Browse Prior Art Database

OTAR USING ONE-TIME PADS

IP.com Disclosure Number: IPCOM000007912D
Original Publication Date: 1996-Nov-01
Included in the Prior Art Database: 2002-May-03
Document File: 1 page(s) / 55K

Publishing Venue

Motorola

Related People

Thomas P. Ryan: AUTHOR [+2]

Abstract

The system is conventional Over-The-Air- Rekeying (OTAR) or is trunking OTAR. OTAR mes- sages, which contain traffic encryption keys (TEKs), are sent from a Key Management Facility (KMF). These OTAR messages are sent to the radio encrypted with the key encryption key (KEK) ofthe radio.

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Technical Developments

OTAR USING ONE-TIME PADS

by Thomas I? Ryan and Hans Christopher Sowa

SYSTEM BACKGROUND:

THE SOLUTION:

  The system is conventional Over-The-Air- Rekeying (OTAR) or is trunking OTAR. OTAR mes- sages, which contain traffic encryption keys (TEKs), are sent from a Key Management Facility (KMF). These OTAR messages are sent to the radio encrypted with the key encryption key (KEK) ofthe radio. THE PROBLEM:

  A cryptanalyst given enough time and processing power will break an encryption key. By attacking a KEK used to encrypt an OTAR message, an adver- sary will know several TEKs at once when the KEK is broken. Further, the KEK is generally changed infrequently so breaking the KEK not only gives an adversary the present TEKs but also TEKs from sev- eral crypt0 periods if all OTAR messages to that unit have been recorded It is in an adversary's advan- tage to attack the KEK first, since more can be gained by attacking a KEK.

  A one-time pad is used to encrypt TEKs sent using OTAR. One-time pads are considered to be the only known unbreakable encryption scheme regardless of time and processing power. Attacking the OTAR message encrypted with a one-time pad is hopeless since it is unbreakable. This forces an adversary to attack the system by attacking each TEK individually as it is used in a voice or data message. This requires an adversary to spend much more time and processing power to break the TEKs.

  The KMF and radio will share a pad (a set of non-rep...