Traditional Public Key Infrastructures (PKI) have not lived up to their promise because there are too many ways to define PKIs, too many cryptographic primitives to build them with, and too many administrative domains with incompatible roots of trust. Alpaca is an authentication and authorization framework that embraces PKI diversity by enabling one PKI to “plug in ” another PKI’s credentials and cryptographic algorithms, allowing users of the latter to authenticate themselves to services using the former using their existing, unmodified certificates. Alpaca builds on Proof-Carrying Authorization (PCA) [8], expressing a credential as an explicit proof of a logical claim. Alpaca generalizes PCA to express not only delegation policies but also the cryptographic primitives, credential formats, and namespace structure needed to use foreign credentials directly. To achieve this goal, Alpaca introduces a method of creating and naming new principals which behave according to arbitrary rules, a modular approach to logical axioms, and a domain-specific language specialized for reasoning about authentication. We have implemented Alpaca as a Python module that assists applications in generating proofs (e.g., in a client requesting access to a resource), and in verifying those proofs via a compact 800-line TCB (e.g., in a server providing that resource). We present examples demonstrating Alpaca’s extensibility in scenarios involving inter-organization PKI interoperability and secure remote PKI upgrade.

Abstract. Let H1, H2 be two hash functions. We wish to construct a new hash function H that is collision resistant if at least one of H1 or H2 is collision resistant. Concatenating the output of H1 and H2 clearly works, but at the cost of doubling the hash output size. We ask whether a better construction exists, namely, can we hedge our bets without doubling the size of the output? We take a step towards answering this question in the negative — we show that any secure construction that evaluates each hash function once cannot output fewer bits than simply concatenating the given functions. 1

We expand a previous result of Dean [Dea99] to provide a second preimage attack on all n-bit iterated hash functions with Damgård-Merkle strengthening and n-bit intermediate states, allowing a second preimage to be found for a 2 k-message-block message with about k × 2 n/2+1 +2 n−k+1 work. Using RIPEMD-160 as an example, our attack can find a second preimage for a 2^60 byte message in about 2^106 work, rather than the previously expected 2^160 work. We also provide slightly cheaper ways to find multicollisions than the method of Joux [Jou04]. Both of these results are based on expandable messages–patterns for producing messages of varying length, which all collide on the intermediate hash result immediately after processing the message. We provide an algorithm for finding expandable messages for any n-bit hash function built using the Damgård-Merkle construction, which requires only a small multiple of the work done to find a single collision in the hash function.

Abstract. This paper presents two algorithms for solving the linear and the affine equivalence problem for arbitrary permutations (S-boxes). For a pair of n × n-bit permutations the complexity of the linear equivalence algorithm (LE) is O(n 3 2 n). The affine equivalence algorithm (AE) has complexity O(n 3 2 2n). The algorithms are efficient and allow to study linear and affine equivalences for bijective S-boxes of all popular sizes (LE is efficient up to n ≤ 32). Using these tools new equivalent representations are found for a variety of ciphers: Rijndael, DES, Camellia, Serpent, Misty, Kasumi, Khazad, etc. The algorithms are furthermore extended for the case of non-bijective n to m-bit S-boxes with a small value of |n − m | and for the case of almost equivalent S-boxes. The algorithms also provide new attacks on a generalized Even-Mansour scheme. Finally, the paper defines a new problem of S-box decomposition in terms of Substitution Permutations Networks (SPN) with layers of smaller S-boxes. Simple information-theoretic bounds are proved for such decompositions. Keywords: Linear, affine equivalence algorithm, S-boxes, Block-ciphers,

Copyright and all rights therein are retained by authors or by other copyright holders. All persons copying this information are expected to adhere to the terms and constraints invoked by each author's copyright. In most cases, these works may not be reposted or mass reproduced without the explicit permission of the copyright holder. Efficient Architecture and Hardware Implementation of the Whirlpool Hash Function Abstract — The latest cryptographical applications demand both high speed and high security. In this paper, an architecture and VLSI implementation of the newest powerful standard in the hash families, Whirlpool, is presented. It reduces the required hardware resources and achieves highspeed performance. The architecture permits a wide variety of implementation tradeoffs. The implementation is examined and compared in the security level and in the performance by using hardware terms. This is the first Whirlpool implementation allowing fast execution, and effective substitution of any previous hash families ’ implementations such as MD5, RIPEMD-160, SHA-1, SHA-2 etc, in any cryptography application 1.

Abstract. We present a new block cipher LED. While dedicated to compact hardware implementation, and offering the smallest silicon footprint among comparable block ciphers, the cipher has been designed to simultaneously tackle three additional goals. First, we explore the role of an ultra-light (in fact non-existent) key schedule. Second, we consider the resistance of ciphers, and LED in particular, to related-key attacks: we are able to derive simple yet interesting AES-like security proofs for LED regarding related- or single-key attacks. And third, while we provide a block cipher that is very compact in hardware, we aim to maintain a reasonable performance profile for software implementation. Key words: lightweight, block cipher, RFID tag, AES. 1

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 2n-bit to n-bit compression functions that use three calls to n-bit 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 permutation-based pseudorandom oracles that outperform the Sponge construction [4] and the MD6 compression function [9] both in terms of security and efficiency.

In this note it is examined whether there exist quadratic relations with certainty over the input and output bits of the S-boxes of Khazad and Whirlpool.

On November 2, 2007, NIST (United States National Institute of Standards and Technology) announced an initiative to design a new secure hash function for this century, to be called SHA-3. The competition will be open and it is planned to conclude in 2012. These developments are quite similar to the recent history of symmetric block ciphers— breaking of the DES (Data Encryption Standard) and emergence of the AES (Advanced Encryption Standard) in 2001 as the winner of a multiyear NIST competition. In this paper we make a case that parallelizability should be one of the properties sought in the new SHA-3 design. We present a design concept for a parallelizable hash function called PHASH based on a block cipher, and we discuss PHASH’s performance and security. 1.

Abstract. In this paper, we study security for a certain class of permutation-based compression functions. Denoted lp231 in [12], they are 2n-bit to n-bit compression functions using three calls to a single n-bit 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