Update files for OpenSSL-1.0.0f import.
[dragonfly.git] / secure / lib / libcrypto / man / EVP_DigestSignInit.3
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124.\" ========================================================================
125.\"
126.IX Title "EVP_DigestSignInit 3"
e3261593 127.TH EVP_DigestSignInit 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
132.SH "NAME"
133EVP_DigestSignInit, EVP_DigestSignUpdate, EVP_DigestSignFinal \- EVP signing functions
134.SH "SYNOPSIS"
135.IX Header "SYNOPSIS"
136.Vb 1
137\& #include <openssl/evp.h>
138\&
139\& int EVP_DigestSignInit(EVP_MD_CTX *ctx, EVP_PKEY_CTX **pctx,
140\& const EVP_MD *type, ENGINE *e, EVP_PKEY *pkey);
141\& int EVP_DigestSignUpdate(EVP_MD_CTX *ctx, const void *d, unsigned int cnt);
142\& int EVP_DigestSignFinal(EVP_MD_CTX *ctx, unsigned char *sig, size_t *siglen);
143.Ve
144.SH "DESCRIPTION"
145.IX Header "DESCRIPTION"
146The \s-1EVP\s0 signature routines are a high level interface to digital signatures.
147.PP
148\&\fIEVP_DigestSignInit()\fR sets up signing context \fBctx\fR to use digest \fBtype\fR from
149\&\s-1ENGINE\s0 \fBimpl\fR and private key \fBpkey\fR. \fBctx\fR must be initialized with
150\&\fIEVP_MD_CTX_init()\fR before calling this function. If \fBpctx\fR is not \s-1NULL\s0 the
151\&\s-1EVP_PKEY_CTX\s0 of the signing operation will be written to \fB*pctx\fR: this can
152be used to set alternative signing options.
153.PP
154\&\fIEVP_DigestSignUpdate()\fR hashes \fBcnt\fR bytes of data at \fBd\fR into the
155signature context \fBctx\fR. This function can be called several times on the
156same \fBctx\fR to include additional data. This function is currently implemented
157usig a macro.
158.PP
159\&\fIEVP_DigestSignFinal()\fR signs the data in \fBctx\fR places the signature in \fBsig\fR.
160If \fBsig\fR is \fB\s-1NULL\s0\fR then the maximum size of the output buffer is written to
161the \fBsiglen\fR parameter. If \fBsig\fR is not \fB\s-1NULL\s0\fR then before the call the
162\&\fBsiglen\fR parameter should contain the length of the \fBsig\fR buffer, if the
163call is successful the signature is written to \fBsig\fR and the amount of data
164written to \fBsiglen\fR.
165.SH "RETURN VALUES"
166.IX Header "RETURN VALUES"
167\&\fIEVP_DigestSignInit()\fR \fIEVP_DigestSignUpdate()\fR and \fIEVP_DigestSignaFinal()\fR return
1681 for success and 0 or a negative value for failure. In particular a return
169value of \-2 indicates the operation is not supported by the public key
170algorithm.
171.PP
172The error codes can be obtained from \fIERR_get_error\fR\|(3).
173.SH "NOTES"
174.IX Header "NOTES"
175The \fB\s-1EVP\s0\fR interface to digital signatures should almost always be used in
176preference to the low level interfaces. This is because the code then becomes
177transparent to the algorithm used and much more flexible.
178.PP
179In previous versions of OpenSSL there was a link between message digest types
180and public key algorithms. This meant that \*(L"clone\*(R" digests such as \fIEVP_dss1()\fR
181needed to be used to sign using \s-1SHA1\s0 and \s-1DSA\s0. This is no longer necessary and
182the use of clone digest is now discouraged.
183.PP
184For some key types and parameters the random number generator must be seeded
185or the operation will fail.
186.PP
187The call to \fIEVP_DigestSignFinal()\fR internally finalizes a copy of the digest
188context. This means that calls to \fIEVP_DigestSignUpdate()\fR and
189\&\fIEVP_DigestSignFinal()\fR can be called later to digest and sign additional data.
190.PP
191Since only a copy of the digest context is ever finalized the context must
192be cleaned up after use by calling \fIEVP_MD_CTX_cleanup()\fR or a memory leak
193will occur.
194.PP
195The use of \fIEVP_PKEY_size()\fR with these functions is discouraged because some
196signature operations may have a signature length which depends on the
197parameters set. As a result \fIEVP_PKEY_size()\fR would have to return a value
198which indicates the maximum possible signature for any set of parameters.
199.SH "SEE ALSO"
200.IX Header "SEE ALSO"
201\&\fIEVP_DigestVerifyInit\fR\|(3),
202\&\fIEVP_DigestInit\fR\|(3), \fIerr\fR\|(3),
203\&\fIevp\fR\|(3), \fIhmac\fR\|(3), \fImd2\fR\|(3),
204\&\fImd5\fR\|(3), \fImdc2\fR\|(3), \fIripemd\fR\|(3),
205\&\fIsha\fR\|(3), \fIdgst\fR\|(1)
206.SH "HISTORY"
207.IX Header "HISTORY"
208\&\fIEVP_DigestSignInit()\fR, \fIEVP_DigestSignUpdate()\fR and \fIEVP_DigestSignFinal()\fR
209were first added to OpenSSL 1.0.0.