 0
- && (bn[bitcount / BIGNUM_INT_BITS + 1] >> (bitcount % BIGNUM_INT_BITS)) == 0) bitcount--;
- return bitcount + 1;
-}
-
-/*
- * Return the byte length of a bignum when SSH-1 encoded.
- */
-int ssh1_bignum_length(Bignum bn)
-{
- return 2 + (bignum_bitcount(bn) + 7) / 8;
-}
-
-/*
- * Return the byte length of a bignum when SSH-2 encoded.
- */
-int ssh2_bignum_length(Bignum bn)
-{
- return 4 + (bignum_bitcount(bn) + 8) / 8;
-}
-
-/*
- * Return a byte from a bignum; 0 is least significant, etc.
- */
-int bignum_byte(Bignum bn, int i)
-{
- if (i >= (int)(BIGNUM_INT_BYTES * bn[0]))
- return 0; /* beyond the end */
- else
- return (bn[i / BIGNUM_INT_BYTES + 1] >>
- ((i % BIGNUM_INT_BYTES)*8)) & 0xFF;
-}
-
-/*
- * Return a bit from a bignum; 0 is least significant, etc.
- */
-int bignum_bit(Bignum bn, int i)
-{
- if (i >= (int)(BIGNUM_INT_BITS * bn[0]))
- return 0; /* beyond the end */
- else
- return (bn[i / BIGNUM_INT_BITS + 1] >> (i % BIGNUM_INT_BITS)) & 1;
-}
-
-/*
- * Set a bit in a bignum; 0 is least significant, etc.
- */
-void bignum_set_bit(Bignum bn, int bitnum, int value)
-{
- if (bitnum >= (int)(BIGNUM_INT_BITS * bn[0]))
- abort(); /* beyond the end */
- else {
- int v = bitnum / BIGNUM_INT_BITS + 1;
- int mask = 1 << (bitnum % BIGNUM_INT_BITS);
- if (value)
- bn[v] |= mask;
- else
- bn[v] &= ~mask;
- }
-}
-
-/*
- * Write a SSH-1-format bignum into a buffer. It is assumed the
- * buffer is big enough. Returns the number of bytes used.
- */
-int ssh1_write_bignum(void *data, Bignum bn)
-{
- unsigned char *p = data;
- int len = ssh1_bignum_length(bn);
- int i;
- int bitc = bignum_bitcount(bn);
-
- *p++ = (bitc >> 8) & 0xFF;
- *p++ = (bitc) & 0xFF;
- for (i = len - 2; i--;)
- *p++ = bignum_byte(bn, i);
- return len;
-}
-
-/*
- * Compare two bignums. Returns like strcmp.
- */
-int bignum_cmp(Bignum a, Bignum b)
-{
- int amax = a[0], bmax = b[0];
- int i = (amax > bmax ? amax : bmax);
- while (i) {
- BignumInt aval = (i > amax ? 0 : a[i]);
- BignumInt bval = (i > bmax ? 0 : b[i]);
- if (aval < bval)
- return -1;
- if (aval > bval)
- return +1;
- i--;
- }
- return 0;
-}
-
-/*
- * Right-shift one bignum to form another.
- */
-Bignum bignum_rshift(Bignum a, int shift)
-{
- Bignum ret;
- int i, shiftw, shiftb, shiftbb, bits;
- BignumInt ai, ai1;
-
- bits = bignum_bitcount(a) - shift;
- ret = newbn((bits + BIGNUM_INT_BITS - 1) / BIGNUM_INT_BITS);
-
- if (ret) {
- shiftw = shift / BIGNUM_INT_BITS;
- shiftb = shift % BIGNUM_INT_BITS;
- shiftbb = BIGNUM_INT_BITS - shiftb;
-
- ai1 = a[shiftw + 1];
- for (i = 1; i <= (int)ret[0]; i++) {
- ai = ai1;
- ai1 = (i + shiftw + 1 <= (int)a[0] ? a[i + shiftw + 1] : 0);
- ret[i] = ((ai >> shiftb) | (ai1 << shiftbb)) & BIGNUM_INT_MASK;
- }
- }
-
- return ret;
-}
-
-/*
- * Non-modular multiplication and addition.
- */
-Bignum bigmuladd(Bignum a, Bignum b, Bignum addend)
-{
- int alen = a[0], blen = b[0];
- int mlen = (alen > blen ? alen : blen);
- int rlen, i, maxspot;
- int wslen;
- BignumInt *workspace;
- Bignum ret;
-
- /* mlen space for a, mlen space for b, 2*mlen for result,
- * plus scratch space for multiplication */
- wslen = mlen * 4 + mul_compute_scratch(mlen);
- workspace = snewn(wslen, BignumInt);
- for (i = 0; i < mlen; i++) {
- workspace[0 * mlen + i] = (mlen - i <= (int)a[0] ? a[mlen - i] : 0);
- workspace[1 * mlen + i] = (mlen - i <= (int)b[0] ? b[mlen - i] : 0);
- }
-
- internal_mul(workspace + 0 * mlen, workspace + 1 * mlen,
- workspace + 2 * mlen, mlen, workspace + 4 * mlen);
-
- /* now just copy the result back */
- rlen = alen + blen + 1;
- if (addend && rlen <= (int)addend[0])
- rlen = addend[0] + 1;
- ret = newbn(rlen);
- maxspot = 0;
- for (i = 1; i <= (int)ret[0]; i++) {
- ret[i] = (i <= 2 * mlen ? workspace[4 * mlen - i] : 0);
- if (ret[i] != 0)
- maxspot = i;
- }
- ret[0] = maxspot;
-
- /* now add in the addend, if any */
- if (addend) {
- BignumDblInt carry = 0;
- for (i = 1; i <= rlen; i++) {
- carry += (i <= (int)ret[0] ? ret[i] : 0);
- carry += (i <= (int)addend[0] ? addend[i] : 0);
- ret[i] = (BignumInt) carry & BIGNUM_INT_MASK;
- carry >>= BIGNUM_INT_BITS;
- if (ret[i] != 0 && i > maxspot)
- maxspot = i;
- }
- }
- ret[0] = maxspot;
-
- for (i = 0; i < wslen; i++)
- workspace[i] = 0;
- sfree(workspace);
- return ret;
-}
-
-/*
- * Non-modular multiplication.
- */
-Bignum bigmul(Bignum a, Bignum b)
-{
- return bigmuladd(a, b, NULL);
-}
-
-/*
- * Simple addition.
- */
-Bignum bigadd(Bignum a, Bignum b)
-{
- int alen = a[0], blen = b[0];
- int rlen = (alen > blen ? alen : blen) + 1;
- int i, maxspot;
- Bignum ret;
- BignumDblInt carry;
-
- ret = newbn(rlen);
-
- carry = 0;
- maxspot = 0;
- for (i = 1; i <= rlen; i++) {
- carry += (i <= (int)a[0] ? a[i] : 0);
- carry += (i <= (int)b[0] ? b[i] : 0);
- ret[i] = (BignumInt) carry & BIGNUM_INT_MASK;
- carry >>= BIGNUM_INT_BITS;
- if (ret[i] != 0 && i > maxspot)
- maxspot = i;
- }
- ret[0] = maxspot;
-
- return ret;
-}
-
-/*
- * Subtraction. Returns a-b, or NULL if the result would come out
- * negative (recall that this entire bignum module only handles
- * positive numbers).
- */
-Bignum bigsub(Bignum a, Bignum b)
-{
- int alen = a[0], blen = b[0];
- int rlen = (alen > blen ? alen : blen);
- int i, maxspot;
- Bignum ret;
- BignumDblInt carry;
-
- ret = newbn(rlen);
-
- carry = 1;
- maxspot = 0;
- for (i = 1; i <= rlen; i++) {
- carry += (i <= (int)a[0] ? a[i] : 0);
- carry += (i <= (int)b[0] ? b[i] ^ BIGNUM_INT_MASK : BIGNUM_INT_MASK);
- ret[i] = (BignumInt) carry & BIGNUM_INT_MASK;
- carry >>= BIGNUM_INT_BITS;
- if (ret[i] != 0 && i > maxspot)
- maxspot = i;
- }
- ret[0] = maxspot;
-
- if (!carry) {
- freebn(ret);
- return NULL;
- }
-
- return ret;
-}
-
-/*
- * Create a bignum which is the bitmask covering another one. That
- * is, the smallest integer which is >= N and is also one less than
- * a power of two.
- */
-Bignum bignum_bitmask(Bignum n)
-{
- Bignum ret = copybn(n);
- int i;
- BignumInt j;
-
- i = ret[0];
- while (n[i] == 0 && i > 0)
- i--;
- if (i <= 0)
- return ret; /* input was zero */
- j = 1;
- while (j < n[i])
- j = 2 * j + 1;
- ret[i] = j;
- while (--i > 0)
- ret[i] = BIGNUM_INT_MASK;
- return ret;
-}
-
-/*
- * Convert a (max 32-bit) long into a bignum.
- */
-Bignum bignum_from_long(unsigned long nn)
-{
- Bignum ret;
- BignumDblInt n = nn;
-
- ret = newbn(3);
- ret[1] = (BignumInt)(n & BIGNUM_INT_MASK);
- ret[2] = (BignumInt)((n >> BIGNUM_INT_BITS) & BIGNUM_INT_MASK);
- ret[3] = 0;
- ret[0] = (ret[2] ? 2 : 1);
- return ret;
-}
-
-/*
- * Add a long to a bignum.
- */
-Bignum bignum_add_long(Bignum number, unsigned long addendx)
-{
- Bignum ret = newbn(number[0] + 1);
- int i, maxspot = 0;
- BignumDblInt carry = 0, addend = addendx;
-
- for (i = 1; i <= (int)ret[0]; i++) {
- carry += addend & BIGNUM_INT_MASK;
- carry += (i <= (int)number[0] ? number[i] : 0);
- addend >>= BIGNUM_INT_BITS;
- ret[i] = (BignumInt) carry & BIGNUM_INT_MASK;
- carry >>= BIGNUM_INT_BITS;
- if (ret[i] != 0)
- maxspot = i;
- }
- ret[0] = maxspot;
- return ret;
-}
-
-/*
- * Compute the residue of a bignum, modulo a (max 16-bit) short.
- */
-unsigned short bignum_mod_short(Bignum number, unsigned short modulus)
-{
- BignumDblInt mod, r;
- int i;
-
- r = 0;
- mod = modulus;
- for (i = number[0]; i > 0; i--)
- r = (r * (BIGNUM_TOP_BIT % mod) * 2 + number[i] % mod) % mod;
- return (unsigned short) r;
-}
-
-#ifdef DEBUG
-void diagbn(char *prefix, Bignum md)
-{
- int i, nibbles, morenibbles;
- static const char hex[] = "0123456789ABCDEF";
-
- debug(("%s0x", prefix ? prefix : ""));
-
- nibbles = (3 + bignum_bitcount(md)) / 4;
- if (nibbles < 1)
- nibbles = 1;
- morenibbles = 4 * md[0] - nibbles;
- for (i = 0; i < morenibbles; i++)
- debug(("-"));
- for (i = nibbles; i--;)
- debug(("%c",
- hex[(bignum_byte(md, i / 2) >> (4 * (i % 2))) & 0xF]));
-
- if (prefix)
- debug(("\n"));
-}
-#endif
-
-/*
- * Simple division.
- */
-Bignum bigdiv(Bignum a, Bignum b)
-{
- Bignum q = newbn(a[0]);
- bigdivmod(a, b, NULL, q);
- return q;
-}
-
-/*
- * Simple remainder.
- */
-Bignum bigmod(Bignum a, Bignum b)
-{
- Bignum r = newbn(b[0]);
- bigdivmod(a, b, r, NULL);
- return r;
-}
-
-/*
- * Greatest common divisor.
- */
-Bignum biggcd(Bignum av, Bignum bv)
-{
- Bignum a = copybn(av);
- Bignum b = copybn(bv);
-
- while (bignum_cmp(b, Zero) != 0) {
- Bignum t = newbn(b[0]);
- bigdivmod(a, b, t, NULL);
- while (t[0] > 1 && t[t[0]] == 0)
- t[0]--;
- freebn(a);
- a = b;
- b = t;
- }
-
- freebn(b);
- return a;
-}
-
-/*
- * Modular inverse, using Euclid's extended algorithm.
- */
-Bignum modinv(Bignum number, Bignum modulus)
-{
- Bignum a = copybn(modulus);
- Bignum b = copybn(number);
- Bignum xp = copybn(Zero);
- Bignum x = copybn(One);
- int sign = +1;
-
- while (bignum_cmp(b, One) != 0) {
- Bignum t = newbn(b[0]);
- Bignum q = newbn(a[0]);
- bigdivmod(a, b, t, q);
- while (t[0] > 1 && t[t[0]] == 0)
- t[0]--;
- freebn(a);
- a = b;
- b = t;
- t = xp;
- xp = x;
- x = bigmuladd(q, xp, t);
- sign = -sign;
- freebn(t);
- freebn(q);
- }
-
- freebn(b);
- freebn(a);
- freebn(xp);
-
- /* now we know that sign * x == 1, and that x < modulus */
- if (sign < 0) {
- /* set a new x to be modulus - x */
- Bignum newx = newbn(modulus[0]);
- BignumInt carry = 0;
- int maxspot = 1;
- int i;
-
- for (i = 1; i <= (int)newx[0]; i++) {
- BignumInt aword = (i <= (int)modulus[0] ? modulus[i] : 0);
- BignumInt bword = (i <= (int)x[0] ? x[i] : 0);
- newx[i] = aword - bword - carry;
- bword = ~bword;
- carry = carry ? (newx[i] >= bword) : (newx[i] > bword);
- if (newx[i] != 0)
- maxspot = i;
- }
- newx[0] = maxspot;
- freebn(x);
- x = newx;
- }
-
- /* and return. */
- return x;
-}
-
-/*
- * Render a bignum into decimal. Return a malloced string holding
- * the decimal representation.
- */
-char *bignum_decimal(Bignum x)
-{
- int ndigits, ndigit;
- int i, iszero;
- BignumDblInt carry;
- char *ret;
- BignumInt *workspace;
-
- /*
- * First, estimate the number of digits. Since log(10)/log(2)
- * is just greater than 93/28 (the joys of continued fraction
- * approximations...) we know that for every 93 bits, we need
- * at most 28 digits. This will tell us how much to malloc.
- *
- * Formally: if x has i bits, that means x is strictly less
- * than 2^i. Since 2 is less than 10^(28/93), this is less than
- * 10^(28i/93). We need an integer power of ten, so we must
- * round up (rounding down might make it less than x again).
- * Therefore if we multiply the bit count by 28/93, rounding
- * up, we will have enough digits.
- *
- * i=0 (i.e., x=0) is an irritating special case.
- */
- i = bignum_bitcount(x);
- if (!i)
- ndigits = 1; /* x = 0 */
- else
- ndigits = (28 * i + 92) / 93; /* multiply by 28/93 and round up */
- ndigits++; /* allow for trailing \0 */
- ret = snewn(ndigits, char);
-
- /*
- * Now allocate some workspace to hold the binary form as we
- * repeatedly divide it by ten. Initialise this to the
- * big-endian form of the number.
- */
- workspace = snewn(x[0], BignumInt);
- for (i = 0; i < (int)x[0]; i++)
- workspace[i] = x[x[0] - i];
-
- /*
- * Next, write the decimal number starting with the last digit.
- * We use ordinary short division, dividing 10 into the
- * workspace.
- */
- ndigit = ndigits - 1;
- ret[ndigit] = '\0';
- do {
- iszero = 1;
- carry = 0;
- for (i = 0; i < (int)x[0]; i++) {
- carry = (carry << BIGNUM_INT_BITS) + workspace[i];
- workspace[i] = (BignumInt) (carry / 10);
- if (workspace[i])
- iszero = 0;
- carry %= 10;
- }
- ret[--ndigit] = (char) (carry + '0');
- } while (!iszero);
-
- /*
- * There's a chance we've fallen short of the start of the
- * string. Correct if so.
- */
- if (ndigit > 0)
- memmove(ret, ret + ndigit, ndigits - ndigit);
-
- /*
- * Done.
- */
- sfree(workspace);
- return ret;
-}
-
-#ifdef TESTBN
-
-#include <stdio.h>
-#include <stdlib.h>
-#include <ctype.h>
-
-/*
- * gcc -g -O0 -DTESTBN -o testbn sshbn.c misc.c -I unix -I charset
- *
- * Then feed to this program's standard input the output of
- * testdata/bignum.py .
- */
-
-void modalfatalbox(char *p, ...)
-{
- va_list ap;
- fprintf(stderr, "FATAL ERROR: ");
- va_start(ap, p);
- vfprintf(stderr, p, ap);
- va_end(ap);
- fputc('\n', stderr);
- exit(1);
-}
-
-#define fromxdigit(c) ( (c)>'9' ? ((c)&0xDF) - 'A' + 10 : (c) - '0' )
-
-int main(int argc, char **argv)
-{
- char *buf;
- int line = 0;
- int passes = 0, fails = 0;
-
- while ((buf = fgetline(stdin)) != NULL) {
- int maxlen = strlen(buf);
- unsigned char *data = snewn(maxlen, unsigned char);
- unsigned char *ptrs[5], *q;
- int ptrnum;
- char *bufp = buf;
-
- line++;
-
- q = data;
- ptrnum = 0;
-
- while (*bufp && !isspace((unsigned char)*bufp))
- bufp++;
- if (bufp)
- *bufp++ = '\0';
-
- while (*bufp) {
- char *start, *end;
- int i;
-
- while (*bufp && !isxdigit((unsigned char)*bufp))
- bufp++;
- start = bufp;
-
- if (!*bufp)
- break;
-
- while (*bufp && isxdigit((unsigned char)*bufp))
- bufp++;
- end = bufp;
-
- if (ptrnum >= lenof(ptrs))
- break;
- ptrs[ptrnum++] = q;
-
- for (i = -((end - start) & 1); i < end-start; i += 2) {
- unsigned char val = (i < 0 ? 0 : fromxdigit(start[i]));
- val = val * 16 + fromxdigit(start[i+1]);
- *q++ = val;
- }
-
- ptrs[ptrnum] = q;
- }
-
- if (!strcmp(buf, "mul")) {
- Bignum a, b, c, p;
-
- if (ptrnum != 3) {
- printf("%d: mul with %d parameters, expected 3\n", line);
- exit(1);
- }
- a = bignum_from_bytes(ptrs[0], ptrs[1]-ptrs[0]);
- b = bignum_from_bytes(ptrs[1], ptrs[2]-ptrs[1]);
- c = bignum_from_bytes(ptrs[2], ptrs[3]-ptrs[2]);
- p = bigmul(a, b);
-
- if (bignum_cmp(c, p) == 0) {
- passes++;
- } else {
- char *as = bignum_decimal(a);
- char *bs = bignum_decimal(b);
- char *cs = bignum_decimal(c);
- char *ps = bignum_decimal(p);
-
- printf("%d: fail: %s * %s gave %s expected %s\n",
- line, as, bs, ps, cs);
- fails++;
-
- sfree(as);
- sfree(bs);
- sfree(cs);
- sfree(ps);
- }
- freebn(a);
- freebn(b);
- freebn(c);
- freebn(p);
- } else if (!strcmp(buf, "pow")) {
- Bignum base, expt, modulus, expected, answer;
-
- if (ptrnum != 4) {
- printf("%d: mul with %d parameters, expected 3\n", line);
- exit(1);
- }
-
- base = bignum_from_bytes(ptrs[0], ptrs[1]-ptrs[0]);
- expt = bignum_from_bytes(ptrs[1], ptrs[2]-ptrs[1]);
- modulus = bignum_from_bytes(ptrs[2], ptrs[3]-ptrs[2]);
- expected = bignum_from_bytes(ptrs[3], ptrs[4]-ptrs[3]);
- answer = modpow(base, expt, modulus);
-
- if (bignum_cmp(expected, answer) == 0) {
- passes++;
- } else {
- char *as = bignum_decimal(base);
- char *bs = bignum_decimal(expt);
- char *cs = bignum_decimal(modulus);
- char *ds = bignum_decimal(answer);
- char *ps = bignum_decimal(expected);
-
- printf("%d: fail: %s ^ %s mod %s gave %s expected %s\n",
- line, as, bs, cs, ds, ps);
- fails++;
-
- sfree(as);
- sfree(bs);
- sfree(cs);
- sfree(ds);
- sfree(ps);
- }
- freebn(base);
- freebn(expt);
- freebn(modulus);
- freebn(expected);
- freebn(answer);
- } else {
- printf("%d: unrecognised test keyword: '%s'\n", line, buf);
- exit(1);
- }
-
- sfree(buf);
- sfree(data);
- }
-
- printf("passed %d failed %d total %d\n", passes, fails, passes+fails);
- return fails != 0;
-}
-
-#endif
+/*
+ * Bignum routines for RSA and DH and stuff.
+ */
+
+#include <stdio.h>
+#include <assert.h>
+#include <stdlib.h>
+#include <string.h>
+#include <limits.h>
+
+#include "misc.h"
+
+/*
+ * Usage notes:
+ * * Do not call the DIVMOD_WORD macro with expressions such as array
+ * subscripts, as some implementations object to this (see below).
+ * * Note that none of the division methods below will cope if the
+ * quotient won't fit into BIGNUM_INT_BITS. Callers should be careful
+ * to avoid this case.
+ * If this condition occurs, in the case of the x86 DIV instruction,
+ * an overflow exception will occur, which (according to a correspondent)
+ * will manifest on Windows as something like
+ * 0xC0000095: Integer overflow
+ * The C variant won't give the right answer, either.
+ */
+
+#if defined __GNUC__ && defined __i386__
+typedef unsigned long BignumInt;
+typedef unsigned long long BignumDblInt;
+#define BIGNUM_INT_MASK 0xFFFFFFFFUL
+#define BIGNUM_TOP_BIT 0x80000000UL
+#define BIGNUM_INT_BITS 32
+#define MUL_WORD(w1, w2) ((BignumDblInt)w1 * w2)
+#define DIVMOD_WORD(q, r, hi, lo, w) \
+ __asm__("div %2" : \
+ "=d" (r), "=a" (q) : \
+ "r" (w), "d" (hi), "a" (lo))
+#elif defined _MSC_VER && defined _M_IX86
+typedef unsigned __int32 BignumInt;
+typedef unsigned __int64 BignumDblInt;
+#define BIGNUM_INT_MASK 0xFFFFFFFFUL
+#define BIGNUM_TOP_BIT 0x80000000UL
+#define BIGNUM_INT_BITS 32
+#define MUL_WORD(w1, w2) ((BignumDblInt)w1 * w2)
+/* Note: MASM interprets array subscripts in the macro arguments as
+ * assembler syntax, which gives the wrong answer. Don't supply them.
+ * <http://msdn2.microsoft.com/en-us/library/bf1dw62z.aspx> */
+#define DIVMOD_WORD(q, r, hi, lo, w) do { \
+ __asm mov edx, hi \
+ __asm mov eax, lo \
+ __asm div w \
+ __asm mov r, edx \
+ __asm mov q, eax \
+} while(0)
+#elif defined _LP64
+/* 64-bit architectures can do 32x32->64 chunks at a time */
+typedef unsigned int BignumInt;
+typedef unsigned long BignumDblInt;
+#define BIGNUM_INT_MASK 0xFFFFFFFFU
+#define BIGNUM_TOP_BIT 0x80000000U
+#define BIGNUM_INT_BITS 32
+#define MUL_WORD(w1, w2) ((BignumDblInt)w1 * w2)
+#define DIVMOD_WORD(q, r, hi, lo, w) do { \
+ BignumDblInt n = (((BignumDblInt)hi) << BIGNUM_INT_BITS) | lo; \
+ q = n / w; \
+ r = n % w; \
+} while (0)
+#elif defined _LLP64
+/* 64-bit architectures in which unsigned long is 32 bits, not 64 */
+typedef unsigned long BignumInt;
+typedef unsigned long long BignumDblInt;
+#define BIGNUM_INT_MASK 0xFFFFFFFFUL
+#define BIGNUM_TOP_BIT 0x80000000UL
+#define BIGNUM_INT_BITS 32
+#define MUL_WORD(w1, w2) ((BignumDblInt)w1 * w2)
+#define DIVMOD_WORD(q, r, hi, lo, w) do { \
+ BignumDblInt n = (((BignumDblInt)hi) << BIGNUM_INT_BITS) | lo; \
+ q = n / w; \
+ r = n % w; \
+} while (0)
+#else
+/* Fallback for all other cases */
+typedef unsigned short BignumInt;
+typedef unsigned long BignumDblInt;
+#define BIGNUM_INT_MASK 0xFFFFU
+#define BIGNUM_TOP_BIT 0x8000U
+#define BIGNUM_INT_BITS 16
+#define MUL_WORD(w1, w2) ((BignumDblInt)w1 * w2)
+#define DIVMOD_WORD(q, r, hi, lo, w) do { \
+ BignumDblInt n = (((BignumDblInt)hi) << BIGNUM_INT_BITS) | lo; \
+ q = n / w; \
+ r = n % w; \
+} while (0)
+#endif
+
+#define BIGNUM_INT_BYTES (BIGNUM_INT_BITS / 8)
+
+#define BIGNUM_INTERNAL
+typedef BignumInt *Bignum;
+
+#include "ssh.h"
+
+BignumInt bnZero[1] = { 0 };
+BignumInt bnOne[2] = { 1, 1 };
+
+/*
+ * The Bignum format is an array of `BignumInt'. The first
+ * element of the array counts the remaining elements. The
+ * remaining elements express the actual number, base 2^BIGNUM_INT_BITS, _least_
+ * significant digit first. (So it's trivial to extract the bit
+ * with value 2^n for any n.)
+ *
+ * All Bignums in this module are positive. Negative numbers must
+ * be dealt with outside it.
+ *
+ * INVARIANT: the most significant word of any Bignum must be
+ * nonzero.
+ */
+
+Bignum Zero = bnZero, One = bnOne;
+
+static Bignum newbn(int length)
+{
+ Bignum b;
+
+ assert(length >= 0 && length < INT_MAX / BIGNUM_INT_BITS);
+
+ b = snewn(length + 1, BignumInt);
+ if (!b)
+ abort(); /* FIXME */
+ memset(b, 0, (length + 1) * sizeof(*b));
+ b[0] = length;
+ return b;
+}
+
+void bn_restore_invariant(Bignum b)
+{
+ while (b[0] > 1 && b[b[0]] == 0)
+ b[0]--;
+}
+
+Bignum copybn(Bignum orig)
+{
+ Bignum b = snewn(orig[0] + 1, BignumInt);
+ if (!b)
+ abort(); /* FIXME */
+ memcpy(b, orig, (orig[0] + 1) * sizeof(*b));
+ return b;
+}
+
+void freebn(Bignum b)
+{
+ /*
+ * Burn the evidence, just in case.
+ */
+ smemclr(b, sizeof(b[0]) * (b[0] + 1));
+ sfree(b);
+}
+
+Bignum bn_power_2(int n)
+{
+ Bignum ret;
+
+ assert(n >= 0);
+
+ ret = newbn(n / BIGNUM_INT_BITS + 1);
+ bignum_set_bit(ret, n, 1);
+ return ret;
+}
+
+/*
+ * Internal addition. Sets c = a - b, where 'a', 'b' and 'c' are all
+ * big-endian arrays of 'len' BignumInts. Returns a BignumInt carried
+ * off the top.
+ */
+static BignumInt internal_add(const BignumInt *a, const BignumInt *b,
+ BignumInt *c, int len)
+{
+ int i;
+ BignumDblInt carry = 0;
+
+ for (i = len-1; i >= 0; i--) {
+ carry += (BignumDblInt)a[i] + b[i];
+ c[i] = (BignumInt)carry;
+ carry >>= BIGNUM_INT_BITS;
+ }
+
+ return (BignumInt)carry;
+}
+
+/*
+ * Internal subtraction. Sets c = a - b, where 'a', 'b' and 'c' are
+ * all big-endian arrays of 'len' BignumInts. Any borrow from the top
+ * is ignored.
+ */
+static void internal_sub(const BignumInt *a, const BignumInt *b,
+ BignumInt *c, int len)
+{
+ int i;
+ BignumDblInt carry = 1;
+
+ for (i = len-1; i >= 0; i--) {
+ carry += (BignumDblInt)a[i] + (b[i] ^ BIGNUM_INT_MASK);
+ c[i] = (BignumInt)carry;
+ carry >>= BIGNUM_INT_BITS;
+ }
+}
+
+/*
+ * Compute c = a * b.
+ * Input is in the first len words of a and b.
+ * Result is returned in the first 2*len words of c.
+ *
+ * 'scratch' must point to an array of BignumInt of size at least
+ * mul_compute_scratch(len). (This covers the needs of internal_mul
+ * and all its recursive calls to itself.)
+ */
+#define KARATSUBA_THRESHOLD 50
+static int mul_compute_scratch(int len)
+{
+ int ret = 0;
+ while (len > KARATSUBA_THRESHOLD) {
+ int toplen = len/2, botlen = len - toplen; /* botlen is the bigger */
+ int midlen = botlen + 1;
+ ret += 4*midlen;
+ len = midlen;
+ }
+ return ret;
+}
+static void internal_mul(const BignumInt *a, const BignumInt *b,
+ BignumInt *c, int len, BignumInt *scratch)
+{
+ if (len > KARATSUBA_THRESHOLD) {
+ int i;
+
+ /*
+ * Karatsuba divide-and-conquer algorithm. Cut each input in
+ * half, so that it's expressed as two big 'digits' in a giant
+ * base D:
+ *
+ * a = a_1 D + a_0
+ * b = b_1 D + b_0
+ *
+ * Then the product is of course
+ *
+ * ab = a_1 b_1 D^2 + (a_1 b_0 + a_0 b_1) D + a_0 b_0
+ *
+ * and we compute the three coefficients by recursively
+ * calling ourself to do half-length multiplications.
+ *
+ * The clever bit that makes this worth doing is that we only
+ * need _one_ half-length multiplication for the central
+ * coefficient rather than the two that it obviouly looks
+ * like, because we can use a single multiplication to compute
+ *
+ * (a_1 + a_0) (b_1 + b_0) = a_1 b_1 + a_1 b_0 + a_0 b_1 + a_0 b_0
+ *
+ * and then we subtract the other two coefficients (a_1 b_1
+ * and a_0 b_0) which we were computing anyway.
+ *
+ * Hence we get to multiply two numbers of length N in about
+ * three times as much work as it takes to multiply numbers of
+ * length N/2, which is obviously better than the four times
+ * as much work it would take if we just did a long
+ * conventional multiply.
+ */
+
+ int toplen = len/2, botlen = len - toplen; /* botlen is the bigger */
+ int midlen = botlen + 1;
+ BignumDblInt carry;
+#ifdef KARA_DEBUG
+ int i;
+#endif
+
+ /*
+ * The coefficients a_1 b_1 and a_0 b_0 just avoid overlapping
+ * in the output array, so we can compute them immediately in
+ * place.
+ */
+
+#ifdef KARA_DEBUG
+ printf("a1,a0 = 0x");
+ for (i = 0; i < len; i++) {
+ if (i == toplen) printf(", 0x");
+ printf("%0*x", BIGNUM_INT_BITS/4, a[i]);
+ }
+ printf("\n");
+ printf("b1,b0 = 0x");
+ for (i = 0; i < len; i++) {
+ if (i == toplen) printf(", 0x");
+ printf("%0*x", BIGNUM_INT_BITS/4, b[i]);
+ }
+ printf("\n");
+#endif
+
+ /* a_1 b_1 */
+ internal_mul(a, b, c, toplen, scratch);
+#ifdef KARA_DEBUG
+ printf("a1b1 = 0x");
+ for (i = 0; i < 2*toplen; i++) {
+ printf("%0*x", BIGNUM_INT_BITS/4, c[i]);
+ }
+ printf("\n");
+#endif
+
+ /* a_0 b_0 */
+ internal_mul(a + toplen, b + toplen, c + 2*toplen, botlen, scratch);
+#ifdef KARA_DEBUG
+ printf("a0b0 = 0x");
+ for (i = 0; i < 2*botlen; i++) {
+ printf("%0*x", BIGNUM_INT_BITS/4, c[2*toplen+i]);
+ }
+ printf("\n");
+#endif
+
+ /* Zero padding. midlen exceeds toplen by at most 2, so just
+ * zero the first two words of each input and the rest will be
+ * copied over. */
+ scratch[0] = scratch[1] = scratch[midlen] = scratch[midlen+1] = 0;
+
+ for (i = 0; i < toplen; i++) {
+ scratch[midlen - toplen + i] = a[i]; /* a_1 */
+ scratch[2*midlen - toplen + i] = b[i]; /* b_1 */
+ }
+
+ /* compute a_1 + a_0 */
+ scratch[0] = internal_add(scratch+1, a+toplen, scratch+1, botlen);
+#ifdef KARA_DEBUG
+ printf("a1plusa0 = 0x");
+ for (i = 0; i < midlen; i++) {
+ printf("%0*x", BIGNUM_INT_BITS/4, scratch[i]);
+ }
+ printf("\n");
+#endif
+ /* compute b_1 + b_0 */
+ scratch[midlen] = internal_add(scratch+midlen+1, b+toplen,
+ scratch+midlen+1, botlen);
+#ifdef KARA_DEBUG
+ printf("b1plusb0 = 0x");
+ for (i = 0; i < midlen; i++) {
+ printf("%0*x", BIGNUM_INT_BITS/4, scratch[midlen+i]);
+ }
+ printf("\n");
+#endif
+
+ /*
+ * Now we can do the third multiplication.
+ */
+ internal_mul(scratch, scratch + midlen, scratch + 2*midlen, midlen,
+ scratch + 4*midlen);
+#ifdef KARA_DEBUG
+ printf("a1plusa0timesb1plusb0 = 0x");
+ for (i = 0; i < 2*midlen; i++) {
+ printf("%0*x", BIGNUM_INT_BITS/4, scratch[2*midlen+i]);
+ }
+ printf("\n");
+#endif
+
+ /*
+ * Now we can reuse the first half of 'scratch' to compute the
+ * sum of the outer two coefficients, to subtract from that
+ * product to obtain the middle one.
+ */
+ scratch[0] = scratch[1] = scratch[2] = scratch[3] = 0;
+ for (i = 0; i < 2*toplen; i++)
+ scratch[2*midlen - 2*toplen + i] = c[i];
+ scratch[1] = internal_add(scratch+2, c + 2*toplen,
+ scratch+2, 2*botlen);
+#ifdef KARA_DEBUG
+ printf("a1b1plusa0b0 = 0x");
+ for (i = 0; i < 2*midlen; i++) {
+ printf("%0*x", BIGNUM_INT_BITS/4, scratch[i]);
+ }
+ printf("\n");
+#endif
+
+ internal_sub(scratch + 2*midlen, scratch,
+ scratch + 2*midlen, 2*midlen);
+#ifdef KARA_DEBUG
+ printf("a1b0plusa0b1 = 0x");
+ for (i = 0; i < 2*midlen; i++) {
+ printf("%0*x", BIGNUM_INT_BITS/4, scratch[2*midlen+i]);
+ }
+ printf("\n");
+#endif
+
+ /*
+ * And now all we need to do is to add that middle coefficient
+ * back into the output. We may have to propagate a carry
+ * further up the output, but we can be sure it won't
+ * propagate right the way off the top.
+ */
+ carry = internal_add(c + 2*len - botlen - 2*midlen,
+ scratch + 2*midlen,
+ c + 2*len - botlen - 2*midlen, 2*midlen);
+ i = 2*len - botlen - 2*midlen - 1;
+ while (carry) {
+ assert(i >= 0);
+ carry += c[i];
+ c[i] = (BignumInt)carry;
+ carry >>= BIGNUM_INT_BITS;
+ i--;
+ }
+#ifdef KARA_DEBUG
+ printf("ab = 0x");
+ for (i = 0; i < 2*len; i++) {
+ printf("%0*x", BIGNUM_INT_BITS/4, c[i]);
+ }
+ printf("\n");
+#endif
+
+ } else {
+ int i;
+ BignumInt carry;
+ BignumDblInt t;
+ const BignumInt *ap, *bp;
+ BignumInt *cp, *cps;
+
+ /*
+ * Multiply in the ordinary O(N^2) way.
+ */
+
+ for (i = 0; i < 2 * len; i++)
+ c[i] = 0;
+
+ for (cps = c + 2*len, ap = a + len; ap-- > a; cps--) {
+ carry = 0;
+ for (cp = cps, bp = b + len; cp--, bp-- > b ;) {
+ t = (MUL_WORD(*ap, *bp) + carry) + *cp;
+ *cp = (BignumInt) t;
+ carry = (BignumInt)(t >> BIGNUM_INT_BITS);
+ }
+ *cp = carry;
+ }
+ }
+}
+
+/*
+ * Variant form of internal_mul used for the initial step of
+ * Montgomery reduction. Only bothers outputting 'len' words
+ * (everything above that is thrown away).
+ */
+static void internal_mul_low(const BignumInt *a, const BignumInt *b,
+ BignumInt *c, int len, BignumInt *scratch)
+{
+ if (len > KARATSUBA_THRESHOLD) {
+ int i;
+
+ /*
+ * Karatsuba-aware version of internal_mul_low. As before, we
+ * express each input value as a shifted combination of two
+ * halves:
+ *
+ * a = a_1 D + a_0
+ * b = b_1 D + b_0
+ *
+ * Then the full product is, as before,
+ *
+ * ab = a_1 b_1 D^2 + (a_1 b_0 + a_0 b_1) D + a_0 b_0
+ *
+ * Provided we choose D on the large side (so that a_0 and b_0
+ * are _at least_ as long as a_1 and b_1), we don't need the
+ * topmost term at all, and we only need half of the middle
+ * term. So there's no point in doing the proper Karatsuba
+ * optimisation which computes the middle term using the top
+ * one, because we'd take as long computing the top one as
+ * just computing the middle one directly.
+ *
+ * So instead, we do a much more obvious thing: we call the
+ * fully optimised internal_mul to compute a_0 b_0, and we
+ * recursively call ourself to compute the _bottom halves_ of
+ * a_1 b_0 and a_0 b_1, each of which we add into the result
+ * in the obvious way.
+ *
+ * In other words, there's no actual Karatsuba _optimisation_
+ * in this function; the only benefit in doing it this way is
+ * that we call internal_mul proper for a large part of the
+ * work, and _that_ can optimise its operation.
+ */
+
+ int toplen = len/2, botlen = len - toplen; /* botlen is the bigger */
+
+ /*
+ * Scratch space for the various bits and pieces we're going
+ * to be adding together: we need botlen*2 words for a_0 b_0
+ * (though we may end up throwing away its topmost word), and
+ * toplen words for each of a_1 b_0 and a_0 b_1. That adds up
+ * to exactly 2*len.
+ */
+
+ /* a_0 b_0 */
+ internal_mul(a + toplen, b + toplen, scratch + 2*toplen, botlen,
+ scratch + 2*len);
+
+ /* a_1 b_0 */
+ internal_mul_low(a, b + len - toplen, scratch + toplen, toplen,
+ scratch + 2*len);
+
+ /* a_0 b_1 */
+ internal_mul_low(a + len - toplen, b, scratch, toplen,
+ scratch + 2*len);
+
+ /* Copy the bottom half of the big coefficient into place */
+ for (i = 0; i < botlen; i++)
+ c[toplen + i] = scratch[2*toplen + botlen + i];
+
+ /* Add the two small coefficients, throwing away the returned carry */
+ internal_add(scratch, scratch + toplen, scratch, toplen);
+
+ /* And add that to the large coefficient, leaving the result in c. */
+ internal_add(scratch, scratch + 2*toplen + botlen - toplen,
+ c, toplen);
+
+ } else {
+ int i;
+ BignumInt carry;
+ BignumDblInt t;
+ const BignumInt *ap, *bp;
+ BignumInt *cp, *cps;
+
+ /*
+ * Multiply in the ordinary O(N^2) way.
+ */
+
+ for (i = 0; i < len; i++)
+ c[i] = 0;
+
+ for (cps = c + len, ap = a + len; ap-- > a; cps--) {
+ carry = 0;
+ for (cp = cps, bp = b + len; bp--, cp-- > c ;) {
+ t = (MUL_WORD(*ap, *bp) + carry) + *cp;
+ *cp = (BignumInt) t;
+ carry = (BignumInt)(t >> BIGNUM_INT_BITS);
+ }
+ }
+ }
+}
+
+/*
+ * Montgomery reduction. Expects x to be a big-endian array of 2*len
+ * BignumInts whose value satisfies 0 <= x < rn (where r = 2^(len *
+ * BIGNUM_INT_BITS) is the Montgomery base). Returns in the same array
+ * a value x' which is congruent to xr^{-1} mod n, and satisfies 0 <=
+ * x' < n.
+ *
+ * 'n' and 'mninv' should be big-endian arrays of 'len' BignumInts
+ * each, containing respectively n and the multiplicative inverse of
+ * -n mod r.
+ *
+ * 'tmp' is an array of BignumInt used as scratch space, of length at
+ * least 3*len + mul_compute_scratch(len).
+ */
+static void monty_reduce(BignumInt *x, const BignumInt *n,
+ const BignumInt *mninv, BignumInt *tmp, int len)
+{
+ int i;
+ BignumInt carry;
+
+ /*
+ * Multiply x by (-n)^{-1} mod r. This gives us a value m such
+ * that mn is congruent to -x mod r. Hence, mn+x is an exact
+ * multiple of r, and is also (obviously) congruent to x mod n.
+ */
+ internal_mul_low(x + len, mninv, tmp, len, tmp + 3*len);
+
+ /*
+ * Compute t = (mn+x)/r in ordinary, non-modular, integer
+ * arithmetic. By construction this is exact, and is congruent mod
+ * n to x * r^{-1}, i.e. the answer we want.
+ *
+ * The following multiply leaves that answer in the _most_
+ * significant half of the 'x' array, so then we must shift it
+ * down.
+ */
+ internal_mul(tmp, n, tmp+len, len, tmp + 3*len);
+ carry = internal_add(x, tmp+len, x, 2*len);
+ for (i = 0; i < len; i++)
+ x[len + i] = x[i], x[i] = 0;
+
+ /*
+ * Reduce t mod n. This doesn't require a full-on division by n,
+ * but merely a test and single optional subtraction, since we can
+ * show that 0 <= t < 2n.
+ *
+ * Proof:
+ * + we computed m mod r, so 0 <= m < r.
+ * + so 0 <= mn < rn, obviously
+ * + hence we only need 0 <= x < rn to guarantee that 0 <= mn+x < 2rn
+ * + yielding 0 <= (mn+x)/r < 2n as required.
+ */
+ if (!carry) {
+ for (i = 0; i < len; i++)
+ if (x[len + i] != n[i])
+ break;
+ }
+ if (carry || i >= len || x[len + i] > n[i])
+ internal_sub(x+len, n, x+len, len);
+}
+
+static void internal_add_shifted(BignumInt *number,
+ unsigned n, int shift)
+{
+ int word = 1 + (shift / BIGNUM_INT_BITS);
+ int bshift = shift % BIGNUM_INT_BITS;
+ BignumDblInt addend;
+
+ addend = (BignumDblInt)n << bshift;
+
+ while (addend) {
+ assert(word <= number[0]);
+ addend += number[word];
+ number[word] = (BignumInt) addend & BIGNUM_INT_MASK;
+ addend >>= BIGNUM_INT_BITS;
+ word++;
+ }
+}
+
+/*
+ * Compute a = a % m.
+ * Input in first alen words of a and first mlen words of m.
+ * Output in first alen words of a
+ * (of which first alen-mlen words will be zero).
+ * The MSW of m MUST have its high bit set.
+ * Quotient is accumulated in the `quotient' array, which is a Bignum
+ * rather than the internal bigendian format. Quotient parts are shifted
+ * left by `qshift' before adding into quot.
+ */
+static void internal_mod(BignumInt *a, int alen,
+ BignumInt *m, int mlen,
+ BignumInt *quot, int qshift)
+{
+ BignumInt m0, m1;
+ unsigned int h;
+ int i, k;
+
+ m0 = m[0];
+ assert(m0 >> (BIGNUM_INT_BITS-1) == 1);
+ if (mlen > 1)
+ m1 = m[1];
+ else
+ m1 = 0;
+
+ for (i = 0; i <= alen - mlen; i++) {
+ BignumDblInt t;
+ unsigned int q, r, c, ai1;
+
+ if (i == 0) {
+ h = 0;
+ } else {
+ h = a[i - 1];
+ a[i - 1] = 0;
+ }
+
+ if (i == alen - 1)
+ ai1 = 0;
+ else
+ ai1 = a[i + 1];
+
+ /* Find q = h:a[i] / m0 */
+ if (h >= m0) {
+ /*
+ * Special case.
+ *
+ * To illustrate it, suppose a BignumInt is 8 bits, and
+ * we are dividing (say) A1:23:45:67 by A1:B2:C3. Then
+ * our initial division will be 0xA123 / 0xA1, which
+ * will give a quotient of 0x100 and a divide overflow.
+ * However, the invariants in this division algorithm
+ * are not violated, since the full number A1:23:... is
+ * _less_ than the quotient prefix A1:B2:... and so the
+ * following correction loop would have sorted it out.
+ *
+ * In this situation we set q to be the largest
+ * quotient we _can_ stomach (0xFF, of course).
+ */
+ q = BIGNUM_INT_MASK;
+ } else {
+ /* Macro doesn't want an array subscript expression passed
+ * into it (see definition), so use a temporary. */
+ BignumInt tmplo = a[i];
+ DIVMOD_WORD(q, r, h, tmplo, m0);
+
+ /* Refine our estimate of q by looking at
+ h:a[i]:a[i+1] / m0:m1 */
+ t = MUL_WORD(m1, q);
+ if (t > ((BignumDblInt) r << BIGNUM_INT_BITS) + ai1) {
+ q--;
+ t -= m1;
+ r = (r + m0) & BIGNUM_INT_MASK; /* overflow? */
+ if (r >= (BignumDblInt) m0 &&
+ t > ((BignumDblInt) r << BIGNUM_INT_BITS) + ai1) q--;
+ }
+ }
+
+ /* Subtract q * m from a[i...] */
+ c = 0;
+ for (k = mlen - 1; k >= 0; k--) {
+ t = MUL_WORD(q, m[k]);
+ t += c;
+ c = (unsigned)(t >> BIGNUM_INT_BITS);
+ if ((BignumInt) t > a[i + k])
+ c++;
+ a[i + k] -= (BignumInt) t;
+ }
+
+ /* Add back m in case of borrow */
+ if (c != h) {
+ t = 0;
+ for (k = mlen - 1; k >= 0; k--) {
+ t += m[k];
+ t += a[i + k];
+ a[i + k] = (BignumInt) t;
+ t = t >> BIGNUM_INT_BITS;
+ }
+ q--;
+ }
+ if (quot)
+ internal_add_shifted(quot, q, qshift + BIGNUM_INT_BITS * (alen - mlen - i));
+ }
+}
+
+/*
+ * Compute (base ^ exp) % mod, the pedestrian way.
+ */
+Bignum modpow_simple(Bignum base_in, Bignum exp, Bignum mod)
+{
+ BignumInt *a, *b, *n, *m, *scratch;
+ int mshift;
+ int mlen, scratchlen, i, j;
+ Bignum base, result;
+
+ /*
+ * The most significant word of mod needs to be non-zero. It
+ * should already be, but let's make sure.
+ */
+ assert(mod[mod[0]] != 0);
+
+ /*
+ * Make sure the base is smaller than the modulus, by reducing
+ * it modulo the modulus if not.
+ */
+ base = bigmod(base_in, mod);
+
+ /* Allocate m of size mlen, copy mod to m */
+ /* We use big endian internally */
+ mlen = mod[0];
+ m = snewn(mlen, BignumInt);
+ for (j = 0; j < mlen; j++)
+ m[j] = mod[mod[0] - j];
+
+ /* Shift m left to make msb bit set */
+ for (mshift = 0; mshift < BIGNUM_INT_BITS-1; mshift++)
+ if ((m[0] << mshift) & BIGNUM_TOP_BIT)
+ break;
+ if (mshift) {
+ for (i = 0; i < mlen - 1; i++)
+ m[i] = (m[i] << mshift) | (m[i + 1] >> (BIGNUM_INT_BITS - mshift));
+ m[mlen - 1] = m[mlen - 1] << mshift;
+ }
+
+ /* Allocate n of size mlen, copy base to n */
+ n = snewn(mlen, BignumInt);
+ i = mlen - base[0];
+ for (j = 0; j < i; j++)
+ n[j] = 0;
+ for (j = 0; j < (int)base[0]; j++)
+ n[i + j] = base[base[0] - j];
+
+ /* Allocate a and b of size 2*mlen. Set a = 1 */
+ a = snewn(2 * mlen, BignumInt);
+ b = snewn(2 * mlen, BignumInt);
+ for (i = 0; i < 2 * mlen; i++)
+ a[i] = 0;
+ a[2 * mlen - 1] = 1;
+
+ /* Scratch space for multiplies */
+ scratchlen = mul_compute_scratch(mlen);
+ scratch = snewn(scratchlen, BignumInt);
+
+ /* Skip leading zero bits of exp. */
+ i = 0;
+ j = BIGNUM_INT_BITS-1;
+ while (i < (int)exp[0] && (exp[exp[0] - i] & (1 << j)) == 0) {
+ j--;
+ if (j < 0) {
+ i++;
+ j = BIGNUM_INT_BITS-1;
+ }
+ }
+
+ /* Main computation */
+ while (i < (int)exp[0]) {
+ while (j >= 0) {
+ internal_mul(a + mlen, a + mlen, b, mlen, scratch);
+ internal_mod(b, mlen * 2, m, mlen, NULL, 0);
+ if ((exp[exp[0] - i] & (1 << j)) != 0) {
+ internal_mul(b + mlen, n, a, mlen, scratch);
+ internal_mod(a, mlen * 2, m, mlen, NULL, 0);
+ } else {
+ BignumInt *t;
+ t = a;
+ a = b;
+ b = t;
+ }
+ j--;
+ }
+ i++;
+ j = BIGNUM_INT_BITS-1;
+ }
+
+ /* Fixup result in case the modulus was shifted */
+ if (mshift) {
+ for (i = mlen - 1; i < 2 * mlen - 1; i++)
+ a[i] = (a[i] << mshift) | (a[i + 1] >> (BIGNUM_INT_BITS - mshift));
+ a[2 * mlen - 1] = a[2 * mlen - 1] << mshift;
+ internal_mod(a, mlen * 2, m, mlen, NULL, 0);
+ for (i = 2 * mlen - 1; i >= mlen; i--)
+ a[i] = (a[i] >> mshift) | (a[i - 1] << (BIGNUM_INT_BITS - mshift));
+ }
+
+ /* Copy result to buffer */
+ result = newbn(mod[0]);
+ for (i = 0; i < mlen; i++)
+ result[result[0] - i] = a[i + mlen];
+ while (result[0] > 1 && result[result[0]] == 0)
+ result[0]--;
+
+ /* Free temporary arrays */
+ smemclr(a, 2 * mlen * sizeof(*a));
+ sfree(a);
+ smemclr(scratch, scratchlen * sizeof(*scratch));
+ sfree(scratch);
+ smemclr(b, 2 * mlen * sizeof(*b));
+ sfree(b);
+ smemclr(m, mlen * sizeof(*m));
+ sfree(m);
+ smemclr(n, mlen * sizeof(*n));
+ sfree(n);
+
+ freebn(base);
+
+ return result;
+}
+
+/*
+ * Compute (base ^ exp) % mod. Uses the Montgomery multiplication
+ * technique where possible, falling back to modpow_simple otherwise.
+ */
+Bignum modpow(Bignum base_in, Bignum exp, Bignum mod)
+{
+ BignumInt *a, *b, *x, *n, *mninv, *scratch;
+ int len, scratchlen, i, j;
+ Bignum base, base2, r, rn, inv, result;
+
+ /*
+ * The most significant word of mod needs to be non-zero. It
+ * should already be, but let's make sure.
+ */
+ assert(mod[mod[0]] != 0);
+
+ /*
+ * mod had better be odd, or we can't do Montgomery multiplication
+ * using a power of two at all.
+ */
+ if (!(mod[1] & 1))
+ return modpow_simple(base_in, exp, mod);
+
+ /*
+ * Make sure the base is smaller than the modulus, by reducing
+ * it modulo the modulus if not.
+ */
+ base = bigmod(base_in, mod);
+
+ /*
+ * Compute the inverse of n mod r, for monty_reduce. (In fact we
+ * want the inverse of _minus_ n mod r, but we'll sort that out
+ * below.)
+ */
+ len = mod[0];
+ r = bn_power_2(BIGNUM_INT_BITS * len);
+ inv = modinv(mod, r);
+ assert(inv); /* cannot fail, since mod is odd and r is a power of 2 */
+
+ /*
+ * Multiply the base by r mod n, to get it into Montgomery
+ * representation.
+ */
+ base2 = modmul(base, r, mod);
+ freebn(base);
+ base = base2;
+
+ rn = bigmod(r, mod); /* r mod n, i.e. Montgomerified 1 */
+
+ freebn(r); /* won't need this any more */
+
+ /*
+ * Set up internal arrays of the right lengths, in big-endian
+ * format, containing the base, the modulus, and the modulus's
+ * inverse.
+ */
+ n = snewn(len, BignumInt);
+ for (j = 0; j < len; j++)
+ n[len - 1 - j] = mod[j + 1];
+
+ mninv = snewn(len, BignumInt);
+ for (j = 0; j < len; j++)
+ mninv[len - 1 - j] = (j < (int)inv[0] ? inv[j + 1] : 0);
+ freebn(inv); /* we don't need this copy of it any more */
+ /* Now negate mninv mod r, so it's the inverse of -n rather than +n. */
+ x = snewn(len, BignumInt);
+ for (j = 0; j < len; j++)
+ x[j] = 0;
+ internal_sub(x, mninv, mninv, len);
+
+ /* x = snewn(len, BignumInt); */ /* already done above */
+ for (j = 0; j < len; j++)
+ x[len - 1 - j] = (j < (int)base[0] ? base[j + 1] : 0);
+ freebn(base); /* we don't need this copy of it any more */
+
+ a = snewn(2*len, BignumInt);
+ b = snewn(2*len, BignumInt);
+ for (j = 0; j < len; j++)
+ a[2*len - 1 - j] = (j < (int)rn[0] ? rn[j + 1] : 0);
+ freebn(rn);
+
+ /* Scratch space for multiplies */
+ scratchlen = 3*len + mul_compute_scratch(len);
+ scratch = snewn(scratchlen, BignumInt);
+
+ /* Skip leading zero bits of exp. */
+ i = 0;
+ j = BIGNUM_INT_BITS-1;
+ while (i < (int)exp[0] && (exp[exp[0] - i] & (1 << j)) == 0) {
+ j--;
+ if (j < 0) {
+ i++;
+ j = BIGNUM_INT_BITS-1;
+ }
+ }
+
+ /* Main computation */
+ while (i < (int)exp[0]) {
+ while (j >= 0) {
+ internal_mul(a + len, a + len, b, len, scratch);
+ monty_reduce(b, n, mninv, scratch, len);
+ if ((exp[exp[0] - i] & (1 << j)) != 0) {
+ internal_mul(b + len, x, a, len, scratch);
+ monty_reduce(a, n, mninv, scratch, len);
+ } else {
+ BignumInt *t;
+ t = a;
+ a = b;
+ b = t;
+ }
+ j--;
+ }
+ i++;
+ j = BIGNUM_INT_BITS-1;
+ }
+
+ /*
+ * Final monty_reduce to get back from the adjusted Montgomery
+ * representation.
+ */
+ monty_reduce(a, n, mninv, scratch, len);
+
+ /* Copy result to buffer */
+ result = newbn(mod[0]);
+ for (i = 0; i < len; i++)
+ result[result[0] - i] = a[i + len];
+ while (result[0] > 1 && result[result[0]] == 0)
+ result[0]--;
+
+ /* Free temporary arrays */
+ smemclr(scratch, scratchlen * sizeof(*scratch));
+ sfree(scratch);
+ smemclr(a, 2 * len * sizeof(*a));
+ sfree(a);
+ smemclr(b, 2 * len * sizeof(*b));
+ sfree(b);
+ smemclr(mninv, len * sizeof(*mninv));
+ sfree(mninv);
+ smemclr(n, len * sizeof(*n));
+ sfree(n);
+ smemclr(x, len * sizeof(*x));
+ sfree(x);
+
+ return result;
+}
+
+/*
+ * Compute (p * q) % mod.
+ * The most significant word of mod MUST be non-zero.
+ * We assume that the result array is the same size as the mod array.
+ */
+Bignum modmul(Bignum p, Bignum q, Bignum mod)
+{
+ BignumInt *a, *n, *m, *o, *scratch;
+ int mshift, scratchlen;
+ int pqlen, mlen, rlen, i, j;
+ Bignum result;
+
+ /*
+ * The most significant word of mod needs to be non-zero. It
+ * should already be, but let's make sure.
+ */
+ assert(mod[mod[0]] != 0);
+
+ /* Allocate m of size mlen, copy mod to m */
+ /* We use big endian internally */
+ mlen = mod[0];
+ m = snewn(mlen, BignumInt);
+ for (j = 0; j < mlen; j++)
+ m[j] = mod[mod[0] - j];
+
+ /* Shift m left to make msb bit set */
+ for (mshift = 0; mshift < BIGNUM_INT_BITS-1; mshift++)
+ if ((m[0] << mshift) & BIGNUM_TOP_BIT)
+ break;
+ if (mshift) {
+ for (i = 0; i < mlen - 1; i++)
+ m[i] = (m[i] << mshift) | (m[i + 1] >> (BIGNUM_INT_BITS - mshift));
+ m[mlen - 1] = m[mlen - 1] << mshift;
+ }
+
+ pqlen = (p[0] > q[0] ? p[0] : q[0]);
+
+ /*
+ * Make sure that we're allowing enough space. The shifting below
+ * will underflow the vectors we allocate if pqlen is too small.
+ */
+ if (2*pqlen <= mlen)
+ pqlen = mlen/2 + 1;
+
+ /* Allocate n of size pqlen, copy p to n */
+ n = snewn(pqlen, BignumInt);
+ i = pqlen - p[0];
+ for (j = 0; j < i; j++)
+ n[j] = 0;
+ for (j = 0; j < (int)p[0]; j++)
+ n[i + j] = p[p[0] - j];
+
+ /* Allocate o of size pqlen, copy q to o */
+ o = snewn(pqlen, BignumInt);
+ i = pqlen - q[0];
+ for (j = 0; j < i; j++)
+ o[j] = 0;
+ for (j = 0; j < (int)q[0]; j++)
+ o[i + j] = q[q[0] - j];
+
+ /* Allocate a of size 2*pqlen for result */
+ a = snewn(2 * pqlen, BignumInt);
+
+ /* Scratch space for multiplies */
+ scratchlen = mul_compute_scratch(pqlen);
+ scratch = snewn(scratchlen, BignumInt);
+
+ /* Main computation */
+ internal_mul(n, o, a, pqlen, scratch);
+ internal_mod(a, pqlen * 2, m, mlen, NULL, 0);
+
+ /* Fixup result in case the modulus was shifted */
+ if (mshift) {
+ for (i = 2 * pqlen - mlen - 1; i < 2 * pqlen - 1; i++)
+ a[i] = (a[i] << mshift) | (a[i + 1] >> (BIGNUM_INT_BITS - mshift));
+ a[2 * pqlen - 1] = a[2 * pqlen - 1] << mshift;
+ internal_mod(a, pqlen * 2, m, mlen, NULL, 0);
+ for (i = 2 * pqlen - 1; i >= 2 * pqlen - mlen; i--)
+ a[i] = (a[i] >> mshift) | (a[i - 1] << (BIGNUM_INT_BITS - mshift));
+ }
+
+ /* Copy result to buffer */
+ rlen = (mlen < pqlen * 2 ? mlen : pqlen * 2);
+ result = newbn(rlen);
+ for (i = 0; i < rlen; i++)
+ result[result[0] - i] = a[i + 2 * pqlen - rlen];
+ while (result[0] > 1 && result[result[0]] == 0)
+ result[0]--;
+
+ /* Free temporary arrays */
+ smemclr(scratch, scratchlen * sizeof(*scratch));
+ sfree(scratch);
+ smemclr(a, 2 * pqlen * sizeof(*a));
+ sfree(a);
+ smemclr(m, mlen * sizeof(*m));
+ sfree(m);
+ smemclr(n, pqlen * sizeof(*n));
+ sfree(n);
+ smemclr(o, pqlen * sizeof(*o));
+ sfree(o);
+
+ return result;
+}
+
+/*
+ * Compute p % mod.
+ * The most significant word of mod MUST be non-zero.
+ * We assume that the result array is the same size as the mod array.
+ * We optionally write out a quotient if `quotient' is non-NULL.
+ * We can avoid writing out the result if `result' is NULL.
+ */
+static void bigdivmod(Bignum p, Bignum mod, Bignum result, Bignum quotient)
+{
+ BignumInt *n, *m;
+ int mshift;
+ int plen, mlen, i, j;
+
+ /*
+ * The most significant word of mod needs to be non-zero. It
+ * should already be, but let's make sure.
+ */
+ assert(mod[mod[0]] != 0);
+
+ /* Allocate m of size mlen, copy mod to m */
+ /* We use big endian internally */
+ mlen = mod[0];
+ m = snewn(mlen, BignumInt);
+ for (j = 0; j < mlen; j++)
+ m[j] = mod[mod[0] - j];
+
+ /* Shift m left to make msb bit set */
+ for (mshift = 0; mshift < BIGNUM_INT_BITS-1; mshift++)
+ if ((m[0] << mshift) & BIGNUM_TOP_BIT)
+ break;
+ if (mshift) {
+ for (i = 0; i < mlen - 1; i++)
+ m[i] = (m[i] << mshift) | (m[i + 1] >> (BIGNUM_INT_BITS - mshift));
+ m[mlen - 1] = m[mlen - 1] << mshift;
+ }
+
+ plen = p[0];
+ /* Ensure plen > mlen */
+ if (plen <= mlen)
+ plen = mlen + 1;
+
+ /* Allocate n of size plen, copy p to n */
+ n = snewn(plen, BignumInt);
+ for (j = 0; j < plen; j++)
+ n[j] = 0;
+ for (j = 1; j <= (int)p[0]; j++)
+ n[plen - j] = p[j];
+
+ /* Main computation */
+ internal_mod(n, plen, m, mlen, quotient, mshift);
+
+ /* Fixup result in case the modulus was shifted */
+ if (mshift) {
+ for (i = plen - mlen - 1; i < plen - 1; i++)
+ n[i] = (n[i] << mshift) | (n[i + 1] >> (BIGNUM_INT_BITS - mshift));
+ n[plen - 1] = n[plen - 1] << mshift;
+ internal_mod(n, plen, m, mlen, quotient, 0);
+ for (i = plen - 1; i >= plen - mlen; i--)
+ n[i] = (n[i] >> mshift) | (n[i - 1] << (BIGNUM_INT_BITS - mshift));
+ }
+
+ /* Copy result to buffer */
+ if (result) {
+ for (i = 1; i <= (int)result[0]; i++) {
+ int j = plen - i;
+ result[i] = j >= 0 ? n[j] : 0;
+ }
+ }
+
+ /* Free temporary arrays */
+ smemclr(m, mlen * sizeof(*m));
+ sfree(m);
+ smemclr(n, plen * sizeof(*n));
+ sfree(n);
+}
+
+/*
+ * Decrement a number.
+ */
+void decbn(Bignum bn)
+{
+ int i = 1;
+ while (i < (int)bn[0] && bn[i] == 0)
+ bn[i++] = BIGNUM_INT_MASK;
+ bn[i]--;
+}
+
+Bignum bignum_from_bytes(const unsigned char *data, int nbytes)
+{
+ Bignum result;
+ int w, i;
+
+ assert(nbytes >= 0 && nbytes < INT_MAX/8);
+
+ w = (nbytes + BIGNUM_INT_BYTES - 1) / BIGNUM_INT_BYTES; /* bytes->words */
+
+ result = newbn(w);
+ for (i = 1; i <= w; i++)
+ result[i] = 0;
+ for (i = nbytes; i--;) {
+ unsigned char byte = *data++;
+ result[1 + i / BIGNUM_INT_BYTES] |= byte << (8*i % BIGNUM_INT_BITS);
+ }
+
+ while (result[0] > 1 && result[result[0]] == 0)
+ result[0]--;
+ return result;
+}
+
+/*
+ * Read an SSH-1-format bignum from a data buffer. Return the number
+ * of bytes consumed, or -1 if there wasn't enough data.
+ */
+int ssh1_read_bignum(const unsigned char *data, int len, Bignum * result)
+{
+ const unsigned char *p = data;
+ int i;
+ int w, b;
+
+ if (len < 2)
+ return -1;
+
+ w = 0;
+ for (i = 0; i < 2; i++)
+ w = (w << 8) + *p++;
+ b = (w + 7) / 8; /* bits -> bytes */
+
+ if (len < b+2)
+ return -1;
+
+ if (!result) /* just return length */
+ return b + 2;
+
+ *result = bignum_from_bytes(p, b);
+
+ return p + b - data;
+}
+
+/*
+ * Return the bit count of a bignum, for SSH-1 encoding.
+ */
+int bignum_bitcount(Bignum bn)
+{
+ int bitcount = bn[0] * BIGNUM_INT_BITS - 1;
+ while (bitcount >= 0
+ && (bn[bitcount / BIGNUM_INT_BITS + 1] >> (bitcount % BIGNUM_INT_BITS)) == 0) bitcount--;
+ return bitcount + 1;
+}
+
+/*
+ * Return the byte length of a bignum when SSH-1 encoded.
+ */
+int ssh1_bignum_length(Bignum bn)
+{
+ return 2 + (bignum_bitcount(bn) + 7) / 8;
+}
+
+/*
+ * Return the byte length of a bignum when SSH-2 encoded.
+ */
+int ssh2_bignum_length(Bignum bn)
+{
+ return 4 + (bignum_bitcount(bn) + 8) / 8;
+}
+
+/*
+ * Return a byte from a bignum; 0 is least significant, etc.
+ */
+int bignum_byte(Bignum bn, int i)
+{
+ if (i < 0 || i >= (int)(BIGNUM_INT_BYTES * bn[0]))
+ return 0; /* beyond the end */
+ else
+ return (bn[i / BIGNUM_INT_BYTES + 1] >>
+ ((i % BIGNUM_INT_BYTES)*8)) & 0xFF;
+}
+
+/*
+ * Return a bit from a bignum; 0 is least significant, etc.
+ */
+int bignum_bit(Bignum bn, int i)
+{
+ if (i < 0 || i >= (int)(BIGNUM_INT_BITS * bn[0]))
+ return 0; /* beyond the end */
+ else
+ return (bn[i / BIGNUM_INT_BITS + 1] >> (i % BIGNUM_INT_BITS)) & 1;
+}
+
+/*
+ * Set a bit in a bignum; 0 is least significant, etc.
+ */
+void bignum_set_bit(Bignum bn, int bitnum, int value)
+{
+ if (bitnum < 0 || bitnum >= (int)(BIGNUM_INT_BITS * bn[0]))
+ abort(); /* beyond the end */
+ else {
+ int v = bitnum / BIGNUM_INT_BITS + 1;
+ int mask = 1 << (bitnum % BIGNUM_INT_BITS);
+ if (value)
+ bn[v] |= mask;
+ else
+ bn[v] &= ~mask;
+ }
+}
+
+/*
+ * Write a SSH-1-format bignum into a buffer. It is assumed the
+ * buffer is big enough. Returns the number of bytes used.
+ */
+int ssh1_write_bignum(void *data, Bignum bn)
+{
+ unsigned char *p = data;
+ int len = ssh1_bignum_length(bn);
+ int i;
+ int bitc = bignum_bitcount(bn);
+
+ *p++ = (bitc >> 8) & 0xFF;
+ *p++ = (bitc) & 0xFF;
+ for (i = len - 2; i--;)
+ *p++ = bignum_byte(bn, i);
+ return len;
+}
+
+/*
+ * Compare two bignums. Returns like strcmp.
+ */
+int bignum_cmp(Bignum a, Bignum b)
+{
+ int amax = a[0], bmax = b[0];
+ int i;
+
+ /* Annoyingly we have two representations of zero */
+ if (amax == 1 && a[amax] == 0)
+ amax = 0;
+ if (bmax == 1 && b[bmax] == 0)
+ bmax = 0;
+
+ assert(amax == 0 || a[amax] != 0);
+ assert(bmax == 0 || b[bmax] != 0);
+
+ i = (amax > bmax ? amax : bmax);
+ while (i) {
+ BignumInt aval = (i > amax ? 0 : a[i]);
+ BignumInt bval = (i > bmax ? 0 : b[i]);
+ if (aval < bval)
+ return -1;
+ if (aval > bval)
+ return +1;
+ i--;
+ }
+ return 0;
+}
+
+/*
+ * Right-shift one bignum to form another.
+ */
+Bignum bignum_rshift(Bignum a, int shift)
+{
+ Bignum ret;
+ int i, shiftw, shiftb, shiftbb, bits;
+ BignumInt ai, ai1;
+
+ assert(shift >= 0);
+
+ bits = bignum_bitcount(a) - shift;
+ ret = newbn((bits + BIGNUM_INT_BITS - 1) / BIGNUM_INT_BITS);
+
+ if (ret) {
+ shiftw = shift / BIGNUM_INT_BITS;
+ shiftb = shift % BIGNUM_INT_BITS;
+ shiftbb = BIGNUM_INT_BITS - shiftb;
+
+ ai1 = a[shiftw + 1];
+ for (i = 1; i <= (int)ret[0]; i++) {
+ ai = ai1;
+ ai1 = (i + shiftw + 1 <= (int)a[0] ? a[i + shiftw + 1] : 0);
+ ret[i] = ((ai >> shiftb) | (ai1 << shiftbb)) & BIGNUM_INT_MASK;
+ }
+ }
+
+ return ret;
+}
+
+/*
+ * Non-modular multiplication and addition.
+ */
+Bignum bigmuladd(Bignum a, Bignum b, Bignum addend)
+{
+ int alen = a[0], blen = b[0];
+ int mlen = (alen > blen ? alen : blen);
+ int rlen, i, maxspot;
+ int wslen;
+ BignumInt *workspace;
+ Bignum ret;
+
+ /* mlen space for a, mlen space for b, 2*mlen for result,
+ * plus scratch space for multiplication */
+ wslen = mlen * 4 + mul_compute_scratch(mlen);
+ workspace = snewn(wslen, BignumInt);
+ for (i = 0; i < mlen; i++) {
+ workspace[0 * mlen + i] = (mlen - i <= (int)a[0] ? a[mlen - i] : 0);
+ workspace[1 * mlen + i] = (mlen - i <= (int)b[0] ? b[mlen - i] : 0);
+ }
+
+ internal_mul(workspace + 0 * mlen, workspace + 1 * mlen,
+ workspace + 2 * mlen, mlen, workspace + 4 * mlen);
+
+ /* now just copy the result back */
+ rlen = alen + blen + 1;
+ if (addend && rlen <= (int)addend[0])
+ rlen = addend[0] + 1;
+ ret = newbn(rlen);
+ maxspot = 0;
+ for (i = 1; i <= (int)ret[0]; i++) {
+ ret[i] = (i <= 2 * mlen ? workspace[4 * mlen - i] : 0);
+ if (ret[i] != 0)
+ maxspot = i;
+ }
+ ret[0] = maxspot;
+
+ /* now add in the addend, if any */
+ if (addend) {
+ BignumDblInt carry = 0;
+ for (i = 1; i <= rlen; i++) {
+ carry += (i <= (int)ret[0] ? ret[i] : 0);
+ carry += (i <= (int)addend[0] ? addend[i] : 0);
+ ret[i] = (BignumInt) carry & BIGNUM_INT_MASK;
+ carry >>= BIGNUM_INT_BITS;
+ if (ret[i] != 0 && i > maxspot)
+ maxspot = i;
+ }
+ }
+ ret[0] = maxspot;
+
+ smemclr(workspace, wslen * sizeof(*workspace));
+ sfree(workspace);
+ return ret;
+}
+
+/*
+ * Non-modular multiplication.
+ */
+Bignum bigmul(Bignum a, Bignum b)
+{
+ return bigmuladd(a, b, NULL);
+}
+
+/*
+ * Simple addition.
+ */
+Bignum bigadd(Bignum a, Bignum b)
+{
+ int alen = a[0], blen = b[0];
+ int rlen = (alen > blen ? alen : blen) + 1;
+ int i, maxspot;
+ Bignum ret;
+ BignumDblInt carry;
+
+ ret = newbn(rlen);
+
+ carry = 0;
+ maxspot = 0;
+ for (i = 1; i <= rlen; i++) {
+ carry += (i <= (int)a[0] ? a[i] : 0);
+ carry += (i <= (int)b[0] ? b[i] : 0);
+ ret[i] = (BignumInt) carry & BIGNUM_INT_MASK;
+ carry >>= BIGNUM_INT_BITS;
+ if (ret[i] != 0 && i > maxspot)
+ maxspot = i;
+ }
+ ret[0] = maxspot;
+
+ return ret;
+}
+
+/*
+ * Subtraction. Returns a-b, or NULL if the result would come out
+ * negative (recall that this entire bignum module only handles
+ * positive numbers).
+ */
+Bignum bigsub(Bignum a, Bignum b)
+{
+ int alen = a[0], blen = b[0];
+ int rlen = (alen > blen ? alen : blen);
+ int i, maxspot;
+ Bignum ret;
+ BignumDblInt carry;
+
+ ret = newbn(rlen);
+
+ carry = 1;
+ maxspot = 0;
+ for (i = 1; i <= rlen; i++) {
+ carry += (i <= (int)a[0] ? a[i] : 0);
+ carry += (i <= (int)b[0] ? b[i] ^ BIGNUM_INT_MASK : BIGNUM_INT_MASK);
+ ret[i] = (BignumInt) carry & BIGNUM_INT_MASK;
+ carry >>= BIGNUM_INT_BITS;
+ if (ret[i] != 0 && i > maxspot)
+ maxspot = i;
+ }
+ ret[0] = maxspot;
+
+ if (!carry) {
+ freebn(ret);
+ return NULL;
+ }
+
+ return ret;
+}
+
+/*
+ * Create a bignum which is the bitmask covering another one. That
+ * is, the smallest integer which is >= N and is also one less than
+ * a power of two.
+ */
+Bignum bignum_bitmask(Bignum n)
+{
+ Bignum ret = copybn(n);
+ int i;
+ BignumInt j;
+
+ i = ret[0];
+ while (n[i] == 0 && i > 0)
+ i--;
+ if (i <= 0)
+ return ret; /* input was zero */
+ j = 1;
+ while (j < n[i])
+ j = 2 * j + 1;
+ ret[i] = j;
+ while (--i > 0)
+ ret[i] = BIGNUM_INT_MASK;
+ return ret;
+}
+
+/*
+ * Convert a (max 32-bit) long into a bignum.
+ */
+Bignum bignum_from_long(unsigned long nn)
+{
+ Bignum ret;
+ BignumDblInt n = nn;
+
+ ret = newbn(3);
+ ret[1] = (BignumInt)(n & BIGNUM_INT_MASK);
+ ret[2] = (BignumInt)((n >> BIGNUM_INT_BITS) & BIGNUM_INT_MASK);
+ ret[3] = 0;
+ ret[0] = (ret[2] ? 2 : 1);
+ return ret;
+}
+
+/*
+ * Add a long to a bignum.
+ */
+Bignum bignum_add_long(Bignum number, unsigned long addendx)
+{
+ Bignum ret = newbn(number[0] + 1);
+ int i, maxspot = 0;
+ BignumDblInt carry = 0, addend = addendx;
+
+ for (i = 1; i <= (int)ret[0]; i++) {
+ carry += addend & BIGNUM_INT_MASK;
+ carry += (i <= (int)number[0] ? number[i] : 0);
+ addend >>= BIGNUM_INT_BITS;
+ ret[i] = (BignumInt) carry & BIGNUM_INT_MASK;
+ carry >>= BIGNUM_INT_BITS;
+ if (ret[i] != 0)
+ maxspot = i;
+ }
+ ret[0] = maxspot;
+ return ret;
+}
+
+/*
+ * Compute the residue of a bignum, modulo a (max 16-bit) short.
+ */
+unsigned short bignum_mod_short(Bignum number, unsigned short modulus)
+{
+ BignumDblInt mod, r;
+ int i;
+
+ r = 0;
+ mod = modulus;
+ for (i = number[0]; i > 0; i--)
+ r = (r * (BIGNUM_TOP_BIT % mod) * 2 + number[i] % mod) % mod;
+ return (unsigned short) r;
+}
+
+#ifdef DEBUG
+void diagbn(char *prefix, Bignum md)
+{
+ int i, nibbles, morenibbles;
+ static const char hex[] = "0123456789ABCDEF";
+
+ debug(("%s0x", prefix ? prefix : ""));
+
+ nibbles = (3 + bignum_bitcount(md)) / 4;
+ if (nibbles < 1)
+ nibbles = 1;
+ morenibbles = 4 * md[0] - nibbles;
+ for (i = 0; i < morenibbles; i++)
+ debug(("-"));
+ for (i = nibbles; i--;)
+ debug(("%c",
+ hex[(bignum_byte(md, i / 2) >> (4 * (i % 2))) & 0xF]));
+
+ if (prefix)
+ debug(("\n"));
+}
+#endif
+
+/*
+ * Simple division.
+ */
+Bignum bigdiv(Bignum a, Bignum b)
+{
+ Bignum q = newbn(a[0]);
+ bigdivmod(a, b, NULL, q);
+ return q;
+}
+
+/*
+ * Simple remainder.
+ */
+Bignum bigmod(Bignum a, Bignum b)
+{
+ Bignum r = newbn(b[0]);
+ bigdivmod(a, b, r, NULL);
+ return r;
+}
+
+/*
+ * Greatest common divisor.
+ */
+Bignum biggcd(Bignum av, Bignum bv)
+{
+ Bignum a = copybn(av);
+ Bignum b = copybn(bv);
+
+ while (bignum_cmp(b, Zero) != 0) {
+ Bignum t = newbn(b[0]);
+ bigdivmod(a, b, t, NULL);
+ while (t[0] > 1 && t[t[0]] == 0)
+ t[0]--;
+ freebn(a);
+ a = b;
+ b = t;
+ }
+
+ freebn(b);
+ return a;
+}
+
+/*
+ * Modular inverse, using Euclid's extended algorithm.
+ */
+Bignum modinv(Bignum number, Bignum modulus)
+{
+ Bignum a = copybn(modulus);
+ Bignum b = copybn(number);
+ Bignum xp = copybn(Zero);
+ Bignum x = copybn(One);
+ int sign = +1;
+
+ assert(number[number[0]] != 0);
+ assert(modulus[modulus[0]] != 0);
+
+ while (bignum_cmp(b, One) != 0) {
+ Bignum t, q;
+
+ if (bignum_cmp(b, Zero) == 0) {
+ /*
+ * Found a common factor between the inputs, so we cannot
+ * return a modular inverse at all.
+ */
+ freebn(b);
+ freebn(a);
+ freebn(xp);
+ freebn(x);
+ return NULL;
+ }
+
+ t = newbn(b[0]);
+ q = newbn(a[0]);
+ bigdivmod(a, b, t, q);
+ while (t[0] > 1 && t[t[0]] == 0)
+ t[0]--;
+ freebn(a);
+ a = b;
+ b = t;
+ t = xp;
+ xp = x;
+ x = bigmuladd(q, xp, t);
+ sign = -sign;
+ freebn(t);
+ freebn(q);
+ }
+
+ freebn(b);
+ freebn(a);
+ freebn(xp);
+
+ /* now we know that sign * x == 1, and that x < modulus */
+ if (sign < 0) {
+ /* set a new x to be modulus - x */
+ Bignum newx = newbn(modulus[0]);
+ BignumInt carry = 0;
+ int maxspot = 1;
+ int i;
+
+ for (i = 1; i <= (int)newx[0]; i++) {
+ BignumInt aword = (i <= (int)modulus[0] ? modulus[i] : 0);
+ BignumInt bword = (i <= (int)x[0] ? x[i] : 0);
+ newx[i] = aword - bword - carry;
+ bword = ~bword;
+ carry = carry ? (newx[i] >= bword) : (newx[i] > bword);
+ if (newx[i] != 0)
+ maxspot = i;
+ }
+ newx[0] = maxspot;
+ freebn(x);
+ x = newx;
+ }
+
+ /* and return. */
+ return x;
+}
+
+/*
+ * Render a bignum into decimal. Return a malloced string holding
+ * the decimal representation.
+ */
+char *bignum_decimal(Bignum x)
+{
+ int ndigits, ndigit;
+ int i, iszero;
+ BignumDblInt carry;
+ char *ret;
+ BignumInt *workspace;
+
+ /*
+ * First, estimate the number of digits. Since log(10)/log(2)
+ * is just greater than 93/28 (the joys of continued fraction
+ * approximations...) we know that for every 93 bits, we need
+ * at most 28 digits. This will tell us how much to malloc.
+ *
+ * Formally: if x has i bits, that means x is strictly less
+ * than 2^i. Since 2 is less than 10^(28/93), this is less than
+ * 10^(28i/93). We need an integer power of ten, so we must
+ * round up (rounding down might make it less than x again).
+ * Therefore if we multiply the bit count by 28/93, rounding
+ * up, we will have enough digits.
+ *
+ * i=0 (i.e., x=0) is an irritating special case.
+ */
+ i = bignum_bitcount(x);
+ if (!i)
+ ndigits = 1; /* x = 0 */
+ else
+ ndigits = (28 * i + 92) / 93; /* multiply by 28/93 and round up */
+ ndigits++; /* allow for trailing \0 */
+ ret = snewn(ndigits, char);
+
+ /*
+ * Now allocate some workspace to hold the binary form as we
+ * repeatedly divide it by ten. Initialise this to the
+ * big-endian form of the number.
+ */
+ workspace = snewn(x[0], BignumInt);
+ for (i = 0; i < (int)x[0]; i++)
+ workspace[i] = x[x[0] - i];
+
+ /*
+ * Next, write the decimal number starting with the last digit.
+ * We use ordinary short division, dividing 10 into the
+ * workspace.
+ */
+ ndigit = ndigits - 1;
+ ret[ndigit] = '\0';
+ do {
+ iszero = 1;
+ carry = 0;
+ for (i = 0; i < (int)x[0]; i++) {
+ carry = (carry << BIGNUM_INT_BITS) + workspace[i];
+ workspace[i] = (BignumInt) (carry / 10);
+ if (workspace[i])
+ iszero = 0;
+ carry %= 10;
+ }
+ ret[--ndigit] = (char) (carry + '0');
+ } while (!iszero);
+
+ /*
+ * There's a chance we've fallen short of the start of the
+ * string. Correct if so.
+ */
+ if (ndigit > 0)
+ memmove(ret, ret + ndigit, ndigits - ndigit);
+
+ /*
+ * Done.
+ */
+ smemclr(workspace, x[0] * sizeof(*workspace));
+ sfree(workspace);
+ return ret;
+}
+
+#ifdef TESTBN
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <ctype.h>
+
+/*
+ * gcc -Wall -g -O0 -DTESTBN -o testbn sshbn.c misc.c conf.c tree234.c unix/uxmisc.c -I. -I unix -I charset
+ *
+ * Then feed to this program's standard input the output of
+ * testdata/bignum.py .
+ */
+
+void modalfatalbox(char *p, ...)
+{
+ va_list ap;
+ fprintf(stderr, "FATAL ERROR: ");
+ va_start(ap, p);
+ vfprintf(stderr, p, ap);
+ va_end(ap);
+ fputc('\n', stderr);
+ exit(1);
+}
+
+#define fromxdigit(c) ( (c)>'9' ? ((c)&0xDF) - 'A' + 10 : (c) - '0' )
+
+int main(int argc, char **argv)
+{
+ char *buf;
+ int line = 0;
+ int passes = 0, fails = 0;
+
+ while ((buf = fgetline(stdin)) != NULL) {
+ int maxlen = strlen(buf);
+ unsigned char *data = snewn(maxlen, unsigned char);
+ unsigned char *ptrs[5], *q;
+ int ptrnum;
+ char *bufp = buf;
+
+ line++;
+
+ q = data;
+ ptrnum = 0;
+
+ while (*bufp && !isspace((unsigned char)*bufp))
+ bufp++;
+ if (bufp)
+ *bufp++ = '\0';
+
+ while (*bufp) {
+ char *start, *end;
+ int i;
+
+ while (*bufp && !isxdigit((unsigned char)*bufp))
+ bufp++;
+ start = bufp;
+
+ if (!*bufp)
+ break;
+
+ while (*bufp && isxdigit((unsigned char)*bufp))
+ bufp++;
+ end = bufp;
+
+ if (ptrnum >= lenof(ptrs))
+ break;
+ ptrs[ptrnum++] = q;
+
+ for (i = -((end - start) & 1); i < end-start; i += 2) {
+ unsigned char val = (i < 0 ? 0 : fromxdigit(start[i]));
+ val = val * 16 + fromxdigit(start[i+1]);
+ *q++ = val;
+ }
+
+ ptrs[ptrnum] = q;
+ }
+
+ if (!strcmp(buf, "mul")) {
+ Bignum a, b, c, p;
+
+ if (ptrnum != 3) {
+ printf("%d: mul with %d parameters, expected 3\n", line, ptrnum);
+ exit(1);
+ }
+ a = bignum_from_bytes(ptrs[0], ptrs[1]-ptrs[0]);
+ b = bignum_from_bytes(ptrs[1], ptrs[2]-ptrs[1]);
+ c = bignum_from_bytes(ptrs[2], ptrs[3]-ptrs[2]);
+ p = bigmul(a, b);
+
+ if (bignum_cmp(c, p) == 0) {
+ passes++;
+ } else {
+ char *as = bignum_decimal(a);
+ char *bs = bignum_decimal(b);
+ char *cs = bignum_decimal(c);
+ char *ps = bignum_decimal(p);
+
+ printf("%d: fail: %s * %s gave %s expected %s\n",
+ line, as, bs, ps, cs);
+ fails++;
+
+ sfree(as);
+ sfree(bs);
+ sfree(cs);
+ sfree(ps);
+ }
+ freebn(a);
+ freebn(b);
+ freebn(c);
+ freebn(p);
+ } else if (!strcmp(buf, "modmul")) {
+ Bignum a, b, m, c, p;
+
+ if (ptrnum != 4) {
+ printf("%d: modmul with %d parameters, expected 4\n",
+ line, ptrnum);
+ exit(1);
+ }
+ a = bignum_from_bytes(ptrs[0], ptrs[1]-ptrs[0]);
+ b = bignum_from_bytes(ptrs[1], ptrs[2]-ptrs[1]);
+ m = bignum_from_bytes(ptrs[2], ptrs[3]-ptrs[2]);
+ c = bignum_from_bytes(ptrs[3], ptrs[4]-ptrs[3]);
+ p = modmul(a, b, m);
+
+ if (bignum_cmp(c, p) == 0) {
+ passes++;
+ } else {
+ char *as = bignum_decimal(a);
+ char *bs = bignum_decimal(b);
+ char *ms = bignum_decimal(m);
+ char *cs = bignum_decimal(c);
+ char *ps = bignum_decimal(p);
+
+ printf("%d: fail: %s * %s mod %s gave %s expected %s\n",
+ line, as, bs, ms, ps, cs);
+ fails++;
+
+ sfree(as);
+ sfree(bs);
+ sfree(ms);
+ sfree(cs);
+ sfree(ps);
+ }
+ freebn(a);
+ freebn(b);
+ freebn(m);
+ freebn(c);
+ freebn(p);
+ } else if (!strcmp(buf, "pow")) {
+ Bignum base, expt, modulus, expected, answer;
+
+ if (ptrnum != 4) {
+ printf("%d: mul with %d parameters, expected 4\n", line, ptrnum);
+ exit(1);
+ }
+
+ base = bignum_from_bytes(ptrs[0], ptrs[1]-ptrs[0]);
+ expt = bignum_from_bytes(ptrs[1], ptrs[2]-ptrs[1]);
+ modulus = bignum_from_bytes(ptrs[2], ptrs[3]-ptrs[2]);
+ expected = bignum_from_bytes(ptrs[3], ptrs[4]-ptrs[3]);
+ answer = modpow(base, expt, modulus);
+
+ if (bignum_cmp(expected, answer) == 0) {
+ passes++;
+ } else {
+ char *as = bignum_decimal(base);
+ char *bs = bignum_decimal(expt);
+ char *cs = bignum_decimal(modulus);
+ char *ds = bignum_decimal(answer);
+ char *ps = bignum_decimal(expected);
+
+ printf("%d: fail: %s ^ %s mod %s gave %s expected %s\n",
+ line, as, bs, cs, ds, ps);
+ fails++;
+
+ sfree(as);
+ sfree(bs);
+ sfree(cs);
+ sfree(ds);
+ sfree(ps);
+ }
+ freebn(base);
+ freebn(expt);
+ freebn(modulus);
+ freebn(expected);
+ freebn(answer);
+ } else {
+ printf("%d: unrecognised test keyword: '%s'\n", line, buf);
+ exit(1);
+ }
+
+ sfree(buf);
+ sfree(data);
+ }
+
+ printf("passed %d failed %d total %d\n", passes, fails, passes+fails);
+ return fails != 0;
+}
+
+#endif
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