Constructing Symmetric Ciphers Using the CAST Design Procedure

Abstract

Abstract. This paper describes the CAST design procedure for constructing a family of DES-like SubstitutionPermutation Network (SPN) cryptosystems which appear to have good resistance to differential cryptanalysis, linear cryptanalysis, and related-key cryptanalysis, along with a number of other desirable cryptographic properties. Details of the design choices in the procedure are given, including those regarding the component substitution boxes (s-boxes), the overall framework, the key schedule, and the round function. An example CAST cipher, an output of this design procedure, is presented as an aid to understanding the concepts and to encourage detailed analysis by the cryptologic community.

Construction of bent functions of 2kvariables from a basis of

“…where the last equality follows from the first equality in expression (1). Analogously, after some algebraic manipulations, we have that…”

“…Boolean functions are widely used in different types of cryptographic applications such as block ciphers, stream ciphers and hash functions [3,5,21], in coding theory [2,15], among others. A cryptographic function should have high nonlinearity in order to prevent attacks based on linear approximation [1,13,19,22]. The functions achieving the maximal possible nonlinearity possess the best resistance to the linear attack and they are called bent functions [27,29].…”

The Stream Cipher Core of the 3GPP Encryption Standard 128-EEA3: Timing Attacks and Countermeasures

“…When the S-boxes are all secret, N = 31 can suffice even though at least 15 input bits are known constants. This is because (i) S-boxes are secret, and (ii) S-boxes with outputs larger than inputs can still accomplish Shannon's confusion [22] (note that Shannon's diffusion, as interpreted by Massey in [15], does not apply to stream ciphers) [1].…”

A Dos Attack Against the Integrity-Less Esp (Ipsec)

“…Hosts are not required to support tunnel mode, but often they do. IPSec supports different encryption algorithms: AES [8,19] is the most commonly used but other block ciphers as DES [16], 3DES [17], CAST128 [1,2], RC5 [24], IDEA [12], and Blowfish [26] are also allowed. All block ciphers are used in CBC mode [23,9].…”