International Association for Cryptologic Research

International Association
for Cryptologic Research

CryptoDB

Marco Macchetti

Publications

Year
Venue
Title
2009
FSE
2005
EPRINT
Characteristics of Key-Dependent S-Boxes: the Case of Twofish
Marco Macchetti
In this paper we analyze and discuss the cryptographic robustness of key-dependent substitution boxes (KDSBs); these can be found in some symmetric-key algorithms such as Khufu, Blowfish, and the AES finalist Twofish. We analyze KDSBs in the framework of composite permutations, completing the theory developed by O'Connor. Under the basic assumption that KDSBs are built choosing permutations randomly from the symmetric group $S_{2^m}$ by means of the key, the expressions of their linear and differential characteristics are derived. These results are used as a statistical tool to show that Twofish KDSBs, although very efficient, can be easily distinguished from truly randomly built KDSBs. We also analyze the motivations that lead to this previously unknown property; it can be concluded that the efficiency of the construction and the small computational complexity of Twofish KDSBs, although very desirable, cannot be easily obtained together with the highest level of security.
2004
ASIACRYPT
2004
EPRINT
Addendum to ``On the Generalized Linear Equivalence of Functions over Finite Fields''
Marco Macchetti
In this paper we discuss the example of APN permutation introduced in the paper ``On the Generalized Linear Equivalence of Functions over Finite Fields'', presented at Asiacrypt 2004. We show that the permutation given there is indeed classically linearly equivalent to a power monomial. More in general, we show that no new class of APN functions can be discovered starting from permutation polynomials of the type used in the paper, and applied on the APN monomial $x^3$.
2002
CHES

Program Committees

CHES 2010
CHES 2009