DSA_sign(3)

NAME
DSA_sign, DSA_sign_setup, DSA_verify - DSA signatures

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. The precomputed values from DSA_sign_setup() MUST NOT be used for more than one signature: using the same dsa->kinv and dsa->r pair twice under the same private key on different plaintexts will result in permanently exposing the DSA private key.

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

SEE ALSO
dsa(3), ERR_get_error(3), rand(3), DSA_do_sign(3)

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