METHOD AND APPARATUS FOR RE-SYNCHRONIZATION OF A STREAM CIPHER DURING HANDOFF

• US 20080013730A1
• Filed: 12/22/2006
• Published: 01/17/2008
• Est. Priority Date: 11/11/1999
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Rose, Gregory
• Granted Patent: US 8,538,024 B2
• Time in Patent Office: Days
• US Class Current: 380/272
• CPC Class Codes: H04L 2209/80 Wireless network architectures or network communication protocols for wireless network security H04W12/00
• CPC Class Codes: H04L 9/065 Encryption by serially and continuously modifying data stream elements, e.g. stream cipher systems, RC4, SEAL or A5/3
• CPC Class Codes: H04L 9/0891 Revocation or update of secret information, e.g. encryption key update or rekeying
• CPC Class Codes: H04L 9/12 Transmitting and receiving encryption devices synchronised or initially set up in a particular manner
• CPC Class Codes: H04W 12/041 Key generation or derivation
• CPC Class Codes: H04W 36/0038 of security context information
• CPC Class Codes: H04W 36/08 Reselecting an access point

Abstract

A method and apparatus for re-synchronizing a stream cipher during soft handoff. Transmitted quasi-secret keying information is used with a secret key to reinitialize a stream cipher generator located in a base station and a stream cipher generator located in a travelling mobile station. Since the quasi-secret keying information is uniquely determined according to each base station in the wireless telephone system, a base station'"'"'s quasi-secret keying information and a shared secret key can also be used to create a new key. Thus, as the mobile station travels from one base station to another base station, a unique new key is generated for each base station.

Claims

1. A method for synchronizing a stream cipher during a mobile station handoff between a first base station and a second base station, comprising:

transmitting a quasi-secret key from the first base station;

initializing the stream cipher based on the quasi-secret key and a secret key at the first base station.

2. The method of claim 1, wherein initializing the stream cipher comprises:

generating a new key from the quasi-secret key and the secret key.

3. The method of claim 2, wherein the quasi-secret key comprises unique non-secret information.

4. The method of claim 1, further comprising:

generating the quasi-secret key from a handoff number, wherein the handoff number indicates the number of base stations with which the mobile station has communicated during a call period.

5. The method of claim 1, further comprising:

generating the quasi-secret key at the first base station.

6. A method for synchronizing a stream cipher during a mobile station handoff between a first base station and a second base station comprising:

receiving a quasi-secret key at the second base station;

using the quasi-secret key and a secret key at the second base station to initialize a stream cipher generator.

7. The method of claim 6, wherein initializing the stream cipher comprises:

generating a new key from the quasi-secret key and the secret key.

8. The method of claim 7, wherein the quasi-secret key comprises unique non-secret information.

9. The method of claim 6, further comprising:

generating the quasi-secret key from a handoff number, wherein the handoff number indicates the number of base stations with which the mobile station has communicated during a call period.

10. The method of claim 6, further comprising:

generating the quasi-secret key from a random number broadcast, wherein the random number broadcast is made by the second base station.

11. Apparatus for synchronizing a stream cipher during a mobile station handoff between a first base station and a second base station comprising:

means for transmitting a quasi-secret key from the first base station;

means for initializing the stream cipher based on the quasi-secret key and a secret key at the first base station.

12. A apparatus for synchronizing a stream cipher during a mobile station handoff between a first base station and a second base station, comprising:

means for receiving a quasi-secret key at the second base station;

means for using the quasi-secret key and a secret key at the second base station to initialize a stream cipher generator.

13. A method for synchronizing a stream cipher during a mobile station handoff between a first base station and a second base station, comprising:

transmitting a quasi-secret key from the first base station;

generating a new key based on the quasi-secret key and a secret key at the first base station.

14. The method of claim 13, wherein generating a new key comprises:

adding the quasi-secret key and the secret key.

15. The method of claim 13, wherein generating a new key comprises:

using the quasi-secret key and the secret key as an input into a hashing function; and

using an output of the hashing function as the new key.

16. A method for synchronizing a stream cipher during a mobile station handoff between a first base station and a second base station comprising:

receiving a quasi-secret key at the second base station;

generating a new key based on the quasi-secret key and a secret key at the second base station.

17. The method of claim 16, wherein generating a new key comprises:

adding the quasi-secret key and the secret key.

18. The method of claim 16, wherein generating a new key comprises:

using the quasi-secret key and the secret key as an input into a hashing function; and

using an output of the hashing function as the new key.

19. Apparatus for synchronizing a stream cipher during a mobile station handoff, comprising:

means for transmitting a quasi-secret key from a base station;

means for generating a new key based on the quasi-secret key and a secret key at a base station.

20. Apparatus for synchronizing a stream cipher during a mobile station handoff, comprising:

means for receiving a quasi-secret key at a base station;

means for generating a new key based on the quasi-secret key and a secret key at the base station.