Showing papers on "Ciphertext published in 1983"

Secure transmission system

Abstract: In a secure digital transmission system that may utilize the Data Encryption Standard, the message signal is encrypted according to a predetermined algorithm and a key. The key is selected from a library of key material according to a key index signal. The key index signal, which is transmitted to all stations that must decrypt the message signal and therefore subject to interception, is itself encrypted at each station to form the library addresses for key selection. Even though the key selection process is initiated by a transmitted signal, security remains high because in the key selection chain, clear text and associated cypher text are not available for analysis. The key for encrypting the key index signal may itself be selected in a similar manner, thereby cascading the system any number of times for further security. A pseudorandom bit stream generated and encrypted at each station and initialized by the transmitted key index signal can address the key library to provide continually changing key.

Randomized Encryption Techniques

Abstract: A randomized encryption procedure enciphers a message by randomly choosing a ciphertext from a set of ciphertexts corresponding to the message under the current encryption key At the cost of increasing the required bandwidth, such procedures may achieve greater cryptographic security than their deterministic counterparts by increasing the apparent size of the message space, eliminating the threat of chosen plaintext attacks, and improving the a priori statistics for the inputs to the encryption algorithms In this paper we explore various ways of using randomization in encryption

Long Key Variants of DES

Abstract: The Federal Data Encryption Standard (DES) [1] is a block product cipher which converts 64-bit blocks of plaintext into 64-bit blocks of cipher text, or vice-versa, under the control of a 56-bit key. There has in the past been considerable controversy over the adequacy of DES key length [2,3,4]. Easily implemented modifications to the DES key schedule (KS) would allow the use of keys longer than 56 bits.

Common control audio decryptor

Abstract: Decryption of a plurality of simultaneously received, randomly phased signals is realized by employing a single data encryption standard module in a time shared manner. A plurality of process state counters, each of which is associated with a received signal, are employed to direct operations of the decryptor on a time shared basis. These operations include the generation on a time shared basis of so-called plain text data for each received signal, generation of corresponding encryption requests, and generation of cipher text data for each received signal which is used to decrypt associated received signal samples.

Drainage and the DES Summary

Abstract: In our paper, we investigate a statistical property of random functions we named drainage. (Definitions for drainage, random function, etc. will be given shortly.) Our motivation for doing so is twofold. First, it generally assumed that a good cryptographic system will exhibit no simple statistical regularity. For example, the function from key to ciphertext when a block cipher is used to encode a fixed plaintext should appear to be completely random. We were therefore interested in studying the behavior of drainage for a random function, and then comparing it to the measured behavior for a real cryptosystem, the DES. Secondly, drainage is closely related to statistical properties which are important to the performance of the generalized cryptanalytic attack proposed by Hellman [1], discussed below.