Link to this headingCOMP128
Link to this headingImplementation
/* An implementation of the GSM A3A8 algorithm. (Specifically, COMP128.)
*
* Copyright 1998, Marc Briceno, Ian Goldberg, and David Wagner.
* All rights reserved.
*
* For expository purposes only. Coded in C merely because C is a much
* more precise, concise form of expression for these purposes. See Judge
* Patel if you have any problems with this...
* Of course, it's only authentication, so it should be exportable for the
* usual boring reasons.
*
*
* This software is free for commercial and non-commercial use as long as
* the following conditions are aheared to.
* Copyright remains the authors' and as such any Copyright notices in
* the code are not to be removed.
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* 1. Redistributions of source code must retain the copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED ``AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHORS OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*
* The license and distribution terms for any publicly available version or
* derivative of this code cannot be changed. i.e. this code cannot simply be
* copied and put under another distribution license
* [including the GNU Public License.]
*/
typedef unsigned char Byte;
/* #define TEST */
/*
* rand[0..15]: the challenge from the base station
* key[0..15]: the SIM's A3/A8 long-term key Ki
* simoutput[0..11]: what you'd get back if you fed rand and key to a real
* SIM.
*
* The GSM spec states that simoutput[0..3] is SRES,
* and simoutput[4..11] is Kc (the A5 session key).
* (See GSM 11.11, Section 8.16. See also the leaked document
* referenced below.)
* Note that Kc is bits 74..127 of the COMP128 output, followed by 10
* zeros.
* In other words, A5 is keyed with only 54 bits of entropy. This
* represents a deliberate weakening of the key used for voice privacy
* by a factor of over 1000.
*
* Verified with a Pacific Bell Schlumberger SIM. Your mileage may vary.
*
* Marc Briceno <[email protected]>, Ian Goldberg <[email protected]>,
* and David Wagner <[email protected]>
*/
void ;
/* The compression tables. */
static const Byte table_0 = , table_1 = , table_2 = , table_3 = , table_4 = , *table = ;
/*
* This code derived from a leaked document from the GSM standards.
* Some missing pieces were filled in by reverse-engineering a working SIM.
* We have verified that this is the correct COMP128 algorithm.
*
* The first page of the document identifies it as
* _Technical Information: GSM System Security Study_.
* 10-1617-01, 10th June 1988.
* The bottom of the title page is marked
* Racal Research Ltd.
* Worton Drive, Worton Grange Industrial Estate,
* Reading, Berks. RG2 0SB, England.
* Telephone: Reading (0734) 868601 Telex: 847152
* The relevant bits are in Part I, Section 20 (pages 66--67). Enjoy!
*
* Note: There are three typos in the spec (discovered by
* reverse-engineering).
* First, "z = (2 * x[n] + x[n]) mod 2^(9-j)" should clearly read
* "z = (2 * x[m] + x[n]) mod 2^(9-j)".
* Second, the "k" loop in the "Form bits from bytes" section is severely
* botched: the k index should run only from 0 to 3, and clearly the range
* on "the (8-k)th bit of byte j" is also off (should be 0..7, not 1..8,
* to be consistent with the subsequent section).
* Third, SRES is taken from the first 8 nibbles of x[], not the last 8 as
* claimed in the document. (And the document doesn't specify how Kc is
* derived, but that was also easily discovered with reverse engineering.)
* All of these typos have been corrected in the following code.
*/
void
int
int