Abstract: In a pseudo-random transposition cipher system and method, sender and receiver each have sets of corresponding identical pseudo-random number generators. To encrypt a message, the sender generates a pseudo-random initializing integer, transmitted along with the encrypted message. The sender, using a key secretly shared with the receiver, selects a set of seed integers for the pseudo-random number generators from the initializing integer. The first number generator produces a set of numerical synonyms (numerical codings) associated one-to-one with a set of sequentially indexed addresses of cardinality at least as great as that of the plaintext alphabet. The second number generator determines a one-to-one mapping of the plaintext alphabet into the set of addresses. Whenever a plaintext alphabet character appears in the message, the numerical synonym sharing the same address is used as the corresponding ciphertext character.

Abstract: A cipher system is disclosed in which each character of a plaintext alphabet has associated with it a randomly distributed collection of integers of a given length. These collections of integers are secretly shared by a sender and receiver pair. The plaintext characters of a message are sequentially coded by randomly selecting representatives from the integer collections corresponding to the plaintex characters. To this sequence of concatenated integers, regarded as a single integer, is added a random integer of length equal to that of the coded-for-message integer stiring. This random integer is taken from a random digits shared by the sender and receiver. The indexing of the random integer in the digit string is transmitted as part of the cryptogram. The summed random integer plus the coding integer string is transmitted as the body of the cryptogram.