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256 lines
7.3 KiB
C
256 lines
7.3 KiB
C
/*****************************************************************************
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* This file is part of iClassCipher. It is a reconstructon of the cipher engine
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* used in iClass, and RFID techology.
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*
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* The implementation is based on the work performed by
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* Flavio D. Garcia, Gerhard de Koning Gans, Roel Verdult and
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* Milosch Meriac in the paper "Dismantling IClass".
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*
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* Copyright (C) 2014 Martin Holst Swende
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*
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* This is free software: you can redistribute it and/or modify
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* it under the terms of the GNU General Public License version 2 as published
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* by the Free Software Foundation.
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*
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* This file is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with IClassCipher. If not, see <http://www.gnu.org/licenses/>.
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****************************************************************************/
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#include "cipher.h"
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#include "cipherutils.h"
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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#include <stdbool.h>
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#include <stdint.h>
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#include <time.h>
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#include "fileutils.h"
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uint8_t keytable[] = { 0,0,0,0,0,0,0,0};
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/**
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* Definition 1 (Cipher state). A cipher state of iClass s is an element of F 40/2
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* consisting of the following four components:
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* 1. the left register l = (l 0 . . . l 7 ) ∈ F 8/2 ;
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* 2. the right register r = (r 0 . . . r 7 ) ∈ F 8/2 ;
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* 3. the top register t = (t 0 . . . t 15 ) ∈ F 16/2 .
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* 4. the bottom register b = (b 0 . . . b 7 ) ∈ F 8/2 .
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**/
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typedef struct {
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uint8_t l;
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uint8_t r;
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uint8_t b;
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uint16_t t;
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} State;
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/**
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* Definition 2. The feedback function for the top register T : F 16/2 → F 2
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* is defined as
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* T (x 0 x 1 . . . . . . x 15 ) = x 0 ⊕ x 1 ⊕ x 5 ⊕ x 7 ⊕ x 10 ⊕ x 11 ⊕ x 14 ⊕ x 15 .
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**/
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bool T(State state)
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{
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bool x0 = state.t & 0x8000;
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bool x1 = state.t & 0x4000;
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bool x5 = state.t & 0x0400;
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bool x7 = state.t & 0x0100;
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bool x10 = state.t & 0x0020;
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bool x11 = state.t & 0x0010;
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bool x14 = state.t & 0x0002;
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bool x15 = state.t & 0x0001;
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return x0 ^ x1 ^ x5 ^ x7 ^ x10 ^ x11 ^ x14 ^ x15;
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}
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/**
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* Similarly, the feedback function for the bottom register B : F 8/2 → F 2 is defined as
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* B(x 0 x 1 . . . x 7 ) = x 1 ⊕ x 2 ⊕ x 3 ⊕ x 7 .
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**/
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bool B(State state)
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{
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bool x1 = state.b & 0x40;
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bool x2 = state.b & 0x20;
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bool x3 = state.b & 0x10;
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bool x7 = state.b & 0x01;
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return x1 ^ x2 ^ x3 ^ x7;
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}
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/**
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* Definition 3 (Selection function). The selection function select : F 2 × F 2 ×
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* F 8/2 → F 3/2 is defined as select(x, y, r) = z 0 z 1 z 2 where
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* z 0 = (r 0 ∧ r 2 ) ⊕ (r 1 ∧ r 3 ) ⊕ (r 2 ∨ r 4 )
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* z 1 = (r 0 ∨ r 2 ) ⊕ (r 5 ∨ r 7 ) ⊕ r 1 ⊕ r 6 ⊕ x ⊕ y
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* z 2 = (r 3 ∧ r 5 ) ⊕ (r 4 ∧ r 6 ) ⊕ r 7 ⊕ x
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**/
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uint8_t _select(bool x, bool y, uint8_t r)
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{
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bool r0 = r >> 7 & 0x1;
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bool r1 = r >> 6 & 0x1;
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bool r2 = r >> 5 & 0x1;
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bool r3 = r >> 4 & 0x1;
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bool r4 = r >> 3 & 0x1;
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bool r5 = r >> 2 & 0x1;
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bool r6 = r >> 1 & 0x1;
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bool r7 = r & 0x1;
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bool z0 = (r0 & r2) ^ (r1 & ~r3) ^ (r2 | r4);
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bool z1 = (r0 | r2) ^ ( r5 | r7) ^ r1 ^ r6 ^ x ^ y;
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bool z2 = (r3 & ~r5) ^ (r4 & r6 ) ^ r7 ^ x;
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// The three bitz z0.. z1 are packed into a uint8_t:
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// 00000ZZZ
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//Return value is a uint8_t
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uint8_t retval = 0;
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retval |= (z0 << 2) & 4;
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retval |= (z1 << 1) & 2;
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retval |= z2 & 1;
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// Return value 0 <= retval <= 7
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return retval;
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}
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/**
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* Definition 4 (Successor state). Let s = l, r, t, b be a cipher state, k ∈ (F 82 ) 8
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* be a key and y ∈ F 2 be the input bit. Then, the successor cipher state s ′ =
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* l ′ , r ′ , t ′ , b ′ is defined as
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* t ′ := (T (t) ⊕ r 0 ⊕ r 4 )t 0 . . . t 14 l ′ := (k [select(T (t),y,r)] ⊕ b ′ ) ⊞ l ⊞ r
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* b ′ := (B(b) ⊕ r 7 )b 0 . . . b 6 r ′ := (k [select(T (t),y,r)] ⊕ b ′ ) ⊞ l
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*
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* @param s - state
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* @param k - array containing 8 bytes
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**/
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State successor(uint8_t* k, State s, bool y)
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{
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bool r0 = s.r >> 7 & 0x1;
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bool r4 = s.r >> 3 & 0x1;
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bool r7 = s.r & 0x1;
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State successor = {0,0,0,0};
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successor.t = s.t >> 1;
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successor.t |= (T(s) ^ r0 ^ r4) << 15;
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successor.b = s.b >> 1;
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successor.b |= (B(s) ^ r7) << 7;
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bool Tt = T(s);
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successor.l = ((k[_select(Tt,y,s.r)] ^ successor.b) + s.l+s.r ) & 0xFF;
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successor.r = ((k[_select(Tt,y,s.r)] ^ successor.b) + s.l ) & 0xFF;
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return successor;
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}
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/**
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* We define the successor function suc which takes a key k ∈ (F 82 ) 8 , a state s and
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* an input y ∈ F 2 and outputs the successor state s ′ . We overload the function suc
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* to multiple bit input x ∈ F n 2 which we define as
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* @param k - array containing 8 bytes
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**/
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State suc(uint8_t* k,State s, BitstreamIn *bitstream)
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{
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if(bitsLeft(bitstream) == 0)
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{
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return s;
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}
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bool lastbit = tailBit(bitstream);
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return successor(k,suc(k,s,bitstream), lastbit);
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}
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/**
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* Definition 5 (Output). Define the function output which takes an internal
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* state s =< l, r, t, b > and returns the bit r 5 . We also define the function output
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* on multiple bits input which takes a key k, a state s and an input x ∈ F n 2 as
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* output(k, s, ǫ) = ǫ
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* output(k, s, x 0 . . . x n ) = output(s) · output(k, s ′ , x 1 . . . x n )
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* where s ′ = suc(k, s, x 0 ).
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**/
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void output(uint8_t* k,State s, BitstreamIn* in, BitstreamOut* out)
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{
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if(bitsLeft(in) == 0)
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{
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return;
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}
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pushBit(out,(s.r >> 2) & 1);
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//Remove first bit
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uint8_t x0 = headBit(in);
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State ss = successor(k,s,x0);
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output(k,ss,in, out);
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}
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/**
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* Definition 6 (Initial state). Define the function init which takes as input a
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* key k ∈ (F 82 ) 8 and outputs the initial cipher state s =< l, r, t, b >
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**/
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State init(uint8_t* k)
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{
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State s = {
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((k[0] ^ 0x4c) + 0xEC) & 0xFF,// l
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((k[0] ^ 0x4c) + 0x21) & 0xFF,// r
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0x4c, // b
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0xE012 // t
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};
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return s;
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}
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void MAC(uint8_t* k, BitstreamIn input, BitstreamOut out)
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{
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uint8_t zeroes_32[] = {0,0,0,0};
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BitstreamIn input_32_zeroes = {zeroes_32,sizeof(zeroes_32)*8,0};
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State initState = suc(k,init(k),&input);
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output(k,initState,&input_32_zeroes,&out);
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}
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void doMAC(uint8_t *cc_nr_p, int length,uint8_t *div_key_p, uint8_t mac[4])
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{
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uint8_t *cc_nr;
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uint8_t div_key[8];
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cc_nr=(uint8_t*)malloc(length+1);
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memcpy(cc_nr,cc_nr_p,length);
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memcpy(div_key,div_key_p,8);
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reverse_arraybytes(cc_nr,length);
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BitstreamIn bitstream = {cc_nr,length * 8,0};
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uint8_t dest []= {0,0,0,0,0,0,0,0};
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BitstreamOut out = { dest, sizeof(dest)*8, 0 };
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MAC(div_key,bitstream, out);
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//The output MAC must also be reversed
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reverse_arraybytes(dest, sizeof(dest));
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memcpy(mac, dest, 4);
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printf("Calculated_MAC\t%02x%02x%02x%02x\n", dest[0],dest[1],dest[2],dest[3]);
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free(cc_nr);
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return 1;
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}
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int testMAC()
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{
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prnlog("[+] Testing MAC calculation...");
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//From the "dismantling.IClass" paper:
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uint8_t cc_nr[] = {0xFE,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0,0,0,0};
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//From the paper
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uint8_t div_key[8] = {0xE0,0x33,0xCA,0x41,0x9A,0xEE,0x43,0xF9};
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uint8_t correct_MAC[4] = {0x1d,0x49,0xC9,0xDA};
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uint8_t calculated_mac[4] = {0};
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doMAC(cc_nr, 12, div_key, calculated_mac);
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if(memcmp(calculated_mac, correct_MAC,4) == 0)
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{
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prnlog("[+] MAC calculation OK!");
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}else
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{
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prnlog("[+] FAILED: MAC calculation failed:");
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printarr(" Calculated_MAC", calculated_mac, 4);
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printarr(" Correct_MAC ", correct_MAC, 4);
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return 1;
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}
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return 0;
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}
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