In the original ElGamal signature scheme and it’s variants, two secret integers-private key and one-time secret key are required to produce a signature on a message, m. The private key of a system will be used throughout the life of the system whereas the one-time secret key only be used once and must be regenerated (different one-time secret key) when signing different message. This paper intr...

Context-based authentication methods enable the unobtrusive establishment of authentication or even secure keys. While several context-based authentication methods have been proposed recently, often the entropy of the seed for the cryptographic keys is not exploited. We study the entropy of audio fingerprints which can be utilized to pair devices in close proximity. In this work, for 600 audio ...

The Data Encryption Standard (DES) is no longer secure because of its small key size. One way to augment the keyspace is to perform multiple encryptions with DES. This paper examines the cryptographic consequences of multiple encryptions with DES through two simplified DES algorithms. Both simplified algorithms, under multiple encryptions, generate the alternating group of permutations on the m...

In undeniable signature schemes, zero-knowledgeness and non-transferability have been identified so far. In this paper, by separating these two notions, we show the first 3-move confirmation and disavowal protocols for Chaum’s undeniable signature scheme which is secure against active and concurrent attacks. Our main observation is that while the signer has one public key and one secret key, th...

We present a number of attacks, some new, on public key protocols. We also advance a number of principles which may help designers avoid many of the pitfalls, and help attackers spot errors which can be exploited.

We point out that the encryption process of [1, 2] is not invertible. This becomes evident through the following, illustrative, example. In accordance with Chang and Wu’s [1] protocol, let us assume that there are n eligible voters U1, . . . , Un, participating in the election. Further assume that the Voting Center chooses a prime number P, for example P 31, and a primitive element e 7 over GF(...

We describe the group structure underlying several popular homomorphic public-key systems and the problems they are based on. We prove several well-known security results using only the group structure and assumptions about the related problems. Then we provide examples of two new instances of this group structure and analyse their security.

Article history: Received 3 November 2008 Received in revised form 15 August 2013 Available online xxxx

Security protocols are small programs that are executed in hostile environments. Many results and tools have been developed to formally analyze the security of a protocol. However even when a protocol has been proved secure, there is absolutely no guarantee if the protocol is executed in an environment where other protocols, possibly sharing some common identities and keys like public keys or l...

We give an overview of the most important public-key cryptosystems and discuss the difficult task of evaluating the merit of such systems.