Patent ID: 6823068
Filing Date: 2004-11-23
Classification: G09C,H04L

Abstract:
A method for encrypting a plaintext message to produce a cyphertext message, based on a symmetric cryptographic key, the method comprising:(a) providing a shared key as a graph, expressed in a computer-readable storage medium, wherein: the graph comprises a plurality of vertices interconnected by a plurality of edges, whereby each edge connects two vertices, such that it is possible to travel from any one of the vertices to any other one of the vertices by following one or more of the edges; each of the plurality of vertices is identified by a letter from a first alphabet; and each of the plurality of edges is identified by a letter from a second alphabet, such that no two edges which connect to the same vertex are marked by the same letter; (b) providing the plaintext message in the first alphabet, where the alphabet is comprised of n letters, and where the provided plaintext message is constructed as follows: (b.1) the original plain language message comprised of the English or other human language alphabet, plus digits and punctuation marks, is expressed via a look-up table through an alphabet comprised of (nâˆ’1) letters, and (b.2) where the plaintext sequence expressed via the (nâˆ’1) alphabet is processed by interposing an n-th letter between any two letters in the sequence where a letter follows the same letter, thereby creating a plaintext sequence expressed through an n-letter alphabet, and that sequence is free from occurrences where a letter follows the same letter; (c) traversing the graph along its edges in accordance with the plaintext message provided in the first alphabet to cover an ordered set of the vertices, the ordered set of the vertices corresponding to the order of the letters of the first alphabet in the plaintext message, wherein a pathway taken among the ordered set of the vertices defines an ordered set of the edges; and where the first vertex in the ordered set of vertices is preset, and is part of the encryption procedure, and where any vertex and any edge can be revisited more than once in the pathway, and some vertices and some edges may not be part of the path at all; (d) forming an ordered set of letters of the second alphabet corresponding to the ordered set of the edges; and (e) taking the ordered set of letters of the second alphabet as the cyphertext message.