Cryptanalysis Method and System

Abstract

A cryptanalysis method comprising:(A) Performing a ciphertext-only direct cryptanalysis of A5/1 and(B) Using results of Step (A) to facilitate the decryption and/or encryption of further communications that are consistent with encryption using the session key and/or decryption using the session key, wherein the cryptanalysis considers part of the bits of the session key to have a known fixed value, and wherein the cryptanalysis finds the session key. An efficient known plaintext attack on AS/2 comprises trying all the possible values for R4, and for each such value solving the linearized system of equations that describe the output;The solution of the equations gives the internal state of RI, R2, and R3;Together with R4, this gives the full internal state which gives a suggestion for the key.

1 . A system for decrypting an encrypted text message, said system comprising:
 communication circuitry adapted to receive the text message, encrypted according to a given encryption algorithm characterized by a given GSM error correction coding;   processing circuitry adapted to recover an encryption key used to encrypt the encrypted digital communication by deriving equations, over bit-streams of the encrypted digital communication, the derived equations describing a kernel of an inverse transformation of a binary matrix defined by a structured redundancy characterizing data streams generated using the given error correction coding.   
     
     
         2 . The system according to  claim 1 , wherein the text message is a wireless communication and said communication circuitry is wireless communication circuitry. 
     
     
         3 . The system according to  claim 2 , wherein the text message is a cellular communication. 
     
     
         4 . A system for decrypting a encrypted text message, said system comprising:
 communication circuitry adapted to receive the encrypted text message, encrypted according to a given encryption algorithm characterized by a given GSM error correction coding;   processing circuitry adapted to recover an encryption key used to encrypt the text message by deriving equations over bit-streams of the encrypted text message, based on a structured redundancy characterizing data streams generated using the given error correction coding.   
     
     
         5 . The system according to  claim 4 , wherein the encrypted text message is a wireless communication and said communication circuitry is wireless communication circuitry. 
     
     
         6 . The system according to  claim 5 , wherein the encrypted text message is a cellular communication. 
     
     
         7 . A system for decrypting an encrypted text message, said system comprising:
 communication circuitry adapted to receive the encrypted text message, encrypted according to a given encryption algorithm characterized by a given GSM error correction coding;   processing circuitry adapted to recover an encryption key used to encrypt the encrypted text message by:
 (i) performing a decryption process of the encrypted text message using a candidate encryption key; 
 (ii) mathematically searching for patterns within an output of the decryption process matching a structural redundancy typical of the given error correction coding; and 
 (iii) repeating steps (i) & (ii) with different candidate encryption keys until a candidate encryption key producing a pattern typical of the given error correction coding is found. 
   
     
     
         8 . The system according to  claim 7 , wherein the encrypted text message is a wireless communication and said communication circuitry is wireless communication circuitry. 
     
     
         9 . The system according to  claim 8 , wherein the encrypted text message is a cellular communication.