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137 .IX Title "EVP_PKEY_sign 3"
138 .TH EVP_PKEY_sign 3 "2014-10-17" "1.0.1n" "OpenSSL"
139 .\" For nroff, turn off justification. Always turn off hyphenation; it makes
140 .\" way too many mistakes in technical documents.
141 .if n .ad l
142 .nh
143 .SH "NAME"
144 EVP_PKEY_sign_init, EVP_PKEY_sign \- sign using a public key algorithm
145 .SH "LIBRARY"
146 libcrypto, -lcrypto
147 .SH "SYNOPSIS"
148 .IX Header "SYNOPSIS"
149 .Vb 1
150 \& #include <openssl/evp.h>
151 \&
152 \& int EVP_PKEY_sign_init(EVP_PKEY_CTX *ctx);
153 \& int EVP_PKEY_sign(EVP_PKEY_CTX *ctx,
154 \& unsigned char *sig, size_t *siglen,
155 \& const unsigned char *tbs, size_t tbslen);
156 .Ve
157 .SH "DESCRIPTION"
158 .IX Header "DESCRIPTION"
159 The \fIEVP_PKEY_sign_init()\fR function initializes a public key algorithm
160 context using key \fBpkey\fR for a signing operation.
161 .PP
162 The \fIEVP_PKEY_sign()\fR function performs a public key signing operation
163 using \fBctx\fR. The data to be signed is specified using the \fBtbs\fR and
164 \&\fBtbslen\fR parameters. If \fBsig\fR is \fB\s-1NULL\s0\fR then the maximum size of the output
165 buffer is written to the \fBsiglen\fR parameter. If \fBsig\fR is not \fB\s-1NULL\s0\fR then
166 before the call the \fBsiglen\fR parameter should contain the length of the
167 \&\fBsig\fR buffer, if the call is successful the signature is written to
168 \&\fBsig\fR and the amount of data written to \fBsiglen\fR.
169 .SH "NOTES"
170 .IX Header "NOTES"
171 \&\fIEVP_PKEY_sign()\fR does not hash the data to be signed, and therefore is
172 normally used to sign digests. For signing arbitrary messages, see the
173 \&\fIEVP_DigestSignInit\fR\|(3) and
174 \&\fIEVP_SignInit\fR\|(3) signing interfaces instead.
175 .PP
176 After the call to \fIEVP_PKEY_sign_init()\fR algorithm specific control
177 operations can be performed to set any appropriate parameters for the
178 operation (see \fIEVP_PKEY_CTX_ctrl\fR\|(3)).
179 .PP
180 The function \fIEVP_PKEY_sign()\fR can be called more than once on the same
181 context if several operations are performed using the same parameters.
182 .SH "RETURN VALUES"
183 .IX Header "RETURN VALUES"
184 \&\fIEVP_PKEY_sign_init()\fR and \fIEVP_PKEY_sign()\fR return 1 for success and 0
185 or a negative value for failure. In particular a return value of \-2
186 indicates the operation is not supported by the public key algorithm.
187 .SH "EXAMPLE"
188 .IX Header "EXAMPLE"
189 Sign data using \s-1RSA\s0 with PKCS#1 padding and \s-1SHA256\s0 digest:
190 .PP
191 .Vb 2
192 \& #include <openssl/evp.h>
193 \& #include <openssl/rsa.h>
194 \&
195 \& EVP_PKEY_CTX *ctx;
196 \& /* md is a SHA\-256 digest in this example. */
197 \& unsigned char *md, *sig;
198 \& size_t mdlen = 32, siglen;
199 \& EVP_PKEY *signing_key;
200 \&
201 \& /*
202 \& * NB: assumes signing_key and md are set up before the next
203 \& * step. signing_key must be an RSA private key and md must
204 \& * point to the SHA\-256 digest to be signed.
205 \& */
206 \& ctx = EVP_PKEY_CTX_new(signing_key, NULL /* no engine */);
207 \& if (!ctx)
208 \& /* Error occurred */
209 \& if (EVP_PKEY_sign_init(ctx) <= 0)
210 \& /* Error */
211 \& if (EVP_PKEY_CTX_set_rsa_padding(ctx, RSA_PKCS1_PADDING) <= 0)
212 \& /* Error */
213 \& if (EVP_PKEY_CTX_set_signature_md(ctx, EVP_sha256()) <= 0)
214 \& /* Error */
215 \&
216 \& /* Determine buffer length */
217 \& if (EVP_PKEY_sign(ctx, NULL, &siglen, md, mdlen) <= 0)
218 \& /* Error */
219 \&
220 \& sig = OPENSSL_malloc(siglen);
221 \&
222 \& if (!sig)
223 \& /* malloc failure */
224 \&
225 \& if (EVP_PKEY_sign(ctx, sig, &siglen, md, mdlen) <= 0)
226 \& /* Error */
227 \&
228 \& /* Signature is siglen bytes written to buffer sig */
229 .Ve
230 .SH "SEE ALSO"
231 .IX Header "SEE ALSO"
232 \&\fIEVP_PKEY_CTX_new\fR\|(3),
233 \&\fIEVP_PKEY_CTX_ctrl\fR\|(3),
234 \&\fIEVP_PKEY_encrypt\fR\|(3),
235 \&\fIEVP_PKEY_decrypt\fR\|(3),
236 \&\fIEVP_PKEY_verify\fR\|(3),
237 \&\fIEVP_PKEY_verify_recover\fR\|(3),
238 \&\fIEVP_PKEY_derive\fR\|(3)
239 .SH "HISTORY"
240 .IX Header "HISTORY"
241 These functions were first added to OpenSSL 1.0.0.