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,
12                       BIO *indata, BIO *out, unsigned int flags);
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14        STACK_OF(X509) *CMS_get0_signers(CMS_ContentInfo *cms);
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DESCRIPTION

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

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

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

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

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

116       ERR_get_error(3), CMS_sign(3)
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119       Copyright 2008-2020 The OpenSSL Project Authors. All Rights Reserved.
120
121       Licensed under the OpenSSL license (the "License").  You may not use
122       this file except in compliance with the License.  You can obtain a copy
123       in the file LICENSE in the source distribution or at
124       <https://www.openssl.org/source/license.html>.
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1281.1.1q                            2023-02-06                     CMS_VERIFY(3)
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