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135 .\" ========================================================================
136 .\"
137 .IX Title "CMS_sign 3"
138 .TH CMS_sign 3 "2009-12-26" "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 .Vb 1
145 \& CMS_sign \- create a CMS SignedData structure
146 .Ve
147 .SH "LIBRARY"
148 libcrypto, -lcrypto
149 .SH "SYNOPSIS"
150 .IX Header "SYNOPSIS"
151 .Vb 1
152 \& #include <openssl/cms.h>
153 \&
154 \& CMS_ContentInfo *CMS_sign(X509 *signcert, EVP_PKEY *pkey, STACK_OF(X509) *certs, BIO *data, unsigned int flags);
155 .Ve
156 .SH "DESCRIPTION"
157 .IX Header "DESCRIPTION"
158 \&\fICMS_sign()\fR creates and returns a \s-1CMS\s0 SignedData structure. \fBsigncert\fR is
159 the certificate to sign with, \fBpkey\fR is the corresponding private key.
160 \&\fBcerts\fR is an optional additional set of certificates to include in the \s-1CMS\s0
161 structure (for example any intermediate CAs in the chain). Any or all of
162 these parameters can be \fB\s-1NULL\s0\fR, see \fB\s-1NOTES\s0\fR below.
163 .PP
164 The data to be signed is read from \s-1BIO \s0\fBdata\fR.
165 .PP
166 \&\fBflags\fR is an optional set of flags.
167 .SH "NOTES"
168 .IX Header "NOTES"
169 Any of the following flags (ored together) can be passed in the \fBflags\fR
170 parameter.
171 .PP
172 Many S/MIME clients expect the signed content to include valid \s-1MIME\s0 headers. If
173 the \fB\s-1CMS_TEXT\s0\fR flag is set \s-1MIME\s0 headers for type \fBtext/plain\fR are prepended
174 to the data.
175 .PP
176 If \fB\s-1CMS_NOCERTS\s0\fR is set the signer's certificate will not be included in the
177 CMS_ContentInfo structure, the signer's certificate must still be supplied in
178 the \fBsigncert\fR parameter though. This can reduce the size of the signature if
179 the signers certificate can be obtained by other means: for example a
180 previously signed message.
181 .PP
182 The data being signed is included in the CMS_ContentInfo structure, unless
183 \&\fB\s-1CMS_DETACHED\s0\fR is set in which case it is omitted. This is used for
184 CMS_ContentInfo detached signatures which are used in S/MIME plaintext signed
185 messages for example.
186 .PP
187 Normally the supplied content is translated into \s-1MIME\s0 canonical format (as
188 required by the S/MIME specifications) if \fB\s-1CMS_BINARY\s0\fR is set no translation
189 occurs. This option should be used if the supplied data is in binary format
190 otherwise the translation will corrupt it.
191 .PP
192 The SignedData structure includes several \s-1CMS\s0 signedAttributes including the
193 signing time, the \s-1CMS\s0 content type and the supported list of ciphers in an
194 SMIMECapabilities attribute. If \fB\s-1CMS_NOATTR\s0\fR is set then no signedAttributes
195 will be used. If \fB\s-1CMS_NOSMIMECAP\s0\fR is set then just the SMIMECapabilities are
196 omitted.
197 .PP
198 If present the SMIMECapabilities attribute indicates support for the following
199 algorithms in preference order: 256 bit \s-1AES,\s0 Gost R3411\-94, Gost 28147\-89, 192
200 bit \s-1AES, 128\s0 bit \s-1AES,\s0 triple \s-1DES, 128\s0 bit \s-1RC2, 64\s0 bit \s-1RC2, DES\s0 and 40 bit \s-1RC2.\s0
201 If any of these algorithms is not available then it will not be included: for example the \s-1GOST\s0 algorithms will not be included if the \s-1GOST ENGINE\s0 is
202 not loaded.
203 .PP
204 OpenSSL will by default identify signing certificates using issuer name
205 and serial number. If \fB\s-1CMS_USE_KEYID\s0\fR is set it will use the subject key
206 identifier value instead. An error occurs if the signing certificate does not
207 have a subject key identifier extension.
208 .PP
209 If the flags \fB\s-1CMS_STREAM\s0\fR is set then the returned \fBCMS_ContentInfo\fR
210 structure is just initialized ready to perform the signing operation. The
211 signing is however \fBnot\fR performed and the data to be signed is not read from
212 the \fBdata\fR parameter. Signing is deferred until after the data has been
213 written. In this way data can be signed in a single pass.
214 .PP
215 If the \fB\s-1CMS_PARTIAL\s0\fR flag is set a partial \fBCMS_ContentInfo\fR structure is
216 output to which additional signers and capabilities can be added before
217 finalization.
218 .PP
219 If the flag \fB\s-1CMS_STREAM\s0\fR is set the returned \fBCMS_ContentInfo\fR structure is
220 \&\fBnot\fR complete and outputting its contents via a function that does not
221 properly finalize the \fBCMS_ContentInfo\fR structure will give unpredictable
222 results.
223 .PP
224 Several functions including \fISMIME_write_CMS()\fR, \fIi2d_CMS_bio_stream()\fR,
225 \&\fIPEM_write_bio_CMS_stream()\fR finalize the structure. Alternatively finalization
226 can be performed by obtaining the streaming \s-1ASN1 \s0\fB\s-1BIO\s0\fR directly using
227 \&\fIBIO_new_CMS()\fR.
228 .PP
229 If a signer is specified it will use the default digest for the signing
230 algorithm. This is \fB\s-1SHA1\s0\fR for both \s-1RSA\s0 and \s-1DSA\s0 keys.
231 .PP
232 If \fBsigncert\fR and \fBpkey\fR are \s-1NULL\s0 then a certificates only \s-1CMS\s0 structure is
233 output.
234 .PP
235 The function \fICMS_sign()\fR is a basic \s-1CMS\s0 signing function whose output will be
236 suitable for many purposes. For finer control of the output format the
237 \&\fBcerts\fR, \fBsigncert\fR and \fBpkey\fR parameters can all be \fB\s-1NULL\s0\fR and the
238 \&\fB\s-1CMS_PARTIAL\s0\fR flag set. Then one or more signers can be added using the
239 function \fICMS_sign_add1_signer()\fR, non default digests can be used and custom
240 attributes added. \fB\f(BICMS_final()\fB\fR must then be called to finalize the
241 structure if streaming is not enabled.
242 .SH "BUGS"
243 .IX Header "BUGS"
244 Some attributes such as counter signatures are not supported.
245 .SH "RETURN VALUES"
246 .IX Header "RETURN VALUES"
247 \&\fICMS_sign()\fR returns either a valid CMS_ContentInfo structure or \s-1NULL\s0 if an error
248 occurred. The error can be obtained from \fIERR_get_error\fR\|(3).
249 .SH "SEE ALSO"
250 .IX Header "SEE ALSO"
251 \&\fIERR_get_error\fR\|(3), \fICMS_verify\fR\|(3)
252 .SH "HISTORY"
253 .IX Header "HISTORY"
254 \&\fICMS_sign()\fR was added to OpenSSL 0.9.8
255 .PP
256 The \fB\s-1CMS_STREAM\s0\fR flag is only supported for detached data in OpenSSL 0.9.8,
257 it is supported for embedded data in OpenSSL 1.0.0 and later.