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Browse Prior Art Database

Triple Data Encryption Standard Cipher Block Chaining Mode With Data Encryption Standard-X

IP.com Disclosure Number: IPCOM000118341D
Original Publication Date: 1996-Dec-01
Included in the Prior Art Database: 2005-Apr-01
Document File: 2 page(s) / 64K

Publishing Venue

IBM

Related People

Coppersmith, D: AUTHOR [+2]

Abstract

Disclosed is a method for enhancing Data Encryption Standard (DES) key security using a cryptographic algorithm called DES-X. DES-X was invented by Ron Rivest, one of the inventors of the RSA algorithm. This disclosure shows how the Electronic Code Book (ECB) mode of DES-X can be extended to define a Cipher Block Chaining (CBC) mode of DES-X.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Triple Data Encryption Standard Cipher Block Chaining Mode With Data
Encryption Standard-X

      Disclosed is a method for enhancing Data Encryption Standard
(DES) key security using a cryptographic algorithm called DES-X.
DES-X was invented by Ron Rivest, one of the inventors of the RSA
algorithm.  This disclosure shows how the Electronic Code Book (ECB)
mode of DES-X can be extended to define a Cipher Block Chaining (CBC)
mode of DES-X.

      The DES-X algorithm is based on the DES.  DES-X uses one
encryption operation and two Exclusive-OR operations, together with 3
independent 64-bit keys (K1, K2, and K3).  A 64-bit input X is
encrypted with DES-X as follows: (1) K1 is Exclusive-ORed with the
input X, (2) the output of step 1 is encrypted with the DES using K2,
and (3) the output of step 2 is Exclusive-ORed with K3 to produce the
64-bit output Y.  Since K2 is a DES key, only 56 bits of the key are
independent key bits.  However, K1 and K3 have 64 independent key
bits.  DES-X decryption is the inverse operation consisting of an
Exclusive-OR operation with K3, DES decryption with K2, and an
Exclusive-OR operation with K1.

      The straightforward way to implement a DES-X CBC mode would be
to employ a feedback from the ciphertext to the plaintext, that is,
to Exclusive-OR ciphertext Yi with plaintext Xi+1 prior to the
encryption operation on Xi+1.  However, one can see that this causes
the input Xi+1 to be masked with Yi, K1, and K3, where K1 and K3 are
secret quantities and Yi is a nonsecret quantity.

      An alternative method for obtaining a Cipher Block Chaining
mode with DES-X is suggested.  It is noted that the cryptographic
security of the DES-X mode itself is based on hiding or masking the
input a...