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1 .\" $NetBSD: CMS_verify.3,v 1.14 2015/06/12 17:01:13 christos Exp $
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135 .\" ========================================================================
136 .\"
137 .IX Title "CMS_verify 3"
138 .TH CMS_verify 3 "2009-07-19" "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_verify \- verify 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 \& int CMS_verify(CMS_ContentInfo *cms, STACK_OF(X509) *certs, X509_STORE *store, BIO *indata, BIO *out, unsigned int flags);
155 \&
156 \& STACK_OF(X509) *CMS_get0_signers(CMS_ContentInfo *cms);
157 .Ve
158 .SH "DESCRIPTION"
159 .IX Header "DESCRIPTION"
160 \&\fICMS_verify()\fR verifies a \s-1CMS\s0 SignedData structure. \fBcms\fR is the CMS_ContentInfo
161 structure to verify. \fBcerts\fR is a set of certificates in which to search for
162 the signing certificate(s). \fBstore\fR is a trusted certificate store used for
163 chain verification. \fBindata\fR is the detached content if the content is not
164 present in \fBcms\fR. The content is written to \fBout\fR if it is not \s-1NULL.\s0
165 .PP
166 \&\fBflags\fR is an optional set of flags, which can be used to modify the verify
167 operation.
168 .PP
169 \&\fICMS_get0_signers()\fR retrieves the signing certificate(s) from \fBcms\fR, it must
170 be called after a successful \fICMS_verify()\fR operation.
171 .SH "VERIFY PROCESS"
172 .IX Header "VERIFY PROCESS"
173 Normally the verify process proceeds as follows.
174 .PP
175 Initially some sanity checks are performed on \fBcms\fR. The type of \fBcms\fR must
176 be SignedData. There must be at least one signature on the data and if
177 the content is detached \fBindata\fR cannot be \fB\s-1NULL\s0\fR.
178 .PP
179 An attempt is made to locate all the signing certificate(s), first looking in
180 the \fBcerts\fR parameter (if it is not \s-1NULL\s0) and then looking in any
181 certificates contained in the \fBcms\fR structure itself. If any signing
182 certificate cannot be located the operation fails.
183 .PP
184 Each signing certificate is chain verified using the \fBsmimesign\fR purpose and
185 the supplied trusted certificate store. Any internal certificates in the message
186 are used as untrusted CAs. If \s-1CRL\s0 checking is enabled in \fBstore\fR any internal
187 CRLs are used in addition to attempting to look them up in \fBstore\fR. If any
188 chain verify fails an error code is returned.
189 .PP
190 Finally the signed content is read (and written to \fBout\fR is it is not \s-1NULL\s0)
191 and the signature's checked.
192 .PP
193 If all signature's verify correctly then the function is successful.
194 .PP
195 Any of the following flags (ored together) can be passed in the \fBflags\fR
196 parameter to change the default verify behaviour.
197 .PP
198 If \fB\s-1CMS_NOINTERN\s0\fR is set the certificates in the message itself are not
199 searched when locating the signing certificate(s). This means that all the
200 signing certificates must be in the \fBcerts\fR parameter.
201 .PP
202 If \fB\s-1CMS_NOCRL\s0\fR is set and \s-1CRL\s0 checking is enabled in \fBstore\fR then any
203 CRLs in the message itself are ignored.
204 .PP
205 If the \fB\s-1CMS_TEXT\s0\fR flag is set \s-1MIME\s0 headers for type \fBtext/plain\fR are deleted
206 from the content. If the content is not of type \fBtext/plain\fR then an error is
207 returned.
208 .PP
209 If \fB\s-1CMS_NO_SIGNER_CERT_VERIFY\s0\fR is set the signing certificates are not
210 verified.
211 .PP
212 If \fB\s-1CMS_NO_ATTR_VERIFY\s0\fR is set the signed attributes signature is not
213 verified.
214 .PP
215 If \fB\s-1CMS_NO_CONTENT_VERIFY\s0\fR is set then the content digest is not checked.
216 .SH "NOTES"
217 .IX Header "NOTES"
218 One application of \fB\s-1CMS_NOINTERN\s0\fR is to only accept messages signed by
219 a small number of certificates. The acceptable certificates would be passed
220 in the \fBcerts\fR parameter. In this case if the signer is not one of the
221 certificates supplied in \fBcerts\fR then the verify will fail because the
222 signer cannot be found.
223 .PP
224 In some cases the standard techniques for looking up and validating
225 certificates are not appropriate: for example an application may wish to
226 lookup certificates in a database or perform customised verification. This
227 can be achieved by setting and verifying the signers certificates manually
228 using the signed data utility functions.
229 .PP
230 Care should be taken when modifying the default verify behaviour, for example
231 setting \fB\s-1CMS_NO_CONTENT_VERIFY\s0\fR will totally disable all content verification
232 and any modified content will be considered valid. This combination is however
233 useful if one merely wishes to write the content to \fBout\fR and its validity
234 is not considered important.
235 .PP
236 Chain verification should arguably be performed using the signing time rather
237 than the current time. However since the signing time is supplied by the
238 signer it cannot be trusted without additional evidence (such as a trusted
239 timestamp).
240 .SH "RETURN VALUES"
241 .IX Header "RETURN VALUES"
242 \&\fICMS_verify()\fR returns 1 for a successful verification and zero if an error
243 occurred.
244 .PP
245 \&\fICMS_get0_signers()\fR returns all signers or \s-1NULL\s0 if an error occurred.
246 .PP
247 The error can be obtained from \fIERR_get_error\fR\|(3)
248 .SH "BUGS"
249 .IX Header "BUGS"
250 The trusted certificate store is not searched for the signing certificate,
251 this is primarily due to the inadequacies of the current \fBX509_STORE\fR
252 functionality.
253 .PP
254 The lack of single pass processing means that the signed content must all
255 be held in memory if it is not detached.
256 .SH "SEE ALSO"
257 .IX Header "SEE ALSO"
258 \&\fIERR_get_error\fR\|(3), \fICMS_sign\fR\|(3)
259 .SH "HISTORY"
260 .IX Header "HISTORY"
261 \&\fICMS_verify()\fR was added to OpenSSL 0.9.8