Algorithm Identifier for CDMF

[Robert Hettinga]

Grab your ankles, ladies and gents. This won't hurt a bit...

Cheers,
Bob Hettinga

<Wait, isn't that a freight train in the distance?>

--- begin forwarded text


From: Bob Baldwin <baldwin at rsa.com>
To: "'set-dev'" <set-dev at terisa.com>
Subject: Algorithm Identifier for CDMF
Date: Wed, 8 Jan 1997 09:41:08 -0800
Mime-Version: 1.0
Sender: owner-set-dev at terisa.com
Precedence: bulk

	The SET protocol needs an algorithm identifier
for a 40 bit variant of des called CDMF for use
with the AcqBackMsg.  This note defines the value for
that identifier.
		--Bob Baldwin

--------------------------

          ALGORITHM IDENTIFIER FOR IBM's CDMF ALGORITHM


INTRODUCTION

The Commercial Data Masking Facility (CDMF) is an
application of DES that weakens the DES key from
56 to 40 bits using a key shortening algorithm
patented by IBM.  Licensing information for the CDMF
patent is available from the Director of Licensing,
IBM Corporation, 500 Columbus Avenue, Thornwood, NY 10594.

This note defines the ASN.1 algorithm identifier and algorithm
parameters for IBM's CDMF that has been registered by RSA Data
Security Inc.

RSA Data Security, Inc.'s Open Systems Interconnection (OSI) object
identifier is 1.2.840.113549 (2a, 0x86, 0x48, 0x86, 0xf7, 0x0d in hex),
as registered by the American National Standards Institute (ANSI).
In the following, the prefix "rsadsi" refers to that object identifier.
All object identifiers registered by RSA Data Security begin with this
prefix.


CDMFCBCPad

This is a Cipher Block Chaining mode of operation with padding
of a 40-bit variant of DES. It is defined in:

  IBM Journal of Research and Development, "The Commercial Data
  Masking Facility (CDMF) Data Privacy Algorithm", Volume 38,
  Number 2, March 1994.

Following the ASN.1 style of the "Agreements for Open Systems
Interconnection Protocols: Part 12 OS Security", it is defined by:

ALGORITHM MACRO ::=
BEGIN
 TYPE NOTATION ::= "PARAMETER" type
 VALUE NOTATION ::= value(VALUE OBJECT IDENTIFIER)
END -- of ALGORITHM

IV8 ::= OCTET STRING (SIZE(8))

CBC8Parameter ::= IV8

CDMFCBCPad ALGORITHM
 PARAMETER CBC8Parameter
 ::= {iso(1) member-body(2) US(840) rsadsi(113549)
      encryptionAlgorithm(3) 10}
-- In hex, the CDMFCBCPad algorithm ID is:
-- { 0x2a, 0x86, 0x48, 0x86, 0xf7, 0x0d, 0x03, 0x0A }

The PARAMETER is needed to specify the Initialization Vector,
which need not be kept secret. It is 8 octets long.

This mode should be used to encrypt multiple blocks, where the
full message is available. The random IV prevents codebook
analysis of the start of the chain. The IV may be public.

This mode will propagate a single bit error in one plaintext
block into all succeeding blocks, and will propagate a single bit
error in the ciphertext into a garbled plaintext block on
decryption as well as a single bit error in the next plaintext
block.

The following padding mechanism should be used if the data
to be encrypted is octet aligned, unless the security policy
dictates otherwise:

The input to the CDMF CBC encryption process must be padded to a
multiple of 8 octet, in the following manner.  Let n be the
length in octets of the input. Pad the input by appending 8-(n
mod 8) octet to the end of the message, each having the value
8-(n mod 8), the number of octets being added. In hexadecimal,
the  possible paddings  are: 01,  0202, 030303,  04040404,
0505050505, 060606060606, 07070707070707, and 0808080808080808.
All input is padded with 1 to 8 octets to produce a multiple of 8
octets in length. The padding can be removed unambiguously after
decryption.

Editor's Note - If adding the padding rules would cause
existing implementations to break, this should be registered
as a separate algorithm identifier.  Note, however, that
[FIPS 81] specifies its own padding rules for padding binary
data, in the absence of application-defined rules such as
those above; those rules require an indication (which could
be conveyed as an algorithm PARAMETER) of whether the data
has been padded or not.

--- end forwarded text



-----------------
Robert Hettinga (rah at shipwright.com), Philodox,
e$, 44 Farquhar Street, Boston, MA 02131 USA
"The cost of anything is the foregone alternative" -- Walter Johnson
The e$ Home Page: http://www.vmeng.com/rah/
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