CMS_VERIFY(3SSL) OpenSSL CMS_VERIFY(3SSL)
NAME
CMS_verify, CMS_SignedData_verify, CMS_get0_signers - verify a CMS
SignedData structure
SYNOPSIS
#include <openssl/cms.h>
int CMS_verify(CMS_ContentInfo *cms, STACK_OF(X509) *certs, X509_STORE *store,
BIO *detached_data, BIO *out, unsigned int flags);
BIO *CMS_SignedData_verify(CMS_SignedData *sd, BIO *detached_data,
STACK_OF(X509) *scerts, X509_STORE *store,
STACK_OF(X509) *extra, STACK_OF(X509_CRL) *crls,
unsigned int flags,
OSSL_LIB_CTX *libctx, const char *propq);
STACK_OF(X509) *CMS_get0_signers(CMS_ContentInfo *cms);
DESCRIPTION
CMS_verify() is very similar to PKCS7_verify(3). It verifies a CMS
SignedData structure contained in a structure of type CMS_ContentInfo.
cms 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. It is also used as a source of untrusted
intermediate CA certificates for chain building. cms may contain extra
untrusted CA certificates that may be used for chain building as well as
CRLs that may be used for certificate validation. store may be NULL or
point to the trusted certificate store to use for chain verification.
detached_data refers to the signed data if the content is detached from
cms. Otherwise detached_data should be NULL and the signed data must be
in cms. The content is written to the BIO out unless it is NULL. flags
is an optional set of flags, which can be used to modify the operation.
CMS_SignedData_verify() is like CMS_verify() except that it operates on
CMS SignedData input in the sd argument, it has some additional
parameters described next, and on success it returns the verified
content as a memory BIO. The optional extra parameter may be used to
provide untrusted CA certificates that may be helpful for chain building
in certificate validation. This list of certificates must not contain
duplicates. The optional crls parameter may be used to provide extra
CRLs. Also the list of CRLs must not contain duplicates. The optional
parameters library context libctx and property query propq are used when
retrieving algorithms from providers.
CMS_get0_signers() retrieves the signing certificate(s) from cms; it may
only be called after a successful CMS_verify() or
CMS_SignedData_verify() operation.
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 detached_data cannot be NULL.
An attempt is made to locate all the signing certificate(s), first
looking in the certs parameter (if it is not NULL) and then looking in
any certificates contained in the cms structure unless CMS_NOINTERN 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
CMS_add1_cert(3), are used as untrusted CAs. If CRL checking is enabled
in store and CMS_NOCRL 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 NULL and any chain verify fails
an error code is returned.
Finally the signed content is read (and written to out unless it is
NULL) 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 CMS_NOINTERN 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 CMS_NOCRL is set and CRL checking is enabled in store then any CRLs
in the message itself and provided via the crls parameter are ignored.
If the CMS_TEXT flag is set MIME 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 CMS_NO_SIGNER_CERT_VERIFY is set the signing certificates are not
chain verified, unless CMS_CADES flag is also set.
If CMS_NO_ATTR_VERIFY is set the signed attributes signature is not
verified, unless CMS_CADES flag is also set.
If CMS_CADES is set, each signer certificate is checked against the ESS
signingCertificate or ESS signingCertificateV2 extension that is
required in the signed attributes of the signature.
If CMS_NO_CONTENT_VERIFY is set then the content digest is not checked.
NOTES
One application of CMS_NOINTERN 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 CMS_NO_CONTENT_VERIFY 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).
RETURN VALUES
CMS_verify() returns 1 for a successful verification and 0 if an error
occurred.
CMS_SignedData_verify() returns a memory BIO containing the verified
content, or NULL on error.
CMS_get0_signers() returns all signers or NULL if an error occurred.
The error can be obtained from ERR_get_error(3).
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.
SEE ALSO
PKCS7_verify(3), CMS_add1_cert(3), CMS_add1_crl(3),
OSSL_ESS_check_signing_certs(3), ERR_get_error(3), CMS_sign(3)
HISTORY
CMS_SignedData_verify() was added in OpenSSL 3.2.
COPYRIGHT
Copyright 2008-2024 The OpenSSL Project Authors. All Rights Reserved.
Licensed under the Apache License 2.0 (the "License"). You may not use
this file except in compliance with the License. You can obtain a copy
in the file LICENSE in the source distribution or at
<https://www.openssl.org/source/license.html>.
3.5.7 2026-06-09 CMS_VERIFY(3SSL)
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