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134 .\" ========================================================================
135 .\"
136 .IX Title "CMS_verify 3"
137 .TH CMS_verify 3 "2008-04-10" "1.1.0-dev" "OpenSSL"
138 .\" For nroff, turn off justification. Always turn off hyphenation; it makes
139 .\" way too many mistakes in technical documents.
140 .if n .ad l
141 .nh
142 .SH "NAME"
143 .Vb 1
144 \& CMS_verify \- verify a CMS SignedData structure
145 .Ve
146 .SH "LIBRARY"
147 libcrypto, -lcrypto
148 .SH "SYNOPSIS"
149 .IX Header "SYNOPSIS"
150 .Vb 1
151 \& #include <openssl/cms.h>
152 \&
153 \& int CMS_verify(CMS_ContentInfo *cms, STACK_OF(X509) *certs, X509_STORE *store, BIO *indata, BIO *out, unsigned int flags);
154 \&
155 \& STACK_OF(X509) *CMS_get0_signers(CMS_ContentInfo *cms);
156 .Ve
157 .SH "DESCRIPTION"
158 .IX Header "DESCRIPTION"
159 \&\fICMS_verify()\fR verifies a \s-1CMS\s0 SignedData structure. \fBcms\fR is the CMS_ContentInfo
160 structure to verify. \fBcerts\fR is a set of certificates in which to search for
161 the signing certificate(s). \fBstore\fR is a trusted certificate store used for
162 chain verification. \fBindata\fR is the detached content if the content is not
163 present in \fBcms\fR. The content is written to \fBout\fR if it is not \s-1NULL\s0.
164 .PP
165 \&\fBflags\fR is an optional set of flags, which can be used to modify the verify
166 operation.
167 .PP
168 \&\fICMS_get0_signers()\fR retrieves the signing certificate(s) from \fBcms\fR, it must
169 be called after a successful \fICMS_verify()\fR operation.
170 .SH "VERIFY PROCESS"
171 .IX Header "VERIFY PROCESS"
172 Normally the verify process proceeds as follows.
173 .PP
174 Initially some sanity checks are performed on \fBcms\fR. The type of \fBcms\fR must
175 be SignedData. There must be at least one signature on the data and if
176 the content is detached \fBindata\fR cannot be \fB\s-1NULL\s0\fR.
177 .PP
178 An attempt is made to locate all the signing certificate(s), first looking in
179 the \fBcerts\fR parameter (if it is not \s-1NULL\s0) and then looking in any
180 certificates contained in the \fBcms\fR structure itself. If any signing
181 certificate cannot be located the operation fails.
182 .PP
183 Each signing certificate is chain verified using the \fBsmimesign\fR purpose and
184 the supplied trusted certificate store. Any internal certificates in the message
185 are used as untrusted CAs. If \s-1CRL\s0 checking is enabled in \fBstore\fR any internal
186 CRLs are used in addition to attempting to look them up in \fBstore\fR. If any
187 chain verify fails an error code is returned.
188 .PP
189 Finally the signed content is read (and written to \fBout\fR is it is not \s-1NULL\s0)
190 and the signature's checked.
191 .PP
192 If all signature's verify correctly then the function is successful.
193 .PP
194 Any of the following flags (ored together) can be passed in the \fBflags\fR
195 parameter to change the default verify behaviour.
196 .PP
197 If \fB\s-1CMS_NOINTERN\s0\fR is set the certificates in the message itself are not
198 searched when locating the signing certificate(s). This means that all the
199 signing certificates must be in the \fBcerts\fR parameter.
200 .PP
201 If \fB\s-1CMS_NOCRL\s0\fR is set and \s-1CRL\s0 checking is enabled in \fBstore\fR then any
202 CRLs in the message itself are ignored.
203 .PP
204 If the \fB\s-1CMS_TEXT\s0\fR flag is set \s-1MIME\s0 headers for type \fBtext/plain\fR are deleted
205 from the content. If the content is not of type \fBtext/plain\fR then an error is
206 returned.
207 .PP
208 If \fB\s-1CMS_NO_SIGNER_CERT_VERIFY\s0\fR is set the signing certificates are not
209 verified.
210 .PP
211 If \fB\s-1CMS_NO_ATTR_VERIFY\s0\fR is set the signed attributes signature is not
212 verified.
213 .PP
214 If \fB\s-1CMS_NO_CONTENT_VERIFY\s0\fR is set then the content digest is not checked.
215 .SH "NOTES"
216 .IX Header "NOTES"
217 One application of \fB\s-1CMS_NOINTERN\s0\fR is to only accept messages signed by
218 a small number of certificates. The acceptable certificates would be passed
219 in the \fBcerts\fR parameter. In this case if the signer is not one of the
220 certificates supplied in \fBcerts\fR then the verify will fail because the
221 signer cannot be found.
222 .PP
223 In some cases the standard techniques for looking up and validating
224 certificates are not appropriate: for example an application may wish to
225 lookup certificates in a database or perform customised verification. This
226 can be achieved by setting and verifying the signers certificates manually
227 using the signed data utility functions.
228 .PP
229 Care should be taken when modifying the default verify behaviour, for example
230 setting \fB\s-1CMS_NO_CONTENT_VERIFY\s0\fR will totally disable all content verification
231 and any modified content will be considered valid. This combination is however
232 useful if one merely wishes to write the content to \fBout\fR and its validity
233 is not considered important.
234 .PP
235 Chain verification should arguably be performed using the signing time rather
236 than the current time. However since the signing time is supplied by the
237 signer it cannot be trusted without additional evidence (such as a trusted
238 timestamp).
239 .SH "RETURN VALUES"
240 .IX Header "RETURN VALUES"
241 \&\fICMS_verify()\fR returns 1 for a successful verification and zero if an error
242 occurred.
243 .PP
244 \&\fICMS_get0_signers()\fR returns all signers or \s-1NULL\s0 if an error occurred.
245 .PP
246 The error can be obtained from \fIERR_get_error\fR\|(3)
247 .SH "BUGS"
248 .IX Header "BUGS"
249 The trusted certificate store is not searched for the signing certificate,
250 this is primarily due to the inadequacies of the current \fBX509_STORE\fR
251 functionality.
252 .PP
253 The lack of single pass processing means that the signed content must all
254 be held in memory if it is not detached.
255 .SH "SEE ALSO"
256 .IX Header "SEE ALSO"
257 \&\fIERR_get_error\fR\|(3), \fICMS_sign\fR\|(3)
258 .SH "HISTORY"
259 .IX Header "HISTORY"
260 \&\fICMS_verify()\fR was added to OpenSSL 0.9.8