Method and apparatus for encryption having a feedback register with selectable taps

A communication device for use in maintaining secure communications through an encryption process between a subscriber unit and a fixed network communication unit of a serving communication system, comprising:

• (a) a pseudo-random bit sequence generator means for generating a non-linear pseudo-random bit sequence, the pseudo-random bit sequence generator means comprising:
• (i) shift register means for storing a predetermined number of bits;
• (ii) first feedback means, coupled to the shift register means, for determining a first input bit as a function of bits stored in the shift register means;
• (iii) second feedback means, coupled to the shift register means, for determining a second input bit as a function of bits stored in the shift register means;
• and
• (iv) control means, coupled to the shift register means, the first feedback means, and the second feedback means, for deterministically selecting and providing a particular input bit to the shift register means, the particular input bit being selected from the group consisting of the first input bit and the second input bit;
• (b) encrypting means, coupled to the pseudo-random bit sequence generator means, for encrypting an input information signal as a function of the non-linear pseudo-random bit sequence;
• and
• (c) transmitting means, coupled to the encrypting means, for transmitting the encrypted information signal over a communication channel.

A communication device for use in maintaining secure communications through an encryption process between a subscriber unit and a fixed network communication unit of a serving communication system, comprising:

• (a) receiving means for receiving an encrypted information signal from a communication channel.
• (b) a pseudo-random bit sequence generator means for generating a non-linear pseudo-random bit sequence, the pseudo-random bit sequence generator means comprising:
• (i) shift register means for storing a predetermined number of bits;
• (ii) first feedback means, coupled to the shift register means, for determining a first input bit as a function of bits stored in the shift register means;
• (iii) second feedback means, coupled to the shift register means, for determining a second input bit as a function of bits stored in the shift register means;
• and
• (iv) control means, coupled to the shift register means, the first feedback means, and the second feedback means, for deterministically selecting and providing a particular input bit to the shift register means, the particular input bit being selected from the group consisting of the first input bit and the second input bit;
• and
• (c) decrypting means, coupled to the receiving means and the pseudo-random bit sequence generator means, for decrypting the received encrypted information signal as a function of the non-linear pseudo-random bit sequence.

A method for generating a pseudo-random bit sequence, comprising:

• (a) determining a first input bit as a function of bits stored in a shift register in accordance with a first feedback algorithm;
• (b) determining a second input bit as a function of bits stored in the shift register in accordance with a second feedback algorithm;
• and
• (c) deterministically selecting and providing a particular input bit to the shift register and producing a non-linear pseudo random sequence by the shift register, the particular input bit being selected from the group consisting of the first input bit and the second input bit.