CMS_verify(3) OpenSSL CMS_verify(3)NAMECMS_verify - verify a CMS SignedData structure
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);
DESCRIPTIONCMS_verify() verifies a CMS SignedData structure. cms is the
CMS_ContentInfo structure to verify. certs is a set of certificates in
which to search for the signing certificate(s). store is a trusted
certificate store used for chain verification. indata is the detached
content if the content is not present in cms. The content is written to
out if it is not NULL.
flags is an optional set of flags, which can be used to modify the
verify operation.
CMS_get0_signers() retrieves the signing certificate(s) from cms, it
must 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 itself. If any signing
certificate cannot be located the operation fails.
Each signing certificate is chain verified using the smimesign purpose
and the supplied trusted certificate store. Any internal certificates
in the message are used as untrusted CAs. If CRL checking is enabled in
store any internal CRLs are used in addition to attempting to look them
up in store. If any chain verify fails an error code is returned.
Finally the signed content is read (and written to out is it is not
NULL) and the signature's checked.
If all signature's 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
verified.
If CMS_NO_ATTR_VERIFY is set the signed attributes signature is not
verified.
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 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 signers
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 VALUESCMS_verify() returns 1 for a successful verification and zero 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 ALSOERR_get_error(3), CMS_sign(3)HISTORYCMS_verify() was added to OpenSSL 0.9.8
1.0.1e 2013-02-11 CMS_verify(3)
