Cryptographic key management apparatus and method

• US 5,341,426 A
• Filed: 12/15/1992
• Issued: 08/23/1994
• Est. Priority Date: 12/15/1992
• Status: Expired due to Term

• Current Assignee: General Dynamics C4 Systems Incorporated (General Dynamics Corporation)
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Barney, George M., Hardy, Douglas A., Balogh, Craig R.
• Primary Examiner(s): Gregory, Bernarr E.
• Application Number:
  US07/991,054
• Time in Patent Office: 616 Days
• Field of Search: 380/9, 380/21, 380/23, 380/25, 380/28, 380/29, 380/30, 380/43, 380/44, 380/45, 380/46, 380/47, 380/49, 380/50, 380/48
• US Class Current: 713/171
• CPC Class Codes: H04L 9/0844 with user authentication or key authentication, e.g. ElGamal, MTI, MQV-Menezes-Qu-Vanstone protocol or Diffie-Hellman protocols using implicitly-certified keys
• CPC Class Codes: H04L 9/12 Transmitting and receiving encryption devices synchronised or initially set up in a particular manner

Abstract

A method for establishing a secure communications link between first and second terminals includes a step of exchanging a first message. The first message contains information describing encryption devices and communications modes available within the terminals and user authentication information. The method also includes a step of selecting, in at least one terminal, a common key generation and ciphering algorithm. The method further includes steps of exchanging a second message for providing data to form traffic keys, exchanging a third message for synchronizing secure communications and initiating secure communication.

Claims

1. A method for establishing a communications link between first and second terminals for exchanging encrypted information, wherein the first and second terminals follow a procedure including steps of:

(a) exchanging a first message containing plaintext information identifying encryption devices and communication modes available within the first and second terminals and containing public key encrypted information describing user authentication information;

(b) selecting in at least one of the first and second terminals a common key generation and encryption and decryption methods;

(c) exchanging a second message containing public-key encrypted data for forming traffic keys;

(d) exchanging a third message for synchronizing encrypted communications; and

(e) initiating encrypted conununication.

2. A method as claimed in claim 1, wherein said step (a) further includes steps of:

(a1) forming in the first terminal a first portion of the first message which contains data indicating a message type, a first terminal type, a label identifying a public decryption key and a label identifying encryption and decryption capabilities of the first terminal, the first portion being plaintext;

(a2) forming in the first terminal a second portion of the first message which contains user identification information, a security activation key serial number, a terminal serial number for the first terminal, a public key expiration date and a first public key encryption vector; and

(a3) forming the second portion of the first message using a fourth message from a key certification authority which may be decrypted using the public decryption key labelled in the first portion of the first message formed in the first terminal.

3. A method as claimed in claim 2, wherein said step (c) further includes steps of:

(c1) generating a first pseudorandom number in the first terminal;

(c2) encrypting the first pseudorandom number using the first public key encryption vector to provide a first encrypted pseudorandom number in the first terminal;

(c3) generating a second pseudorandom number in the second terminal;

(c4) encrypting the second pseudorandom number using a second public key encryption vector to provide a second encrypted pseudorandom number in the second terminal;

(c5) exchanging the first and second encrypted pseudorandom numbers between the first and second terminals; and

(c6) forming identical traffic keys in the first and second terminals from the first and second pseudorandom numbers.

4. A method as claimed in claim 3, wherein said step (c6) further includes steps of:

(c7) decrypting the second encrypted pseudorandom number in the first terminal to provide a decrypted second pseudorandom number;

(c8) combining the decrypted second pseudorandom number with the first pseudorandom number to form a third pseudorandom number, the third pseudorandom number comprising a first traffic key; and

(c9) using the first traffic key as an encryption and decryption key for the conunon encryption and decryption methods selected in said step (b).

5. A method as claimed in claim 3, wherein said step (c6) further includes steps of:

(c10) decrypting the first encrypted pseudorandom number in the second terminal to provide a decrypted first pseudorandom number;

(c11) combining the decrypted first pseudorandom number with the second pseudorandom number to form a fourth pseudorandom number, the fourth pseudorandom number comprising a second traffic key; and

(c12) using the second traffic key as an encryption and decryption for the common encryption and decryption methods selected in said step (b).

6. A method as claimed in claim 1, wherein said step (d) further includes steps of:

(d1) encrypting a known data pattern using the information from said step (c) to provide an encrypted known data pattern;

(d2) transmitting the encrypted known data pattern;

(d3) receiving the encrypted known data pattern as a received encrypted known data pattern;

(d4) decrypting the received encrypted known data pattern using a traffic key derived from said step (c) to form a decrypted received encrypted known data pattern; and

(d5) comparing the decrypted received encrypted known data pattern to a stored known data pattern to determine agreement.

7. A method for establishing a communication link between at least a first and a second terminal, wherein each of the first and second terminals follows a procedure comprising steps of:

(a) transmitting a first message comprising an Authentication Package for Data, the Authentication Package for Data identifying encryption and decryption capabilities, certified user authentication data and a first public encryption key;

(b) receiving a second message comprising an Authentication Package for Data, the Authentication Package for Data identifying encryption and decryption capabilities, certified user authentication data and a second public encryption key;

(c) transmitting a first Random Component Message including a first pseudorandom number;

(d) receiving a second Random Component Message including a second pseudorandom number;

(e) forming a traffic key from the first and second pseudorandom numbers;

(f) interchanging Cryptographic Synchronization messages; and

(g) initiating interchange of encrypted information.

8. A method as claimed in claim 7, wherein said step (a) further includes steps of:

(a1) identifying encryption and decryption capabilities in plaintext;

(a2) identifying a third public decryption key in plaintext;

(a3) identifying a security activation key serial number in public key encrypted ciphertext; and

(a4) providing a public key encryption vector in ciphertext encrypted using a third encryption key which is privately held in a key certifying authority.

9. A method as claimed in claim 8, wherein said step (a) further includes steps of:

(a5) identifying a terminal serial number in public key encrypted ciphertext encrypted using the third enciphering key;

(a6) identifying a first public key encryption vector expiration date in public key encrypted ciphertext encrypted using the third encryption key; and

(a7) providing the first public key encryption vector in public key encrypted ciphertext encrypted using the third encryption key.

10. A method as claimed in claim 7, wherein said step (a) further includes steps of:

exchanging a first portion or header of the Authentication Package for Data which is plaintext; and

exchanging a second part or body of the Authentication Package for Data encrypted using a public encryption key corresponding to the third public decryption key, wherein the third public decryption key is labelled in the first portion or header of the Authentication Package for Data.

11. A method as claimed in claim 7, wherein said step (a) further includes a step of selecting encryption and decryption algorithms common to both the first and second terminals according to an automatic programmed hierarchy of encrypted information interchange methods.

12. An apparatus for providing encrypted communication between first and second terminals, said apparatus comprising:

means for encrypting and decrypting using a plurality of different encryption and decryption algorithms;

means for transmitting messages, said transmitting means coupled to said encrypting and decrypting means;

means for receiving messages, said receiving means coupled to said encrypting and decrypting means; and

controller means coupled to said encrypting and decrypting, transmitting and receiving means, said controller means, transmitting means and receiving means for;

(i) sending a first message to said second terminal, the first message comprising a first plaintext portion providing information identifying encryption and decryption algorithms and communication modes available within said first terminal and comprising a second encrypted portion identifying terminal authentication information;

(ii) sending a second message to said second terminal for providing pseudorandom data; and

(iii) initiating encrypted communication with said second terminal using a traffic key formed from said pseudoramdom data.

13. An apparatus as claimed in claim 12, wherein said controller means further comprises means for sending a third message to said second terminal for synchronizing said encrypted communication.

14. An apparatus as claimed in claim 12, wherein said receiving means further comprises means for receiving from said second terminal plaintext information identifying encryption and decryption algorithms and communication modes available in said second terminal and wherein said controller means further comprises means for selecting encryption and decryption algorithms and a data rate common to said first and second terminals.

15. An apparatus as claimed in claim 14, further comprising means for storing within said apparatus information concerning which encryption and decryption algorithms and conununication modes are preferred, so that if more than one encryption and decryption algorithm or communication mode are common to said first and second terminals, said controller means automatically chooses an encryption and decryption algorithm or communication mode to be used, according to stored preference information.

16. An apparatus as claimed in claim 12, further comprising means for generating a first pseudorandom number for transmission to said second terminal, said generating means coupled to said encrypting and decrypting means and to said transmitting means.

17. An apparatus as claimed in claim 16, further comprising means for combining said first pseudorandom number with a second pseudorandom number received from said second terminal to form said traffic key for encrypting messages sent therebetween, said combining means coupled to said encrypting and decrypting means and to said generating means.

18. A communication apparatus comprising:

means for providing different encryption modes, decryption modes and conununication modes;

means for sending messages including a first capabilities and authentication message to and receiving messages including a second capabilities and authentication message from another conununication apparatus, said first and said second capabilities and authentication messages having predetermined plaintext data fields identifying said different encryption modes, decryption modes and communication modes resident in said communication apparatus and in said another communication apparatus, having further predetermined plaintext data fields labelling current and previous public decryption keys and having predetermined encrypted data fields providing a user public key; and

means for comparing said first and said second capabilities and authentication messages to identify and select compatible encryption modes, compatible decryption modes and compatible communication modes according to a stored preference protocol.

19. An apparatus as claimed in claim 18, further including:

means for generating, encrypting and transmitting a first pseudorandom number to said another communication apparatus;

means for receiving and decrypting a second pseudorandom nunsher from said another communication apparatus; and

means for combining said first and second pseudorandom numbers to form a traffic key for use with said compatible encryption mode.

20. An apparatus as claimed in claim 19, further including:

means for decrypting said predetermined encrypted data fields of said second capabilities and authentication message from said another communication apparatus to decrypt said user public key to provide a decrypted user public key; and

wherein said receiving and decrypting means employs said decrypted user public key to decrypt said second pseudorandom number.