1CMS_verify(3)                       OpenSSL                      CMS_verify(3)
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NAME

6       CMS_verify, CMS_get0_signers - verify a CMS SignedData structure
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SYNOPSIS

9        #include <openssl/cms.h>
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11        int CMS_verify(CMS_ContentInfo *cms, STACK_OF(X509) *certs, X509_STORE *store, BIO *indata, BIO *out, unsigned int flags);
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13        STACK_OF(X509) *CMS_get0_signers(CMS_ContentInfo *cms);
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DESCRIPTION

16       CMS_verify() verifies a CMS SignedData structure. cms is the
17       CMS_ContentInfo structure to verify. certs is a set of certificates in
18       which to search for the signing certificate(s). store is a trusted
19       certificate store used for chain verification. indata is the detached
20       content if the content is not present in cms. The content is written to
21       out if it is not NULL.
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23       flags is an optional set of flags, which can be used to modify the
24       verify operation.
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26       CMS_get0_signers() retrieves the signing certificate(s) from cms, it
27       must be called after a successful CMS_verify() operation.
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VERIFY PROCESS

30       Normally the verify process proceeds as follows.
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32       Initially some sanity checks are performed on cms. The type of cms must
33       be SignedData. There must be at least one signature on the data and if
34       the content is detached indata cannot be NULL.
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36       An attempt is made to locate all the signing certificate(s), first
37       looking in the certs parameter (if it is not NULL) and then looking in
38       any certificates contained in the cms structure itself. If any signing
39       certificate cannot be located the operation fails.
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41       Each signing certificate is chain verified using the smimesign purpose
42       and the supplied trusted certificate store. Any internal certificates
43       in the message are used as untrusted CAs. If CRL checking is enabled in
44       store any internal CRLs are used in addition to attempting to look them
45       up in store. If any chain verify fails an error code is returned.
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47       Finally the signed content is read (and written to out is it is not
48       NULL) and the signature's checked.
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50       If all signature's verify correctly then the function is successful.
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52       Any of the following flags (ored together) can be passed in the flags
53       parameter to change the default verify behaviour.
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55       If CMS_NOINTERN is set the certificates in the message itself are not
56       searched when locating the signing certificate(s). This means that all
57       the signing certificates must be in the certs parameter.
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59       If CMS_NOCRL is set and CRL checking is enabled in store then any CRLs
60       in the message itself are ignored.
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62       If the CMS_TEXT flag is set MIME headers for type text/plain are
63       deleted from the content. If the content is not of type text/plain then
64       an error is returned.
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66       If CMS_NO_SIGNER_CERT_VERIFY is set the signing certificates are not
67       verified.
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69       If CMS_NO_ATTR_VERIFY is set the signed attributes signature is not
70       verified.
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72       If CMS_NO_CONTENT_VERIFY is set then the content digest is not checked.
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NOTES

75       One application of CMS_NOINTERN is to only accept messages signed by a
76       small number of certificates. The acceptable certificates would be
77       passed in the certs parameter. In this case if the signer is not one of
78       the certificates supplied in certs then the verify will fail because
79       the signer cannot be found.
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81       In some cases the standard techniques for looking up and validating
82       certificates are not appropriate: for example an application may wish
83       to lookup certificates in a database or perform customised
84       verification. This can be achieved by setting and verifying the signers
85       certificates manually using the signed data utility functions.
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87       Care should be taken when modifying the default verify behaviour, for
88       example setting CMS_NO_CONTENT_VERIFY will totally disable all content
89       verification and any modified content will be considered valid. This
90       combination is however useful if one merely wishes to write the content
91       to out and its validity is not considered important.
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93       Chain verification should arguably be performed using the signing time
94       rather than the current time. However since the signing time is
95       supplied by the signer it cannot be trusted without additional evidence
96       (such as a trusted timestamp).
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RETURN VALUES

99       CMS_verify() returns 1 for a successful verification and zero if an
100       error occurred.
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102       CMS_get0_signers() returns all signers or NULL if an error occurred.
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104       The error can be obtained from ERR_get_error(3)
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BUGS

107       The trusted certificate store is not searched for the signing
108       certificate, this is primarily due to the inadequacies of the current
109       X509_STORE functionality.
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111       The lack of single pass processing means that the signed content must
112       all be held in memory if it is not detached.
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SEE ALSO

115       ERR_get_error(3), CMS_sign(3)
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HISTORY

118       CMS_verify() was added to OpenSSL 0.9.8
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1221.0.2o                            2019-09-10                     CMS_verify(3)