1CMS_VERIFY(3ossl)                   OpenSSL                  CMS_VERIFY(3ossl)
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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, unless CMS_CADES flag is also set.
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70       If CMS_NO_ATTR_VERIFY is set the signed attributes signature is not
71       verified, unless CMS_CADES flag is also set.
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73       If CMS_CADES is set, each signer certificate is checked against the ESS
74       signingCertificate or ESS signingCertificateV2 extension that is
75       required in the signed attributes of the signature.
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77       If CMS_NO_CONTENT_VERIFY is set then the content digest is not checked.
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NOTES

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

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

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

120       OSSL_ESS_check_signing_certs(3), ERR_get_error(3), CMS_sign(3)
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123       Copyright 2008-2021 The OpenSSL Project Authors. All Rights Reserved.
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125       Licensed under the Apache License 2.0 (the "License").  You may not use
126       this file except in compliance with the License.  You can obtain a copy
127       in the file LICENSE in the source distribution or at
128       <https://www.openssl.org/source/license.html>.
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1323.0.5                             2022-07-05                 CMS_VERIFY(3ossl)
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