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1 | =pod |
2 | ||
3 | =head1 NAME | |
4 | ||
5 | PKCS7_verify - verify a PKCS#7 signedData structure | |
6 | ||
7 | =head1 SYNOPSIS | |
8 | ||
9 | int PKCS7_verify(PKCS7 *p7, STACK_OF(X509) *certs, X509_STORE *store, BIO *indata, BIO *out, int flags); | |
10 | ||
90890074 | 11 | STACK_OF(X509) *PKCS7_get0_signers(PKCS7 *p7, STACK_OF(X509) *certs, int flags); |
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12 | |
13 | =head1 DESCRIPTION | |
14 | ||
15 | PKCS7_verify() verifies a PKCS#7 signedData structure. B<p7> is the PKCS7 | |
16 | structure to verify. B<certs> is a set of certificates in which to search for | |
17 | the signer's certificate. B<store> is a trusted certficate store (used for | |
18 | chain verification). B<indata> is the signed data if the content is not | |
19 | present in B<p7> (that is it is detached). The content is written to B<out> | |
20 | if it is not NULL. | |
21 | ||
22 | B<flags> is an optional set of flags, which can be used to modify the verify | |
23 | operation. | |
24 | ||
25 | PKCS7_get0_signers() retrieves the signer's certificates from B<p7>, it does | |
26 | B<not> check their validity or whether any signatures are valid. The B<certs> | |
27 | and B<flags> parameters have the same meanings as in PKCS7_verify(). | |
28 | ||
29 | =head1 VERIFY PROCESS | |
30 | ||
31 | Normally the verify process proceeds as follows. | |
32 | ||
33 | Initially some sanity checks are performed on B<p7>. The type of B<p7> must | |
34 | be signedData. There must be at least one signature on the data and if | |
35 | the content is detached B<indata> cannot be B<NULL>. | |
36 | ||
37 | An attempt is made to locate all the signer's certificates, first looking in | |
38 | the B<certs> parameter (if it is not B<NULL>) and then looking in any certificates | |
39 | contained in the B<p7> structure itself. If any signer's certificates cannot be | |
40 | located the operation fails. | |
41 | ||
42 | Each signer's certificate is chain verified using the B<smimesign> purpose and | |
43 | the supplied trusted certificate store. Any internal certificates in the message | |
44 | are used as untrusted CAs. If any chain verify fails an error code is returned. | |
45 | ||
46 | Finally the signed content is read (and written to B<out> is it is not NULL) and | |
47 | the signature's checked. | |
48 | ||
49 | If all signature's verify correctly then the function is successful. | |
50 | ||
51 | Any of the following flags (ored together) can be passed in the B<flags> parameter | |
52 | to change the default verify behaviour. Only the flag B<PKCS7_NOINTERN> is | |
53 | meaningful to PKCS7_get0_signers(). | |
54 | ||
55 | If B<PKCS7_NOINTERN> is set the certificates in the message itself are not | |
56 | searched when locating the signer's certificate. This means that all the signers | |
57 | certificates must be in the B<certs> parameter. | |
58 | ||
59 | If the B<PKCS7_TEXT> flag is set MIME headers for type B<text/plain> are deleted | |
60 | from the content. If the content is not of type B<text/plain> then an error is | |
61 | returned. | |
62 | ||
63 | If B<PKCS7_NOVERIFY> is set the signer's certificates are not chain verified. | |
64 | ||
65 | If B<PKCS7_NOCHAIN> is set then the certificates contained in the message are | |
66 | not used as untrusted CAs. This means that the whole verify chain (apart from | |
67 | the signer's certificate) must be contained in the trusted store. | |
68 | ||
69 | If B<PKCS7_NOSIGS> is set then the signatures on the data are not checked. | |
70 | ||
71 | =head1 NOTES | |
72 | ||
73 | One application of B<PKCS7_NOINTERN> is to only accept messages signed by | |
74 | a small number of certificates. The acceptable certificates would be passed | |
75 | in the B<certs> parameter. In this case if the signer is not one of the | |
76 | certificates supplied in B<certs> then the verify will fail because the | |
77 | signer cannot be found. | |
78 | ||
79 | Care should be taken when modifying the default verify behaviour, for example | |
80 | setting B<PKCS7_NOVERIFY|PKCS7_NOSIGS> will totally disable all verification | |
81 | and any signed message will be considered valid. This combination is however | |
82 | useful if one merely wishes to write the content to B<out> and its validity | |
83 | is not considered important. | |
84 | ||
85 | Chain verification should arguably be performed using the signing time rather | |
86 | than the current time. However since the signing time is supplied by the | |
87 | signer it cannot be trusted without additional evidence (such as a trusted | |
88 | timestamp). | |
89 | ||
90 | =head1 RETURN VALUES | |
91 | ||
92 | PKCS7_verify() returns 1 for a successful verification and zero or a negative | |
93 | value if an error occurs. | |
94 | ||
95 | PKCS7_get0_signers() returns all signers or B<NULL> if an error occurred. | |
96 | ||
97 | The error can be obtained from L<ERR_get_error(3)|ERR_get_error(3)> | |
98 | ||
99 | =head1 BUGS | |
100 | ||
101 | The trusted certificate store is not searched for the signers certificate, | |
102 | this is primarily due to the inadequacies of the current B<X509_STORE> | |
103 | functionality. | |
104 | ||
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105 | The lack of single pass processing and need to hold all data in memory as |
106 | mentioned in PKCS7_sign() also applies to PKCS7_verify(). | |
107 | ||
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108 | =head1 SEE ALSO |
109 | ||
110 | L<ERR_get_error(3)|ERR_get_error(3)>, L<PKCS7_sign(3)|PKCS7_sign(3)> | |
111 | ||
112 | =head1 HISTORY | |
113 | ||
4e1b50e2 | 114 | PKCS7_verify() was added to OpenSSL 0.9.5 |
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115 | |
116 | =cut |