SYNOPSIS

#include <openssl/dsa.h>
int DSA_sign(int type, const unsigned char *dgst, int len,
unsigned char *sigret, unsigned int *siglen, DSA *dsa);
int DSA_sign_setup(DSA *dsa, BN_CTX *ctx, BIGNUM **kinvp,
BIGNUM **rp);
int DSA_verify(int type, const unsigned char *dgst, int len,
unsigned char *sigbuf, int siglen, DSA *dsa);

DESCRIPTION

DSA_sign() computes a digital signature on the len byte message digest dgst using the private key dsa and places its ASN.1 DER encoding at sigret. The length of the signature is places in *siglen. sigret must point to DSA_size(dsa) bytes of memory.

DSA_sign_setup() may be used to precompute part of the signing operation in case signature generation is time-critical. It expects dsa to contain DSA parameters. It places the precomputed values in newly allocated BIGNUMs at *kinvp and *rp, after freeing the old ones unless *kinvp and *rp are NULL. These values may be passed to DSA_sign() in dsa->kinv and dsa->r. ctx is a pre-allocated BN_CTX or NULL.

DSA_verify() verifies that the signature sigbuf of size siglen matches a given message digest dgst of size len. dsa is the signer's public key.

The type parameter is ignored.

The PRNG must be seeded before DSA_sign() (or DSA_sign_setup()) is called.

RETURN VALUES

DSA_sign() and DSA_sign_setup() return 1 on success, 0 on error. DSA_verify() returns 1 for a valid signature, 0 for an incorrect signature and -1 on error. The error codes can be obtained by ERR_get_error(3).

CONFORMING TO

US Federal Information Processing Standard FIPS 186 (Digital Signature Standard, DSS), ANSI X9.30

HISTORY

DSA_sign() and DSA_verify() are available in all versions of SSLeay. DSA_sign_setup() was added in SSLeay 0.8.