Cryptography – Key management – Having particular key generator
Reexamination Certificate
1998-03-06
2002-01-15
Decady, Albert (Department: 2132)
Cryptography
Key management
Having particular key generator
C380S044000, C708S250000, C331S078000
Reexamination Certificate
active
06339645
ABSTRACT:
The present invention relates generally to the generation of pseudo-random number sequences used, for example, in encryption procedures. More particularly, the present invention relates to a pseudo-random number sequence generator, and an associated method, by which to generate a pseudo-random number sequence corresponding to a sequence generated by a selected windmill polynomial. The present invention further relates to a manner by which to determine compatibility between different configurations of windmill polynomial-based pseudo-random sequence generators.
Word-oriented memory elements are used to store words which form the pseudo-random number sequence. The sizes of the memory words are selected such that sizes of sequence portions generated by the windmill generator during successive iterations of operations can be readily increased, as desired, thereby to facilitate the generation of the same pseudo-random number sequence at increased rates, corresponding to alternate, compatible windmill generator constructions.
The pseudo-random number sequence generated through operation of an embodiment of the present invention is advantageously utilized as part of a system to encrypt data to be communicated over a radio link, such as a radio link formed between a mobile terminal and a radio base station of a cellular communication system. The pseudo-random number sequence generated through operation of an embodiment of the present invention is also advantageously utilized in spread-spectrum (e.g., Code Division Multiple Access) communications, in automated ranging systems, in voice signal compression methods, and in radar systems.
BACKGROUND OF THE INVENTION
A communication system is operable to communicate information between a sending station and a receiving station by way of a communication channel. In a wireline communication system, the communication channel is formed of a fixed connection between the sending and receiving stations. And, in a radio communication system, the communication channel forms a portion of the electromagnetic frequency spectrum. Because a fixed connection is not required to form the communication channel between the sending and receiving stations of a radio communication system, communications are possible when a fixed connection between the sending and receiving stations would be impractical.
A digital communication system is a communication system in which information to be communicated by a sending station to a receiving station is digitized. A digital communication system can be implemented in both a wireline communication system and a radio communication system. A digital communication system permits more efficient utilization of the communication channel extending between the sending and receiving stations, thereby permitting the communication capacity of the communication system to be increased over that of a conventional, analog communication system.
Communications between sending and receiving stations are sometimes desired to be private in nature. That is to say, parties sending and receiving the communication signals intend only for the sending and receiving parties to be able to access the informational content of the communication signals. Particularly when the communication channel is a radio communication channel of a radio communication system, privacy of the communications between the sending and receiving stations becomes problematical. As a radio channel is inherently public in nature, a communication signal transmitted upon the radio communication channel can be detected by any receiving station, within range of the communication signal, and tuned to the radio channel. An unauthorized party, for instance, is able to tune a radio receiver to the frequency of the radio channel upon which the communication signal is transmitted, thereby to receive the communication signal. Analogous security problems are also of concern in wireline communication systems in the event that an unauthorized party gains access to the wireline communication channel.
One manner by which to improve the security of communications in a communication system is to encrypt the information forming a communication signal into encrypted form. If only authorized parties are able to de-encrypt the encrypted communication signal, an unauthorized party is unable to discern the informational content of the communication signal transmitted upon the communication channel. Thereby, privacy of communications is better assured.
A digital information signal is particularly amenable to an encryption process. A digital information signal is formed of sequences of bits, and each bit, if desired, of the information signal can be encoded into encrypted form at the sending station prior to its transmission upon the communication channel. An unauthorized party, without knowledge of the manner by which the information signal is encrypted is unable to de-encrypt a receive signal to recover the informational content of the transmitted signal. Only a receiving station capable of de-encrypting the encrypted signal is able to recover the informational content of the receive signal.
Various manners are used by which to encrypt the digital information signal. A typical encryption scheme, such as that used in cellular communications, utilizes an encryption process by which the digitized bits of an information signal are combined with the bits of a pseudo-random sequence generated by a pseudo-random sequence generator. The pseudo-random sequence generator is operable in conjunction with a secret key which, in a symmetrical encryption technique, is known to the sending station and to an authorized receiving station. The secret key is used at the authorized receiving station to de-encrypt the encrypted signal received thereat, thereby to recover the informational content of the transmitted signal.
The pseudo-random number sequences are sometimes derived by the calculation of a windmill polynomial. Constructions, whether hardware or software implemented, which form pseudo-random number sequences in this manner are sometimes referred to as windmill generators. Output bits generated by a windmill generator form the pseudo-random number sequences which are used, inter alia, to encrypt an information signal. A windmill generator is directly related to a selected, primitive polynomial over some finite field GF(q). When q=2, the finite field GF(
2
) is referred to as the binary case and is of significance particularly in digital communications. The number of primitive polynomials from which a windmill generator can be derived is limited due to many constraints placed on the polynomial. Especially in the binary case when the polynomial is required to exhibit, to minimize processing operations needed to generate outputs therefrom, only a few non-zero coefficients, the number of suitable polynomials which can be used to form a windmill polynomial is limited. The number of non-zero coefficients of a polynomial is referred to as the weight of the polynomial.
Tables exist which list primitive polynomials, such as, for the binary case of GF(
2
), primitive polynomials with three or five non-zero coefficients and with degrees of up to five thousand.
The randomness of outputs, sometimes herein referred to as “n-tuples”, generated by a binary windmill polynomial of weight=3 is generally poor, so to increase the randomness of the outputs, a high-weight polynomial is required. But, such improved randomness occurs at the expense of increased processing requirements. Existing tables cannot always be used to select a windmill polynomial suitable from which to derive a pseudo-random number sequence as such existing tables do not necessarily show all primitive polynomials with a selected, e.g., three or five, number of non-zero coefficients. Particularly when the pseudo-random number sequences are used for an encryption process, knowledge of all windmill polynomials of a selected degree over the finite field GF(
2
) is valuable. Methods are not available by which to derive such knowledge. Instead, conventi
De'cady Albert
Jenkens & Gilchrist
Kabakoff Stephen
Telefonaktiebolaget LM Ericsson (publ)
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