On the Interpolation Attacks on Block Ciphers

Abstract. The complexity of interpolation attacks on block ciphers depends on the degree of the polynomial approximation and or on the number of terms in the polynomial approximation expression. In some situations, the round function or the S-boxes of the block cipher are expressed explicitly in terms of algebraic function, yet in many other occasions the S-boxes are expressed in terms of their Boolean function representation. In this case, the cryptanalyst has to evaluate the algebraic description of the S-boxes or the round function using the Lagrange interpolation formula. A natural question is what is the e ect of the choice of the irreducible polynomial used to construct the nite eld on the degree of the resulting polynomial. Another question is whether or not there exists a simple linear transformation on the input or output bits of the S-boxes or the round function such that the resulting polynomial has a less degree or smaller number of non-zero coe cients. In this paper we giv...

• Type: Conference
• Year: 2000
• Where: FSE
• Authors: Amr M. Youssef, Guang Gong
• Keywords: Cryptology, FSE 2000, Lagrange Interpolation Formula, Polynomial, Polynomial Approximation