Reduction of message redundancy by multiple substitution: a message preprocessing scheme for secure communications
OwnerLin-nan Lee, Shyue-Ching Luinventors
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Abstract
The strength of a cryptosystem is increased by providing multiple characters for one or more of the characters being encoded to thereby reduce redundancy.
Claims9
In a method of maintaining communications security, including the steps of enciphering an input message signal comprising a plurality of characters a.sub.i to form a cryptogram signal, transmitting and receiving said cryptogram signal and decipering the cryptogram to recover the original input message signal, the improvement comprising:
- preprocessing the message signal prior to enciphering by substituting for each character a.sub.i in the original alphabet A of the original message signal a character a'.sub.i in a subset A'.sub.i, of a new alphabet A', which is assigned to said character a.sub.i, to thereby form a new stream of characters a'.sub.i, wherein the subset A'.sub.i for at least one character a.sub.i comprises at least two charaacters from which a'.sub.1 is selected;
- enciphering said stream of characters a'.sub.i to form said cryptogram signal;
- deciphering the received cryptogram signal to obtain a stream of characters a'.sub.i ;
- and
- postprocessing the stream of characters a'.sub.i by substituting for each character a'.sub.i the character a.sub.i in the original message signal to which said character a'.sub.i corresponds.
In a communications security system of the type having a message source for providing a message having characters a.sub.i belonging to an alphabet A, an encipherer for enciphering said message to form a cryptogram, and a deipherer for deciphering said cryptogram to recover the enciphered message, the improvement comprising:
- preprocessing means between said message source and encipherer for receiving said message and substituting for each character a.sub.i a new character a'.sub.i belonging to a subset A'.sub.i, of a new alphabet A', which is assigned to said character a.sub.j, at least one of said subsets A'.sub.i having plural characters a'.sub.j ;
- said encipherer enciphering the characters a'.sub.i to form said cryptogram;
- said decipherer deciphering said cryptogram to obtain said characters a'.sub.j ;
- and
- postprocessing means for receiving the decipherer output and substituting for each letter a'.sub.i the corresponding character a.sub.i.
Dependencies are inferred from the claim text.