Update files for OpenSSL-1.0.0f import.
[dragonfly.git] / secure / lib / libcrypto / man / EVP_SignInit.3
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124.\" ========================================================================
125.\"
126.IX Title "EVP_SignInit 3"
e3261593 127.TH EVP_SignInit 3 "2012-01-04" "1.0.0f" "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
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160\&\fIEVP_SignFinal()\fR signs the data in \fBctx\fR using the private key \fBpkey\fR and
161places the signature in \fBsig\fR. The number of bytes of data written (i.e. the
162length of the signature) will be written to the integer at \fBs\fR, at most
e257b235 163EVP_PKEY_size(pkey) bytes will be written.
984263bc 164.PP
8b0cefbb 165\&\fIEVP_SignInit()\fR initializes a signing context \fBctx\fR to use the default
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166implementation of digest \fBtype\fR.
167.PP
8b0cefbb 168\&\fIEVP_PKEY_size()\fR returns the maximum size of a signature in bytes. The actual
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169signature returned by \fIEVP_SignFinal()\fR may be smaller.
170.SH "RETURN VALUES"
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171.IX Header "RETURN VALUES"
172\&\fIEVP_SignInit_ex()\fR, \fIEVP_SignUpdate()\fR and \fIEVP_SignFinal()\fR return 1
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173for success and 0 for failure.
174.PP
8b0cefbb 175\&\fIEVP_PKEY_size()\fR returns the maximum size of a signature in bytes.
984263bc 176.PP
8b0cefbb 177The error codes can be obtained by \fIERR_get_error\fR\|(3).
984263bc 178.SH "NOTES"
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179.IX Header "NOTES"
180The \fB\s-1EVP\s0\fR interface to digital signatures should almost always be used in
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181preference to the low level interfaces. This is because the code then becomes
182transparent to the algorithm used and much more flexible.
183.PP
184Due to the link between message digests and public key algorithms the correct
185digest algorithm must be used with the correct public key type. A list of
186algorithms and associated public key algorithms appears in
8b0cefbb 187\&\fIEVP_DigestInit\fR\|(3).
984263bc 188.PP
8b0cefbb 189When signing with \s-1DSA\s0 private keys the random number generator must be seeded
984263bc 190or the operation will fail. The random number generator does not need to be
8b0cefbb 191seeded for \s-1RSA\s0 signatures.
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192.PP
193The call to \fIEVP_SignFinal()\fR internally finalizes a copy of the digest context.
194This means that calls to \fIEVP_SignUpdate()\fR and \fIEVP_SignFinal()\fR can be called
195later to digest and sign additional data.
196.PP
197Since only a copy of the digest context is ever finalized the context must
198be cleaned up after use by calling \fIEVP_MD_CTX_cleanup()\fR or a memory leak
199will occur.
200.SH "BUGS"
8b0cefbb 201.IX Header "BUGS"
984263bc 202Older versions of this documentation wrongly stated that calls to
8b0cefbb 203\&\fIEVP_SignUpdate()\fR could not be made after calling \fIEVP_SignFinal()\fR.
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204.PP
205Since the private key is passed in the call to \fIEVP_SignFinal()\fR any error
206relating to the private key (for example an unsuitable key and digest
207combination) will not be indicated until after potentially large amounts of
208data have been passed through \fIEVP_SignUpdate()\fR.
209.PP
210It is not possible to change the signing parameters using these function.
211.PP
212The previous two bugs are fixed in the newer EVP_SignDigest*() function.
984263bc 213.SH "SEE ALSO"
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214.IX Header "SEE ALSO"
215\&\fIEVP_VerifyInit\fR\|(3),
216\&\fIEVP_DigestInit\fR\|(3), \fIerr\fR\|(3),
217\&\fIevp\fR\|(3), \fIhmac\fR\|(3), \fImd2\fR\|(3),
218\&\fImd5\fR\|(3), \fImdc2\fR\|(3), \fIripemd\fR\|(3),
219\&\fIsha\fR\|(3), \fIdgst\fR\|(1)
984263bc 220.SH "HISTORY"
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221.IX Header "HISTORY"
222\&\fIEVP_SignInit()\fR, \fIEVP_SignUpdate()\fR and \fIEVP_SignFinal()\fR are
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223available in all versions of SSLeay and OpenSSL.
224.PP
8b0cefbb 225\&\fIEVP_SignInit_ex()\fR was added in OpenSSL 0.9.7.