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Creating 40-Bit Keys for DES

Document Type Expired Internet-Draft (individual)
Expired & archived
Authors Russ Housley , Paul E. Hoffman
Last updated 1999-05-03
RFC stream (None)
Intended RFC status (None)
Stream Stream state (No stream defined)
Consensus boilerplate Unknown
RFC Editor Note (None)
IESG IESG state Expired
Telechat date (None)
Responsible AD (None)
Send notices to (None)

This Internet-Draft is no longer active. A copy of the expired Internet-Draft is available in these formats:


This document describes an method for shortening DES keys from 56 bits to 40 bits. The shortened keys are generally known as 'DES-40'. The motivation for this weakening is that some localities (such as the United States) give special preference to applications that use 40-bit keys. The weakened keys are then used with the DES encryption algorithm in the same manner as full-strength keys. There are many possible methods for reducing a 56-bit key to a 40-bit key. The method in this draft was chosen because one method is needed for interoperability. Further, this method has been known to occasionally have been approved for export from the United States.


Russ Housley
Paul E. Hoffman

(Note: The e-mail addresses provided for the authors of this Internet-Draft may no longer be valid.)