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124 .\" ========================================================================
126 .IX Title "EVP_PKEY_verifyrecover 3"
127 .TH EVP_PKEY_verifyrecover 3 "2012-04-19" "1.0.1a" "OpenSSL"
128 .\" For nroff, turn off justification. Always turn off hyphenation; it makes
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133 EVP_PKEY_verifyrecover_init, EVP_PKEY_verifyrecover \- recover signature using a public key algorithm
135 .IX Header "SYNOPSIS"
137 \& #include <openssl/evp.h>
139 \& int EVP_PKEY_verifyrecover_init(EVP_PKEY_CTX *ctx);
140 \& int EVP_PKEY_verifyrecover(EVP_PKEY_CTX *ctx,
141 \& unsigned char *rout, size_t *routlen,
142 \& const unsigned char *sig, size_t siglen);
145 .IX Header "DESCRIPTION"
146 The \fIEVP_PKEY_verifyrecover_init()\fR function initializes a public key algorithm
147 context using key \fBpkey\fR for a verify recover operation.
149 The \fIEVP_PKEY_verifyrecover()\fR function recovers signed data
150 using \fBctx\fR. The signature is specified using the \fBsig\fR and
151 \&\fBsiglen\fR parameters. If \fBrout\fR is \fB\s-1NULL\s0\fR then the maximum size of the output
152 buffer is written to the \fBroutlen\fR parameter. If \fBrout\fR is not \fB\s-1NULL\s0\fR then
153 before the call the \fBroutlen\fR parameter should contain the length of the
154 \&\fBrout\fR buffer, if the call is successful recovered data is written to
155 \&\fBrout\fR and the amount of data written to \fBroutlen\fR.
158 Normally an application is only interested in whether a signature verification
159 operation is successful in those cases the \fIEVP_verify()\fR function should be
162 Sometimes however it is useful to obtain the data originally signed using a
163 signing operation. Only certain public key algorithms can recover a signature
164 in this way (for example \s-1RSA\s0 in \s-1PKCS\s0 padding mode).
166 After the call to \fIEVP_PKEY_verifyrecover_init()\fR algorithm specific control
167 operations can be performed to set any appropriate parameters for the
170 The function \fIEVP_PKEY_verifyrecover()\fR can be called more than once on the same
171 context if several operations are performed using the same parameters.
173 .IX Header "RETURN VALUES"
174 \&\fIEVP_PKEY_verifyrecover_init()\fR and \fIEVP_PKEY_verifyrecover()\fR return 1 for success
175 and 0 or a negative value for failure. In particular a return value of \-2
176 indicates the operation is not supported by the public key algorithm.
179 Recover digest originally signed using PKCS#1 and \s-1SHA256\s0 digest:
182 \& #include <openssl/evp.h>
183 \& #include <openssl/rsa.h>
185 \& EVP_PKEY_CTX *ctx;
186 \& unsigned char *rout, *sig;
187 \& size_t routlen, siglen;
188 \& EVP_PKEY *verify_key;
189 \& /* NB: assumes verify_key, sig and siglen are already set up
190 \& * and that verify_key is an RSA public key
192 \& ctx = EVP_PKEY_CTX_new(verify_key);
194 \& /* Error occurred */
195 \& if (EVP_PKEY_verifyrecover_init(ctx) <= 0)
197 \& if (EVP_PKEY_CTX_set_rsa_padding(ctx, RSA_PKCS1_PADDING) <= 0)
199 \& if (EVP_PKEY_CTX_set_signature_md(ctx, EVP_sha256()) <= 0)
202 \& /* Determine buffer length */
203 \& if (EVP_PKEY_verifyrecover(ctx, NULL, &routlen, sig, siglen) <= 0)
206 \& rout = OPENSSL_malloc(routlen);
209 \& /* malloc failure */
211 \& if (EVP_PKEY_verifyrecover(ctx, rout, &routlen, sig, siglen) <= 0)
214 \& /* Recovered data is routlen bytes written to buffer rout */
217 .IX Header "SEE ALSO"
218 \&\fIEVP_PKEY_CTX_new\fR\|(3),
219 \&\fIEVP_PKEY_encrypt\fR\|(3),
220 \&\fIEVP_PKEY_decrypt\fR\|(3),
221 \&\fIEVP_PKEY_sign\fR\|(3),
222 \&\fIEVP_PKEY_verify\fR\|(3),
223 \&\fIEVP_PKEY_derive\fR\|(3)
226 These functions were first added to OpenSSL 1.0.0.