Combinatorics on words in information security: Unavoidable regularities   in the construction of multicollision attacks on iterated hash functions
  Classically in combinatorics on words one studies unavoidable regularities that appear in sufficiently long strings of symbols over a fixed size alphabet. In this paper we take another viewpoint and focus on combinatorial properties of long words in which the number of occurrences of any symbol is restritced by a fixed constant. We then demonstrate the connection of these properties to constructing multicollision attacks on so called generalized iterated hash functions. 
Juha Kortelainen (Department of Information Processing Science,   University of Oulu, Finland)
cs.FL