The increasing use of digital documents, and the need to refer to them conveniently and unambiguously, raise an important question: can one "name" a digital document in a way that conveniently enables users to find it, and at the same time enables a user in possession of a document to be sure that it is indeed the one that is referred to by the name? One crucial piece of a complete solution to this problem would be a method that provides a cryptographically verifiable label for any bit-string (for example, the content, in a particular format, of the document). This problem has become even more acute with the emergence of the WorldWide Web, where a document (whose only existence may be on-line) is now typically named by giving its URL, which is merely a pointer to its virtual location at a particular moment in time. Using a one-way hash function to call files by their hash values is cryptographically verifiable, but the resulting names are unwieldy, because of their length and randomn...

Abstract. This paper compares the parameters sizes and software performance of several recent constructions for universal hash functions: bucket hashing, polynomial hashing, Toeplitz hashing, division hashing, evaluation hashing, and MMH hashing. An objective comparison between these widely varying approaches is achieved by defining constructions that offer a comparable security level. It is also demonstrated how the security of these constructions compares favorably to existing MAC algorithms, the security of which is less understood. 1

We introduce the notion of key stretching, a mechanism to convert short s-bit keys into longer keys, such that the complexity required to brute-force search a s + t-bit keyspace is the same as the time required to brute-force search a s-bit key stretched by t bits.

Abstract. Textbooks tell us that a birthday attack on a hash function h with range size r requires r 1/2 trials (hash computations) to find a collision. But this is quite misleading, being true only if h is regular, meaning all points in the range have the same number of pre-images under h; if h is not regular, fewer trials may be required. But how much fewer? This paper addresses this question by introducing a measure of the “amount of regularity ” of a hash function that we call its balance, and then providing estimates of the success-rate of the birthday attack, and the expected number of trials to find a collision, as a function of the balance of the hash function being attacked. In particular, we will see that the number of trials can be significantly less than r 1/2 for hash functions of low balance. This leads us to examine popular design principles, such as the MD (Merkle-Damg˚ard) transform, from the point of view of balance preservation, and to mount experiments to determine the balance of popular hash functions. 1

We present a cryptographic module that can be used both as a cryptographic hash function and as a stream cipher. High performance is achieved through a combination of low work-factor and a high degree of parallelism. Throughputs of 5.1 bits/cycle for the hashing mode and 4.7 bits/cycle for the stream cipher mode are demonstrated on a commercially available VLIW micro-processor.

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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.

This paper examines proposals for three cryptographic primitives: block ciphers, stream ciphers, and hash functions. It provides an overview of the design principles of a large number of recent proposals, which includes the global structure, the number of rounds, the way of introducing non-linearity and diffusion, and the key schedule. The software performance of about twenty primitives is compared based on highly optimized implementations for the Pentium. The goal of the paper is to provided a technical perspective on the wide variety of primitives that exist today.

To enhance system performance computer architectures tend to incorporate an increasing number of parallel execution units. This paper shows that the new generation of MD4-based customized hash functions (RIPEMD-128, RIPEMD-160, SHA-1) contains much more software parallelism than any of these computer architectures is currently able to provide. It is conjectured that the parallelism found in SHA-1 is a design principle. The critical path of SHA-1 is twice as short as that of its closest contender RIPEMD-160, but realizing it would require a 7-way multiple-issue architecture. It will also be shown that, due to the organization of RIPEMD-160 in two independent lines, it will probably be easier for future architectures to exploit its software parallelism.