Merge branch 'vendor/OPENSSL'
[dragonfly.git] / secure / lib / libcrypto / man / EVP_SignInit.3
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132.\" ========================================================================
133.\"
134.IX Title "EVP_SignInit 3"
fc468453 135.TH EVP_SignInit 3 "2010-02-27" "0.9.8m" "OpenSSL"
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136.\" For nroff, turn off justification. Always turn off hyphenation; it makes
137.\" way too many mistakes in technical documents.
138.if n .ad l
139.nh
984263bc 140.SH "NAME"
74dab6c2 141EVP_SignInit, EVP_SignUpdate, EVP_SignFinal \- EVP signing functions
984263bc 142.SH "SYNOPSIS"
8b0cefbb 143.IX Header "SYNOPSIS"
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144.Vb 1
145\& #include <openssl/evp.h>
e257b235 146\&
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147\& int EVP_SignInit_ex(EVP_MD_CTX *ctx, const EVP_MD *type, ENGINE *impl);
148\& int EVP_SignUpdate(EVP_MD_CTX *ctx, const void *d, unsigned int cnt);
149\& int EVP_SignFinal(EVP_MD_CTX *ctx,unsigned char *sig,unsigned int *s, EVP_PKEY *pkey);
e257b235 150\&
984263bc 151\& void EVP_SignInit(EVP_MD_CTX *ctx, const EVP_MD *type);
e257b235 152\&
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153\& int EVP_PKEY_size(EVP_PKEY *pkey);
154.Ve
155.SH "DESCRIPTION"
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156.IX Header "DESCRIPTION"
157The \s-1EVP\s0 signature routines are a high level interface to digital
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158signatures.
159.PP
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160\&\fIEVP_SignInit_ex()\fR sets up signing context \fBctx\fR to use digest
161\&\fBtype\fR from \s-1ENGINE\s0 \fBimpl\fR. \fBctx\fR must be initialized with
162\&\fIEVP_MD_CTX_init()\fR before calling this function.
984263bc 163.PP
8b0cefbb 164\&\fIEVP_SignUpdate()\fR hashes \fBcnt\fR bytes of data at \fBd\fR into the
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165signature context \fBctx\fR. This function can be called several times on the
166same \fBctx\fR to include additional data.
167.PP
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168\&\fIEVP_SignFinal()\fR signs the data in \fBctx\fR using the private key \fBpkey\fR and
169places the signature in \fBsig\fR. The number of bytes of data written (i.e. the
170length of the signature) will be written to the integer at \fBs\fR, at most
e257b235 171EVP_PKEY_size(pkey) bytes will be written.
984263bc 172.PP
8b0cefbb 173\&\fIEVP_SignInit()\fR initializes a signing context \fBctx\fR to use the default
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174implementation of digest \fBtype\fR.
175.PP
8b0cefbb 176\&\fIEVP_PKEY_size()\fR returns the maximum size of a signature in bytes. The actual
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177signature returned by \fIEVP_SignFinal()\fR may be smaller.
178.SH "RETURN VALUES"
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179.IX Header "RETURN VALUES"
180\&\fIEVP_SignInit_ex()\fR, \fIEVP_SignUpdate()\fR and \fIEVP_SignFinal()\fR return 1
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181for success and 0 for failure.
182.PP
8b0cefbb 183\&\fIEVP_PKEY_size()\fR returns the maximum size of a signature in bytes.
984263bc 184.PP
8b0cefbb 185The error codes can be obtained by \fIERR_get_error\fR\|(3).
984263bc 186.SH "NOTES"
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187.IX Header "NOTES"
188The \fB\s-1EVP\s0\fR interface to digital signatures should almost always be used in
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189preference to the low level interfaces. This is because the code then becomes
190transparent to the algorithm used and much more flexible.
191.PP
192Due to the link between message digests and public key algorithms the correct
193digest algorithm must be used with the correct public key type. A list of
194algorithms and associated public key algorithms appears in
8b0cefbb 195\&\fIEVP_DigestInit\fR\|(3).
984263bc 196.PP
8b0cefbb 197When signing with \s-1DSA\s0 private keys the random number generator must be seeded
984263bc 198or the operation will fail. The random number generator does not need to be
8b0cefbb 199seeded for \s-1RSA\s0 signatures.
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200.PP
201The call to \fIEVP_SignFinal()\fR internally finalizes a copy of the digest context.
202This means that calls to \fIEVP_SignUpdate()\fR and \fIEVP_SignFinal()\fR can be called
203later to digest and sign additional data.
204.PP
205Since only a copy of the digest context is ever finalized the context must
206be cleaned up after use by calling \fIEVP_MD_CTX_cleanup()\fR or a memory leak
207will occur.
208.SH "BUGS"
8b0cefbb 209.IX Header "BUGS"
984263bc 210Older versions of this documentation wrongly stated that calls to
8b0cefbb 211\&\fIEVP_SignUpdate()\fR could not be made after calling \fIEVP_SignFinal()\fR.
984263bc 212.SH "SEE ALSO"
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213.IX Header "SEE ALSO"
214\&\fIEVP_VerifyInit\fR\|(3),
215\&\fIEVP_DigestInit\fR\|(3), \fIerr\fR\|(3),
216\&\fIevp\fR\|(3), \fIhmac\fR\|(3), \fImd2\fR\|(3),
217\&\fImd5\fR\|(3), \fImdc2\fR\|(3), \fIripemd\fR\|(3),
218\&\fIsha\fR\|(3), \fIdgst\fR\|(1)
984263bc 219.SH "HISTORY"
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220.IX Header "HISTORY"
221\&\fIEVP_SignInit()\fR, \fIEVP_SignUpdate()\fR and \fIEVP_SignFinal()\fR are
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222available in all versions of SSLeay and OpenSSL.
223.PP
8b0cefbb 224\&\fIEVP_SignInit_ex()\fR was added in OpenSSL 0.9.7.