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1 | =pod |
2 | ||
3 | =head1 NAME | |
4 | ||
aafbe1cc | 5 | CMS_verify, CMS_get0_signers - verify a CMS SignedData structure |
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6 | |
7 | =head1 SYNOPSIS | |
8 | ||
9 | #include <openssl/cms.h> | |
10 | ||
11 | int CMS_verify(CMS_ContentInfo *cms, STACK_OF(X509) *certs, X509_STORE *store, BIO *indata, BIO *out, unsigned int flags); | |
12 | ||
13 | STACK_OF(X509) *CMS_get0_signers(CMS_ContentInfo *cms); | |
14 | ||
15 | =head1 DESCRIPTION | |
16 | ||
360bb61d | 17 | CMS_verify() verifies a CMS SignedData structure. B<cms> is the CMS_ContentInfo |
e33ffaca | 18 | structure to verify. B<certs> is a set of certificates in which to search for |
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19 | the signing certificate(s). B<store> is a trusted certificate store used for |
20 | chain verification. B<indata> is the detached content if the content is not | |
21 | present in B<cms>. The content is written to B<out> if it is not NULL. | |
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22 | |
23 | B<flags> is an optional set of flags, which can be used to modify the verify | |
24 | operation. | |
25 | ||
38d3a738 | 26 | CMS_get0_signers() retrieves the signing certificate(s) from B<cms>, it must |
c420fab5 | 27 | be called after a successful CMS_verify() operation. |
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28 | |
29 | =head1 VERIFY PROCESS | |
30 | ||
31 | Normally the verify process proceeds as follows. | |
32 | ||
33 | Initially some sanity checks are performed on B<cms>. The type of B<cms> must | |
360bb61d | 34 | be SignedData. There must be at least one signature on the data and if |
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35 | the content is detached B<indata> cannot be B<NULL>. |
36 | ||
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37 | An attempt is made to locate all the signing certificate(s), first looking in |
38 | the B<certs> parameter (if it is not NULL) and then looking in any | |
39 | certificates contained in the B<cms> structure itself. If any signing | |
40 | certificate cannot be located the operation fails. | |
e33ffaca | 41 | |
38d3a738 | 42 | Each signing certificate is chain verified using the B<smimesign> purpose and |
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43 | the supplied trusted certificate store. Any internal certificates in the message |
44 | are used as untrusted CAs. If CRL checking is enabled in B<store> any internal | |
38d3a738 | 45 | CRLs are used in addition to attempting to look them up in B<store>. If any |
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46 | chain verify fails an error code is returned. |
47 | ||
48 | Finally the signed content is read (and written to B<out> is it is not NULL) | |
49 | and the signature's checked. | |
50 | ||
51 | If all signature's verify correctly then the function is successful. | |
52 | ||
53 | Any of the following flags (ored together) can be passed in the B<flags> | |
54 | parameter to change the default verify behaviour. | |
55 | ||
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56 | If B<CMS_NOINTERN> is set the certificates in the message itself are not |
57 | searched when locating the signing certificate(s). This means that all the | |
58 | signing certificates must be in the B<certs> parameter. | |
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59 | |
60 | If B<CMS_NOCRL> is set and CRL checking is enabled in B<store> then any | |
61 | CRLs in the message itself are ignored. | |
62 | ||
63 | If the B<CMS_TEXT> flag is set MIME headers for type B<text/plain> are deleted | |
64 | from the content. If the content is not of type B<text/plain> then an error is | |
65 | returned. | |
66 | ||
38d3a738 | 67 | If B<CMS_NO_SIGNER_CERT_VERIFY> is set the signing certificates are not |
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68 | verified. |
69 | ||
70 | If B<CMS_NO_ATTR_VERIFY> is set the signed attributes signature is not | |
71 | verified. | |
72 | ||
73 | If B<CMS_NO_CONTENT_VERIFY> is set then the content digest is not checked. | |
74 | ||
75 | =head1 NOTES | |
76 | ||
77 | One application of B<CMS_NOINTERN> is to only accept messages signed by | |
78 | a small number of certificates. The acceptable certificates would be passed | |
79 | in the B<certs> parameter. In this case if the signer is not one of the | |
80 | certificates supplied in B<certs> then the verify will fail because the | |
81 | signer cannot be found. | |
82 | ||
83 | In some cases the standard techniques for looking up and validating | |
84 | certificates are not appropriate: for example an application may wish to | |
85 | lookup certificates in a database or perform customised verification. This | |
86 | can be achieved by setting and verifying the signers certificates manually | |
87 | using the signed data utility functions. | |
88 | ||
89 | Care should be taken when modifying the default verify behaviour, for example | |
90 | setting B<CMS_NO_CONTENT_VERIFY> will totally disable all content verification | |
91 | and any modified content will be considered valid. This combination is however | |
92 | useful if one merely wishes to write the content to B<out> and its validity | |
93 | is not considered important. | |
94 | ||
95 | Chain verification should arguably be performed using the signing time rather | |
96 | than the current time. However since the signing time is supplied by the | |
97 | signer it cannot be trusted without additional evidence (such as a trusted | |
98 | timestamp). | |
99 | ||
100 | =head1 RETURN VALUES | |
101 | ||
102 | CMS_verify() returns 1 for a successful verification and zero if an error | |
c420fab5 | 103 | occurred. |
e33ffaca | 104 | |
38d3a738 | 105 | CMS_get0_signers() returns all signers or NULL if an error occurred. |
e33ffaca | 106 | |
9b86974e | 107 | The error can be obtained from L<ERR_get_error(3)> |
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108 | |
109 | =head1 BUGS | |
110 | ||
38d3a738 | 111 | The trusted certificate store is not searched for the signing certificate, |
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112 | this is primarily due to the inadequacies of the current B<X509_STORE> |
113 | functionality. | |
114 | ||
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115 | The lack of single pass processing means that the signed content must all |
116 | be held in memory if it is not detached. | |
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117 | |
118 | =head1 SEE ALSO | |
119 | ||
9b86974e | 120 | L<ERR_get_error(3)>, L<CMS_sign(3)> |
e33ffaca | 121 | |
e33ffaca | 122 | =cut |