Verifies the signature of the current message.
Object Oriented Interface
public function doVerifySignature();
This method attempts to verify the signature of the input message. If the message does not have a certificate attached, the class will attempt to verify the signature using the certificate supplied in SignerCert (if any). If no certificate is found, the class fails with an error.
If this method is successful, the SignerCert property will contain the certificate information of the message signer.
NOTE: This function does not attempt to check the validity of the signing certificate itself.