1=pod 2 3=head1 NAME 4 5CMS_verify, CMS_get0_signers - verify a CMS SignedData structure 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, 12 BIO *indata, BIO *out, unsigned int flags); 13 14 STACK_OF(X509) *CMS_get0_signers(CMS_ContentInfo *cms); 15 16=head1 DESCRIPTION 17 18CMS_verify() verifies a CMS SignedData structure. B<cms> is the CMS_ContentInfo 19structure to verify. B<certs> is a set of certificates in which to search for 20the signing certificate(s). B<store> is a trusted certificate store used for 21chain verification. B<indata> is the detached content if the content is not 22present in B<cms>. The content is written to B<out> if it is not NULL. 23 24B<flags> is an optional set of flags, which can be used to modify the verify 25operation. 26 27CMS_get0_signers() retrieves the signing certificate(s) from B<cms>, it must 28be called after a successful CMS_verify() operation. 29 30=head1 VERIFY PROCESS 31 32Normally the verify process proceeds as follows. 33 34Initially some sanity checks are performed on B<cms>. The type of B<cms> must 35be SignedData. There must be at least one signature on the data and if 36the content is detached B<indata> cannot be B<NULL>. 37 38An attempt is made to locate all the signing certificate(s), first looking in 39the B<certs> parameter (if it is not NULL) and then looking in any 40certificates contained in the B<cms> structure itself. If any signing 41certificate cannot be located the operation fails. 42 43Each signing certificate is chain verified using the B<smimesign> purpose and 44the supplied trusted certificate store. Any internal certificates in the message 45are used as untrusted CAs. If CRL checking is enabled in B<store> any internal 46CRLs are used in addition to attempting to look them up in B<store>. If any 47chain verify fails an error code is returned. 48 49Finally the signed content is read (and written to B<out> if it is not NULL) 50and the signature's checked. 51 52If all signature's verify correctly then the function is successful. 53 54Any of the following flags (ored together) can be passed in the B<flags> 55parameter to change the default verify behaviour. 56 57If B<CMS_NOINTERN> is set the certificates in the message itself are not 58searched when locating the signing certificate(s). This means that all the 59signing certificates must be in the B<certs> parameter. 60 61If B<CMS_NOCRL> is set and CRL checking is enabled in B<store> then any 62CRLs in the message itself are ignored. 63 64If the B<CMS_TEXT> flag is set MIME headers for type B<text/plain> are deleted 65from the content. If the content is not of type B<text/plain> then an error is 66returned. 67 68If B<CMS_NO_SIGNER_CERT_VERIFY> is set the signing certificates are not 69verified. 70 71If B<CMS_NO_ATTR_VERIFY> is set the signed attributes signature is not 72verified. 73 74If B<CMS_NO_CONTENT_VERIFY> is set then the content digest is not checked. 75 76=head1 NOTES 77 78One application of B<CMS_NOINTERN> is to only accept messages signed by 79a small number of certificates. The acceptable certificates would be passed 80in the B<certs> parameter. In this case if the signer is not one of the 81certificates supplied in B<certs> then the verify will fail because the 82signer cannot be found. 83 84In some cases the standard techniques for looking up and validating 85certificates are not appropriate: for example an application may wish to 86lookup certificates in a database or perform customised verification. This 87can be achieved by setting and verifying the signers certificates manually 88using the signed data utility functions. 89 90Care should be taken when modifying the default verify behaviour, for example 91setting B<CMS_NO_CONTENT_VERIFY> will totally disable all content verification 92and any modified content will be considered valid. This combination is however 93useful if one merely wishes to write the content to B<out> and its validity 94is not considered important. 95 96Chain verification should arguably be performed using the signing time rather 97than the current time. However since the signing time is supplied by the 98signer it cannot be trusted without additional evidence (such as a trusted 99timestamp). 100 101=head1 RETURN VALUES 102 103CMS_verify() returns 1 for a successful verification and zero if an error 104occurred. 105 106CMS_get0_signers() returns all signers or NULL if an error occurred. 107 108The error can be obtained from L<ERR_get_error(3)> 109 110=head1 BUGS 111 112The trusted certificate store is not searched for the signing certificate, 113this is primarily due to the inadequacies of the current B<X509_STORE> 114functionality. 115 116The lack of single pass processing means that the signed content must all 117be held in memory if it is not detached. 118 119=head1 SEE ALSO 120 121L<ERR_get_error(3)>, L<CMS_sign(3)> 122 123=head1 COPYRIGHT 124 125Copyright 2008-2019 The OpenSSL Project Authors. All Rights Reserved. 126 127Licensed under the OpenSSL license (the "License"). You may not use 128this file except in compliance with the License. You can obtain a copy 129in the file LICENSE in the source distribution or at 130L<https://www.openssl.org/source/license.html>. 131 132=cut 133