DPCP (DisplayPort Content Protection) is an optional copy-protection from Philips, which uses 128-bit AES encryption, with modern cryptography ciphers. It also features full authentication and session key establishment (each encryption session is independent). There is an independent revocation system. This portion of the standard is licensed separately. It also adds support for verifying the proximity of the receiver and transmitter, a technique intended to ensure users are not bypassing content protection system to send data out to distant, unauthorized users.