Patent ID: 6014446
Filing Date: 2000-01-11
Classification: H03K,H04L

Abstract:
An encryption method for generating a unique keystream output value for every frame of bearer traffic to provide an output from a combination of x(n+1).sub.low and x(n+1).sub.high in accordance with equations of a form:x(n+1).sub.low ={x(n).sub.low *R1.sub.low +R2.sub.low } mod R3.sub.lowx(n+1).sub.high ={x(n).sub.high *R2.sub.high +R1.sub.high } mod R3.sub.highwhere R1, R2, and R3 are linear feedback shift registers, R4 is a shift control register coupled to a clock utilized for tap configuration control of R1, R2 and R3, and values x(n) and x(n+1) represent previous and current output values, the encryption method comprising the steps of:initializing R1, R2, R3 and R4 according to a predetermined scheme;generating the output by operating on one of:a first and second predetermined selection of bits of registers R1, R2, and R3; andwhere the first selection of bits are represented by Rx.sub.low and the second selection of bits are represented by Rx.sub.high, respectively, where x=1, 2, 3;setting a two most significant bits of the first selection of bits and of the second selection of bits in register R3 to `11`;processing x(n+1) in separate low and high bit portions, wherein the low and high bit portions are determined by computing:x(n+1).sub.low ={x(n).sub.low *R1.sub.low +R2.sub.low } mod R3.sub.lowx(n+1).sub.high ={x(n).sub.high *R2.sub.high +R1.sub.high } mod R3.sub.highthen rotating the low portion a first predetermined number of bits, and the high portion a second predetermined number of bits and producing a keystream output value by a logic exclusive-OR operation on rotated high and low portions.