The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
Nov. 16, 1999
Filed:
Aug. 18, 1997
Craig S Clapp, Boxford, MA (US);
PictureTel Corporation, Andover, MA (US);
Abstract
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.