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Title "CMS_VERIFY 3" For nroff, turn off justification. Always turn off hyphenation; it makes
way too many mistakes in technical documents.
CMS_verify, CMS_get0_signers - verify a CMS SignedData structure Header "SYNOPSIS" .Vb 1 #include <openssl/cms.h> \& int CMS_verify(CMS_ContentInfo *cms, STACK_OF(X509) *certs, X509_STORE *store, BIO *indata, BIO *out, unsigned int flags); \& STACK_OF(X509) *CMS_get0_signers(CMS_ContentInfo *cms); .Ve Header "DESCRIPTION" \fBCMS_verify() is very similar to PKCS7_verify\|(3). It verifies a \fB\s-1CMS\s0 SignedData structure contained in a structure of type CMS_ContentInfo. \fIcms points to the CMS_ContentInfo structure to verify. The optional certs parameter refers to a set of certificates in which to search for signing certificates. \fIcms may contain extra untrusted \s-1CA\s0 certificates that may be used for chain building as well as CRLs that may be used for certificate validation. \fIstore may be \s-1NULL\s0 or point to the trusted certificate store to use for chain verification. \fIindata refers to the signed data if the content is detached from cms. Otherwise indata should be \s-1NULL\s0 and the signed data must be in cms. The content is written to the \s-1BIO\s0 out unless it is \s-1NULL.\s0 \fIflags is an optional set of flags, which can be used to modify the operation.

\fBCMS_get0_signers() retrieves the signing certificate(s) from cms, it may only be called after a successful CMS_verify() operation.

Header "VERIFY PROCESS" Normally the verify process proceeds as follows.

Initially some sanity checks are performed on cms. The type of cms must be SignedData. There must be at least one signature on the data and if the content is detached indata cannot be \s-1NULL.\s0

An attempt is made to locate all the signing certificate(s), first looking in the certs parameter (if it is not \s-1NULL\s0) and then looking in any certificates contained in the cms structure unless \s-1CMS_NOINTERN\s0 is set. If any signing certificate cannot be located the operation fails.

Each signing certificate is chain verified using the smimesign purpose and using the trusted certificate store store if supplied. Any internal certificates in the message, which may have been added using \fBCMS_add1_cert\|(3), are used as untrusted CAs. If \s-1CRL\s0 checking is enabled in store and \s-1CMS_NOCRL\s0 is not set, any internal CRLs, which may have been added using CMS_add1_crl\|(3), are used in addition to attempting to look them up in store. If store is not \s-1NULL\s0 and any chain verify fails an error code is returned.

Finally the signed content is read (and written to out unless it is \s-1NULL\s0) and the signature is checked.

If all signatures verify correctly then the function is successful.

Any of the following flags (ored together) can be passed in the flags parameter to change the default verify behaviour.

If \s-1CMS_NOINTERN\s0 is set the certificates in the message itself are not searched when locating the signing certificate(s). This means that all the signing certificates must be in the certs parameter.

If \s-1CMS_NOCRL\s0 is set and \s-1CRL\s0 checking is enabled in store then any CRLs in the message itself are ignored.

If the \s-1CMS_TEXT\s0 flag is set \s-1MIME\s0 headers for type text/plain are deleted from the content. If the content is not of type text/plain then an error is returned.

If \s-1CMS_NO_SIGNER_CERT_VERIFY\s0 is set the signing certificates are not chain verified, unless \s-1CMS_CADES\s0 flag is also set.

If \s-1CMS_NO_ATTR_VERIFY\s0 is set the signed attributes signature is not verified, unless \s-1CMS_CADES\s0 flag is also set.

If \s-1CMS_CADES\s0 is set, each signer certificate is checked against the \s-1ESS\s0 signingCertificate or \s-1ESS\s0 signingCertificateV2 extension that is required in the signed attributes of the signature.

If \s-1CMS_NO_CONTENT_VERIFY\s0 is set then the content digest is not checked.

Header "NOTES" One application of \s-1CMS_NOINTERN\s0 is to only accept messages signed by a small number of certificates. The acceptable certificates would be passed in the certs parameter. In this case if the signer certificate is not one of the certificates supplied in certs then the verify will fail because the signer cannot be found.

In some cases the standard techniques for looking up and validating certificates are not appropriate: for example an application may wish to lookup certificates in a database or perform customised verification. This can be achieved by setting and verifying the signer certificates manually using the signed data utility functions.

Care should be taken when modifying the default verify behaviour, for example setting \s-1CMS_NO_CONTENT_VERIFY\s0 will totally disable all content verification and any modified content will be considered valid. This combination is however useful if one merely wishes to write the content to out and its validity is not considered important.

Chain verification should arguably be performed using the signing time rather than the current time. However, since the signing time is supplied by the signer it cannot be trusted without additional evidence (such as a trusted timestamp).

Header "RETURN VALUES" \fBCMS_verify() returns 1 for a successful verification and 0 if an error occurred.

\fBCMS_get0_signers() returns all signers or \s-1NULL\s0 if an error occurred.

The error can be obtained from ERR_get_error\|(3)

Header "BUGS" The trusted certificate store is not searched for the signing certificate. This is primarily due to the inadequacies of the current X509_STORE functionality.

The lack of single pass processing means that the signed content must all be held in memory if it is not detached.

Header "SEE ALSO" \fBPKCS7_verify\|(3), CMS_add1_cert\|(3), CMS_add1_crl\|(3), \fBOSSL_ESS_check_signing_certs\|(3), \fBERR_get_error\|(3), CMS_sign\|(3) Header "COPYRIGHT" Copyright 2008-2022 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the Apache License 2.0 (the \*(L"License\*(R"). You may not use this file except in compliance with the License. You can obtain a copy in the file \s-1LICENSE\s0 in the source distribution or at <https://www.openssl.org/source/license.html>.