Message format for secure communication over data links

• US 4,322,576 A
• Filed: 12/28/1979
• Issued: 03/30/1982
• Est. Priority Date: 12/28/1979
• Status: Expired due to Term

• Current Assignee: Racal-Guardata Limited
• Original Assignee: Racal-Milgo Incorporated
• Inventors: Miller, William J.
• Primary Examiner(s): Birmiel, Howard A.
• Application Number:
  US06/108,039
• Time in Patent Office: 823 Days
• Field of Search: 178/22, 375/2, 375/117, 375/36, 375/106, 375/107, 375/112, 375/114, 375/116, 370/49, 370/99
• US Class Current: 380/29
• CPC Class Codes: D21H 5/0002 Flame-resistant papers; (complex) compositions rendering paper fire-resistant
• CPC Class Codes: H04L 1/0083 Formatting with frames or packets; Protocol or part of protocol for error control
• CPC Class Codes: H04L 2209/60 Digital content management, e.g. content distribution
• CPC Class Codes: H04L 9/0625 with splitting of the data block into left and right halves, e.g. Feistel based algorithms, DES, FEAL, IDEA or KASUMI
• CPC Class Codes: H04L 9/0637 Modes of operation, e.g. cipher block chaining [CBC], electronic codebook [ECB] or Galois/counter mode [GCM]
• CPC Class Codes: H04L 9/12 Transmitting and receiving encryption devices synchronised or initially set up in a particular manner

Abstract

Communication over data links using binary synchronous protocol that is to be made secure according to the Federal data encryption standard (DES) is enhanced by utilizing an encrypted message format wherein the initialization vector for the DES algorithm is at the trailing end of the message. Additional information or control words may also be strung at the trailing end of the encrypted message format without causing throughput loss while enhancing the security and flexibility of the encrypted message in both point-to-point and multipoint systems.

Claims

1. In a data link communication system utilizing a synchronous protocol and having an encryption/decryption device at each end of the data link, the improvement in said encryption/decryption device comprising:

means for generating a multi-bit random number to be used as an initialization vector;

means for enciphering message text according to the DES algorithm in the cipher feedback mode; and

means for supplying said initialization vector to said enciphering means prior to the start of the next message enciphering, and supplying the same initialization vector to the receiving encryptor/decryptor device as the trailing end of the previous encrypted message, whereby said initializing vector is supplied to the deciphering portion of the receiving encryptor/decryptor device for the purpose of initializing it for reception of the next cipher.

2. The improvement of claim 1 wherein in addition to the multi-bit initialization vector said supplying means provide an information word at the trailing end of the encrypted message.

3. The improvement of claim 2 wherein the information word comprises ABORT characters.

4. The improvement of claim 2 wherein the information word comprises ETX characters and BCC characters transmitted in the clear.

5. The improvement of claim 2 wherein the information word comprises SEQ characters.

6. The improvement of claim 2 wherein the information word comprises SIG characters.

7. In a data link communication system utilizing a synchronous protocol and having a master encryption/decryption device at a central location and an encryption/decryption device at each of a plurality of tributary locations, said master encryption/decryption device storing a plurality of multi-bit secret keys, one for each of the tributary encryption/decryption devices, the improvement in the encryption/decryption device comprising:

means for storing a multi-bit random number to be used as an initialization vector;

means for enciphering message text according to the DES algorithm in the cipher feedback mode;

means for supplying the initialization vector to said message enciphering means prior to the start of the next message enciphering by said enciphering means; and

means for supplying the same initialization vector to each of the tributary encryption/decryption devices as the trailing end of the previous encrypted message whereby the initialization vector is supplied to the deciphering portion of each tributary encryption/decryption device for the purpose of initializing it for reception of the next cipher.

8. The improvement of claim 7 wherein in addition to the multi-bit initialization vector said supplying means provides an information word at the trailing end of the encrypted message.

9. The improvement of claim 8 wherein the information word comprises ABORT characters.

10. The improvement of claim 8 wherein the information word comprises ETX characters and BCC characters transmitted in the clear.

11. The improvement of claim 8 wherein the information word comprises SEQ characters.

12. The improvement of claim 8 wherein the information word comprises SIG characters.

13. In a data link communication system utilizing a synchronous protocol and having an encryption/decryption device at each end of the data link, one of the encryption/decryption devices being a master and the other being the tributary device, each encryption/decryption device enciphering and deciphering message text according to the DES algorithm in the cipher feedback mode with the use of a secret key for each data link, the initialization of the master and tributary encryption/decryption device prior to a cipher transmission being controlled by a multi-bit initialization vector genereated at the master encryption/decryption device and transmitted to the tributary encryption/decryption device, the improvement therein comprising:

means for supplying the initialization vector to the master encryption/decryption device prior to the start of the next message enciphering; and

means for supplying the same initialization vector to the tributary device as the trailing end of the previous encrypted message whereby said initializing vector is supplied to the deciphering portion of the tributary device for the purpose of initializing it for reception of the next cipher.

14. The improvement of claim 13 wherein in addition to the multi-bit initialization vector said supplying means provides an information word at the trailing end of the encrypted message.

15. The improvement of claim 14 wherein the information word comprises ABORT characters.

16. The improvement of claim 14 wherein the information word comprises ETX characters and BCC characters transmitted in the clear.

17. The improvement of claim 14 wherein the information word comprises SEQ characters.

18. The improvement of claim 14 wherein the information word comprises SIG characters.