openssl: Update version/date in the manual pages.
[dragonfly.git] / secure / lib / libcrypto / man / EVP_SignInit.3
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124.\" ========================================================================
125.\"
126.IX Title "EVP_SignInit 3"
6bd02a9f 127.TH EVP_SignInit 3 "2014-10-15" "1.0.1j" "OpenSSL"
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128.\" For nroff, turn off justification. Always turn off hyphenation; it makes
129.\" way too many mistakes in technical documents.
130.if n .ad l
131.nh
984263bc 132.SH "NAME"
74dab6c2 133EVP_SignInit, EVP_SignUpdate, EVP_SignFinal \- EVP signing functions
984263bc 134.SH "SYNOPSIS"
8b0cefbb 135.IX Header "SYNOPSIS"
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136.Vb 1
137\& #include <openssl/evp.h>
e257b235 138\&
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139\& int EVP_SignInit_ex(EVP_MD_CTX *ctx, const EVP_MD *type, ENGINE *impl);
140\& int EVP_SignUpdate(EVP_MD_CTX *ctx, const void *d, unsigned int cnt);
141\& int EVP_SignFinal(EVP_MD_CTX *ctx,unsigned char *sig,unsigned int *s, EVP_PKEY *pkey);
e257b235 142\&
984263bc 143\& void EVP_SignInit(EVP_MD_CTX *ctx, const EVP_MD *type);
e257b235 144\&
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145\& int EVP_PKEY_size(EVP_PKEY *pkey);
146.Ve
147.SH "DESCRIPTION"
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148.IX Header "DESCRIPTION"
149The \s-1EVP\s0 signature routines are a high level interface to digital
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150signatures.
151.PP
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152\&\fIEVP_SignInit_ex()\fR sets up signing context \fBctx\fR to use digest
153\&\fBtype\fR from \s-1ENGINE\s0 \fBimpl\fR. \fBctx\fR must be initialized with
154\&\fIEVP_MD_CTX_init()\fR before calling this function.
984263bc 155.PP
8b0cefbb 156\&\fIEVP_SignUpdate()\fR hashes \fBcnt\fR bytes of data at \fBd\fR into the
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157signature context \fBctx\fR. This function can be called several times on the
158same \fBctx\fR to include additional data.
159.PP
a561f9ff 160\&\fIEVP_SignFinal()\fR signs the data in \fBctx\fR using the private key \fBpkey\fR and
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161places the signature in \fBsig\fR. \fBsig\fR must be at least EVP_PKEY_size(pkey)
162bytes in size. \fBs\fR is an \s-1OUT\s0 paramter, and not used as an \s-1IN\s0 parameter.
163The number of bytes of data written (i.e. the length of the signature)
164will be written to the integer at \fBs\fR, at most EVP_PKEY_size(pkey) bytes
165will be written.
984263bc 166.PP
8b0cefbb 167\&\fIEVP_SignInit()\fR initializes a signing context \fBctx\fR to use the default
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168implementation of digest \fBtype\fR.
169.PP
8b0cefbb 170\&\fIEVP_PKEY_size()\fR returns the maximum size of a signature in bytes. The actual
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171signature returned by \fIEVP_SignFinal()\fR may be smaller.
172.SH "RETURN VALUES"
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173.IX Header "RETURN VALUES"
174\&\fIEVP_SignInit_ex()\fR, \fIEVP_SignUpdate()\fR and \fIEVP_SignFinal()\fR return 1
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175for success and 0 for failure.
176.PP
8b0cefbb 177\&\fIEVP_PKEY_size()\fR returns the maximum size of a signature in bytes.
984263bc 178.PP
8b0cefbb 179The error codes can be obtained by \fIERR_get_error\fR\|(3).
984263bc 180.SH "NOTES"
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181.IX Header "NOTES"
182The \fB\s-1EVP\s0\fR interface to digital signatures should almost always be used in
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183preference to the low level interfaces. This is because the code then becomes
184transparent to the algorithm used and much more flexible.
185.PP
186Due to the link between message digests and public key algorithms the correct
187digest algorithm must be used with the correct public key type. A list of
188algorithms and associated public key algorithms appears in
8b0cefbb 189\&\fIEVP_DigestInit\fR\|(3).
984263bc 190.PP
8b0cefbb 191When signing with \s-1DSA\s0 private keys the random number generator must be seeded
984263bc 192or the operation will fail. The random number generator does not need to be
8b0cefbb 193seeded for \s-1RSA\s0 signatures.
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194.PP
195The call to \fIEVP_SignFinal()\fR internally finalizes a copy of the digest context.
196This means that calls to \fIEVP_SignUpdate()\fR and \fIEVP_SignFinal()\fR can be called
197later to digest and sign additional data.
198.PP
199Since only a copy of the digest context is ever finalized the context must
200be cleaned up after use by calling \fIEVP_MD_CTX_cleanup()\fR or a memory leak
201will occur.
202.SH "BUGS"
8b0cefbb 203.IX Header "BUGS"
984263bc 204Older versions of this documentation wrongly stated that calls to
8b0cefbb 205\&\fIEVP_SignUpdate()\fR could not be made after calling \fIEVP_SignFinal()\fR.
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206.PP
207Since the private key is passed in the call to \fIEVP_SignFinal()\fR any error
208relating to the private key (for example an unsuitable key and digest
209combination) will not be indicated until after potentially large amounts of
210data have been passed through \fIEVP_SignUpdate()\fR.
211.PP
212It is not possible to change the signing parameters using these function.
213.PP
214The previous two bugs are fixed in the newer EVP_SignDigest*() function.
984263bc 215.SH "SEE ALSO"
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216.IX Header "SEE ALSO"
217\&\fIEVP_VerifyInit\fR\|(3),
218\&\fIEVP_DigestInit\fR\|(3), \fIerr\fR\|(3),
219\&\fIevp\fR\|(3), \fIhmac\fR\|(3), \fImd2\fR\|(3),
220\&\fImd5\fR\|(3), \fImdc2\fR\|(3), \fIripemd\fR\|(3),
221\&\fIsha\fR\|(3), \fIdgst\fR\|(1)
984263bc 222.SH "HISTORY"
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223.IX Header "HISTORY"
224\&\fIEVP_SignInit()\fR, \fIEVP_SignUpdate()\fR and \fIEVP_SignFinal()\fR are
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225available in all versions of SSLeay and OpenSSL.
226.PP
8b0cefbb 227\&\fIEVP_SignInit_ex()\fR was added in OpenSSL 0.9.7.