/usr/man/cat.3/CMS_get0_signers.3

CMS_verify(3)                OpenSSL                CMS_verify(3)

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 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.

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CMS_verify(3)                OpenSSL                CMS_verify(3)

     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

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CMS_verify(3)                OpenSSL                CMS_verify(3)

     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 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

     ERR_get_error(3), CMS_sign(3)

HISTORY

     CMS_verify() was added to OpenSSL 0.9.8

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See also CMS_verify(3)