//-----------------------------------------------------------------------------
// Borrowed initially from https://github.com/holiman/loclass
// Copyright (C) 2014 Martin Holst Swende
// Copyright (C) Proxmark3 contributors. See AUTHORS.md for details.
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU General Public License for more details.
//
// See LICENSE.txt for the text of the license.
//-----------------------------------------------------------------------------
// WARNING
//
// THIS CODE IS CREATED FOR EXPERIMENTATION AND EDUCATIONAL USE ONLY.
//
// USAGE OF THIS CODE IN OTHER WAYS MAY INFRINGE UPON THE INTELLECTUAL
// PROPERTY OF OTHER PARTIES, SUCH AS INSIDE SECURE AND HID GLOBAL,
// AND MAY EXPOSE YOU TO AN INFRINGEMENT ACTION FROM THOSE PARTIES.
//
// THIS CODE SHOULD NEVER BE USED TO INFRINGE PATENTS OR INTELLECTUAL PROPERTY RIGHTS.
//-----------------------------------------------------------------------------
// It is a reconstruction of the cipher engine used in iClass, and RFID techology.
//
// The implementation is based on the work performed by
// Flavio D. Garcia, Gerhard de Koning Gans, Roel Verdult and
// Milosch Meriac in the paper "Dismantling IClass".
//-----------------------------------------------------------------------------
/**
From "Dismantling iclass":
This section describes in detail the built-in key diversification algorithm of iClass.
Besides the obvious purpose of deriving a card key from a master key, this
algorithm intends to circumvent weaknesses in the cipher by preventing the
usage of certain ‘weak’ keys. In order to compute a diversified key, the iClass
reader first encrypts the card identity id with the master key K, using single
DES. The resulting ciphertext is then input to a function called loclass_hash0 which
outputs the diversified key k.
k = loclass_hash0(DES enc (id, K))
Here the DES encryption of id with master key K outputs a cryptogram c
of 64 bits. These 64 bits are divided as c = x, y, z [0] , . . . , z [7] ∈ F 82 × F 82 × (F 62 ) 8
which is used as input to the loclass_hash0 function. This function introduces some
obfuscation by performing a number of permutations, complement and modulo
operations, see Figure 2.5. Besides that, it checks for and removes patterns like
similar key bytes, which could produce a strong bias in the cipher. Finally, the
output of loclass_hash0 is the diversified card key k = k [0] , . . . , k [7] ∈ (F 82 ) 8 .
**/
#include "optimized_ikeys.h"
#include <stdint.h>
#include <stdbool.h>
#include <inttypes.h>
#include <mbedtls/des.h>
#include "optimized_cipherutils.h"
static const uint8_t loclass_pi[35] = {
0x0F, 0x17, 0x1B, 0x1D, 0x1E, 0x27, 0x2B, 0x2D,
0x2E, 0x33, 0x35, 0x39, 0x36, 0x3A, 0x3C, 0x47,
0x4B, 0x4D, 0x4E, 0x53, 0x55, 0x56, 0x59, 0x5A,
0x5C, 0x63, 0x65, 0x66, 0x69, 0x6A, 0x6C, 0x71,
0x72, 0x74, 0x78
};
/**
* @brief The key diversification algorithm uses 6-bit bytes.
* This implementation uses 64 bit uint to pack seven of them into one
* variable. When they are there, they are placed as follows:
* XXXX XXXX N0 .... N7, occupying the last 48 bits.
*
* This function picks out one from such a collection
* @param all
* @param n bitnumber
* @return
*/
static uint8_t loclass_getSixBitByte(uint64_t c, int n) {
return (c >> (42 - 6 * n)) & 0x3F;
}
/**
* @brief Puts back a six-bit 'byte' into a uint64_t.
* @param c buffer
* @param z the value to place there
* @param n bitnumber.
*/
static void loclass_pushbackSixBitByte(uint64_t *c, uint8_t z, int n) {
//0x XXXX YYYY ZZZZ ZZZZ ZZZZ
// ^z0 ^z7
//z0: 1111 1100 0000 0000
uint64_t masked = z & 0x3F;
uint64_t eraser = 0x3F;
masked <<= 42 - 6 * n;
eraser <<= 42 - 6 * n;
//masked <<= 6*n;
//eraser <<= 6*n;
eraser = ~eraser;
(*c) &= eraser;
(*c) |= masked;
}
/**
* @brief Swaps the z-values.
* If the input value has format XYZ0Z1...Z7, the output will have the format
* XYZ7Z6...Z0 instead
* @param c
* @return
*/
static uint64_t loclass_swapZvalues(uint64_t c) {
uint64_t newz = 0;
loclass_pushbackSixBitByte(&newz, loclass_getSixBitByte(c, 0), 7);
loclass_pushbackSixBitByte(&newz, loclass_getSixBitByte(c, 1), 6);
loclass_pushbackSixBitByte(&newz, loclass_getSixBitByte(c, 2), 5);
loclass_pushbackSixBitByte(&newz, loclass_getSixBitByte(c, 3), 4);
loclass_pushbackSixBitByte(&newz, loclass_getSixBitByte(c, 4), 3);
loclass_pushbackSixBitByte(&newz, loclass_getSixBitByte(c, 5), 2);
loclass_pushbackSixBitByte(&newz, loclass_getSixBitByte(c, 6), 1);
loclass_pushbackSixBitByte(&newz, loclass_getSixBitByte(c, 7), 0);
newz |= (c & 0xFFFF000000000000);
return newz;
}
/**
* @return 4 six-bit bytes chunked into a uint64_t,as 00..00a0a1a2a3
*/
static uint64_t loclass_ck(int i, int j, uint64_t z) {
if (i == 1 && j == -1) {
// loclass_ck(1, −1, z [0] . . . z [3] ) = z [0] . . . z [3]
return z;
} else if (j == -1) {
// loclass_ck(i, −1, z [0] . . . z [3] ) = loclass_ck(i − 1, i − 2, z [0] . . . z [3] )
return loclass_ck(i - 1, i - 2, z);
}
if (loclass_getSixBitByte(z, i) == loclass_getSixBitByte(z, j)) {
//loclass_ck(i, j − 1, z [0] . . . z [i] ← j . . . z [3] )
uint64_t newz = 0;
int c;
for (c = 0; c < 4; c++) {
uint8_t val = loclass_getSixBitByte(z, c);
if (c == i)
loclass_pushbackSixBitByte(&newz, j, c);
else
loclass_pushbackSixBitByte(&newz, val, c);
}
return loclass_ck(i, j - 1, newz);
} else {
return loclass_ck(i, j - 1, z);
}
}
/**
Definition 8.
Let the function check : (F 62 ) 8 → (F 62 ) 8 be defined as
check(z [0] . . . z [7] ) = loclass_ck(3, 2, z [0] . . . z [3] ) · loclass_ck(3, 2, z [4] . . . z [7] )
where loclass_ck : N × N × (F 62 ) 4 → (F 62 ) 4 is defined as
loclass_ck(1, −1, z [0] . . . z [3] ) = z [0] . . . z [3]
loclass_ck(i, −1, z [0] . . . z [3] ) = loclass_ck(i − 1, i − 2, z [0] . . . z [3] )
loclass_ck(i, j, z [0] . . . z [3] ) =
loclass_ck(i, j − 1, z [0] . . . z [i] ← j . . . z [3] ), if z [i] = z [j] ;
loclass_ck(i, j − 1, z [0] . . . z [3] ), otherwise
otherwise.
**/
static uint64_t loclass_check(uint64_t z) {
//These 64 bits are divided as c = x, y, z [0] , . . . , z [7]
// loclass_ck(3, 2, z [0] . . . z [3] )
uint64_t ck1 = loclass_ck(3, 2, z);
// loclass_ck(3, 2, z [4] . . . z [7] )
uint64_t ck2 = loclass_ck(3, 2, z << 24);
//The loclass_ck function will place the values
// in the middle of z.
ck1 &= 0x00000000FFFFFF000000;
ck2 &= 0x00000000FFFFFF000000;
return ck1 | ck2 >> 24;
}
static void loclass_permute(LoclassBitstreamIn_t *p_in, uint64_t z, int l, int r, LoclassBitstreamOut_t *out) {
if (loclass_bitsLeft(p_in) == 0)
return;
bool pn = loclass_tailBit(p_in);
if (pn) { // pn = 1
uint8_t zl = loclass_getSixBitByte(z, l);
loclass_push6bits(out, zl + 1);
loclass_permute(p_in, z, l + 1, r, out);
} else { // otherwise
uint8_t zr = loclass_getSixBitByte(z, r);
loclass_push6bits(out, zr);
loclass_permute(p_in, z, l, r + 1, out);
}
}
/**
* @brief
*Definition 11. Let the function loclass_hash0 : F 82 × F 82 × (F 62 ) 8 → (F 82 ) 8 be defined as
* loclass_hash0(x, y, z [0] . . . z [7] ) = k [0] . . . k [7] where
* z'[i] = (z[i] mod (63-i)) + i i = 0...3
* z'[i+4] = (z[i+4] mod (64-i)) + i i = 0...3
* ẑ = check(z');
* @param c
* @param k this is where the diversified key is put (should be 8 bytes)
* @return
*/
void loclass_hash0(uint64_t c, uint8_t k[8]) {
c = loclass_swapZvalues(c);
//These 64 bits are divided as c = x, y, z [0] , . . . , z [7]
// x = 8 bits
// y = 8 bits
// z0-z7 6 bits each : 48 bits
uint8_t x = (c & 0xFF00000000000000) >> 56;
uint8_t y = (c & 0x00FF000000000000) >> 48;
uint64_t zP = 0;
for (int n = 0; n < 4 ; n++) {
uint8_t zn = loclass_getSixBitByte(c, n);
uint8_t zn4 = loclass_getSixBitByte(c, n + 4);
uint8_t _zn = (zn % (63 - n)) + n;
uint8_t _zn4 = (zn4 % (64 - n)) + n;
loclass_pushbackSixBitByte(&zP, _zn, n);
loclass_pushbackSixBitByte(&zP, _zn4, n + 4);
}
uint64_t zCaret = loclass_check(zP);
uint8_t p = loclass_pi[x % 35];
if (x & 1) //Check if x7 is 1
p = ~p;
LoclassBitstreamIn_t p_in = { &p, 8, 0 };
uint8_t outbuffer[] = {0, 0, 0, 0, 0, 0, 0, 0};
LoclassBitstreamOut_t out = {outbuffer, 0, 0};
loclass_permute(&p_in, zCaret, 0, 4, &out); //returns 48 bits? or 6 8-bytes
//Out is now a buffer containing six-bit bytes, should be 48 bits
// if all went well
//Shift z-values down onto the lower segment
uint64_t zTilde = loclass_x_bytes_to_num(outbuffer, sizeof(outbuffer));
zTilde >>= 16;
for (int i = 0; i < 8; i++) {
// the key on index i is first a bit from y
// then six bits from z,
// then a bit from p
// Init with zeroes
k[i] = 0;
// First, place yi leftmost in k
//k[i] |= (y << i) & 0x80 ;
// First, place y(7-i) leftmost in k
k[i] |= (y << (7 - i)) & 0x80 ;
uint8_t zTilde_i = loclass_getSixBitByte(zTilde, i);
// zTildeI is now on the form 00XXXXXX
// with one leftshift, it'll be
// 0XXXXXX0
// So after leftshift, we can OR it into k
// However, when doing complement, we need to
// again MASK 0XXXXXX0 (0x7E)
zTilde_i <<= 1;
//Finally, add bit from p or p-mod
//Shift bit i into rightmost location (mask only after complement)
uint8_t p_i = p >> i & 0x1;
if (k[i]) { // yi = 1
k[i] |= ~zTilde_i & 0x7E;
k[i] |= p_i & 1;
k[i] += 1;
} else { // otherwise
k[i] |= zTilde_i & 0x7E;
k[i] |= (~p_i) & 1;
}
}
}
/**
* @brief Performs Elite-class key diversification
* @param csn
* @param key
* @param div_key
*/
void loclass_diversifyKey(uint8_t *csn, const uint8_t *key, uint8_t *div_key) {
mbedtls_des_context loclass_ctx_enc;
// Prepare the DES key
mbedtls_des_setkey_enc(&loclass_ctx_enc, key);
uint8_t crypted_csn[8] = {0};
// Calculate DES(CSN, KEY)
mbedtls_des_crypt_ecb(&loclass_ctx_enc, csn, crypted_csn);
//Calculate HASH0(DES))
uint64_t c_csn = loclass_x_bytes_to_num(crypted_csn, sizeof(crypted_csn));
loclass_hash0(c_csn, div_key);
}