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| -rw-r--r-- | A5.1/C/calculate_chain.c | 367 |
1 files changed, 367 insertions, 0 deletions
diff --git a/A5.1/C/calculate_chain.c b/A5.1/C/calculate_chain.c new file mode 100644 index 0000000..23361a3 --- /dev/null +++ b/A5.1/C/calculate_chain.c @@ -0,0 +1,367 @@ +/* + * A pedagogical implementation of A5/1. + * + * Copyright (C) 1998-1999: Marc Briceno, Ian Goldberg, and David Wagner + * + * The source code below is optimized for instructional value and clarity. + * Performance will be terrible, but that's not the point. + * The algorithm is written in the C programming language to avoid ambiguities + * inherent to the English language. Complain to the 9th Circuit of Appeals + * if you have a problem with that. + * + * This software may be export-controlled by US law. + * + * 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.] + * + * Background: The Global System for Mobile communications is the most widely + * deployed cellular telephony system in the world. GSM makes use of + * four core cryptographic algorithms, neither of which has been published by + * the GSM MOU. This failure to subject the algorithms to public review is all + * the more puzzling given that over 100 million GSM + * subscribers are expected to rely on the claimed security of the system. + * + * The four core GSM algorithms are: + * A3 authentication algorithm + * A5/1 "strong" over-the-air voice-privacy algorithm + * A5/2 "weak" over-the-air voice-privacy algorithm + * A8 voice-privacy key generation algorithm + * + * In April of 1998, our group showed that COMP128, the algorithm used by the + * overwhelming majority of GSM providers for both A3 and A8 + * functionality was fatally flawed and allowed for cloning of GSM mobile + * phones. + * Furthermore, we demonstrated that all A8 implementations we could locate, + * including the few that did not use COMP128 for key generation, had been + * deliberately weakened by reducing the keyspace from 64 bits to 54 bits. + * The remaining 10 bits are simply set to zero! + * + * See http://www.scard.org/gsm for additional information. + * + * The question so far unanswered is if A5/1, the "stronger" of the two + * widely deployed voice-privacy algorithm is at least as strong as the + * key. Meaning: "Does A5/1 have a work factor of at least 54 bits"? + * Absent a publicly available A5/1 reference implementation, this question + * could not be answered. We hope that our reference implementation below, + * which has been verified against official A5/1 test vectors, will provide + * the cryptographic community with the base on which to construct the + * answer to this important question. + * + * Initial indications about the strength of A5/1 are not encouraging. + * A variant of A5, while not A5/1 itself, has been estimated to have a + * work factor of well below 54 bits. See http://jya.com/crack-a5.htm for + * background information and references. + * + * With COMP128 broken and A5/1 published below, we will now turn our attention + * to A5/2. The latter has been acknowledged by the GSM community to have + * been specifically designed by intelligence agencies for lack of security. + * + * We hope to publish A5/2 later this year. + * + * -- Marc Briceno <marc@scard.org> + * Voice: +1 (925) 798-4042 + * + */ + + +#include <stdio.h> +#include <stdlib.h> +#include <unistd.h> +#include <string.h> +#include <math.h> + +/* Masks for the three shift registers */ +#define R1MASK 0x07FFFF /* 19 bits, numbered 0..18 */ +#define R2MASK 0x3FFFFF /* 22 bits, numbered 0..21 */ +#define R3MASK 0x7FFFFF /* 23 bits, numbered 0..22 */ + +/* Middle bit of each of the three shift registers, for clock control */ +#define R1MID 0x000100 /* bit 8 */ +#define R2MID 0x000400 /* bit 10 */ +#define R3MID 0x000400 /* bit 10 */ + +/* Feedback taps, for clocking the shift registers. + * These correspond to the primitive polynomials + * x^19 + x^5 + x^2 + x + 1, x^22 + x + 1, + * and x^23 + x^15 + x^2 + x + 1. */ +#define R1TAPS 0x072000 /* bits 18,17,16,13 */ +#define R2TAPS 0x300000 /* bits 21,20 */ +#define R3TAPS 0x700080 /* bits 22,21,20,7 */ + +/* Output taps, for output generation */ +#define R1OUT 0x040000 /* bit 18 (the high bit) */ +#define R2OUT 0x200000 /* bit 21 (the high bit) */ +#define R3OUT 0x400000 /* bit 22 (the high bit) */ + +typedef unsigned char byte; +typedef unsigned long word; +typedef word bit; + +/* Calculate the parity of a 32-bit word, i.e. the sum of its bits modulo 2 */ +bit parity(word x) { + x ^= x>>16; + x ^= x>>8; + x ^= x>>4; + x ^= x>>2; + x ^= x>>1; + return x&1; +} + +/* Clock one shift register */ +word clockone(word reg, word mask, word taps) { + word t = reg & taps; + reg = (reg << 1) & mask; + reg |= parity(t); + return reg; +} + +/* The three shift registers. They're in global variables to make the code + * easier to understand. + * A better implementation would not use global variables. */ +word R1, R2, R3; + +/* Look at the middle bits of R1,R2,R3, take a vote, and + * return the majority value of those 3 bits. */ +bit majority() { + int sum; + sum = parity(R1&R1MID) + parity(R2&R2MID) + parity(R3&R3MID); + if (sum >= 2) + return 1; + else + return 0; +} + +/* Clock two or three of R1,R2,R3, with clock control + * according to their middle bits. + * Specifically, we clock Ri whenever Ri's middle bit + * agrees with the majority value of the three middle bits.*/ +inline void clock() { + bit maj = majority(); + if (((R1&R1MID)!=0) == maj) + R1 = clockone(R1, R1MASK, R1TAPS); + if (((R2&R2MID)!=0) == maj) + R2 = clockone(R2, R2MASK, R2TAPS); + if (((R3&R3MID)!=0) == maj) + R3 = clockone(R3, R3MASK, R3TAPS); +} + +/* Clock all three of R1,R2,R3, ignoring their middle bits. + * This is only used for key setup. */ +void clockallthree() { + R1 = clockone(R1, R1MASK, R1TAPS); + R2 = clockone(R2, R2MASK, R2TAPS); + R3 = clockone(R3, R3MASK, R3TAPS); +} + +/* Generate an output bit from the current state. + * You grab a bit from each register via the output generation taps; + * then you XOR the resulting three bits. */ +bit getbit() { + return parity(R1&R1OUT)^parity(R2&R2OUT)^parity(R3&R3OUT); +} + +/* Do the A5/1 key setup. This routine accepts a 64-bit key and + * a 22-bit frame number. */ +void keysetup(byte key[8], word frame) { + int i; + bit keybit, framebit; + + /* Zero out the shift registers. */ + R1 = R2 = R3 = 0; + + /* Load the key into the shift registers, + * LSB of first byte of key array first, + * clocking each register once for every + * key bit loaded. (The usual clock + * control rule is temporarily disabled.) */ + for (i=0; i<64; i++) { + clockallthree(); /* always clock */ + keybit = (key[i/8] >> (i&7)) & 1; /* The i-th bit of the key */ + R1 ^= keybit; R2 ^= keybit; R3 ^= keybit; + } + + /* Load the frame number into the shift + * registers, LSB first, + * clocking each register once for every + * key bit loaded. (The usual clock + * control rule is still disabled.) */ + for (i=0; i<22; i++) { + clockallthree(); /* always clock */ + framebit = (frame >> i) & 1; /* The i-th bit of the frame # */ + R1 ^= framebit; R2 ^= framebit; R3 ^= framebit; + } + + /* Run the shift registers for 100 clocks + * to mix the keying material and frame number + * together with output generation disabled, + * so that there is sufficient avalanche. + * We re-enable the majority-based clock control + * rule from now on. */ + for (i=0; i<100; i++) { + clock(); + } + + /* Now the key is properly set up. */ +} + +/* Generate output. We generate 228 bits of + * keystream output. The first 114 bits is for + * the A->B frame; the next 114 bits is for the + * B->A frame. You allocate a 15-byte buffer + * for each direction, and this function fills + * it in. */ +void run(byte AtoBkeystream[], byte BtoAkeystream[]) { + int i; + + /* Zero out the output buffers. */ + for (i=0; i<=113/8; i++) + AtoBkeystream[i] = BtoAkeystream[i] = 0; + + /* Generate 114 bits of keystream for the + * A->B direction. Store it, MSB first. */ + for (i=0; i<114; i++) { + clock(); + AtoBkeystream[i/8] |= getbit() << (7-(i&7)); + } + + /* Generate 114 bits of keystream for the + * B->A direction. Store it, MSB first. */ + for (i=0; i<114; i++) { + clock(); + BtoAkeystream[i/8] |= getbit() << (7-(i&7)); + } +} + +/* Test the code by comparing it against + * a known-good test vector. */ +void test() { + byte key[8] = {0x12, 0x23, 0x45, 0x67, 0x89, 0xAB, 0xCD, 0xEF}; + word frame = 0x134; + byte goodAtoB[15] = { 0x53, 0x4E, 0xAA, 0x58, 0x2F, 0xE8, 0x15, + 0x1A, 0xB6, 0xE1, 0x85, 0x5A, 0x72, 0x8C, 0x00 }; + byte goodBtoA[15] = { 0x24, 0xFD, 0x35, 0xA3, 0x5D, 0x5F, 0xB6, + 0x52, 0x6D, 0x32, 0xF9, 0x06, 0xDF, 0x1A, 0xC0 }; + byte AtoB[15], BtoA[15]; + int i, failed=0; + + keysetup(key, frame); + run(AtoB, BtoA); + + /* Compare against the test vector. */ + for (i=0; i<15; i++) + if (AtoB[i] != goodAtoB[i]) + failed = 1; + for (i=0; i<15; i++) + if (BtoA[i] != goodBtoA[i]) + failed = 1; + + /* Print some debugging output. */ + printf("key: 0x"); + for (i=0; i<8; i++) + printf("%02X", key[i]); + printf("\n"); + printf("frame number: 0x%06X\n", (unsigned int)frame); + printf("known good output:\n"); + printf(" A->B: 0x"); + for (i=0; i<15; i++) + printf("%02X", goodAtoB[i]); + printf(" B->A: 0x"); + for (i=0; i<15; i++) + printf("%02X", goodBtoA[i]); + printf("\n"); + printf("observed output:\n"); + printf(" A->B: 0x"); + for (i=0; i<15; i++) + printf("%02X", AtoB[i]); + printf(" B->A: 0x"); + for (i=0; i<15; i++) + printf("%02X", BtoA[i]); + printf("\n"); + + if (!failed) { + printf("Self-check succeeded: everything looks ok.\n"); + return; + } else { + /* Problems! The test vectors didn't compare*/ + printf("\nI don't know why this broke; contact the authors.\n"); + exit(1); + } +} + +word bin2hex (char *string) +{ + int i; + word res = 0; + int length; + + length = strlen (string); + + for (i = 0; i < length; i++) + { + res = res << 1; + if (string[0] == '1') res += 1; + string++; + } + return res; + +} + +inline word calculate_link (word input, word count) { + word result=0; + int i; + + input ^= count ^ (count << 23) ^ (count << (22 + 23)); + + R1 = (input >> (22 + 23)) & R1MASK; + R2 = (input >> 23) & R2MASK; + R3 = input & R3MASK; + + for(i=0;i<64;i++) { + result = (result << 1)| getbit(); + clock(); + } + return result; +} + + +int main(int argc, char* argv[]) { + int i,j; + word current; + + sscanf(argv[1], "%16lx", ¤t); + + for(i=pow(2,21);i>0;i--) { + current = calculate_link(current, i); + } + + printf("%16.16lx\n", current); + return 0; +} |