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Diffstat (limited to 'openssl/doc/crypto/EVP_DigestSignInit.pod')
| -rw-r--r-- | openssl/doc/crypto/EVP_DigestSignInit.pod | 87 |
1 files changed, 87 insertions, 0 deletions
diff --git a/openssl/doc/crypto/EVP_DigestSignInit.pod b/openssl/doc/crypto/EVP_DigestSignInit.pod new file mode 100644 index 000000000..37d960e3b --- /dev/null +++ b/openssl/doc/crypto/EVP_DigestSignInit.pod @@ -0,0 +1,87 @@ +=pod + +=head1 NAME + +EVP_DigestSignInit, EVP_DigestSignUpdate, EVP_DigestSignFinal - EVP signing functions + +=head1 SYNOPSIS + + #include <openssl/evp.h> + + int EVP_DigestSignInit(EVP_MD_CTX *ctx, EVP_PKEY_CTX **pctx, + const EVP_MD *type, ENGINE *e, EVP_PKEY *pkey); + int EVP_DigestSignUpdate(EVP_MD_CTX *ctx, const void *d, unsigned int cnt); + int EVP_DigestSignFinal(EVP_MD_CTX *ctx, unsigned char *sig, size_t *siglen); + +=head1 DESCRIPTION + +The EVP signature routines are a high level interface to digital signatures. + +EVP_DigestSignInit() sets up signing context B<ctx> to use digest B<type> from +ENGINE B<impl> and private key B<pkey>. B<ctx> must be initialized with +EVP_MD_CTX_init() before calling this function. If B<pctx> is not NULL the +EVP_PKEY_CTX of the signing operation will be written to B<*pctx>: this can +be used to set alternative signing options. + +EVP_DigestSignUpdate() hashes B<cnt> bytes of data at B<d> into the +signature context B<ctx>. This function can be called several times on the +same B<ctx> to include additional data. This function is currently implemented +usig a macro. + +EVP_DigestSignFinal() signs the data in B<ctx> places the signature in B<sig>. +If B<sig> is B<NULL> then the maximum size of the output buffer is written to +the B<siglen> parameter. If B<sig> is not B<NULL> then before the call the +B<siglen> parameter should contain the length of the B<sig> buffer, if the +call is successful the signature is written to B<sig> and the amount of data +written to B<siglen>. + +=head1 RETURN VALUES + +EVP_DigestSignInit() EVP_DigestSignUpdate() and EVP_DigestSignaFinal() return +1 for success and 0 or a negative value for failure. In particular a return +value of -2 indicates the operation is not supported by the public key +algorithm. + +The error codes can be obtained from L<ERR_get_error(3)|ERR_get_error(3)>. + +=head1 NOTES + +The B<EVP> interface to digital signatures should almost always be used in +preference to the low level interfaces. This is because the code then becomes +transparent to the algorithm used and much more flexible. + +In previous versions of OpenSSL there was a link between message digest types +and public key algorithms. This meant that "clone" digests such as EVP_dss1() +needed to be used to sign using SHA1 and DSA. This is no longer necessary and +the use of clone digest is now discouraged. + +For some key types and parameters the random number generator must be seeded +or the operation will fail. + +The call to EVP_DigestSignFinal() internally finalizes a copy of the digest +context. This means that calls to EVP_DigestSignUpdate() and +EVP_DigestSignFinal() can be called later to digest and sign additional data. + +Since only a copy of the digest context is ever finalized the context must +be cleaned up after use by calling EVP_MD_CTX_cleanup() or a memory leak +will occur. + +The use of EVP_PKEY_size() with these functions is discouraged because some +signature operations may have a signature length which depends on the +parameters set. As a result EVP_PKEY_size() would have to return a value +which indicates the maximum possible signature for any set of parameters. + +=head1 SEE ALSO + +L<EVP_DigestVerifyInit(3)|EVP_DigestVerifyInit(3)>, +L<EVP_DigestInit(3)|EVP_DigestInit(3)>, L<err(3)|err(3)>, +L<evp(3)|evp(3)>, L<hmac(3)|hmac(3)>, L<md2(3)|md2(3)>, +L<md5(3)|md5(3)>, L<mdc2(3)|mdc2(3)>, L<ripemd(3)|ripemd(3)>, +L<sha(3)|sha(3)>, L<dgst(1)|dgst(1)> + +=head1 HISTORY + +EVP_DigestSignInit(), EVP_DigestSignUpdate() and EVP_DigestSignFinal() +were first added to OpenSSL 1.0.0. + +=cut |