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(3), rand(3), DSA_do_sign(3)

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


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