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1 .\" $NetBSD: PKCS7_verify.3,v 1.14 2015/06/12 17:01:14 christos Exp $
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135 .\" ========================================================================
136 .\"
137 .IX Title "PKCS7_verify 3"
138 .TH PKCS7_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 PKCS7_verify \- verify a PKCS#7 signedData structure
145 .SH "LIBRARY"
146 libcrypto, -lcrypto
147 .SH "SYNOPSIS"
148 .IX Header "SYNOPSIS"
149 .Vb 1
150 \& #include <openssl/pkcs7.h>
151 \&
152 \& int PKCS7_verify(PKCS7 *p7, STACK_OF(X509) *certs, X509_STORE *store, BIO *indata, BIO *out, int flags);
153 \&
154 \& STACK_OF(X509) *PKCS7_get0_signers(PKCS7 *p7, STACK_OF(X509) *certs, int flags);
155 .Ve
156 .SH "DESCRIPTION"
157 .IX Header "DESCRIPTION"
158 \&\fIPKCS7_verify()\fR verifies a PKCS#7 signedData structure. \fBp7\fR is the \s-1PKCS7\s0
159 structure to verify. \fBcerts\fR is a set of certificates in which to search for
160 the signer's certificate. \fBstore\fR is a trusted certficate store (used for
161 chain verification). \fBindata\fR is the signed data if the content is not
162 present in \fBp7\fR (that is it is detached). The content is written to \fBout\fR
163 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 \&\fIPKCS7_get0_signers()\fR retrieves the signer's certificates from \fBp7\fR, it does
169 \&\fBnot\fR check their validity or whether any signatures are valid. The \fBcerts\fR
170 and \fBflags\fR parameters have the same meanings as in \fIPKCS7_verify()\fR.
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 \fBp7\fR. The type of \fBp7\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 signer's certificates, first looking in
180 the \fBcerts\fR parameter (if it is not \fB\s-1NULL\s0\fR) and then looking in any certificates
181 contained in the \fBp7\fR structure itself. If any signer's certificates cannot be
182 located the operation fails.
183 .PP
184 Each signer's 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 any chain verify fails an error code is returned.
187 .PP
188 Finally the signed content is read (and written to \fBout\fR is it is not \s-1NULL\s0) and
189 the signature's checked.
190 .PP
191 If all signature's verify correctly then the function is successful.
192 .PP
193 Any of the following flags (ored together) can be passed in the \fBflags\fR parameter
194 to change the default verify behaviour. Only the flag \fB\s-1PKCS7_NOINTERN\s0\fR is
195 meaningful to \fIPKCS7_get0_signers()\fR.
196 .PP
197 If \fB\s-1PKCS7_NOINTERN\s0\fR is set the certificates in the message itself are not
198 searched when locating the signer's certificate. This means that all the signers
199 certificates must be in the \fBcerts\fR parameter.
200 .PP
201 If the \fB\s-1PKCS7_TEXT\s0\fR flag is set \s-1MIME\s0 headers for type \fBtext/plain\fR are deleted
202 from the content. If the content is not of type \fBtext/plain\fR then an error is
203 returned.
204 .PP
205 If \fB\s-1PKCS7_NOVERIFY\s0\fR is set the signer's certificates are not chain verified.
206 .PP
207 If \fB\s-1PKCS7_NOCHAIN\s0\fR is set then the certificates contained in the message are
208 not used as untrusted CAs. This means that the whole verify chain (apart from
209 the signer's certificate) must be contained in the trusted store.
210 .PP
211 If \fB\s-1PKCS7_NOSIGS\s0\fR is set then the signatures on the data are not checked.
212 .SH "NOTES"
213 .IX Header "NOTES"
214 One application of \fB\s-1PKCS7_NOINTERN\s0\fR is to only accept messages signed by
215 a small number of certificates. The acceptable certificates would be passed
216 in the \fBcerts\fR parameter. In this case if the signer is not one of the
217 certificates supplied in \fBcerts\fR then the verify will fail because the
218 signer cannot be found.
219 .PP
220 Care should be taken when modifying the default verify behaviour, for example
221 setting \fBPKCS7_NOVERIFY|PKCS7_NOSIGS\fR will totally disable all verification
222 and any signed message will be considered valid. This combination is however
223 useful if one merely wishes to write the content to \fBout\fR and its validity
224 is not considered important.
225 .PP
226 Chain verification should arguably be performed using the signing time rather
227 than the current time. However since the signing time is supplied by the
228 signer it cannot be trusted without additional evidence (such as a trusted
229 timestamp).
230 .SH "RETURN VALUES"
231 .IX Header "RETURN VALUES"
232 \&\fIPKCS7_verify()\fR returns 1 for a successful verification and zero or a negative
233 value if an error occurs.
234 .PP
235 \&\fIPKCS7_get0_signers()\fR returns all signers or \fB\s-1NULL\s0\fR if an error occurred.
236 .PP
237 The error can be obtained from \fIERR_get_error\fR\|(3)
238 .SH "BUGS"
239 .IX Header "BUGS"
240 The trusted certificate store is not searched for the signers certificate,
241 this is primarily due to the inadequacies of the current \fBX509_STORE\fR
242 functionality.
243 .PP
244 The lack of single pass processing and need to hold all data in memory as
245 mentioned in \fIPKCS7_sign()\fR also applies to \fIPKCS7_verify()\fR.
246 .SH "SEE ALSO"
247 .IX Header "SEE ALSO"
248 \&\fIERR_get_error\fR\|(3), \fIPKCS7_sign\fR\|(3)
249 .SH "HISTORY"
250 .IX Header "HISTORY"
251 \&\fIPKCS7_verify()\fR was added to OpenSSL 0.9.5