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324 lines
10 KiB
C
324 lines
10 KiB
C
/*****************************************************************************
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* WARNING
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*
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* THIS CODE IS CREATED FOR EXPERIMENTATION AND EDUCATIONAL USE ONLY.
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*
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* USAGE OF THIS CODE IN OTHER WAYS MAY INFRINGE UPON THE INTELLECTUAL
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* PROPERTY OF OTHER PARTIES, SUCH AS INSIDE SECURE AND HID GLOBAL,
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* AND MAY EXPOSE YOU TO AN INFRINGEMENT ACTION FROM THOSE PARTIES.
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*
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* THIS CODE SHOULD NEVER BE USED TO INFRINGE PATENTS OR INTELLECTUAL PROPERTY RIGHTS.
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*
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*****************************************************************************
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*
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* This file is part of loclass. 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, or, at your option, any later version.
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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 loclass. If not, see <http://www.gnu.org/licenses/>.
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*
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*
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****************************************************************************/
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/**
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From "Dismantling iclass":
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This section describes in detail the built-in key diversification algorithm of iClass.
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Besides the obvious purpose of deriving a card key from a master key, this
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algorithm intends to circumvent weaknesses in the cipher by preventing the
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usage of certain ‘weak’ keys. In order to compute a diversified key, the iClass
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reader first encrypts the card identity id with the master key K, using single
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DES. The resulting ciphertext is then input to a function called hash0 which
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outputs the diversified key k.
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k = hash0(DES enc (id, K))
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Here the DES encryption of id with master key K outputs a cryptogram c
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of 64 bits. These 64 bits are divided as c = x, y, z [0] , . . . , z [7] ∈ F 82 × F 82 × (F 62 ) 8
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which is used as input to the hash0 function. This function introduces some
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obfuscation by performing a number of permutations, complement and modulo
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operations, see Figure 2.5. Besides that, it checks for and removes patterns like
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similar key bytes, which could produce a strong bias in the cipher. Finally, the
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output of hash0 is the diversified card key k = k [0] , . . . , k [7] ∈ (F 82 ) 8 .
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**/
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#include "optimized_ikeys.h"
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#include <stdint.h>
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#include <stdbool.h>
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#include <inttypes.h>
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#include "mbedtls/des.h"
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#include "optimized_cipherutils.h"
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static uint8_t pi[35] = {
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0x0F, 0x17, 0x1B, 0x1D, 0x1E, 0x27, 0x2B, 0x2D,
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0x2E, 0x33, 0x35, 0x39, 0x36, 0x3A, 0x3C, 0x47,
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0x4B, 0x4D, 0x4E, 0x53, 0x55, 0x56, 0x59, 0x5A,
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0x5C, 0x63, 0x65, 0x66, 0x69, 0x6A, 0x6C, 0x71,
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0x72, 0x74, 0x78
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};
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static mbedtls_des_context ctx_enc;
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/**
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* @brief The key diversification algorithm uses 6-bit bytes.
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* This implementation uses 64 bit uint to pack seven of them into one
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* variable. When they are there, they are placed as follows:
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* XXXX XXXX N0 .... N7, occupying the last 48 bits.
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*
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* This function picks out one from such a collection
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* @param all
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* @param n bitnumber
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* @return
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*/
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static uint8_t getSixBitByte(uint64_t c, int n) {
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return (c >> (42 - 6 * n)) & 0x3F;
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}
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/**
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* @brief Puts back a six-bit 'byte' into a uint64_t.
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* @param c buffer
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* @param z the value to place there
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* @param n bitnumber.
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*/
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static void pushbackSixBitByte(uint64_t *c, uint8_t z, int n) {
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//0x XXXX YYYY ZZZZ ZZZZ ZZZZ
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// ^z0 ^z7
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//z0: 1111 1100 0000 0000
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uint64_t masked = z & 0x3F;
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uint64_t eraser = 0x3F;
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masked <<= 42 - 6 * n;
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eraser <<= 42 - 6 * n;
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//masked <<= 6*n;
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//eraser <<= 6*n;
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eraser = ~eraser;
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(*c) &= eraser;
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(*c) |= masked;
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}
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/**
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* @brief Swaps the z-values.
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* If the input value has format XYZ0Z1...Z7, the output will have the format
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* XYZ7Z6...Z0 instead
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* @param c
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* @return
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*/
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static uint64_t swapZvalues(uint64_t c) {
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uint64_t newz = 0;
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pushbackSixBitByte(&newz, getSixBitByte(c, 0), 7);
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pushbackSixBitByte(&newz, getSixBitByte(c, 1), 6);
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pushbackSixBitByte(&newz, getSixBitByte(c, 2), 5);
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pushbackSixBitByte(&newz, getSixBitByte(c, 3), 4);
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pushbackSixBitByte(&newz, getSixBitByte(c, 4), 3);
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pushbackSixBitByte(&newz, getSixBitByte(c, 5), 2);
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pushbackSixBitByte(&newz, getSixBitByte(c, 6), 1);
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pushbackSixBitByte(&newz, getSixBitByte(c, 7), 0);
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newz |= (c & 0xFFFF000000000000);
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return newz;
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}
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/**
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* @return 4 six-bit bytes chunked into a uint64_t,as 00..00a0a1a2a3
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*/
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static uint64_t ck(int i, int j, uint64_t z) {
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if (i == 1 && j == -1) {
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// ck(1, −1, z [0] . . . z [3] ) = z [0] . . . z [3]
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return z;
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} else if (j == -1) {
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// ck(i, −1, z [0] . . . z [3] ) = ck(i − 1, i − 2, z [0] . . . z [3] )
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return ck(i - 1, i - 2, z);
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}
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if (getSixBitByte(z, i) == getSixBitByte(z, j)) {
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//ck(i, j − 1, z [0] . . . z [i] ← j . . . z [3] )
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uint64_t newz = 0;
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int c;
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for (c = 0; c < 4; c++) {
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uint8_t val = getSixBitByte(z, c);
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if (c == i)
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pushbackSixBitByte(&newz, j, c);
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else
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pushbackSixBitByte(&newz, val, c);
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}
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return ck(i, j - 1, newz);
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} else {
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return ck(i, j - 1, z);
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}
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}
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/**
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Definition 8.
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Let the function check : (F 62 ) 8 → (F 62 ) 8 be defined as
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check(z [0] . . . z [7] ) = ck(3, 2, z [0] . . . z [3] ) · ck(3, 2, z [4] . . . z [7] )
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where ck : N × N × (F 62 ) 4 → (F 62 ) 4 is defined as
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ck(1, −1, z [0] . . . z [3] ) = z [0] . . . z [3]
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ck(i, −1, z [0] . . . z [3] ) = ck(i − 1, i − 2, z [0] . . . z [3] )
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ck(i, j, z [0] . . . z [3] ) =
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ck(i, j − 1, z [0] . . . z [i] ← j . . . z [3] ), if z [i] = z [j] ;
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ck(i, j − 1, z [0] . . . z [3] ), otherwise
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otherwise.
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**/
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static uint64_t check(uint64_t z) {
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//These 64 bits are divided as c = x, y, z [0] , . . . , z [7]
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// ck(3, 2, z [0] . . . z [3] )
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uint64_t ck1 = ck(3, 2, z);
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// ck(3, 2, z [4] . . . z [7] )
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uint64_t ck2 = ck(3, 2, z << 24);
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//The ck function will place the values
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// in the middle of z.
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ck1 &= 0x00000000FFFFFF000000;
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ck2 &= 0x00000000FFFFFF000000;
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return ck1 | ck2 >> 24;
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}
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static void permute(BitstreamIn_t *p_in, uint64_t z, int l, int r, BitstreamOut_t *out) {
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if (bitsLeft(p_in) == 0)
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return;
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bool pn = tailBit(p_in);
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if (pn) { // pn = 1
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uint8_t zl = getSixBitByte(z, l);
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push6bits(out, zl + 1);
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permute(p_in, z, l + 1, r, out);
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} else { // otherwise
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uint8_t zr = getSixBitByte(z, r);
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push6bits(out, zr);
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permute(p_in, z, l, r + 1, out);
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}
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}
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/**
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* @brief
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*Definition 11. Let the function hash0 : F 82 × F 82 × (F 62 ) 8 → (F 82 ) 8 be defined as
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* hash0(x, y, z [0] . . . z [7] ) = k [0] . . . k [7] where
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* z'[i] = (z[i] mod (63-i)) + i i = 0...3
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* z'[i+4] = (z[i+4] mod (64-i)) + i i = 0...3
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* ẑ = check(z');
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* @param c
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* @param k this is where the diversified key is put (should be 8 bytes)
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* @return
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*/
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void hash0(uint64_t c, uint8_t k[8]) {
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c = swapZvalues(c);
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//These 64 bits are divided as c = x, y, z [0] , . . . , z [7]
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// x = 8 bits
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// y = 8 bits
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// z0-z7 6 bits each : 48 bits
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uint8_t x = (c & 0xFF00000000000000) >> 56;
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uint8_t y = (c & 0x00FF000000000000) >> 48;
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uint64_t zP = 0;
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for (int n = 0; n < 4 ; n++) {
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uint8_t zn = getSixBitByte(c, n);
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uint8_t zn4 = getSixBitByte(c, n + 4);
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uint8_t _zn = (zn % (63 - n)) + n;
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uint8_t _zn4 = (zn4 % (64 - n)) + n;
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pushbackSixBitByte(&zP, _zn, n);
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pushbackSixBitByte(&zP, _zn4, n + 4);
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}
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uint64_t zCaret = check(zP);
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uint8_t p = pi[x % 35];
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if (x & 1) //Check if x7 is 1
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p = ~p;
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BitstreamIn_t p_in = { &p, 8, 0 };
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uint8_t outbuffer[] = {0, 0, 0, 0, 0, 0, 0, 0};
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BitstreamOut_t out = {outbuffer, 0, 0};
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permute(&p_in, zCaret, 0, 4, &out); //returns 48 bits? or 6 8-bytes
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//Out is now a buffer containing six-bit bytes, should be 48 bits
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// if all went well
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//Shift z-values down onto the lower segment
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uint64_t zTilde = x_bytes_to_num(outbuffer, sizeof(outbuffer));
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zTilde >>= 16;
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for (int i = 0; i < 8; i++) {
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// the key on index i is first a bit from y
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// then six bits from z,
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// then a bit from p
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// Init with zeroes
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k[i] = 0;
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// First, place yi leftmost in k
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//k[i] |= (y << i) & 0x80 ;
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// First, place y(7-i) leftmost in k
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k[i] |= (y << (7 - i)) & 0x80 ;
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uint8_t zTilde_i = getSixBitByte(zTilde, i);
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// zTildeI is now on the form 00XXXXXX
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// with one leftshift, it'll be
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// 0XXXXXX0
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// So after leftshift, we can OR it into k
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// However, when doing complement, we need to
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// again MASK 0XXXXXX0 (0x7E)
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zTilde_i <<= 1;
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//Finally, add bit from p or p-mod
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//Shift bit i into rightmost location (mask only after complement)
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uint8_t p_i = p >> i & 0x1;
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if (k[i]) { // yi = 1
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k[i] |= ~zTilde_i & 0x7E;
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k[i] |= p_i & 1;
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k[i] += 1;
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} else { // otherwise
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k[i] |= zTilde_i & 0x7E;
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k[i] |= (~p_i) & 1;
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}
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}
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}
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/**
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* @brief Performs Elite-class key diversification
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* @param csn
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* @param key
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* @param div_key
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*/
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void diversifyKey(uint8_t *csn, uint8_t *key, uint8_t *div_key) {
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// Prepare the DES key
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mbedtls_des_setkey_enc(&ctx_enc, key);
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uint8_t crypted_csn[8] = {0};
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// Calculate DES(CSN, KEY)
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mbedtls_des_crypt_ecb(&ctx_enc, csn, crypted_csn);
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//Calculate HASH0(DES))
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uint64_t c_csn = x_bytes_to_num(crypted_csn, sizeof(crypted_csn));
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hash0(c_csn, div_key);
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}
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