MAGENTA or Multifunctional Algorithm for General-purpose Encryption and Network Telecommunication Applications is a block cipher; it was Deutsche Telekom's entry in the AES competition. Like all AES candidates, it uses 128-bit blocks and supports key sizes of 128, 192 or 256 bits. It is a Feistel cipher with six or eight rounds.
MAGENTA  is often cited as an example of Kerckhoffs' Principle, a demonstration of why unpublished and therefore unanalysed ciphers cannot be trusted. Of the fifteen candidates in the AES competition, fourteen were made public before the first AES conference. The MAGENTA team were the one exception; they made nothing public until their conference presentation. That presentation was given one morning, to an audience that included many of the world's top cryptographers. Some saw flaws, and there was intense discussion over lunch. By that evening, a draft paper on breaking the cipher was circulating and the final version  was presented at the second AES conference. The attackers included members of both the Twofish and Serpent teams, plus others.