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.

       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.