Pseudo-random transposition cipher system and method

• US 5,533,128 A
• Filed: 01/18/1995
• Issued: 07/02/1996
• Est. Priority Date: 01/18/1995
• Status: Expired due to Fees

• Current Assignee: Arnold Vobach
• Original Assignee: Arnold Vobach
• Inventors: Vobach, Arnold
• Primary Examiner(s): Gregory, Bernarr E.
• Application Number:
  US08/374,314
• Time in Patent Office: 531 Days
• Field of Search: 380/9, 380/21, 380/28, 380/36, 380/37, 380/42, 380/44, 380/46, 380/49, 380/47
• US Class Current: 380/28
• CPC Class Codes: H04L 9/0662 with particular pseudorandom sequence generator

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. After use of a plaintext character, a third number generator locates a new address so that the numerical synonym residing there can be transposed with the one last used for, and at the address of, the plaintext character. To decrypt, the receiver uses the secret key and initializing integer to recover the pseudo-random number generator seeds and undoes the encrypting process described above.

Claims

1. A cipher system for use by a sender and a receiver, comprising:

a. a source of plaintext alphabet characters;

b. a sender central processing unit to receive a plaintext message of plaintext alphabet characters from the source and to encode each character, the central processing unit comprising;

i. means for assigning a pseudo-randomly determined numerical synonym to each address from a serially numbered collection, of cardinality at least as great as that of the plaintext alphabet;

ii. means for pseudo-randomly assigning an address to each plaintext alphabet character; and

iii. means for inducing a transpostion of the numerical synonym used to represent the plaintext character with the numerical synonym at another address by each use of a plaintext alphabet character;

the sender central processing unit further comprising a memory unit to store the addresses and their assigned numerical synonyms and plaintext alphabet characters;

c. a sender number generator to develop an initializing integer, transmitted to the receiver, which the sender central processing unit uses to determine the choices of the numerical synonyms, the assignment of alphabet characters to addresses, and the generation of transpositions of numerical synonyms;

d. a first number generator for each of the sender and receiver to generate a digit string to be used by sender and receiver to determine the sequence of numerical synonyms to be assigned to the sequentially labeled addresses;

e. a second number generator for each of the sender and receiver to generate a digit string to be used by sender and receiver to determine the assignment of plaintext alphabet characters to addresses;

f. a third number generator for each of the sender and receiver to generate a digit string to be used by sender and receiver to determine the transpositions of numerical synonyms associated with successive uses of plaintext alphabet characters;

g. a receiver central processing unit to receive an encrypted message and, utilizing the initializing integer and secret key, to decrypt each message, the receiver central processing unit comprising;

i. means for determining distinct numerical synonyms to be associated with each of the set of addresses of a set of addresses equal in number to those of the sender central processing unit, the numerical synonyms provided from a string of digits available to both sender and receiver;

ii. means for further assigning the plaintext alphabet characters to distinct addresses as determined by a digit string available to both sender and receiver;

iii. means for providing for the transposition of the numerical synonyms of plaintext alphabet characters, after each successive use of each alphabet character, with those at other addresses, as determined by a digit string available to both sender and receiver; and

iv. means for reproducing the plaintext message, having determined the correct alphabet characters to be associated with the received numerical synonyms;

the receiver central processing unit further comprising a memory to store the addresses and their assigned numerical synonyms and plaintext alphabet characters; and

h. a message delay unit for each of the sender and receiver central processing units to buffer alphabet characters or digit strings received by the sender or receiver central processing units, respectively.

2. The system of claim 1, wherein the initializing integer is transmitted with the encrypted message.

3. A cryptographic method between a sender and a receiver, the method comprising the steps of:

a. generating a pseudo-random initializing integer, by which, using a shared secret key, the sender and the receiver initialize number generators to determine their outputs and, hence, the choices of numerical synonyms, the assignment of alphabet characters to addresses, and the generation of transpositions of numerical synonyms;

b. generating a plaintext alphabet, each character of which is pseudo-randomly assigned its own unique address from a set of addresses, the cardinality of the set of addresses being at least as great as that of the plaintext alphabet;

c. assigning pseudo-randomly and one-to-one and onto, a set of distinct numerical synonyms to the set of addresses; and

d. determining pseudo-randomly a transposition of numerical synonyms between addresses each time a plaintext alphabet character appears in a plaintext message.

4. The method of claim 3, wherein the initializing integer is transmitted with the encrypted message.

5. The method of claim 3, wherein the sources for pseudo-randomly determining numerical synonyms, assignment of alphabet characters to addresses and transpositions of numerical synonyms are pseudo-random number generators or shared strings of random digits.