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Editing: DSA_sign_setup.3
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Always turn off hyphenation; it makes .\" way too many mistakes in technical documents. .if n .ad l .nh .SH "NAME" DSA_sign, DSA_sign_setup, DSA_verify \- DSA signatures .SH "SYNOPSIS" .IX Header "SYNOPSIS" .Vb 1 \& #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); .Ve .SH "DESCRIPTION" .IX Header "DESCRIPTION" \&\fBDSA_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.1 DER\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 \&\fBDSA_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 \fBDSA_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 The precomputed values from \fBDSA_sign_setup()\fR \fB\s-1MUST NOT\s0 be used\fR for more than one signature: using the same \fBdsa\->kinv\fR and \&\fBdsa\->r\fR pair twice under the same private key on different plaintexts will result in permanently exposing the \s-1DSA\s0 private key. .PP \&\fBDSA_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 \fBDSA_sign()\fR (or \fBDSA_sign_setup()\fR) is called. .SH "RETURN VALUES" .IX Header "RETURN VALUES" \&\fBDSA_sign()\fR and \fBDSA_sign_setup()\fR return 1 on success, 0 on error. \&\fBDSA_verify()\fR returns 1 for a valid signature, 0 for an incorrect signature and \-1 on error. The error codes can be obtained by \&\fBERR_get_error\fR\|(3). .SH "CONFORMING TO" .IX Header "CONFORMING TO" \&\s-1US\s0 Federal Information Processing Standard \s-1FIPS 186\s0 (Digital Signature Standard, \s-1DSS\s0), \s-1ANSI X9.30\s0 .SH "SEE ALSO" .IX Header "SEE ALSO" \&\fBdsa\fR\|(3), \fBERR_get_error\fR\|(3), \fBrand\fR\|(3), \&\fBDSA_do_sign\fR\|(3) .SH "HISTORY" .IX Header "HISTORY" \&\fBDSA_sign()\fR and \fBDSA_verify()\fR are available in all versions of SSLeay. \&\fBDSA_sign_setup()\fR was added in SSLeay 0.8.
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