|First published||April 2000|
|Key sizes||128 bits|
|Block sizes||4096 bits|
|Best public cryptanalysis|
|Scott Fluhrer's differential attack breaks the cipher.|
The block size is 4096 bits—unusually large for a block cipher, but a standard disk sector size. Mercy uses a 128-bit secret key, along with a 128-bit non-secret tweak for each block. In disk encryption, the sector number would be used as a tweak. Mercy uses a 6-round Feistel network structure with partial key whitening. The round function uses a key-dependent state machine which borrows some structure from the stream cipher WAKE, with key-dependent S-boxes based on the Nyberg S-boxes also used in AES.
- Paul Crowley, Mercy: A fast large block cipher for disk sector encryption. In Bruce Schneier, editor, Fast Software Encryption: 7th International Workshop, volume 1978 of Lecture Notes in Computer Science, pages 49-63, New York City, USA, April 2000. Springer-Verlag.
- Scott Fluhrer (2 April 2006). Cryptanalysis of the Mercy Block Cipher (PostScript). Fast Software Encryption Workshop 2001. Royal Park Hotel Nikko, Yokohama, Japan: Cisco Systems, Inc. Retrieved 15 December 2006.