Libelle (cipher)
Libelle is a German cipher system developed by the Federal Office for Information Security. The algorithm is not published, in an attempt to make cryptanalysis more difficult. In order to keep the algorithm secret, it is only distributed as a microchip named Jupiter, not as a piece of software.
It is possible to have a secret cipher algorithm while still reaping the benefits of public cryptography research: one way is to make a non-weakening change to a public algorithm, e.g. changing the nothing-up-my-sleeve numbers or chaining the public cipher with an unrelated secret cipher.
A BSI specification document about Pluto gives these numbers: 64 bit block size, 160 bit key size. Supported modes: Electronic Codebook, Cipher Block Chaining, Cipher Feedback /Output Feedback with 1,8,16,32 or 64 bits.
