Data encryption technique

• US 6,088,456 A
• Filed: 11/13/1997
• Issued: 07/11/2000
• Est. Priority Date: 11/15/1996
• Status: Expired due to Fees

• Current Assignee: Desktop Guardian Limited
• Original Assignee: Desktop Guardian Limited
• Inventors: Leith, James Milne, Burey, William Richard, McCracken, Douglas William
• Primary Examiner(s): Swann, Tod R.
• Assistant Examiner(s): Callahan, Paul E.
• Application Number:
  US08/969,668
• Time in Patent Office: 971 Days
• Field of Search: 380/255, 380/277, 380/259, 380/262, 380/268, 380/280, 380/283, 380/282
• US Class Current: 380/259
• CPC Class Codes: H04L 2209/30 Compression, e.g. Merkle-Damgard construction
• CPC Class Codes: H04L 9/0656 Pseudorandom key sequence combined element-for-element with data sequence, e.g. one-time-pad [OTP] or Vernam's cipher

Abstract

A method of encrypting data is described in which a random variable (6A-6D) is generated in binary digital form. A first set of data (8A-8J) representing a plaintext message in binary digital form is combined with the random variable (6A-6D) to generate a second data set (9A-9J) in binary digital form. The data bits representing the random variable (6A-6D) are inserted into the second data set (9A-9J) according to a first predetermined set of rules and the order of the data bits in the second data set (9A-9J) is altered according to a second predetermined set of rules. A third data set (17A-17N) for transmission as a ciphertext message is thus generated.

Claims

1. A method of encrypting data in which:

a random variable for use as a key is generated in binary digital form,

a first set of data representing a plaintext message in binary digital form is combined with the random variable to generate a second data set in binary digital form,

the data bits representing the random variable are inserted into the second data set according to a first predetermined set of rules,

and the order of the data bits in the second data set is altered according to a second predetermined set of rules, thereby generating a third data set for transmission as a ciphertext message,

said third data set containing in encrypted form the data representing both the plaintext message and the key.

2. A method according to claim 1, in which the first set of data is combined with the random variable by means of the XOR function.

3. A method according to claim 1, in which the random variable comprises a plurality of random numbers and those random numbers are combined with the first set of data according to a third predetermined set of rules.

4. A method according to claim 3, in which the first set of data is combined by means of the XOR function with the random numbers a plurality of times, the order of said random numbers being changed each time.

5. A method according to claim 3, in which the first set of data, the random numbers and the modified data set are all in the form of 8-bit words.

6. A method according to claim 5, in which the second data set is divided into 5-bit words, which are expanded to 7-bit words by the inclusion of the data representing the random numbers and then re-divided into 8-bit words.

7. A method according to claim 6, in which the plaintext message is encrypted in groups of ten characters, which are represented in the first data set as ten 8-bit words and are combined with four 8-bit random numbers to produce a third data set of fourteen 8-bit words.

8. A method according to claim 7, in which a plaintext message of ten characters is converted to a ciphertext message of fourteen characters during encryption.

9. A method according to claim 1, in which the plaintext message is compressed prior to encryption.

10. A method according to claim 1, in which a message header is added to the plaintext message and is encrypted together with the plaintext message.

11. A method according to claim 10, in which the message header includes data identifying the intended recipient of the plaintext message.

12. A method according to claim 11, in which the message header includes data identifying the sender of the plaintext message.

13. A method according to claim 12, in which the identity of the sender is verified before data identifying the sender is included in the message header.

14. A method of decrypting data that has been encrypted using a method according to claim 1, in which:

the data bits representing the random variable are extracted from the third data set according to a first predetermined set of complementary rules,

the random variable representing the key is recreated from the extracted data bits,

the order of the data in the third data set is altered according to a second predetermined set of complementary rules to regenerate the second data set,

and the second data set is combined with the random variable representing the key to regenerate the first set of digital data representing the plaintext message.

15. A method of decrypting data that has been encrypted using a method according to claim 10, in which:

the data bits representing the random variable are extracted from the third data set according to a first predetermined set of complementary rules,

the random variable representing the key is recreated from the extracted data bits,

the order of the data in the third data set is altered according to a second predetermined set of complementary rules to regenerate the second data set,

and the second data set is combined with the random variable representing the key to regenerate the first set of digital data representing the plaintext message, and

the message header is decrypted before the plaintext message.

16. A method according to claim 15, in which the message header includes data identifying the intended recipient of the plaintext message and, after receiving, the data identifying the intended recipient of the plaintext message is extracted, the identity of the actual recipient is verified and the plaintext message is decrypted only if the actual recipient is the intended recipient.

25. A method according to claim 1, in which the data representing a plaintext message is divided into a plurality of data blocks, and each data block is combined with a different random variable to generate the second data set.

17. A method of encrypting and decrypting data, in which a random variable for use as a key is generated in binary digital form,

a first set of data representing a plaintext message in binary digital form is combined with the random variable to generate a second data set in binary digital form,

the data bits representing the random variable are inserted into the second data set according to a first predetermined set of rules,

and the order of the data bits in the second data set is altered according to a second predetermined set of rules, thereby generating a third data set for transmission as a ciphertext message,

said third data set containing in encrypted form the data representing both the plaintext message and the key,

the data bits representing the random variable are extracted from the third data set according to a first predetermined set of complementary rules,

the random variable representing the key is recreated from the extracted data bits,

the order of the data in the third data set is altered according to a second predetermined set of complementary rules to regenerate the second data set,

and the second data set is combined with the random variable representing the key to regenerate the first set of digital data representing the plaintext message.

22. A method of manufacturing means for implementing an encryption and decryption method according to claim 17, the method including the steps of:

extracting data representing complementary sets of predetermined rules from a database,

processing the data representing the complementary sets of predetermined rules to incorporate those rules into algorithms for encrypting and decrypting the data,

and recording data representing those algorithms in a data recording means for use in implementing the encryption and decryption methods.

23. A method according to claim 22, in which after the data representing complementary sets of predetermined rules has been extracted from the database, the database is marked to prevent those rules being used again.

24. A method according to claim 23, in which the steps of extracting the complementary sets of predetermined rules from the database and incorporating those rules into the algorithms for encrypting and decrypting the data are carried out automatically and without any record being made of the predetermined rules incorporated into the means for implementing the encryption and decryption methods.

18. A device for decrypting data, the device including:

input means for receiving a first set of data representing a plaintext message in binary digital form,

generator means for generating a random variable for use as a key in binary digital form,

processor means for combining said first set of data with said random variable to generate a second data set in binary digital form, for inserting the data bits representing the random variable into the second data set according to a first predetermined set of rules and for altering the order of the data bits in the second data set according to a second predetermined set of rules, thereby generating a third data set representing a ciphertext message,

said third data set containing in encrypted form the data representing both the plaintext message and the key,

and output means for transmitting said ciphertext message.

19. A device according to claim 18, in which said processor means includes means for adding to said ciphertext message an encrypted message header containing data identifying the intended recipient of the message.

20. A device for decrypting data that has been encrypted using a device according to claim 18, said device including:

input means for receiving said ciphertext message,

processor means for extracting data bits representing said random variable from said ciphertext message according to a first predetermined set of complementary rules, for altering the order of the data in said ciphertext message according to a second predetermined set of complementary rules, for recreating the random variable representing the key from the extracted data bits, and for combining data in said ciphertext message with the random variable representing the key to regenerate the plaintext message,

and output means for said plaintext message.

21. A device according to claim 20, in which said processor means includes means for extracting from said encrypted message header said data identifying the intended recipient of the message, verifying the identity of the actual recipient and comparing the identity of the actual recipient with that of the intended recipient, said processor means being arranged to decrypt said ciphertext message only if the actual recipient is the intended recipient.