MISTY1

''MISTY redirects here. For other meanings, see Misty

In cryptography, MISTY1 (or MISTY-1) is a block cipher designed in 1995 by Mitsuru Matsui and others for Mitsubishi Electric. MISTY1 is one of the selected algorithms in the European NESSIE project, and has been recommended for Japanese government use by the CRYPTREC project. KASUMI is a strengthened version of the MISTY1 cipher and has been adopted as the standard encryption algorithm for European mobile phones. In 2005, KASUMI was broken, but there is no practical attack against it yet; see the article for more details.

"MISTY" can stand for "Mitsubishi Improved Security Technology", it is also the initials of the researchers involved in its development: Matsui Mitsuru, Ichikawa Tetsuya, Sorimachi Toru, Tokita Toshio, and Yamagishi Atsuhiro

MISTY1 is covered by patents, although the algorithm is freely available for academic (non-profit) use. RFC 2994.

Security

MISTY1 is a Feistel network with a variable number of rounds (any multiple of 4), though 8 are recommended. The cipher operates on 64-bit blocks and has a key size of 128 bits. MISTY1 has an innovative recursive structure; the round function itself uses a 3-round Feistel network. MISTY1 claims to be provably secure against linear and differential cryptanalysis.

In the paper "Block Ciphers and Stream Ciphers" by Alex Biryukov, it is noted that KASUMI, also termed A5/3, is a strengthened version of block cipher MISTY1 running in a Counter mode.

References

M. Matsui. Block encryption algorithm MISTY. In Fast Software Encryption, 4th International Workshop, FSE '97, LNCS 1267, pages 64–74. Springer-Verlag, 1997.
Mitsuru Matsui. "Block encryption algorithm MISTY." Technical report of IEICE ISEC96-11 (1996-07). (In Japanese).
Alex Biryukov. "Block Ciphers and Stream Ciphers: The State of the Art", 2004, (PDF)
Elad Barkan, Eli Biham and Nathan Keller, Instant Ciphertext-Only Cryptanalysis of GSM Encrypted Communication, CRYPTO 2003, pp600–616 (PDF)