Showing papers on "Ciphertext published in 1990"

Public-key cryptosystems provably secure against chosen ciphertext attacks

Abstract: We show how to construct a public-key cryptosystem (as originally defined by DiNe and Hellman) secure against chosen ciphertezt attacks, given a public-key cryptosystern secure against passive eavesdropping and a noninteractive zero-knowledge proof system in the shared string model. No such secure cryptosystems were known before. A concrete implementation can be based on quadratic residuosity intractability.

Digital signature scheme based on error-correcting codes

Abstract: A new digital signature scheme based on error-correcting codes is proposed. The security of this scheme relies on the difficulty of factoring large matrices and the properties of error-correcting codes. The features of the author's scheme are that the ciphertext for a given message M is not repeated and errors in the ciphertext received can be detected and corrected. If this scheme is combined with the McEliece public-key cryptosystem, a scheme is obtained that cannot only sign, but also encipher, messages.

A Statistical Attack of the FEAL-8 Cryptosystem

Abstract: This paper presents a chosen plaintext cryptanalysis of the FEAL-8 cryptosystem. The attack requires the ciphertext corresponding to approximately 10000 pairs of 64 bit plaintext blocks. The difference (bitwise xor) between the two blocks of each pair is equal to an appropriately selected constant. We first state that some differential statistics for intermediate values of the data randomizer are non uniform and independent of the encryption key. We then show that these statistics can be used to compute gradually the expanded key of the data randomizer.In 1989 some announcements were made that the so-called FEAL-8, 8 round version of the FEAL cryptosystem, was vulnerable to a chosen plaintext attack [1], So far, however, only the cryptanalysis of the 4 round version FEAL-4 by Bert Den Boer [2] was published. In this paper we present a chosen plaintext attack of FEAL-8 based on some differential statistics of its data randomization scheme.

Key scheduling in DES type cryptosystems

Abstract: This paper reviews some possible design criteria for the key schedule in a DES style cryptosystem. The key schedule involves a Key Rotation component, and the permutation PC2. Together these provide for a diffusion of dependency of ciphertext bits on key bits. Some empirical rules which seem to account for the derivation of the key schedule used in the DES are first presented. A number of trials were run with various key schedules, and some further design rules were derived. An alternative form of key schedule was then tested. This used either a null PC2, or one in which permutations only occurred within the inputs to a given S-box, and a much larger rotation schedule than used in the DES. This was found to be as effective as the key schedule used in the current DES, and is proposed for use in new cryptosystems.

Varying feedback shift registers

Abstract: It is well known that a stream cipher system can be described in terms of a Vernam scheme using a Pseudo-Random Number Generator as key generator. Each character mt of the plaintext (viewed as an integer) is enciphered by adding the corresponding pseudo-random key character st. Deciphering is obtained by subtracting the same value stream from the ciphertext (see Fig.1).

The swedish hc-9 ciphering machine challenge

Abstract: Several readers solved the HC-9 challenge ciphier and describe how they did it. Another challenge message using a different alphabet sheet and punched card, plus a less obvious key then used previously, is provided. Lengthy plaintext with matching ciphertext offers some help.