Abstract: A method and apparatus are disclosed for compressing Rabin signatures. The disclosed compression scheme compresses a Rabin signature, s, for a user having a public key, n, based on a continued fraction expansion of s/n. The continued fraction expansion of s/n can be performed by (i) computing principal convergents, ui/vi, for i equal to 1 to k, of a continued fraction expansion of s/n, where k is a largest integer for which principal convergents are defined; establishing an index l, such that vl<?{square root over (n)}?vl+1; and generating a compressed Rabin signature (vl, m) for a message, m.

Abstract: A system for, and method of, controlling access to a resource of a computer system. In one embodiment, the system includes: (1) a database of problems and corresponding precalculated solutions, (2) a problem retriever that responds to a request from a client for access to the resource by retrieving one of the problems from the database and transmitting the one of the problems to the client and (3) a solution evaluator that, upon receiving a putative solution from the client, employs the database to validate the putative solution and, if the putative solution is valid, grants the client access to the resource.

Abstract: A method and apparatus are disclosed for compressing Rabin signatures. The disclosed compression scheme compresses a Rabin signature, s, for a user having a public key, n, based on a continued fraction expansion of s/n. The continued fraction expansion of s/n can be performed by (i) computing principal convergents, ui/vi, for i equal to 1 to k, of a continued fraction expansion of s/n, where k is a largest integer for which principal convergents are defined; establishing an index l, such that vl<{square root}{square root over (n)}?vl+1; and generating a compressed Rabin signature (vl, m) for a message, m.

Abstract: A system for restricting access to transmitted programming content is disclosed, which transmits a program identifier with the encrypted programming content. A set-top terminal or similar mechanism restricts access to the transmitted multimedia information using stored decryption keys. The set-top terminal receives entitlement information periodically from the head-end, corresponding to one or more packages of programs that the customer is entitled to for a given period. Each program is encrypted by the head-end server prior to transmission, using a program key, Kp, which may be unique to the program. The set-top terminal uses the received program identifier, p, together with the stored entitlement information, to derive the decryption key necessary to decrypt the program. Each of the k-bit program keys, Kp, used to encrypt transmitted programs is obtained by applying one or more pseudo-random hash functions, H, such as a length-doubling hash function, H, to a master key, m.