System and method for encrypting information within a communications network

(54) SYSTEM AND METHOD FOR ENCRYPTING INFORMATION WITHIN A COMMUNICATIONS NETWORK

(75) Inventor: Robert T. Bell, Bountiful, UT (US)

(73) Assignee: Cisco Technology, Inc., San Jose, CA (US)

( * ) Notice: Subject to any disclaimer, the term of this patent is extended or adjusted under 35 U.S.C. 154(b) by 0 days.

(21) Appl. No.: 09/450,861

(22) Filed: Nov. 29, 1999

(51) Int. CI.7 G06F 01/24

(52) U.S. CI 380/46; 380/23; 380/43;

380/50

(58) Field of Search 380/46, 43, 50,

380/23

(56) References Cited

U.S. PATENT DOCUMENTS

5,008,938 A * 4/1991 Freeburg et al 380/265

6,560,727 Bl * 5/2003 Pierson et al 714/704

* cited by examiner

Primary Examiner—-Thomas R. Peeso

(74) Attorney, Agent, or Firm—Baker Botts L.L.P.

(57) ABSTRACT

Within a communications system, first and second end stations coupled to a network participate in a communications session with one another using the network. Each end station includes an encryptor having at least a first linear feedback shift register (LFSR) and at least an associated first interconnect mask of a length not longer than the length of the first LFSR. At a particular one of the end stations, the encryptor generates an output sequence using the first LFSR and the first interconnect mask. An interconnect mask table contains polynomials that each correspond to an available interconnect mask. The end station receives a session key specifying the first interconnect mask. The end station uses the output sequence of the encryptor to encrypt an information stream during the session. In one particular embodiment, the network includes a local area network (LAN) that supports Internet Protocol (IP) and the end stations use real time protocol (RTP) to communicate audio information streams.

41 Claims, 4 Drawing Sheets