A proposed mode for triple-DES encryption

We propose a new mode of multiple encryption—triple-DES external feedback cipher block chaining with output feedback masking. The aim is to provide increased protection against certain attacks (dictionary attacks and matching ciphertext attacks) which exploit the short message-block size of DES. The new mode obtains this protection through the introduction of secret masking values that are exclusive-ORed with the intermediate outputs of each triple-DES encryption operation. The secret mask value is derived from a fourth encryption operation per message block, in addition to the three used in previous modes. The new mode is part of a suite of encryption modes proposed in the ANSI X9.F.1 triple-DES draft standard (X9.52).