Cryptanalysis of White-Box Implementations
A white-box implementation of a block cipher is a software implementation from which it is difficult for an attacker to extract the cryptographic key. Chow et al. published white-box implementations for AES and DES that both have been cryptanalyzed. However, these white-box implementations are based on ideas that can easily be used to derive white-box implementations for other block ciphers as well. As the cryptanalyses published use typical properties of AES and DES, it remains an open question whether the white-box techniques proposed by Chow et al. can result in a secure white-box implementation for other ciphers than AES and DES. In this paper we identify a generic class of block ciphers for which the white-box techniques of Chow et al. do not result in a secure white-box implementation. The result can serve as a basis to design block ciphers and to develop white-box techniques that do result in secure white-box implementations.
A polarisation based Visual Crypto System and its Secret Sharing Schemes
In this paper, we present a new visual crypto system based on the polarisation of light and investigate the existence and structure of the associated threshold visual secret sharing schemes. It is shown that very efficient $(n,n)$ schemes exist and that $(2,n)$ schemes are equivalent to binary codes. The existence of $(k,n)$ schemes is shown in general by two explicit constructions. Finally, bounds on the physical properties as contrast and resolution are derived.
An addition to the paper: A polarisation based visual crypto system and its secret sharing schemes
An (n,k) pair is a pair of binary nxm matrices (A,B), such that the weight of the modulo-two sum of any i rows, 1\leq i \leq k, from A or B is equal to a_i or b_i, respectively, and moreover, a_i=b_i, for 1\leq i < k, while a_k \neq b_k. In this note we first show how to construct an (n,k) Threshold Visual Secret Sharing Scheme from an (n,k) pair. Then, we explicitly construct an (n,k)-pair for all n and k with 1 \leq k <n.