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Distinguisher and RelatedKey Attack on the Full AES256
 Advances in Cryptology – CRYPTO 2009, Proceedings, volume 5677 of Lecture Notes in Computer Science
, 2009
"... Abstract. In this paper we construct a chosenkey distinguisher and a relatedkey attack on the full 256bit key AES. We define a notion of differential qmulticollision and show that for AES256 qmulticollisions can be constructed in time q · 2 67 and with negligible memory, while we prove that th ..."
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Cited by 26 (2 self)
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Abstract. In this paper we construct a chosenkey distinguisher and a relatedkey attack on the full 256bit key AES. We define a notion of differential qmulticollision and show that for AES256 qmulticollisions can be constructed in time q · 2 67 and with negligible memory, while we prove that the same task for an ideal cipher of the same block size would require at least O(q · 2 q−1 q+1 128) time. Using similar approach and with the same complexity we can also construct qpseudo collisions for AES256 in DaviesMeyer hashing mode, a scheme which is provably secure in the idealcipher model. We have also computed partial qmulticollisions in time q · 2 37 on a PC to verify our results. These results show that AES256 can not model an ideal cipher in theoretical constructions. Finally we extend our results to find the first publicly known attack on the full 14round AES256: a relatedkey distinguisher which works for one out of every 2 35 keys with 2 120 data and time complexity and negligible memory. This distinguisher is translated into a keyrecovery attack with total complexity of 2 131 time and 2 65 memory. Keywords: AES, relatedkey attack, chosen key distinguisher, DaviesMeyer, ideal cipher.
Constructing cryptographic hash functions from fixedkey blockciphers. Full version of this paper
, 2008
"... Abstract. We propose a family of compression functions built from fixedkey blockciphers and investigate their collision and preimage security in the idealcipher model. The constructions have security approaching and in many cases equaling the security upper bounds found in previous work of the aut ..."
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Cited by 18 (5 self)
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Abstract. We propose a family of compression functions built from fixedkey blockciphers and investigate their collision and preimage security in the idealcipher model. The constructions have security approaching and in many cases equaling the security upper bounds found in previous work of the authors [24]. In particular, we describe a 2nbit to nbit compression function using three nbit permutation calls that has collision security N 0.5,whereN =2 n, and we describe 3nbit to 2nbit compression functions using five and six permutation calls and having collision security of at least N 0.55 and N 0.63. Key words: blockcipherbased hashing, collisionresistant hashing, compression functions, cryptographic hash functions, idealcipher model. 1
Building a collisionresistant compression function from noncompressing primitives
 In ICALP 2008, Part II
, 2008
"... Abstract. We consider how to build an efficient compression function from a small number of random, noncompressing primitives. Our main goal is to achieve a level of collision resistance as close as possible to the optimal birthday bound. We present a 2nton bit compression function based on three ..."
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Cited by 15 (3 self)
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Abstract. We consider how to build an efficient compression function from a small number of random, noncompressing primitives. Our main goal is to achieve a level of collision resistance as close as possible to the optimal birthday bound. We present a 2nton bit compression function based on three independent nton bit random functions, each called only once. We show that if the three random functions are treated as black boxes then finding collisions requires Θ(2 n/2 /n c) queries for c ≈ 1. This result remains valid if two of the three random functions are replaced by a fixedkey ideal cipher in DaviesMeyer mode (i.e., EK(x) ⊕ x for permutation EK). We also give a heuristic, backed by experimental results, suggesting that the security loss is at most four bits for block sizes up to 256 bits. We believe this is the best result to date on the matter of building a collisionresistant compression function from noncompressing functions. It also relates to an open question from Black et al. (Eurocrypt’05), who showed that compression functions that invoke a single noncompressing random function cannot suffice. We also explore the relationship of our problem with that of doubling the output of a hash function and we show how our compression function can be used to double the output length of ideal hashes.
The security of abreastdm in the ideal cipher model
"... Abstract. In this paper, we give a security proof for AbreastDM in terms of collision resistance and preimage resistance. As old as TandemDM, the compression function AbreastDM is one of the most wellknown constructions for double block length compression functions. The bounds on the number of q ..."
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Cited by 6 (3 self)
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Abstract. In this paper, we give a security proof for AbreastDM in terms of collision resistance and preimage resistance. As old as TandemDM, the compression function AbreastDM is one of the most wellknown constructions for double block length compression functions. The bounds on the number of queries for collision resistance and preimage resistance are given by O (2 n). Based on a novel technique using queryresponse cycles, our security proof is simpler than those for MDC2 and TandemDM. We also present a wide class of AbreastDM variants that enjoy a birthdaytype security guarantee with a simple proof. 1
On the Security of TandemDM
"... Abstract. We provide the first proof of security for TandemDM, one of the oldest and most wellknown constructions for turning a blockcipher with nbit blocklength and 2nbit keylength into a 2nbit cryptographic hash function. We prove, that when TandemDM is instantiated with AES256, i.e. blockle ..."
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Cited by 6 (2 self)
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Abstract. We provide the first proof of security for TandemDM, one of the oldest and most wellknown constructions for turning a blockcipher with nbit blocklength and 2nbit keylength into a 2nbit cryptographic hash function. We prove, that when TandemDM is instantiated with AES256, i.e. blocklength 128 bits and keylength 256 bits, any adversary that asks less than 2 120.4 queries cannot find a collision with success probability greater than 1/2. We also prove a bound for preimage resistance of TandemDM. Interestingly, as there is only one practical construction known (FSE’06, Hirose) turning such an (n,2n)bit blockcipher into a 2nbit compression function that has provably birthdaytype collision resistance, TandemDM is one out of two structures that possess this desirable feature.
Hash functions and RFID tags: Mind the gap
 of Lecture Notes in Computer Science
, 2008
"... Abstract. The security challenges posed by RFIDtag deployments are wellknown. In response there is a rich literature on new cryptographic protocols and an ontag hash function is often assumed by protocol designers. Yet cheap tags pose severe implementation challenges and it is far from clear that ..."
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Cited by 4 (0 self)
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Abstract. The security challenges posed by RFIDtag deployments are wellknown. In response there is a rich literature on new cryptographic protocols and an ontag hash function is often assumed by protocol designers. Yet cheap tags pose severe implementation challenges and it is far from clear that a suitable hash function even exists. In this paper we consider the options available, including constructions based around compact block ciphers. While we describe the most compact hash functions available today, our work serves to highlight the difficulties in designing lightweight hash functions and (echoing [17]) we urge caution when routinely appealing to a hash function in an RFIDtag protocol. 1
Adaptive Preimage Resistance and Permutationbased Hash Functions. Available at http://eprint.iacr.org/2009/066
"... Abstract. In this paper, we introduce a new notion of security, called adaptive preimage resistance. We prove that a compression function that is collision resistant and adaptive preimage resistant can be combined with a public random function to yield a hash function that is indifferentiable from a ..."
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Cited by 4 (1 self)
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Abstract. In this paper, we introduce a new notion of security, called adaptive preimage resistance. We prove that a compression function that is collision resistant and adaptive preimage resistant can be combined with a public random function to yield a hash function that is indifferentiable from a random oracle. Specifically, we analyze adaptive preimage resistance of 2nbit to nbit compression functions that use three calls to nbit public random permutations. This analysis also provides a simpler proof of their collision resistance and preimage resistance than the one provided by Rogaway and Steinberger [19]. By using such compression functions as building blocks, we obtain permutationbased pseudorandom oracles that outperform the Sponge construction [4] and the MD6 compression function [9] both in terms of security and efficiency.
Fast HashBased Signatures on Constrained Devices
"... Abstract. Digital signatures are one of the most important applications of microprocessor smart cards. The most widely used algorithms for digital signatures, RSA and ECDSA, depend on finite field engines. On 8bit microprocessors these engines either require costly coprocessors, or the implementati ..."
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Cited by 3 (0 self)
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Abstract. Digital signatures are one of the most important applications of microprocessor smart cards. The most widely used algorithms for digital signatures, RSA and ECDSA, depend on finite field engines. On 8bit microprocessors these engines either require costly coprocessors, or the implementations become very large and very slow. Hence the need for better methods is highly visible. One alternative to RSA and ECDSA is the Merkle signature scheme which provides digital signatures using hash functions only, without relying on any number theoretic assumptions. In this paper, we present an implementation of the Merkle signature scheme on an 8bit smart card microprocessor. Our results show that the Merkle signature scheme provides comparable timings compared to state of the art implementations of RSA and ECDSA, while maintaining a smaller code size.
Security of Singlepermutationbased Compression Functions
"... Abstract. In this paper, we study security for a certain class of permutationbased compression functions. Denoted lp231 in [12], they are 2nbit to nbit compression functions using three calls to a single nbit random permutation. We prove that lp231 is asymptotically preimage resistant up to (2 2 ..."
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Cited by 1 (1 self)
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Abstract. In this paper, we study security for a certain class of permutationbased compression functions. Denoted lp231 in [12], they are 2nbit to nbit compression functions using three calls to a single nbit random permutation. We prove that lp231 is asymptotically preimage resistant up to (2 2n 3 /n) queries, adaptive preimage resistant up to (2 n 2 /n) queries/commitments, and collision resistant up to (2 n 2 /n 1+ɛ) queries for ɛ> 0. 1
More Insights on BlockcipherBased Hash Functions
"... Abstract. In this paper we give more insights on the security of blockcipherbased hash functions. We give a very simple criterion to build a secure large class of SingleBlockLength (SBL) or double call DoubleBlockLength (DBL) compression functions based on (kn, n) blockciphers, where kn is the k ..."
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Abstract. In this paper we give more insights on the security of blockcipherbased hash functions. We give a very simple criterion to build a secure large class of SingleBlockLength (SBL) or double call DoubleBlockLength (DBL) compression functions based on (kn, n) blockciphers, where kn is the key length and n is the block length and k is an integer. This criterion is simpler than previous works in the literature. Based on the criterion, we can get many results from this criterion, and we can get a conclusion on such class of blockcipherbased hash functions. We solved the open problem left by Hirose. Our results show that to build a secure double call DBL compression function, it is required k> = m + 1 where m is the number of message blocks. Thus, we can only build rate 1/2 secure double DBL blockcipherbased compression functions if k = = 2. At last, we pointed out flaws in Stam’s theorem about supercharged functions and gave a revision of this theorem and added another condition for the security of supercharged compression functions. 1