.\"	$NetBSD: DSA_sign.3,v 1.5 2001/04/12 10:45:37 itojun Exp $
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.\" ======================================================================
.\"
.IX Title "DSA_sign 3"
.TH DSA_sign 3 "0.9.6a" "2000-07-22" "OpenSSL"
.UC
.SH "NAME"
DSA_sign, DSA_sign_setup, DSA_verify \- \s-1DSA\s0 signatures
.SH "LIBRARY"
libcrypto, -lcrypto
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\& #include <openssl/dsa.h>
.Ve
.Vb 2
\& int    DSA_sign(int type, const unsigned char *dgst, int len,
\&                unsigned char *sigret, unsigned int *siglen, DSA *dsa);
.Ve
.Vb 2
\& int    DSA_sign_setup(DSA *dsa, BN_CTX *ctx, BIGNUM **kinvp,
\&                BIGNUM **rp);
.Ve
.Vb 2
\& int    DSA_verify(int type, const unsigned char *dgst, int len,
\&                unsigned char *sigbuf, int siglen, DSA *dsa);
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
\&\fIDSA_sign()\fR computes a digital signature on the \fBlen\fR byte message
digest \fBdgst\fR using the private key \fBdsa\fR and places its \s-1ASN\s0.1 \s-1DER\s0
encoding at \fBsigret\fR. The length of the signature is places in
*\fBsiglen\fR. \fBsigret\fR must point to DSA_size(\fBdsa\fR) bytes of memory.
.PP
\&\fIDSA_sign_setup()\fR may be used to precompute part of the signing
operation in case signature generation is time-critical. It expects
\&\fBdsa\fR to contain \s-1DSA\s0 parameters. It places the precomputed values
in newly allocated \fB\s-1BIGNUM\s0\fRs at *\fBkinvp\fR and *\fBrp\fR, after freeing
the old ones unless *\fBkinvp\fR and *\fBrp\fR are \s-1NULL\s0. These values may
be passed to \fIDSA_sign()\fR in \fBdsa->kinv\fR and \fBdsa->r\fR.
\&\fBctx\fR is a pre-allocated \fB\s-1BN_CTX\s0\fR or \s-1NULL\s0.
.PP
\&\fIDSA_verify()\fR verifies that the signature \fBsigbuf\fR of size \fBsiglen\fR
matches a given message digest \fBdgst\fR of size \fBlen\fR.
\&\fBdsa\fR is the signer's public key.
.PP
The \fBtype\fR parameter is ignored.
.PP
The \s-1PRNG\s0 must be seeded before \fIDSA_sign()\fR (or \fIDSA_sign_setup()\fR)
is called.
.SH "RETURN VALUES"
.IX Header "RETURN VALUES"
\&\fIDSA_sign()\fR and \fIDSA_sign_setup()\fR return 1 on success, 0 on error.
\&\fIDSA_verify()\fR 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).
.SH "CONFORMING TO"
.IX Header "CONFORMING TO"
\&\s-1US\s0 Federal Information Processing Standard \s-1FIPS\s0 186 (Digital Signature
Standard, \s-1DSS\s0), \s-1ANSI\s0 X9.30
.SH "SEE ALSO"
.IX Header "SEE ALSO"
openssl_dsa(3), openssl_err(3), openssl_rand(3),
DSA_do_sign(3)
.SH "HISTORY"
.IX Header "HISTORY"
\&\fIDSA_sign()\fR and \fIDSA_verify()\fR are available in all versions of SSLeay.
\&\fIDSA_sign_setup()\fR was added in SSLeay 0.8.