=pod =head1 NAME EVP_SignInit, EVP_SignUpdate, EVP_SignFinal - EVP signing functions =head1 SYNOPSIS #include <openssl/evp.h> void EVP_SignInit(EVP_MD_CTX *ctx, const EVP_MD *type); void 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); int EVP_PKEY_size(EVP_PKEY *pkey); =head1 DESCRIPTION The EVP signature routines are a high level interface to digital signatures. EVP_SignInit() initializes a signing context B<ctx> to using digest B<type>: this will typically be supplied by a function such as EVP_sha1(). EVP_SignUpdate() 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. EVP_SignFinal() signs the data in B<ctx> using the private key B<pkey> and places the signature in B<sig>. If the B<s> parameter is not NULL then the number of bytes of data written (i.e. the length of the signature) will be written to the integer at B<s>, at most EVP_PKEY_size(pkey) bytes will be written. After calling EVP_SignFinal() no additional calls to EVP_SignUpdate() can be made, but EVP_SignInit() can be called to initialize a new signature operation. 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() and EVP_SignUpdate() do not return values. EVP_SignFinal() returns 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<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. 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<EVP_DigestInit(3)|EVP_DigestInit(3)>. 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. =head1 BUGS Several of the functions do not return values: maybe they should. Although the internal digest operations will never fail some future hardware based operations might. =head1 SEE ALSO L<EVP_VerifyInit(3)|EVP_VerifyInit(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_SignInit(), EVP_SignUpdate() and EVP_SignFinal() are available in all versions of SSLeay and OpenSSL. =cut