1=pod
2
3=head1 NAME
4
5PKCS7_verify, PKCS7_get0_signers - verify a PKCS#7 signedData structure
6
7=head1 SYNOPSIS
8
9 #include <openssl/pkcs7.h>
10
11 int PKCS7_verify(PKCS7 *p7, STACK_OF(X509) *certs, X509_STORE *store,
12                  BIO *indata, BIO *out, int flags);
13
14 STACK_OF(X509) *PKCS7_get0_signers(PKCS7 *p7, STACK_OF(X509) *certs, int flags);
15
16=head1 DESCRIPTION
17
18PKCS7_verify() verifies a PKCS#7 signedData structure. B<p7> is the PKCS7
19structure to verify. B<certs> is a set of certificates in which to search for
20the signer's certificate. B<store> is a trusted certificate store (used for
21chain verification). B<indata> is the signed data if the content is not
22present in B<p7> (that is it is detached). The content is written to B<out>
23if it is not NULL.
24
25B<flags> is an optional set of flags, which can be used to modify the verify
26operation.
27
28PKCS7_get0_signers() retrieves the signer's certificates from B<p7>, it does
29B<not> check their validity or whether any signatures are valid. The B<certs>
30and B<flags> parameters have the same meanings as in PKCS7_verify().
31
32=head1 VERIFY PROCESS
33
34Normally the verify process proceeds as follows.
35
36Initially some sanity checks are performed on B<p7>. The type of B<p7> must
37be signedData. There must be at least one signature on the data and if
38the content is detached B<indata> cannot be B<NULL>.  If the content is
39not detached and B<indata> is not B<NULL>, then the structure has both
40embedded and external content. To treat this as an error, use the flag
41B<PKCS7_NO_DUAL_CONTENT>.
42The default behavior allows this, for compatibility with older
43versions of OpenSSL.
44
45An attempt is made to locate all the signer's certificates, first looking in
46the B<certs> parameter (if it is not B<NULL>) and then looking in any certificates
47contained in the B<p7> structure itself. If any signer's certificates cannot be
48located the operation fails.
49
50Each signer's certificate is chain verified using the B<smimesign> purpose and
51the supplied trusted certificate store. Any internal certificates in the message
52are used as untrusted CAs. If any chain verify fails an error code is returned.
53
54Finally the signed content is read (and written to B<out> is it is not NULL) and
55the signature's checked.
56
57If all signature's verify correctly then the function is successful.
58
59Any of the following flags (ored together) can be passed in the B<flags> parameter
60to change the default verify behaviour. Only the flag B<PKCS7_NOINTERN> is
61meaningful to PKCS7_get0_signers().
62
63If B<PKCS7_NOINTERN> is set the certificates in the message itself are not
64searched when locating the signer's certificate. This means that all the signers
65certificates must be in the B<certs> parameter.
66
67If the B<PKCS7_TEXT> flag is set MIME headers for type B<text/plain> are deleted
68from the content. If the content is not of type B<text/plain> then an error is
69returned.
70
71If B<PKCS7_NOVERIFY> is set the signer's certificates are not chain verified.
72
73If B<PKCS7_NOCHAIN> is set then the certificates contained in the message are
74not used as untrusted CAs. This means that the whole verify chain (apart from
75the signer's certificate) must be contained in the trusted store.
76
77If B<PKCS7_NOSIGS> is set then the signatures on the data are not checked.
78
79=head1 NOTES
80
81One application of B<PKCS7_NOINTERN> is to only accept messages signed by
82a small number of certificates. The acceptable certificates would be passed
83in the B<certs> parameter. In this case if the signer is not one of the
84certificates supplied in B<certs> then the verify will fail because the
85signer cannot be found.
86
87Care should be taken when modifying the default verify behaviour, for example
88setting C<PKCS7_NOVERIFY|PKCS7_NOSIGS> will totally disable all verification
89and any signed message will be considered valid. This combination is however
90useful if one merely wishes to write the content to B<out> and its validity
91is not considered important.
92
93Chain verification should arguably be performed  using the signing time rather
94than the current time. However, since the signing time is supplied by the
95signer it cannot be trusted without additional evidence (such as a trusted
96timestamp).
97
98=head1 RETURN VALUES
99
100PKCS7_verify() returns one for a successful verification and zero
101if an error occurs.
102
103PKCS7_get0_signers() returns all signers or B<NULL> if an error occurred.
104
105The error can be obtained from L<ERR_get_error(3)>
106
107=head1 BUGS
108
109The trusted certificate store is not searched for the signers certificate,
110this is primarily due to the inadequacies of the current B<X509_STORE>
111functionality.
112
113The lack of single pass processing and need to hold all data in memory as
114mentioned in PKCS7_sign() also applies to PKCS7_verify().
115
116=head1 SEE ALSO
117
118L<ERR_get_error(3)>, L<PKCS7_sign(3)>
119
120=head1 COPYRIGHT
121
122Copyright 2002-2020 The OpenSSL Project Authors. All Rights Reserved.
123
124Licensed under the Apache License 2.0 (the "License").  You may not use
125this file except in compliance with the License.  You can obtain a copy
126in the file LICENSE in the source distribution or at
127L<https://www.openssl.org/source/license.html>.
128
129=cut
130