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[dragonfly.git] / secure / lib / libcrypto / man / EVP_SignInit.3
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129.\" ========================================================================
130.\"
131.IX Title "EVP_SignInit 3"
aac4ff6f 132.TH EVP_SignInit 3 "2008-09-06" "0.9.8h" "OpenSSL"
984263bc 133.SH "NAME"
74dab6c2 134EVP_SignInit, EVP_SignUpdate, EVP_SignFinal \- EVP signing functions
984263bc 135.SH "SYNOPSIS"
8b0cefbb 136.IX Header "SYNOPSIS"
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137.Vb 1
138\& #include <openssl/evp.h>
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139.Ve
140.PP
141.Vb 3
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142\& int EVP_SignInit_ex(EVP_MD_CTX *ctx, const EVP_MD *type, ENGINE *impl);
143\& int EVP_SignUpdate(EVP_MD_CTX *ctx, const void *d, unsigned int cnt);
144\& int EVP_SignFinal(EVP_MD_CTX *ctx,unsigned char *sig,unsigned int *s, EVP_PKEY *pkey);
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145.Ve
146.PP
147.Vb 1
984263bc 148\& void EVP_SignInit(EVP_MD_CTX *ctx, const EVP_MD *type);
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149.Ve
150.PP
151.Vb 1
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152\& int EVP_PKEY_size(EVP_PKEY *pkey);
153.Ve
154.SH "DESCRIPTION"
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155.IX Header "DESCRIPTION"
156The \s-1EVP\s0 signature routines are a high level interface to digital
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157signatures.
158.PP
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159\&\fIEVP_SignInit_ex()\fR sets up signing context \fBctx\fR to use digest
160\&\fBtype\fR from \s-1ENGINE\s0 \fBimpl\fR. \fBctx\fR must be initialized with
161\&\fIEVP_MD_CTX_init()\fR before calling this function.
984263bc 162.PP
8b0cefbb 163\&\fIEVP_SignUpdate()\fR hashes \fBcnt\fR bytes of data at \fBd\fR into the
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164signature context \fBctx\fR. This function can be called several times on the
165same \fBctx\fR to include additional data.
166.PP
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167\&\fIEVP_SignFinal()\fR signs the data in \fBctx\fR using the private key \fBpkey\fR and
168places the signature in \fBsig\fR. The number of bytes of data written (i.e. the
169length of the signature) will be written to the integer at \fBs\fR, at most
aac4ff6f 170EVP_PKEY_size(pkey) bytes will be written.
984263bc 171.PP
8b0cefbb 172\&\fIEVP_SignInit()\fR initializes a signing context \fBctx\fR to use the default
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173implementation of digest \fBtype\fR.
174.PP
8b0cefbb 175\&\fIEVP_PKEY_size()\fR returns the maximum size of a signature in bytes. The actual
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176signature returned by \fIEVP_SignFinal()\fR may be smaller.
177.SH "RETURN VALUES"
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178.IX Header "RETURN VALUES"
179\&\fIEVP_SignInit_ex()\fR, \fIEVP_SignUpdate()\fR and \fIEVP_SignFinal()\fR return 1
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180for success and 0 for failure.
181.PP
8b0cefbb 182\&\fIEVP_PKEY_size()\fR returns the maximum size of a signature in bytes.
984263bc 183.PP
8b0cefbb 184The error codes can be obtained by \fIERR_get_error\fR\|(3).
984263bc 185.SH "NOTES"
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186.IX Header "NOTES"
187The \fB\s-1EVP\s0\fR interface to digital signatures should almost always be used in
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188preference to the low level interfaces. This is because the code then becomes
189transparent to the algorithm used and much more flexible.
190.PP
191Due to the link between message digests and public key algorithms the correct
192digest algorithm must be used with the correct public key type. A list of
193algorithms and associated public key algorithms appears in
8b0cefbb 194\&\fIEVP_DigestInit\fR\|(3).
984263bc 195.PP
8b0cefbb 196When signing with \s-1DSA\s0 private keys the random number generator must be seeded
984263bc 197or the operation will fail. The random number generator does not need to be
8b0cefbb 198seeded for \s-1RSA\s0 signatures.
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199.PP
200The call to \fIEVP_SignFinal()\fR internally finalizes a copy of the digest context.
201This means that calls to \fIEVP_SignUpdate()\fR and \fIEVP_SignFinal()\fR can be called
202later to digest and sign additional data.
203.PP
204Since only a copy of the digest context is ever finalized the context must
205be cleaned up after use by calling \fIEVP_MD_CTX_cleanup()\fR or a memory leak
206will occur.
207.SH "BUGS"
8b0cefbb 208.IX Header "BUGS"
984263bc 209Older versions of this documentation wrongly stated that calls to
8b0cefbb 210\&\fIEVP_SignUpdate()\fR could not be made after calling \fIEVP_SignFinal()\fR.
984263bc 211.SH "SEE ALSO"
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212.IX Header "SEE ALSO"
213\&\fIEVP_VerifyInit\fR\|(3),
214\&\fIEVP_DigestInit\fR\|(3), \fIerr\fR\|(3),
215\&\fIevp\fR\|(3), \fIhmac\fR\|(3), \fImd2\fR\|(3),
216\&\fImd5\fR\|(3), \fImdc2\fR\|(3), \fIripemd\fR\|(3),
217\&\fIsha\fR\|(3), \fIdgst\fR\|(1)
984263bc 218.SH "HISTORY"
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219.IX Header "HISTORY"
220\&\fIEVP_SignInit()\fR, \fIEVP_SignUpdate()\fR and \fIEVP_SignFinal()\fR are
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221available in all versions of SSLeay and OpenSSL.
222.PP
8b0cefbb 223\&\fIEVP_SignInit_ex()\fR was added in OpenSSL 0.9.7.