Probabilistic cryptographic processing method

US5235644A · kind A · utility

Assignee

• Digital Equipment Corporation · US

Inventors

• Amar Gupta · Marlborough, US
• Butler W. Lampson · Portola Valley, US
• William Hawe · Pepperell, US
• Joseph Tardo · Palo Alto, US
• Charles W. Kaufman · Northborough, US
• Mark F. Kempf · Glen Ellyn, US
• Morrie Gasser · Hopkinton, US
• B. J. Herbison · Bolton, US

Key dates

• Filing date: Jun 29, 1990
• Grant date: Aug 10, 1993
• Expiry date: Jun 29, 2010

Classification

• Technology area (CPC H): Electricity
• CPC primary: H04L2209/125
• WIPO field: Control
• WIPO sector: Instruments

Abstract

A decryption method, and associated cryptographic processor, for performing in-line decryption of information frames received from a communication network through a first in-line processing stage. As an information packet is streamed into the cryptographic processor, a determination is made to an acceptable level of probability whether the packet contains data that should be decrypted. The decision whether or not decrypt is made by analyzing the incoming packet header, recognizing a limited number of packet formats, and further parsing the packet to locate any encrypted data and to make sure that the packet is not a segment of a larger message. Falsely decrypted packets are looped back through the cryptographic processor, to regenerate the data that was falsely decrypted. Decryption and encryption are performed in such a manner that a false decryption is completely reversible without loss of data. Special treatment is provided for packets containing data that cannot be divided into an integral number of standard blocks required for decryption processing.