=pod =head1 NAME EVP_SignInit, EVP_SignUpdate, EVP_SignFinal - EVP signing functions =head1 SYNOPSIS #include int EVP_SignInit_ex(EVP_MD_CTX *ctx, const EVP_MD *type, ENGINE *impl); int EVP_SignUpdate(EVP_MD_CTX *ctx, const void *d, unsigned int cnt); int EVP_SignFinal(EVP_MD_CTX *ctx,unsigned char *sig,unsigned int *s, EVP_PKEY *pkey); void EVP_SignInit(EVP_MD_CTX *ctx, const EVP_MD *type); int EVP_PKEY_size(EVP_PKEY *pkey); =head1 DESCRIPTION The EVP signature routines are a high level interface to digital signatures. EVP_SignInit_ex() sets up signing context B to use digest B from ENGINE B. B must be initialized with EVP_MD_CTX_init() before calling this function. EVP_SignUpdate() hashes B bytes of data at B into the signature context B. This function can be called several times on the same B to include additional data. EVP_SignFinal() signs the data in B using the private key B and places the signature in B. B must be at least EVP_PKEY_size(pkey) bytes in size. B is an OUT parameter, and not used as an IN parameter. The number of bytes of data written (i.e. the length of the signature) will be written to the integer at B, at most EVP_PKEY_size(pkey) bytes will be written. EVP_SignInit() initializes a signing context B to use the default implementation of digest B. EVP_PKEY_size() returns the maximum size of a signature in bytes. The actual signature returned by EVP_SignFinal() may be smaller. =head1 RETURN VALUES EVP_SignInit_ex(), EVP_SignUpdate() and EVP_SignFinal() return 1 for success and 0 for failure. EVP_PKEY_size() returns the maximum size of a signature in bytes. The error codes can be obtained by L. =head1 NOTES The B 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. Due to the link between message digests and public key algorithms the correct digest algorithm must be used with the correct public key type. A list of algorithms and associated public key algorithms appears in L. When signing with DSA private keys the random number generator must be seeded or the operation will fail. The random number generator does not need to be seeded for RSA signatures. The call to EVP_SignFinal() internally finalizes a copy of the digest context. This means that calls to EVP_SignUpdate() and EVP_SignFinal() 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. =head1 BUGS Older versions of this documentation wrongly stated that calls to EVP_SignUpdate() could not be made after calling EVP_SignFinal(). Since the private key is passed in the call to EVP_SignFinal() any error relating to the private key (for example an unsuitable key and digest combination) will not be indicated until after potentially large amounts of data have been passed through EVP_SignUpdate(). It is not possible to change the signing parameters using these function. The previous two bugs are fixed in the newer EVP_SignDigest*() function. =head1 SEE ALSO L, L, L, L, L, L, L, L, L, L, L =head1 HISTORY EVP_SignInit(), EVP_SignUpdate() and EVP_SignFinal() are available in all versions of SSLeay and OpenSSL. EVP_SignInit_ex() was added in OpenSSL 0.9.7. =cut