Update files for OpenSSL-1.0.0f import.
[dragonfly.git] / secure / lib / libcrypto / man / EVP_PKEY_verifyrecover.3
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124.\" ========================================================================
125.\"
126.IX Title "EVP_PKEY_verifyrecover 3"
e3261593 127.TH EVP_PKEY_verifyrecover 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_PKEY_verifyrecover_init, EVP_PKEY_verifyrecover \- recover signature using a public key algorithm
134.SH "SYNOPSIS"
135.IX Header "SYNOPSIS"
136.Vb 1
137\& #include <openssl/evp.h>
138\&
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);
143.Ve
144.SH "DESCRIPTION"
145.IX Header "DESCRIPTION"
146The \fIEVP_PKEY_verifyrecover_init()\fR function initializes a public key algorithm
147context using key \fBpkey\fR for a verify recover operation.
148.PP
149The \fIEVP_PKEY_verifyrecover()\fR function recovers signed data
150using \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
152buffer is written to the \fBroutlen\fR parameter. If \fBrout\fR is not \fB\s-1NULL\s0\fR then
153before 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.
156.SH "NOTES"
157.IX Header "NOTES"
158Normally an application is only interested in whether a signature verification
159operation is successful in those cases the \fIEVP_verify()\fR function should be
160used.
161.PP
162Sometimes however it is useful to obtain the data originally signed using a
163signing operation. Only certain public key algorithms can recover a signature
164in this way (for example \s-1RSA\s0 in \s-1PKCS\s0 padding mode).
165.PP
166After the call to \fIEVP_PKEY_verifyrecover_init()\fR algorithm specific control
167operations can be performed to set any appropriate parameters for the
168operation.
169.PP
170The function \fIEVP_PKEY_verifyrecover()\fR can be called more than once on the same
171context if several operations are performed using the same parameters.
172.SH "RETURN VALUES"
173.IX Header "RETURN VALUES"
174\&\fIEVP_PKEY_verifyrecover_init()\fR and \fIEVP_PKEY_verifyrecover()\fR return 1 for success
175and 0 or a negative value for failure. In particular a return value of \-2
176indicates the operation is not supported by the public key algorithm.
177.SH "EXAMPLE"
178.IX Header "EXAMPLE"
179Recover digest originally signed using PKCS#1 and \s-1SHA256\s0 digest:
180.PP
181.Vb 2
182\& #include <openssl/evp.h>
183\& #include <openssl/rsa.h>
184\&
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
191\& */
192\& ctx = EVP_PKEY_CTX_new(verify_key);
193\& if (!ctx)
194\& /* Error occurred */
195\& if (EVP_PKEY_verifyrecover_init(ctx) <= 0)
196\& /* Error */
197\& if (EVP_PKEY_CTX_set_rsa_padding(ctx, RSA_PKCS1_PADDING) <= 0)
198\& /* Error */
199\& if (EVP_PKEY_CTX_set_signature_md(ctx, EVP_sha256()) <= 0)
200\& /* Error */
201\&
202\& /* Determine buffer length */
b911043f 203\& if (EVP_PKEY_verifyrecover(ctx, NULL, &routlen, sig, siglen) <= 0)
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204\& /* Error */
205\&
206\& rout = OPENSSL_malloc(routlen);
207\&
208\& if (!rout)
209\& /* malloc failure */
210\&
211\& if (EVP_PKEY_verifyrecover(ctx, rout, &routlen, sig, siglen) <= 0)
212\& /* Error */
213\&
214\& /* Recovered data is routlen bytes written to buffer rout */
215.Ve
216.SH "SEE ALSO"
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)
224.SH "HISTORY"
225.IX Header "HISTORY"
226These functions were first added to OpenSSL 1.0.0.