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() is very similar to L<PKCS7_verify(3)>. It verifies a 19B<CMS SignedData> structure contained in a structure of type B<CMS_ContentInfo>. 20I<cms> points to the B<CMS_ContentInfo> structure to verify. 21The optional I<certs> parameter refers to a set of certificates 22in which to search for signing certificates. 23I<cms> may contain extra untrusted CA certificates that may be used for 24chain building as well as CRLs that may be used for certificate validation. 25I<store> may be NULL or point to 26the trusted certificate store to use for chain verification. 27I<indata> refers to the signed data if the content is detached from I<cms>. 28Otherwise I<indata> should be NULL and the signed data must be in I<cms>. 29The content is written to the BIO I<out> unless it is NULL. 30I<flags> is an optional set of flags, which can be used to modify the operation. 31 32CMS_get0_signers() retrieves the signing certificate(s) from I<cms>, it may only 33be called after a successful CMS_verify() operation. 34 35=head1 VERIFY PROCESS 36 37Normally the verify process proceeds as follows. 38 39Initially some sanity checks are performed on I<cms>. The type of I<cms> must 40be SignedData. There must be at least one signature on the data and if 41the content is detached I<indata> cannot be NULL. 42 43An attempt is made to locate all the signing certificate(s), first looking in 44the I<certs> parameter (if it is not NULL) and then looking in any 45certificates contained in the I<cms> structure unless B<CMS_NOINTERN> is set. 46If any signing certificate cannot be located the operation fails. 47 48Each signing certificate is chain verified using the I<smimesign> purpose and 49using the trusted certificate store I<store> if supplied. 50Any internal certificates in the message, which may have been added using 51L<CMS_add1_cert(3)>, are used as untrusted CAs. 52If CRL checking is enabled in I<store> and B<CMS_NOCRL> is not set, 53any internal CRLs, which may have been added using L<CMS_add1_crl(3)>, 54are used in addition to attempting to look them up in I<store>. 55If I<store> is not NULL and any chain verify fails an error code is returned. 56 57Finally the signed content is read (and written to I<out> unless it is NULL) 58and the signature is checked. 59 60If all signatures verify correctly then the function is successful. 61 62Any of the following flags (ored together) can be passed in the I<flags> 63parameter to change the default verify behaviour. 64 65If B<CMS_NOINTERN> is set the certificates in the message itself are not 66searched when locating the signing certificate(s). 67This means that all the signing certificates must be in the I<certs> parameter. 68 69If B<CMS_NOCRL> is set and CRL checking is enabled in I<store> then any 70CRLs in the message itself are ignored. 71 72If the B<CMS_TEXT> flag is set MIME headers for type B<text/plain> are deleted 73from the content. If the content is not of type B<text/plain> then an error is 74returned. 75 76If B<CMS_NO_SIGNER_CERT_VERIFY> is set the signing certificates are not 77chain verified, unless B<CMS_CADES> flag is also set. 78 79If B<CMS_NO_ATTR_VERIFY> is set the signed attributes signature is not 80verified, unless CMS_CADES flag is also set. 81 82If B<CMS_CADES> is set, each signer certificate is checked against the 83ESS signingCertificate or ESS signingCertificateV2 extension 84that is required in the signed attributes of the signature. 85 86If B<CMS_NO_CONTENT_VERIFY> is set then the content digest is not checked. 87 88=head1 NOTES 89 90One application of B<CMS_NOINTERN> is to only accept messages signed by 91a small number of certificates. The acceptable certificates would be passed 92in the I<certs> parameter. In this case if the signer certificate is not one 93of the certificates supplied in I<certs> then the verify will fail because the 94signer cannot be found. 95 96In some cases the standard techniques for looking up and validating 97certificates are not appropriate: for example an application may wish to 98lookup certificates in a database or perform customised verification. This 99can be achieved by setting and verifying the signer certificates manually 100using the signed data utility functions. 101 102Care should be taken when modifying the default verify behaviour, for example 103setting B<CMS_NO_CONTENT_VERIFY> will totally disable all content verification 104and any modified content will be considered valid. This combination is however 105useful if one merely wishes to write the content to I<out> and its validity 106is not considered important. 107 108Chain verification should arguably be performed using the signing time rather 109than the current time. However, since the signing time is supplied by the 110signer it cannot be trusted without additional evidence (such as a trusted 111timestamp). 112 113=head1 RETURN VALUES 114 115CMS_verify() returns 1 for a successful verification and 0 if an error occurred. 116 117CMS_get0_signers() returns all signers or NULL if an error occurred. 118 119The error can be obtained from L<ERR_get_error(3)> 120 121=head1 BUGS 122 123The trusted certificate store is not searched for the signing certificate. 124This is primarily due to the inadequacies of the current B<X509_STORE> 125functionality. 126 127The lack of single pass processing means that the signed content must all 128be held in memory if it is not detached. 129 130=head1 SEE ALSO 131 132L<PKCS7_verify(3)>, L<CMS_add1_cert(3)>, L<CMS_add1_crl(3)>, 133L<OSSL_ESS_check_signing_certs(3)>, 134L<ERR_get_error(3)>, L<CMS_sign(3)> 135 136=head1 COPYRIGHT 137 138Copyright 2008-2022 The OpenSSL Project Authors. All Rights Reserved. 139 140Licensed under the Apache License 2.0 (the "License"). You may not use 141this file except in compliance with the License. You can obtain a copy 142in the file LICENSE in the source distribution or at 143L<https://www.openssl.org/source/license.html>. 144 145=cut 146