cryptography Cryptography, or cryptology (from grc, , translit=kryptós "hidden, secret"; and ''graphein'', "to write", or ''-logia'', "study", respectively), is the practice and study of techniques for secure communication in the presence of adver ...

, KN-Cipher is a

block cipher In cryptography, a block cipher is a deterministic algorithm operating on fixed-length groups of bits, called ''blocks''. Block ciphers are specified cryptographic primitive, elementary components in the design of many cryptographic protocols and ...

created by

Kaisa Nyberg Kaisa Nyberg is a Finnish cryptographer and computer security researcher. Contributions Nyberg's research includes the theory of perfect nonlinear S-boxes (now known as Nyberg S-boxes), provably secure block cipher design (resulting in KN-Cipher ...

and

Lars Knudsen Lars Ramkilde Knudsen (born 21 February 1962) is a Danish researcher in cryptography, particularly interested in the design and analysis of block ciphers, hash functions and message authentication codes (MACs). Academic After some early work in ...

in 1995. One of the first ciphers designed to be

provably secure Provable security refers to any type or level of computer security that can be proved. It is used in different ways by different fields. Usually, this refers to mathematical proofs, which are common in cryptography. In such a proof, the capabiliti ...

against ordinary

differential cryptanalysis Differential cryptanalysis is a general form of cryptanalysis applicable primarily to block ciphers, but also to stream ciphers and cryptographic hash functions. In the broadest sense, it is the study of how differences in information input can aff ...

, KN-Cipher was later broken using higher order differential cryptanalysis. Presented as "a prototype...compatible with

DES Des is a masculine given name, mostly a short form (hypocorism) of Desmond. People named Des include: People * Des Buckingham, English football manager * Des Corcoran, (1928–2004), Australian politician * Des Dillon (disambiguation), sever ...

", the algorithm has a 64-bit block size and a 6-round

Feistel network In cryptography, a Feistel cipher (also known as Luby–Rackoff block cipher) is a symmetric structure used in the construction of block ciphers, named after the German-born physicist and cryptographer Horst Feistel, who did pioneering research whi ...

structure. The round function is based on the

cube In geometry, a cube is a three-dimensional solid object bounded by six square faces, facets or sides, with three meeting at each vertex. Viewed from a corner it is a hexagon and its net is usually depicted as a cross. The cube is the only r ...

operation in the

finite field In mathematics, a finite field or Galois field (so-named in honor of Évariste Galois) is a field that contains a finite number of elements. As with any field, a finite field is a set on which the operations of multiplication, addition, subtr ...

GF(2³³). The designers did not specify any

key schedule In cryptography, the so-called product ciphers are a certain kind of cipher, where the (de-)ciphering of data is typically done as an iteration of ''rounds''. The setup for each round is generally the same, except for round-specific fixed valu ...

for the cipher; they state, "All round keys should be independent, therefore we need at least 198 key bits."

Cryptanalysis

Jakobsen & Knudsen's higher order differential cryptanalysis breaks KN-Cipher with only 512 chosen plaintexts and 2⁴¹ running time, or with 32 chosen plaintexts and 2⁷⁰ running time.

References

{{Cryptography navbox , block, state=collapsed Broken block ciphers Feistel ciphers