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New Parallel Domain Extenders for UOWHF
 Lecture Notes in Computer Science
"... Abstract. We present two new parallel algorithms for extending the domain of a UOWHF. The first algorithm is complete binary tree based construction and has less key length expansion than Sarkar’s construction which is the previously best known complete binary tree based construction. But only disad ..."
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Abstract. We present two new parallel algorithms for extending the domain of a UOWHF. The first algorithm is complete binary tree based construction and has less key length expansion than Sarkar’s construction which is the previously best known complete binary tree based construction. But only disadvantage is that here we need more key length expansion than that of Shoup’s sequential algorithm. But it is not too large as in all practical situations we need just two more masks than Shoup’s. Our second algorithm is based on noncomplete lary tree and has the same optimal key length expansion as Shoup’s which has the most efficient key length expansion known so far. Using the recent result [9], we can also prove that the key length expansion of this algorithm and Shoup’s sequential algorithm are the minimum possible for any algorithms in a large class of “natural ” domain extending algorithms. But its parallelizability performance is less efficient than complete tree based constructions. However if l is getting larger, then the parallelizability of the construction is also getting near to that of complete tree based constructions. We also give a sufficient condition for valid domain extension in sequential domain extension.
Masking Based Domain Extenders for UOWHFs: Bounds and Constructions
 CRYPTOLOGY EPRINT ARCHIVE
, 2003
"... We study the class of masking based domain extenders for UOWHFs. Our first contribution is to show that any correct masking based domain extender for UOWHF which invokes the compression UOWHF s times must use at least ⌈log 2 s⌉ masks. As a consequence, we obtain the key expansion optimality of sev ..."
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We study the class of masking based domain extenders for UOWHFs. Our first contribution is to show that any correct masking based domain extender for UOWHF which invokes the compression UOWHF s times must use at least ⌈log 2 s⌉ masks. As a consequence, we obtain the key expansion optimality of several known algorithms among the class of all masking based domain extending algorithms. Our second contribution is to present a new parallel domain extender for UOWHF. The new algorithm achieves asymptotically optimal speedup over the sequential algorithm and the key expansion is almost everywhere optimal, i.e., it is optimal for almost all possible number of invocations of the compression UOWHF. Our algorithm compares favourably with all previously known masking based domain extending algorithms.
Higher Order Universal OneWay Hash Functions
 Asiacrypt'04, LNCS 3329
, 2004
"... Abstract. Universal OneWay Hash Functions (UOWHFs) are families of cryptographic hash functions for which first a target input is chosen and subsequently a key which selects a member from the family. Their main security property is that it should be hard to find a second input that collides with th ..."
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Abstract. Universal OneWay Hash Functions (UOWHFs) are families of cryptographic hash functions for which first a target input is chosen and subsequently a key which selects a member from the family. Their main security property is that it should be hard to find a second input that collides with the target input. This paper generalizes the concept of UOWHFs to UOWHFs of order r. We demonstrate that it is possible to build UOWHFs with much shorter keys than existing constructions from fixedsize UOWHFs of order r. UOWHFs of order r can be used both in the linear (r + 1)round MerkleDamg˚ard construction and in a tree construction.