=pod =head1 NAME EVP_PKEY_sign_init, EVP_PKEY_sign - sign using a public key algorithm =head1 SYNOPSIS #include <openssl/evp.h> int EVP_PKEY_sign_init(EVP_PKEY_CTX *ctx); int EVP_PKEY_sign(EVP_PKEY_CTX *ctx, unsigned char *sig, size_t *siglen, const unsigned char *tbs, size_t tbslen); =head1 DESCRIPTION The EVP_PKEY_sign_init() function initializes a public key algorithm context using key B<pkey> for a signing operation. The EVP_PKEY_sign() function performs a public key signing operation using B<ctx>. The data to be signed is specified using the B<tbs> and B<tbslen> parameters. 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 NOTES After the call to EVP_PKEY_sign_init() algorithm specific control operations can be performed to set any appropriate parameters for the operation. The function EVP_PKEY_sign() can be called more than once on the same context if several operations are performed using the same parameters. =head1 RETURN VALUES EVP_PKEY_sign_init() and EVP_PKEY_sign() 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. =head1 EXAMPLE Sign data using RSA with PKCS#1 padding and SHA256 digest: #include <openssl/evp.h> #include <openssl/rsa.h> EVP_PKEY_CTX *ctx; unsigned char *md, *sig; size_t mdlen, siglen; EVP_PKEY *signing_key; /* NB: assumes signing_key, md and mdlen are already set up * and that signing_key is an RSA private key */ ctx = EVP_PKEY_CTX_new(signing_key); if (!ctx) /* Error occurred */ if (EVP_PKEY_sign_init(ctx) <= 0) /* Error */ if (EVP_PKEY_CTX_set_rsa_padding(ctx, RSA_PKCS1_PADDING) <= 0) /* Error */ if (EVP_PKEY_CTX_set_signature_md(ctx, EVP_sha256()) <= 0) /* Error */ /* Determine buffer length */ if (EVP_PKEY_sign(ctx, NULL, &siglen, md, mdlen) <= 0) /* Error */ sig = OPENSSL_malloc(siglen); if (!sig) /* malloc failure */ if (EVP_PKEY_sign(ctx, sig, &siglen, md, mdlen) <= 0) /* Error */ /* Signature is siglen bytes written to buffer sig */ =head1 SEE ALSO L<EVP_PKEY_CTX_new(3)|EVP_PKEY_CTX_new(3)>, L<EVP_PKEY_encrypt(3)|EVP_PKEY_encrypt(3)>, L<EVP_PKEY_decrypt(3)|EVP_PKEY_decrypt(3)>, L<EVP_PKEY_verify(3)|EVP_PKEY_verify(3)>, L<EVP_PKEY_verifyrecover(3)|EVP_PKEY_verifyrecover(3)>, L<EVP_PKEY_derive(3)|EVP_PKEY_derive(3)> =head1 HISTORY These functions were first added to OpenSSL 1.0.0. =cut