Picturetel Corporation

Craig S Clapp

Anthony M Duys

A public-key method of cryptographic key exchange using modular exponentiation in which memory, for storing pre-computed results, can be flexibly traded off against the computational complexity of key-exchange. In a typical embodiment, the invention performs key exchange by the method of Diffie-Hellman but with exponents having a constrained form such that by use of a small table of pre-computed powers of a user's public key, any possible shared secret key within the allowed set can be computed with many fewer modular multiplications than the number of bits of effective key-length thereby obtained. The table of pre-computed powers is transmitted as part of the key exchange protocol. The party in receipt of the table uses the pre-computed powers of the sender's public key to replace calculations that would otherwise need to be done at key-exchange time. The method allows a flexible trade-off between computation and table size. The method of accelerating modular exponentiation can also be applied to other cryptographic operations in which the number to be raised to a power is fixed or known in advance and where the exponent is allowed to be of the specified form.

Cryptographic key exchange using pre-computation

In a finite state machine having a plurality of registers, a stream of pseudo-random numbers is generated by a method having characteristic non-zero integral value N. Repeatedly, over a series of time steps, a set of N combined values is calculated by applying N non-linear combining functions to N input sets of values and registering each combined value in one of N registers. At any time step after N time steps each input set consists of combined values, except that one input set may include as one value the result of combining a combined value with a value from an input stream, and at least two input sets comprise only registered values from distinct registers.

Pseudo-random number generator capable of efficiently exploiting

A finite state machine for producing a stream of pseudo-random numbers, having characteristic positive integral values S and T. The finite state machine has a w-bit non-linear combiner having an input and an output, a plurality of w-bit registers including at least a chained series of S registers and a chained series of T registers. The non-linear combiner receives as the input data from the last of the chained series of S registers and from the last of the chained series of T registers. The first of the chained series of T registers receives input from the last of the chained series of S registers. The first of the chained series of S registers receives input from the output of the non-linear combiner.

w-bit non-linear combiner for pseudo-random number generation

A camera stand for directing a video camera at, alternately, a room scene and a document scene, where the document in the document scene is oriented to be read by a person seated in the room scene, featuring a supporting arm and a rotatable connection connecting the video camera to, and supporting the video camera at a supporting end of, the arm. The rotatable connection allows the video camera to be alternately rotated between a position directed substantially vertically down at the document scene and a position directed substantially horizontally at the room scene. The rotatable connection has a rotation axis inclined at substantially a forty-five degree angle to the vertical, and is connected to the arm so that the video camera rotates from viewing the room scene right-side-up to viewing the document scene right-side-up.

Growing community of inventors

Boxford, MA, United States of America

Craig S Clapp