Generating a symmetric key to secure a communication link

• US 9,071,426 B2
• Filed: 11/29/2013
• Issued: 06/30/2015
• Est. Priority Date: 04/04/2005
• Status: Active Grant

• Current Assignee: Malikie Innovations Limited (Key Patent Innovations Limited)
• Original Assignee: Blackberry Limited
• Inventors: Brown, Michael Kenneth, Little, Herbert Anthony, Brown, Michael Stephen, Adams, Neil Patrick
• Primary Examiner(s): Schwartz, Darren B
• Application Number:
  US14/093,253
• Publication Number:
  US 20140237246A1
• Time in Patent Office: 578 Days
• US Class Current: 1/1
• CPC Class Codes: H04L 63/0435 wherein the sending and receiving network entities apply symmetric encryption, i.e. same key used for encryption and decryption cryptographic mechanisms or cryptographic arrangements for symmetric key encryption H04L9/06
• CPC Class Codes: H04L 63/062 for key distribution, e.g. centrally by trusted party cryptographic mechanisms or cryptographic arrangements for key distribution involving a central third party H04L9/0819
• CPC Class Codes: H04L 63/0853 using an additional device, e.g. smartcard, SIM or a different communication terminal cryptographic mechanisms or cryptographic arrangements for entity authentication involving additional secure or trusted devices H04L9/3234
• CPC Class Codes: H04L 63/205 involving negotiation or determination of the one or more network security mechanisms to be used, e.g. by negotiation between the client and the server or between peers or by selection according to the capabilities of the entities involved negotiation of communication capabilities H04L69/24
• CPC Class Codes: H04L 9/0861 Generation of secret information including derivation or calculation of cryptographic keys or passwords
• CPC Class Codes: H04L 9/0869 involving random numbers or seeds
• CPC Class Codes: H04W 12/04 Key management, e.g. using generic bootstrapping architecture [GBA]
• CPC Class Codes: H04W 12/06 Authentication
• CPC Class Codes: H04W 12/50 Secure pairing of devices
• CPC Class Codes: H04W 88/02 Terminal devices

Abstract

A symmetric key to be used to secure a communication link between a first device and a second device is generated as follows: a first symmetric key is generated; a second symmetric key is generated; packets communicated between the first device and the second device over communication link are hashed to create a hash result; the first symmetric key, the second symmetric key and the hash result are hashed to generate a third symmetric key to be used to secure the communication link.

Claims

1. A method for securing a communication link between a first device and a second device, the method comprising:

the first device generating a first symmetric key, wherein generating the first symmetric key includes the first device sending to the second device a first public key in one or more first packets over the communication link and the first device receiving from the second device a second public key in one or more second packets over the communication link, the first public key and the second public key both based on a secret shared by the first device and the second device;

the first device generating a second symmetric key, wherein generating the second symmetric key includes the first device sending to the second device a third public key in one or more third packets over the communication link and the first device receiving from the second device a fourth public key in one or more fourth packets over the communication link;

the first device creating a hash result by hashing the one or more first packets, the one or more second packets, the one or more third packets and the one or more fourth packets;

the first device generating a third symmetric key by hashing the first symmetric key, the second symmetric key and the hash result; and

one or more of the following;

the first device encrypting first data using a symmetric algorithm keyed by the third symmetric key to produce first encrypted data, and sending to the second device the first encrypted data over the communication link;

or

the first device receiving from the second device second encrypted data over the communication link, and decrypting the second encrypted data using the symmetric algorithm keyed by the third symmetric key to produce decrypted data.

2. The method of claim 1, wherein generating the first symmetric key includes:

the first device applying a function to the secret to obtain a generator element of a mathematical group;

the first device raising the generator element to a first random number to obtain another element of the group;

the first device sending the other element, which is the first public key, to the second device over the communication link;

the first device receiving from the second device over the communication link a further element of the group, which is the second public key, the further element having been created by the second device raising the generator element to a second random number; and

the first device raising the further element to the first random number to obtain the first symmetric key.

3. The method of claim 1, wherein the third public key and the fourth public key are generated according to a Diffie-Hellman algorithm on an elliptical curve group.

4. The method of claim 1, wherein the third public key and the fourth public key are generated according to a Diffie-Hellman algorithm on a large prime-order finite group.

5. The method of claim 1, wherein generating the second symmetric key includes:

the first device raising a known generator element of a mathematical group to a first random number to obtain another element of the group;

the first device sending the other element, which is the third public kev, to the second device over the communication link;

the first device receiving from the second device over the communication link a further element of the group, which is the fourth public key, the further element having been created by the second device raising the known generator element to a second random number; and

the first device raising the further element to the first random number to obtain the second symmetric key.

6. The method of claim 1, wherein hashing the one or more first packets, the one or more second packets, the one or more third packets and the one or more fourth packets comprises hashing the one or more first packets, the one or more second packets, the one or more third packets and the one or more fourth packets according to a Secure Hashing Algorithm 2 (SHA-2).

7. The method of claim 1, wherein hashing the one or more first packets, the one or more second packets, the one or more third packets and the one or more fourth packets comprises hashing the one or more first packets, the one or more second packets, the one or more third packets and the one or more fourth packets according to a Message Digest 5 (MD5) algorithm.

8. The method of claim 1, wherein hashing the one or more first packets, the one or more second packets, the one or more third packets and the one or more fourth packets employs a first hash function and hashing the first symmetric key, the second symmetric key and the hash result employs a second hash function that differs from the first hash function.

9. The method of claim 1, wherein hashing the one or more first packets, the one or more second packets, the one or more third packets and the one or more fourth packets employs a first hash function and hashing the first symmetric key, the second symmetric key and the hash result employs the first hash function.

10. The method of claim 1, wherein the first data is a hash of contents of a message.

11. The method of claim 1, wherein the first data is a hash of contents of a message to be sent by the first device, the method further comprising:

the first device receiving from the second device over the communication link a digital signature produced by the second device from the hash; and

the first device transmitting the digital signature and the message to a recipient.

12. The method of claim 1, wherein the decrypted data is a session key.

13. The method of claim 12, the method further comprising:

the first device decrypting a received message using a symmetric algorithm keyed by the session key.

14. A first device comprising:

a processor;

a communication interface through which the first device is able to establish a communication link with a second device, the communication interface coupled to the processor; and

a memory able to store executable code which, when executed by the processor, causes the first device to;

generate a first symmetric key, wherein generating the first symmetric key includes the first device sending to the second device a first public key in one or more first packets over the communication link and the first device receiving from the second device a second public key in one or more second packets over the communication link, the first public key and the second public key both based on a secret shared by the first device and the second device;

generate a second symmetric key, wherein generating the second symmetric key includes the first device sending to the second device a third public key in one or more third packets over the communication link and the first device receiving from the second device a fourth public key in one or more fourth packets over the communication link;

create a hash result by hashing the one or more first packets, the one or more second packets, the one or more third packets and the one or more fourth packets;

generate a third symmetric key by hashing the first symmetric key, the second symmetric key and the hash result; and

one or more of the following;

encrypt first data using a symmetric algorithm keyed by the third symmetric key to produce first encrypted data, and send to the second device the first encrypted data over the communication link;

or

receive from the second device second encrypted data over the communication link, and decrypt the second encrypted data using the symmetric algorithm keyed by the third symmetric key to produce decrypted data.

15. The first device of claim 14, wherein generating the first symmetric key includes:

the first device applying a function to the secret to obtain a generator element of a mathematical group;

the first device raising the generator element to a first random number to obtain another element of the group;

the first device sending the other element, which is the first public key, to the second device over the communication link;

the first device receiving from the second device over the communication link a further element of the group, which is the second public key, the further element having been created by the second device raising the generator element to a second random number; and

the first device raising the further element to the first random number to obtain the first symmetric key.

16. The first device of claim 14, wherein the third public key and the fourth public key are generated according to a Diffie-Hellman algorithm on an elliptical curve group.

17. The first device of claim 14, wherein the third public key and the fourth public key are generated according to a Diffie-Hellman algorithm on a large prime-order finite group.

18. The first device of claim 14, wherein generating the second symmetric key includes:

the first device raising a known generator element of a mathematical group to a first random number to obtain another element of the group;

the first device sending the other element, which is the third public key, to the second device over the communication link;

the first device receiving from the second device over the communication link a further element of the group, which is the fourth public key, the further element having been created by the second device raising the known generator element to a second random number; and

the first device raising the further element to the first random number to obtain the second symmetric key.

19. The first device of claim 14, wherein the first data is a hash of contents of a message.

20. The first device of claim 14, wherein the first data is a hash of contents of a message to be sent by the first device, and the executable code, when executed by the processor, causes the first device to:

receive from the second device over the communication link a digital signature produced by the second device from the hash; and

transmit the digital signature and the message to a recipient.

21. The first device of claim 14, wherein the decrypted data is a session key.

22. The first device of claim 21, wherein the executable code, when executed by the processor, causes the first device to decrypt a received message using a symmetric algorithm keyed by the session key.

23. A non-transitory computer-readable medium having stored thereon instructions which, when executed by a first device, result in:

generating a first symmetric key, wherein generating the first symmetric key includes the first device sending to a second device a first public key in one or more first packets over a communication link and the first device receiving from the second device a second public key in one or more second packets over the communication link, the first public key and the second public key both based on a secret shared by the first device and the second device;

generating a second symmetric key, wherein generating the second symmetric key includes the first device sending to the second device a third public key in one or more third packets over the communication link and the first device receiving from the second device a fourth public key in one or more fourth packets over the communication link;

creating a hash result by hashing the one or more first packets, the one or more second packets, the one or more third packets and the one or more fourth packets;

generating a third symmetric key by hashing the first symmetric key, the second symmetric key and the hash result; and

one or more of the following;

encrypting first data using a symmetric algorithm keyed by the third symmetric key to produce first encrypted data, and sending to the second device the first encrypted data over the communication link;

or

receiving from the second device second encrypted data over the communication link, and decrypting the second encrypted data using the symmetric algorithm keyed by the third symmetric key to produce decrypted data.