On diamond structures and Trojan message attacks

Abstract

The first part of this paper considers the diamond structures which were first introduced and applied in the herding attack by Kelsey and Kohno [7]. We present a new method for the construction of a diamond structure with 2 d chaining values the message complexity of which is O(2 n+d/2). Here n is the length of the compression function used. The aforementioned complexity was (with intuitive reasoning) suggested to be true in [7] and later disputed by Blackburn et al. in [3]. In the second part of our paper we give new, efficient variants for the two types of Trojan message attacks against Merkle-Damgård hash functions presented by Andreeva et al. [1] The message complexities of the Collision Trojan Attack and the stronger Herding Trojan Attack in [1] are O(2n/2+r) and O(22n/3 + 2n/2+r), respectively. Our variants of the above two attack types are the Weak Trojan Attack and the Strong Trojan Attack having the complexities O(2n+r/2) and O(22n-s/3) + 2n+r/2), respectively. Here 2r is the cardinality of the prefix set and 2 s is the length of the Trojan message in the Strong Trojan Attack. © 2013 Springer-Verlag.