Updated: 2022/Sep/29
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CMS_verify(3) OpenSSL CMS_verify(3)
NAME
CMS_verify, CMS_get0_signers - verify a CMS SignedData structure
LIBRARY
libcrypto, -lcrypto
SYNOPSIS
#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);
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. 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. indata refers to the
signed data if the content is detached from cms. Otherwise indata
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_get0_signers() retrieves the signing certificate(s) from cms, it
may only be called after a successful CMS_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 indata 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 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_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)
COPYRIGHT
Copyright 2008-2022 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>.
3.0.12 2023-05-07 CMS_verify(3)