certificate revocation checking(A way to see if a certificate used to sign a message is valid. Outlook can check the status of the certificate from the issuing certification authority's database)
content revocation string(A string that is generated by the content owner or content packager and is based on their public and private signing keys. This string is shared with the license issuer, who includes it in all licenses. Computers that receive a license with this string are no longer able to play files packaged with that particular signing key pair)