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131 .IX Title "EVP_PKEY_verify_recover 3"
132 .TH EVP_PKEY_verify_recover 3 "2017-12-07" "1.0.2n" "OpenSSL"
133 .\" For nroff, turn off justification. Always turn off hyphenation; it makes
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138 EVP_PKEY_verify_recover_init, EVP_PKEY_verify_recover \- recover signature using a public key algorithm
140 .IX Header "SYNOPSIS"
142 \& #include <openssl/evp.h>
144 \& int EVP_PKEY_verify_recover_init(EVP_PKEY_CTX *ctx);
145 \& int EVP_PKEY_verify_recover(EVP_PKEY_CTX *ctx,
146 \& unsigned char *rout, size_t *routlen,
147 \& const unsigned char *sig, size_t siglen);
150 .IX Header "DESCRIPTION"
151 The \fIEVP_PKEY_verify_recover_init()\fR function initializes a public key algorithm
152 context using key \fBpkey\fR for a verify recover operation.
154 The \fIEVP_PKEY_verify_recover()\fR function recovers signed data
155 using \fBctx\fR. The signature is specified using the \fBsig\fR and
156 \&\fBsiglen\fR parameters. If \fBrout\fR is \fB\s-1NULL\s0\fR then the maximum size of the output
157 buffer is written to the \fBroutlen\fR parameter. If \fBrout\fR is not \fB\s-1NULL\s0\fR then
158 before the call the \fBroutlen\fR parameter should contain the length of the
159 \&\fBrout\fR buffer, if the call is successful recovered data is written to
160 \&\fBrout\fR and the amount of data written to \fBroutlen\fR.
163 Normally an application is only interested in whether a signature verification
164 operation is successful in those cases the \fIEVP_verify()\fR function should be
167 Sometimes however it is useful to obtain the data originally signed using a
168 signing operation. Only certain public key algorithms can recover a signature
169 in this way (for example \s-1RSA\s0 in \s-1PKCS\s0 padding mode).
171 After the call to \fIEVP_PKEY_verify_recover_init()\fR algorithm specific control
172 operations can be performed to set any appropriate parameters for the
175 The function \fIEVP_PKEY_verify_recover()\fR can be called more than once on the same
176 context if several operations are performed using the same parameters.
178 .IX Header "RETURN VALUES"
179 \&\fIEVP_PKEY_verify_recover_init()\fR and \fIEVP_PKEY_verify_recover()\fR return 1 for success
180 and 0 or a negative value for failure. In particular a return value of \-2
181 indicates the operation is not supported by the public key algorithm.
184 Recover digest originally signed using PKCS#1 and \s-1SHA256\s0 digest:
187 \& #include <openssl/evp.h>
188 \& #include <openssl/rsa.h>
190 \& EVP_PKEY_CTX *ctx;
191 \& unsigned char *rout, *sig;
192 \& size_t routlen, siglen;
193 \& EVP_PKEY *verify_key;
194 \& /* NB: assumes verify_key, sig and siglen are already set up
195 \& * and that verify_key is an RSA public key
197 \& ctx = EVP_PKEY_CTX_new(verify_key);
199 \& /* Error occurred */
200 \& if (EVP_PKEY_verify_recover_init(ctx) <= 0)
202 \& if (EVP_PKEY_CTX_set_rsa_padding(ctx, RSA_PKCS1_PADDING) <= 0)
204 \& if (EVP_PKEY_CTX_set_signature_md(ctx, EVP_sha256()) <= 0)
207 \& /* Determine buffer length */
208 \& if (EVP_PKEY_verify_recover(ctx, NULL, &routlen, sig, siglen) <= 0)
211 \& rout = OPENSSL_malloc(routlen);
214 \& /* malloc failure */
216 \& if (EVP_PKEY_verify_recover(ctx, rout, &routlen, sig, siglen) <= 0)
219 \& /* Recovered data is routlen bytes written to buffer rout */
222 .IX Header "SEE ALSO"
223 \&\fIEVP_PKEY_CTX_new\fR\|(3),
224 \&\fIEVP_PKEY_encrypt\fR\|(3),
225 \&\fIEVP_PKEY_decrypt\fR\|(3),
226 \&\fIEVP_PKEY_sign\fR\|(3),
227 \&\fIEVP_PKEY_verify\fR\|(3),
228 \&\fIEVP_PKEY_derive\fR\|(3)
231 These functions were first added to OpenSSL 1.0.0.