CMS_verify (3)

Leading comments

Automatically generated by Pod::Man 4.07 (Pod::Simple 3.32)

Standard preamble:
========================================================================

(The comments found at the beginning of the groff file "man3/CMS_verify.3ssl".)

NAME

CMS_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 *indata, BIO *out, unsigned int flags);

 STACK_OF(X509) *CMS_get0_signers(CMS_ContentInfo *cms);

DESCRIPTION

CMS_verify() verifies a 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

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

.

An attempt is made to locate all the signing certificate(s), first looking in the certs parameter (if it is not

) 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

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

) 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

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

is set and checking is enabled in store then any CRLs in the message itself are ignored.

If the

flag is set 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

is set the signing certificates are not verified.

If

is set the signed attributes signature is not verified.

If

is set then the content digest is not checked.

NOTES

One application of 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

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 zero if an error occurred.

CMS_get0_signers() returns all signers or

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

ERR_get_error(3), CMS_sign(3)

HISTORY

CMS_verify() was added to OpenSSL 0.9.8