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[dragonfly.git] / secure / lib / libcrypto / man / EVP_SignInit.3
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138.\" ======================================================================
139.\"
140.IX Title "EVP_SignInit 3"
141.TH EVP_SignInit 3 "0.9.7a" "2003-02-19" "OpenSSL"
142.UC
143.SH "NAME"
144EVP_SignInit, EVP_SignUpdate, EVP_SignFinal \- \s-1EVP\s0 signing functions
145.SH "SYNOPSIS"
146.IX Header "SYNOPSIS"
147.Vb 1
148\& #include <openssl/evp.h>
149.Ve
150.Vb 3
151\& int EVP_SignInit_ex(EVP_MD_CTX *ctx, const EVP_MD *type, ENGINE *impl);
152\& int EVP_SignUpdate(EVP_MD_CTX *ctx, const void *d, unsigned int cnt);
153\& int EVP_SignFinal(EVP_MD_CTX *ctx,unsigned char *sig,unsigned int *s, EVP_PKEY *pkey);
154.Ve
155.Vb 1
156\& void EVP_SignInit(EVP_MD_CTX *ctx, const EVP_MD *type);
157.Ve
158.Vb 1
159\& int EVP_PKEY_size(EVP_PKEY *pkey);
160.Ve
161.SH "DESCRIPTION"
162.IX Header "DESCRIPTION"
163The \s-1EVP\s0 signature routines are a high level interface to digital
164signatures.
165.PP
166\&\fIEVP_SignInit_ex()\fR sets up signing context \fBctx\fR to use digest
167\&\fBtype\fR from \s-1ENGINE\s0 \fBimpl\fR. \fBctx\fR must be initialized with
168\&\fIEVP_MD_CTX_init()\fR before calling this function.
169.PP
170\&\fIEVP_SignUpdate()\fR hashes \fBcnt\fR bytes of data at \fBd\fR into the
171signature context \fBctx\fR. This function can be called several times on the
172same \fBctx\fR to include additional data.
173.PP
174\&\fIEVP_SignFinal()\fR signs the data in \fBctx\fR using the private key \fBpkey\fR
175and places the signature in \fBsig\fR. If the \fBs\fR parameter is not \s-1NULL\s0
176then the number of bytes of data written (i.e. the length of the signature)
177will be written to the integer at \fBs\fR, at most EVP_PKEY_size(pkey) bytes
178will be written.
179.PP
180\&\fIEVP_SignInit()\fR initializes a signing context \fBctx\fR to use the default
181implementation of digest \fBtype\fR.
182.PP
183\&\fIEVP_PKEY_size()\fR returns the maximum size of a signature in bytes. The actual
184signature returned by \fIEVP_SignFinal()\fR may be smaller.
185.SH "RETURN VALUES"
186.IX Header "RETURN VALUES"
187\&\fIEVP_SignInit_ex()\fR, \fIEVP_SignUpdate()\fR and \fIEVP_SignFinal()\fR return 1
188for success and 0 for failure.
189.PP
190\&\fIEVP_PKEY_size()\fR returns the maximum size of a signature in bytes.
191.PP
192The error codes can be obtained by ERR_get_error(3).
193.SH "NOTES"
194.IX Header "NOTES"
195The \fB\s-1EVP\s0\fR interface to digital signatures should almost always be used in
196preference to the low level interfaces. This is because the code then becomes
197transparent to the algorithm used and much more flexible.
198.PP
199Due to the link between message digests and public key algorithms the correct
200digest algorithm must be used with the correct public key type. A list of
201algorithms and associated public key algorithms appears in
202EVP_DigestInit(3).
203.PP
204When signing with \s-1DSA\s0 private keys the random number generator must be seeded
205or the operation will fail. The random number generator does not need to be
206seeded for \s-1RSA\s0 signatures.
207.PP
208The call to \fIEVP_SignFinal()\fR internally finalizes a copy of the digest context.
209This means that calls to \fIEVP_SignUpdate()\fR and \fIEVP_SignFinal()\fR can be called
210later to digest and sign additional data.
211.PP
212Since only a copy of the digest context is ever finalized the context must
213be cleaned up after use by calling \fIEVP_MD_CTX_cleanup()\fR or a memory leak
214will occur.
215.SH "BUGS"
216.IX Header "BUGS"
217Older versions of this documentation wrongly stated that calls to
218\&\fIEVP_SignUpdate()\fR could not be made after calling \fIEVP_SignFinal()\fR.
219.SH "SEE ALSO"
220.IX Header "SEE ALSO"
221EVP_VerifyInit(3),
222EVP_DigestInit(3), err(3),
223evp(3), hmac(3), md2(3),
224md5(3), mdc2(3), ripemd(3),
225sha(3), dgst(1)
226.SH "HISTORY"
227.IX Header "HISTORY"
228\&\fIEVP_SignInit()\fR, \fIEVP_SignUpdate()\fR and \fIEVP_SignFinal()\fR are
229available in all versions of SSLeay and OpenSSL.
230.PP
231\&\fIEVP_SignInit_ex()\fR was added in OpenSSL 0.9.7.