Browse Prior Art Database

Memory Privacy Device

IP.com Disclosure Number: IPCOM000076811D
Original Publication Date: 1972-Apr-01
Included in the Prior Art Database: 2005-Feb-24
Document File: 2 page(s) / 24K

Publishing Venue

IBM

Related People

Painter, JA: AUTHOR

Abstract

A data processing system is shown having a "privacy device" 10 inserted in the data flow path, between the memory bus 11 (to one or more memory units 12) and each central processing unit (CPU) 13 and I/O device 14. When data is transferred from a user (via I/O) or a using CPU to memory, it is encrypted by the privacy device. When it is transferred from memory to a user, it is decrypted by the privacy device.

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Memory Privacy Device

A data processing system is shown having a "privacy device" 10 inserted in the data flow path, between the memory bus 11 (to one or more memory units
12) and each central processing unit (CPU) 13 and I/O device 14. When data is transferred from a user (via I/O) or a using CPU to memory, it is encrypted by the privacy device. When it is transferred from memory to a user, it is decrypted by the privacy device.

The privacy device includes a small high-speed memory 15 of 2/n/ words of M bits each, where M is the number of bits in the data path and n is a design parameter. During initialization, the memory is filled with the keys for encryption and decryption, each user being assigned 2/n/ words of key. Whenever he is allocated a resource by the supervisor, the supervisor initializes the appropriate privacy device with the user's key. During encryption, a memory address and M bits of data are sent from the user to the privacy device. The low-order n bits of the memory address are used to select one word from the 2n words of the privacy device memory. The entire memory address is sent unchanged to the memory bus. The user supplied data and the contents of the selected word of the privacy device memory are combined bit-by-bit via an "exclusive OR" function to encrypt the data. During decryption, the encrypted data is "exclusive OR"ed with the same selected word and sent to the user as decrypted data.

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