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124.\" ========================================================================
125.\"
126.IX Title "EVP_VerifyInit 3"
127.TH EVP_VerifyInit 3 "2010-06-01" "1.0.0a" "OpenSSL"
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_VerifyInit, EVP_VerifyUpdate, EVP_VerifyFinal \- EVP signature verification functions
134.SH "SYNOPSIS"
135.IX Header "SYNOPSIS"
136.Vb 1
137\& #include <openssl/evp.h>
138\&
139\& int EVP_VerifyInit_ex(EVP_MD_CTX *ctx, const EVP_MD *type, ENGINE *impl);
140\& int EVP_VerifyUpdate(EVP_MD_CTX *ctx, const void *d, unsigned int cnt);
141\& int EVP_VerifyFinal(EVP_MD_CTX *ctx,unsigned char *sigbuf, unsigned int siglen,EVP_PKEY *pkey);
142\&
143\& int EVP_VerifyInit(EVP_MD_CTX *ctx, const EVP_MD *type);
144.Ve
145.SH "DESCRIPTION"
146.IX Header "DESCRIPTION"
147The \s-1EVP\s0 signature verification routines are a high level interface to digital
148signatures.
149.PP
150\&\fIEVP_VerifyInit_ex()\fR sets up verification context \fBctx\fR to use digest
151\&\fBtype\fR from \s-1ENGINE\s0 \fBimpl\fR. \fBctx\fR must be initialized by calling
152\&\fIEVP_MD_CTX_init()\fR before calling this function.
153.PP
154\&\fIEVP_VerifyUpdate()\fR hashes \fBcnt\fR bytes of data at \fBd\fR into the
155verification context \fBctx\fR. This function can be called several times on the
156same \fBctx\fR to include additional data.
157.PP
158\&\fIEVP_VerifyFinal()\fR verifies the data in \fBctx\fR using the public key \fBpkey\fR
159and against the \fBsiglen\fR bytes at \fBsigbuf\fR.
160.PP
161\&\fIEVP_VerifyInit()\fR initializes verification context \fBctx\fR to use the default
162implementation of digest \fBtype\fR.
163.SH "RETURN VALUES"
164.IX Header "RETURN VALUES"
165\&\fIEVP_VerifyInit_ex()\fR and \fIEVP_VerifyUpdate()\fR return 1 for success and 0 for
166failure.
167.PP
168\&\fIEVP_VerifyFinal()\fR returns 1 for a correct signature, 0 for failure and \-1 if some
169other error occurred.
170.PP
171The error codes can be obtained by \fIERR_get_error\fR\|(3).
172.SH "NOTES"
173.IX Header "NOTES"
174The \fB\s-1EVP\s0\fR interface to digital signatures should almost always be used in
175preference to the low level interfaces. This is because the code then becomes
176transparent to the algorithm used and much more flexible.
177.PP
178Due to the link between message digests and public key algorithms the correct
179digest algorithm must be used with the correct public key type. A list of
180algorithms and associated public key algorithms appears in
181\&\fIEVP_DigestInit\fR\|(3).
182.PP
183The call to \fIEVP_VerifyFinal()\fR internally finalizes a copy of the digest context.
184This means that calls to \fIEVP_VerifyUpdate()\fR and \fIEVP_VerifyFinal()\fR can be called
185later to digest and verify additional data.
186.PP
187Since only a copy of the digest context is ever finalized the context must
188be cleaned up after use by calling \fIEVP_MD_CTX_cleanup()\fR or a memory leak
189will occur.
190.SH "BUGS"
191.IX Header "BUGS"
192Older versions of this documentation wrongly stated that calls to
193\&\fIEVP_VerifyUpdate()\fR could not be made after calling \fIEVP_VerifyFinal()\fR.
194.PP
195Since the public key is passed in the call to \fIEVP_SignFinal()\fR any error
196relating to the private key (for example an unsuitable key and digest
197combination) will not be indicated until after potentially large amounts of
198data have been passed through \fIEVP_SignUpdate()\fR.
199.PP
200It is not possible to change the signing parameters using these function.
201.PP
202The previous two bugs are fixed in the newer EVP_VerifyDigest*() function.
203.SH "SEE ALSO"
204.IX Header "SEE ALSO"
205\&\fIevp\fR\|(3),
206\&\fIEVP_SignInit\fR\|(3),
207\&\fIEVP_DigestInit\fR\|(3), \fIerr\fR\|(3),
208\&\fIevp\fR\|(3), \fIhmac\fR\|(3), \fImd2\fR\|(3),
209\&\fImd5\fR\|(3), \fImdc2\fR\|(3), \fIripemd\fR\|(3),
210\&\fIsha\fR\|(3), \fIdgst\fR\|(1)
211.SH "HISTORY"
212.IX Header "HISTORY"
213\&\fIEVP_VerifyInit()\fR, \fIEVP_VerifyUpdate()\fR and \fIEVP_VerifyFinal()\fR are
214available in all versions of SSLeay and OpenSSL.
215.PP
216\&\fIEVP_VerifyInit_ex()\fR was added in OpenSSL 0.9.7