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Contract signing is a fundamental service in the environment of the electronic commerce. It is a kind of fair exchange of values: a signature on a text contract for another signature on the same text. We present a fair protocol that requires the existence and possible involvement of a TTP (trusted third party), but it only intervenes in case of exception (it plays a subsidiary role). The protocol...
A new scheme for electronic sealed-bid auctions that preserves losing bids is presented. By this scheme, the computational complexity of the opening phase can be reduced to O(log ℓ); previous works required O(N⁗ℓ) or O(N⁗log ℓ) where the number of bidders is N and the range of bids is ℓ. The proposed scheme has two technical points. One is that computational complexity is independent of the number...
Within the NESSIE (New European Schemes for Signatures, Integrity, and Encryption) project, the signature schemes FLASH and SFLASH have been proposed for the use on low-cost smartcards. We show theoretically how differential power analysis (DPA) can be used to reveal the complete secret key in possible smartcard implementations of FLASH and SFLASH. To our knowledge no smartcard implementations...
We introduce polynomial approximations and consider the particular case of quadratic approximations. We establish an isomorphism between the set of quadratic Boolean functions and graphs. As its consequence, we can reduce problems involvingquadratic Boolean functions into problems with graphs and vice-versa. We present the problem of findinga minimum representation of quadratic functions, and prove...
Some algorithms to search for power residues close to a desired value are reported. They are used in the cryptanalysis of low exponent RSA with partially known clear text.
For making elliptic curve point multiplication secure against side-channel attacks, various methods have been proposed using special point representations for specifically chosen elliptic curves. We show that the same goal can be achieved based on conventional elliptic curve arithmetic implementations. Our point multiplication method is much more general than the proposals requiring non-standard point...
In this paper we propose a new proactive password checker, a program which prevents the choice of easy-to-guess passwords. The checker uses a decision tree which has been set up applying the Minimum Description LengthPrinciple and a Pessimistic Pruning Technique to refine its predictive power. Experimental results show a substantial improvement in performances of this checker with respect to previous...
Batch verification is a useful tool in verifying a large number of cryptographic items all at one time. It is especially effective in verifying predicates based on modular exponentiation. In some cases, however, the items can be incorrect although they pass batch verification together. Such leniency can be eliminated by checking the domain of each item in advance. With this in mind, we investigate...
In this paper, we present the results of the first phase of a project aimed at implementing a full suite of IPSec cryptographic transformations in reconfigurable hardware. Full implementations of the new Advanced Encryption Standard, Rijndael, and the older American federal standard, Triple DES, were developed and experimentally tested using the SLAAC-1V FPGA accelerator board, based on Xilinx Virtex...
Focusing on servers that process many signatures or ciphertexts, this paper proposes two techniques for parallel computing with SIMD, which significantly enhances the speed of elliptic curve scalar multiplication. We also evaluate one of them based on a real implementation on a Pentium III, which incorporates the SIMD architecture. The results show that the proposed method is about 4.4 times faster...
This paper discusses the design and implementation of the Confidentiality and Integrity algorithms, which have been standardized by the 3- rdGeneration Partnership Project. Both algorithms use a modified version of the MISTY scheme, named KASUMI, as a basic cryptographic engine. Various architectural approaches have been examined and implemented in different hardware platforms (FPGAs, ASICs) providing...
This paper presents an efficient implementation of elliptic curve cryptosystems over a prime field on ARM7 with the help of a hardware accelerator. The hardware accelerator has two dedicated large number arithmetic units (LNAU’s). Three different implementation platforms are considered: ARM7, ARM7 with one LNAU, and ARM7 with two LNAU’s. The time costs for performing point multiplication are measured...
Most of the work on multimedia medical images security until now has focused on cryptographic approaches. While valuable, cryptography is not enough to control access to images. Therefore additional protection approaches should be applied at a higher level. Role-based access control (RBAC) is a good candidate to provide access control in a multimedia medical image DBMS. However, in a multimedia medical...
Secure publication over the Internet of XML data is becoming a crucial need as XML is rapidly becoming a standard for document representation and exchange over the Web. Publishing services must have a mechanism that ensures that a user receives all and only those portions of information he/she is entitled to access (for instance those for which the user has paid a subscription fee). Furthermore, such...
In this paper we investigate the issues concerning with the use of a single server across a network, the Key Distribution Center, to enable private communications within groups of users. After providing several motivations, showing the advantages related to the distribution of the task accomplished by this server, we describe a model for such a distribution, and present bounds on the amount of resources...
Secret key agreement protocol between legal parties based on reconciliation and privacy amplification procedure has been considered in [2]. The so called privacy amplification theorem is used to estimate the amount of Shannon’s information leaking to an illegal party (passive eavesdropper) about the final key.We consider a particular case where one of the legal parties (Alice) sends to another legal...
Several automated techniques exist to transform ciphertext into text that “looks like” natural-language text while retaining the ability to recover the original ciphertext. This transformation changes the ciphertext so that it doesn’t attract undue attention from, for example, attackers or agencies or organizations that might want to detect or censor encrypted communication. Although it is relatively...
This article presents a new and robust watermarking method in the frequency domain that improves over the existing ones. It is robust to JPEG compression, very configurable, simple, efficient and very easy to implement. Apart from JPEG test, it shows very good results in all tests applied.
Watermarking stays the main technical safeguard of electronic copyright. This paper presents the first public-domain oblivious watermarking scheme for images which survives scaling and geometric distortion attacks. Previous proposals are either proprietary, non-oblivious or require scaling or geometric distortion to be undone prior to mark recovery, which may not be practical in oblivious watermarking...
Information hiding is attracting an increasing attention from the research community. Most of this research has centered around hiding information, such as watermarks and fingerprints, in images or digital audio and video signals. Text has generally been treated as a black & white image with special properties. All of the current methods of hiding information in text are vulnerable to scanning...
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