Andrew Boyson / crypto

A simple library to support serving https.

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aes-cbc/aes128cbc.c@20:197c3e6e8b8d, 2019-10-16 (annotated)

Committer:
andrewboyson
Date:
Wed Oct 16 11:11:03 2019 +0000
Revision:
20:197c3e6e8b8d
Parent:
aes/aes128cbc.c@19:f22327e8be7b 
Updated aes128cbc to remove some hard to follow casting between a 1d buffer and a 2d array of rows and columns.

Who changed what in which revision?

UserRevisionLine numberNew contents of line
andrewboyson 19:f22327e8be7b 1 /*
andrewboyson 19:f22327e8be7b 2 This is an implementation of the AES algorithm, specifically ECB, CTR and CBC mode.
andrewboyson 19:f22327e8be7b 3 Block size can be chosen in aes.h - available choices are AES128, AES192, AES256.
andrewboyson 19:f22327e8be7b 4 The implementation is verified against the test vectors in:
andrewboyson 19:f22327e8be7b 5 National Institute of Standards and Technology Special Publication 800-38A 2001 ED
andrewboyson 19:f22327e8be7b 6 ECB-AES128
andrewboyson 19:f22327e8be7b 7 ----------
andrewboyson 19:f22327e8be7b 8 plain-text:
andrewboyson 19:f22327e8be7b 9 6bc1bee22e409f96e93d7e117393172a
andrewboyson 19:f22327e8be7b 10 ae2d8a571e03ac9c9eb76fac45af8e51
andrewboyson 19:f22327e8be7b 11 30c81c46a35ce411e5fbc1191a0a52ef
andrewboyson 19:f22327e8be7b 12 f69f2445df4f9b17ad2b417be66c3710
andrewboyson 19:f22327e8be7b 13 key:
andrewboyson 19:f22327e8be7b 14 2b7e151628aed2a6abf7158809cf4f3c
andrewboyson 19:f22327e8be7b 15 resulting cipher
andrewboyson 19:f22327e8be7b 16 3ad77bb40d7a3660a89ecaf32466ef97
andrewboyson 19:f22327e8be7b 17 f5d3d58503b9699de785895a96fdbaaf
andrewboyson 19:f22327e8be7b 18 43b1cd7f598ece23881b00e3ed030688
andrewboyson 19:f22327e8be7b 19 7b0c785e27e8ad3f8223207104725dd4
andrewboyson 19:f22327e8be7b 20 NOTE: String length must be evenly divisible by 16byte (str_len % 16 == 0)
andrewboyson 19:f22327e8be7b 21 You should pad the end of the string with zeros if this is not the case.
andrewboyson 19:f22327e8be7b 22 For AES192/256 the key size is proportionally larger.
andrewboyson 19:f22327e8be7b 23 */
andrewboyson 19:f22327e8be7b 24
andrewboyson 19:f22327e8be7b 25 #include <stdint.h>
andrewboyson 19:f22327e8be7b 26 #include <string.h> // CBC mode, for memset
andrewboyson 19:f22327e8be7b 27 #include "aes128cbc.h"
andrewboyson 19:f22327e8be7b 28
andrewboyson 20:197c3e6e8b8d 29 #define NB 4 // The number of columns comprising a state in AES. This is a constant in AES. Value=4
andrewboyson 20:197c3e6e8b8d 30 #define NK 4 // The number of 32 bit words in a key.
andrewboyson 20:197c3e6e8b8d 31 #define NR 10 // The number of rounds in AES Cipher.
andrewboyson 19:f22327e8be7b 32
andrewboyson 20:197c3e6e8b8d 33 /*
andrewboyson 20:197c3e6e8b8d 34 union state_u
andrewboyson 19:f22327e8be7b 35 {
andrewboyson 20:197c3e6e8b8d 36 uint8_t d1[16];
andrewboyson 20:197c3e6e8b8d 37 uint8_t d2[4][4];
andrewboyson 19:f22327e8be7b 38 };
andrewboyson 20:197c3e6e8b8d 39 typedef union state_u state_t; // state - array holding the intermediate results during decryption.
andrewboyson 20:197c3e6e8b8d 40 */
andrewboyson 19:f22327e8be7b 41 static const uint8_t sbox[256] = {
andrewboyson 19:f22327e8be7b 42 //0 1 2 3 4 5 6 7 8 9 A B C D E F
andrewboyson 19:f22327e8be7b 43 0x63, 0x7c, 0x77, 0x7b, 0xf2, 0x6b, 0x6f, 0xc5, 0x30, 0x01, 0x67, 0x2b, 0xfe, 0xd7, 0xab, 0x76,
andrewboyson 19:f22327e8be7b 44 0xca, 0x82, 0xc9, 0x7d, 0xfa, 0x59, 0x47, 0xf0, 0xad, 0xd4, 0xa2, 0xaf, 0x9c, 0xa4, 0x72, 0xc0,
andrewboyson 19:f22327e8be7b 45 0xb7, 0xfd, 0x93, 0x26, 0x36, 0x3f, 0xf7, 0xcc, 0x34, 0xa5, 0xe5, 0xf1, 0x71, 0xd8, 0x31, 0x15,
andrewboyson 19:f22327e8be7b 46 0x04, 0xc7, 0x23, 0xc3, 0x18, 0x96, 0x05, 0x9a, 0x07, 0x12, 0x80, 0xe2, 0xeb, 0x27, 0xb2, 0x75,
andrewboyson 19:f22327e8be7b 47 0x09, 0x83, 0x2c, 0x1a, 0x1b, 0x6e, 0x5a, 0xa0, 0x52, 0x3b, 0xd6, 0xb3, 0x29, 0xe3, 0x2f, 0x84,
andrewboyson 19:f22327e8be7b 48 0x53, 0xd1, 0x00, 0xed, 0x20, 0xfc, 0xb1, 0x5b, 0x6a, 0xcb, 0xbe, 0x39, 0x4a, 0x4c, 0x58, 0xcf,
andrewboyson 19:f22327e8be7b 49 0xd0, 0xef, 0xaa, 0xfb, 0x43, 0x4d, 0x33, 0x85, 0x45, 0xf9, 0x02, 0x7f, 0x50, 0x3c, 0x9f, 0xa8,
andrewboyson 19:f22327e8be7b 50 0x51, 0xa3, 0x40, 0x8f, 0x92, 0x9d, 0x38, 0xf5, 0xbc, 0xb6, 0xda, 0x21, 0x10, 0xff, 0xf3, 0xd2,
andrewboyson 19:f22327e8be7b 51 0xcd, 0x0c, 0x13, 0xec, 0x5f, 0x97, 0x44, 0x17, 0xc4, 0xa7, 0x7e, 0x3d, 0x64, 0x5d, 0x19, 0x73,
andrewboyson 19:f22327e8be7b 52 0x60, 0x81, 0x4f, 0xdc, 0x22, 0x2a, 0x90, 0x88, 0x46, 0xee, 0xb8, 0x14, 0xde, 0x5e, 0x0b, 0xdb,
andrewboyson 19:f22327e8be7b 53 0xe0, 0x32, 0x3a, 0x0a, 0x49, 0x06, 0x24, 0x5c, 0xc2, 0xd3, 0xac, 0x62, 0x91, 0x95, 0xe4, 0x79,
andrewboyson 19:f22327e8be7b 54 0xe7, 0xc8, 0x37, 0x6d, 0x8d, 0xd5, 0x4e, 0xa9, 0x6c, 0x56, 0xf4, 0xea, 0x65, 0x7a, 0xae, 0x08,
andrewboyson 19:f22327e8be7b 55 0xba, 0x78, 0x25, 0x2e, 0x1c, 0xa6, 0xb4, 0xc6, 0xe8, 0xdd, 0x74, 0x1f, 0x4b, 0xbd, 0x8b, 0x8a,
andrewboyson 19:f22327e8be7b 56 0x70, 0x3e, 0xb5, 0x66, 0x48, 0x03, 0xf6, 0x0e, 0x61, 0x35, 0x57, 0xb9, 0x86, 0xc1, 0x1d, 0x9e,
andrewboyson 19:f22327e8be7b 57 0xe1, 0xf8, 0x98, 0x11, 0x69, 0xd9, 0x8e, 0x94, 0x9b, 0x1e, 0x87, 0xe9, 0xce, 0x55, 0x28, 0xdf,
andrewboyson 19:f22327e8be7b 58 0x8c, 0xa1, 0x89, 0x0d, 0xbf, 0xe6, 0x42, 0x68, 0x41, 0x99, 0x2d, 0x0f, 0xb0, 0x54, 0xbb, 0x16 };
andrewboyson 19:f22327e8be7b 59
andrewboyson 19:f22327e8be7b 60 static const uint8_t rsbox[256] = {
andrewboyson 19:f22327e8be7b 61 0x52, 0x09, 0x6a, 0xd5, 0x30, 0x36, 0xa5, 0x38, 0xbf, 0x40, 0xa3, 0x9e, 0x81, 0xf3, 0xd7, 0xfb,
andrewboyson 19:f22327e8be7b 62 0x7c, 0xe3, 0x39, 0x82, 0x9b, 0x2f, 0xff, 0x87, 0x34, 0x8e, 0x43, 0x44, 0xc4, 0xde, 0xe9, 0xcb,
andrewboyson 19:f22327e8be7b 63 0x54, 0x7b, 0x94, 0x32, 0xa6, 0xc2, 0x23, 0x3d, 0xee, 0x4c, 0x95, 0x0b, 0x42, 0xfa, 0xc3, 0x4e,
andrewboyson 19:f22327e8be7b 64 0x08, 0x2e, 0xa1, 0x66, 0x28, 0xd9, 0x24, 0xb2, 0x76, 0x5b, 0xa2, 0x49, 0x6d, 0x8b, 0xd1, 0x25,
andrewboyson 19:f22327e8be7b 65 0x72, 0xf8, 0xf6, 0x64, 0x86, 0x68, 0x98, 0x16, 0xd4, 0xa4, 0x5c, 0xcc, 0x5d, 0x65, 0xb6, 0x92,
andrewboyson 19:f22327e8be7b 66 0x6c, 0x70, 0x48, 0x50, 0xfd, 0xed, 0xb9, 0xda, 0x5e, 0x15, 0x46, 0x57, 0xa7, 0x8d, 0x9d, 0x84,
andrewboyson 19:f22327e8be7b 67 0x90, 0xd8, 0xab, 0x00, 0x8c, 0xbc, 0xd3, 0x0a, 0xf7, 0xe4, 0x58, 0x05, 0xb8, 0xb3, 0x45, 0x06,
andrewboyson 19:f22327e8be7b 68 0xd0, 0x2c, 0x1e, 0x8f, 0xca, 0x3f, 0x0f, 0x02, 0xc1, 0xaf, 0xbd, 0x03, 0x01, 0x13, 0x8a, 0x6b,
andrewboyson 19:f22327e8be7b 69 0x3a, 0x91, 0x11, 0x41, 0x4f, 0x67, 0xdc, 0xea, 0x97, 0xf2, 0xcf, 0xce, 0xf0, 0xb4, 0xe6, 0x73,
andrewboyson 19:f22327e8be7b 70 0x96, 0xac, 0x74, 0x22, 0xe7, 0xad, 0x35, 0x85, 0xe2, 0xf9, 0x37, 0xe8, 0x1c, 0x75, 0xdf, 0x6e,
andrewboyson 19:f22327e8be7b 71 0x47, 0xf1, 0x1a, 0x71, 0x1d, 0x29, 0xc5, 0x89, 0x6f, 0xb7, 0x62, 0x0e, 0xaa, 0x18, 0xbe, 0x1b,
andrewboyson 19:f22327e8be7b 72 0xfc, 0x56, 0x3e, 0x4b, 0xc6, 0xd2, 0x79, 0x20, 0x9a, 0xdb, 0xc0, 0xfe, 0x78, 0xcd, 0x5a, 0xf4,
andrewboyson 19:f22327e8be7b 73 0x1f, 0xdd, 0xa8, 0x33, 0x88, 0x07, 0xc7, 0x31, 0xb1, 0x12, 0x10, 0x59, 0x27, 0x80, 0xec, 0x5f,
andrewboyson 19:f22327e8be7b 74 0x60, 0x51, 0x7f, 0xa9, 0x19, 0xb5, 0x4a, 0x0d, 0x2d, 0xe5, 0x7a, 0x9f, 0x93, 0xc9, 0x9c, 0xef,
andrewboyson 19:f22327e8be7b 75 0xa0, 0xe0, 0x3b, 0x4d, 0xae, 0x2a, 0xf5, 0xb0, 0xc8, 0xeb, 0xbb, 0x3c, 0x83, 0x53, 0x99, 0x61,
andrewboyson 19:f22327e8be7b 76 0x17, 0x2b, 0x04, 0x7e, 0xba, 0x77, 0xd6, 0x26, 0xe1, 0x69, 0x14, 0x63, 0x55, 0x21, 0x0c, 0x7d };
andrewboyson 19:f22327e8be7b 77
andrewboyson 19:f22327e8be7b 78 // The round constant word array, Rcon[i], contains the values given by
andrewboyson 19:f22327e8be7b 79 // x to the power (i-1) being powers of x (x is denoted as {02}) in the field GF(2^8)
andrewboyson 19:f22327e8be7b 80 static const uint8_t Rcon[11] = { 0x8d, 0x01, 0x02, 0x04, 0x08, 0x10, 0x20, 0x40, 0x80, 0x1b, 0x36 };
andrewboyson 19:f22327e8be7b 81
andrewboyson 19:f22327e8be7b 82 // This function produces Nb(Nr+1) round keys. The round keys are used in each round to decrypt the states.
andrewboyson 20:197c3e6e8b8d 83 static void keyExpansion(uint8_t* roundKey, const uint8_t* key)
andrewboyson 19:f22327e8be7b 84 {
andrewboyson 19:f22327e8be7b 85 unsigned i, j, k;
andrewboyson 19:f22327e8be7b 86 uint8_t tempa[4]; // Used for the column/row operations
andrewboyson 19:f22327e8be7b 87
andrewboyson 19:f22327e8be7b 88 // The first round key is the key itself.
andrewboyson 20:197c3e6e8b8d 89 for (i = 0; i < NK; ++i)
andrewboyson 19:f22327e8be7b 90 {
andrewboyson 20:197c3e6e8b8d 91 roundKey[i * 4 + 0] = key[i * 4 + 0];
andrewboyson 20:197c3e6e8b8d 92 roundKey[i * 4 + 1] = key[i * 4 + 1];
andrewboyson 20:197c3e6e8b8d 93 roundKey[i * 4 + 2] = key[i * 4 + 2];
andrewboyson 20:197c3e6e8b8d 94 roundKey[i * 4 + 3] = key[i * 4 + 3];
andrewboyson 19:f22327e8be7b 95 }
andrewboyson 19:f22327e8be7b 96
andrewboyson 19:f22327e8be7b 97 // All other round keys are found from the previous round keys.
andrewboyson 20:197c3e6e8b8d 98 for (i = NK; i < NB * (NR + 1); ++i)
andrewboyson 19:f22327e8be7b 99 {
andrewboyson 19:f22327e8be7b 100 {
andrewboyson 19:f22327e8be7b 101 k = (i - 1) * 4;
andrewboyson 20:197c3e6e8b8d 102 tempa[0] = roundKey[k + 0];
andrewboyson 20:197c3e6e8b8d 103 tempa[1] = roundKey[k + 1];
andrewboyson 20:197c3e6e8b8d 104 tempa[2] = roundKey[k + 2];
andrewboyson 20:197c3e6e8b8d 105 tempa[3] = roundKey[k + 3];
andrewboyson 19:f22327e8be7b 106
andrewboyson 19:f22327e8be7b 107 }
andrewboyson 19:f22327e8be7b 108
andrewboyson 20:197c3e6e8b8d 109 if (i % NK == 0)
andrewboyson 19:f22327e8be7b 110 {
andrewboyson 19:f22327e8be7b 111 // This function shifts the 4 bytes in a word to the left once.
andrewboyson 19:f22327e8be7b 112 // [a0,a1,a2,a3] becomes [a1,a2,a3,a0]
andrewboyson 19:f22327e8be7b 113
andrewboyson 19:f22327e8be7b 114 // Function RotWord()
andrewboyson 19:f22327e8be7b 115 {
andrewboyson 19:f22327e8be7b 116 const uint8_t u8tmp = tempa[0];
andrewboyson 19:f22327e8be7b 117 tempa[0] = tempa[1];
andrewboyson 19:f22327e8be7b 118 tempa[1] = tempa[2];
andrewboyson 19:f22327e8be7b 119 tempa[2] = tempa[3];
andrewboyson 19:f22327e8be7b 120 tempa[3] = u8tmp;
andrewboyson 19:f22327e8be7b 121 }
andrewboyson 19:f22327e8be7b 122
andrewboyson 19:f22327e8be7b 123 // SubWord() is a function that takes a four-byte input word and
andrewboyson 19:f22327e8be7b 124 // applies the S-box to each of the four bytes to produce an output word.
andrewboyson 19:f22327e8be7b 125
andrewboyson 19:f22327e8be7b 126 // Function Subword()
andrewboyson 19:f22327e8be7b 127 {
andrewboyson 20:197c3e6e8b8d 128 tempa[0] = sbox[tempa[0]];
andrewboyson 20:197c3e6e8b8d 129 tempa[1] = sbox[tempa[1]];
andrewboyson 20:197c3e6e8b8d 130 tempa[2] = sbox[tempa[2]];
andrewboyson 20:197c3e6e8b8d 131 tempa[3] = sbox[tempa[3]];
andrewboyson 19:f22327e8be7b 132 }
andrewboyson 19:f22327e8be7b 133
andrewboyson 20:197c3e6e8b8d 134 tempa[0] = tempa[0] ^ Rcon[i/NK];
andrewboyson 19:f22327e8be7b 135 }
andrewboyson 20:197c3e6e8b8d 136 j = i * 4; k=(i - NK) * 4;
andrewboyson 20:197c3e6e8b8d 137 roundKey[j + 0] = roundKey[k + 0] ^ tempa[0];
andrewboyson 20:197c3e6e8b8d 138 roundKey[j + 1] = roundKey[k + 1] ^ tempa[1];
andrewboyson 20:197c3e6e8b8d 139 roundKey[j + 2] = roundKey[k + 2] ^ tempa[2];
andrewboyson 20:197c3e6e8b8d 140 roundKey[j + 3] = roundKey[k + 3] ^ tempa[3];
andrewboyson 19:f22327e8be7b 141 }
andrewboyson 19:f22327e8be7b 142 }
andrewboyson 19:f22327e8be7b 143
andrewboyson 19:f22327e8be7b 144 // This function adds the round key to state.
andrewboyson 19:f22327e8be7b 145 // The round key is added to the state by an XOR function.
andrewboyson 20:197c3e6e8b8d 146 static void addRoundKey(uint8_t round, uint8_t* state, const uint8_t* roundKey)
andrewboyson 19:f22327e8be7b 147 {
andrewboyson 20:197c3e6e8b8d 148 uint8_t i,j;
andrewboyson 20:197c3e6e8b8d 149 for (i = 0; i < 4; ++i)
andrewboyson 19:f22327e8be7b 150 {
andrewboyson 20:197c3e6e8b8d 151 for (j = 0; j < 4; ++j)
andrewboyson 20:197c3e6e8b8d 152 {
andrewboyson 20:197c3e6e8b8d 153 *(state + i*4 + j) ^= roundKey[(round * NB * 4) + (i * NB) + j];
andrewboyson 20:197c3e6e8b8d 154 }
andrewboyson 19:f22327e8be7b 155 }
andrewboyson 19:f22327e8be7b 156 }
andrewboyson 19:f22327e8be7b 157
andrewboyson 19:f22327e8be7b 158 // The SubBytes Function Substitutes the values in the
andrewboyson 19:f22327e8be7b 159 // state matrix with values in an S-box.
andrewboyson 20:197c3e6e8b8d 160 static void subBytes(uint8_t* state)
andrewboyson 19:f22327e8be7b 161 {
andrewboyson 20:197c3e6e8b8d 162 uint8_t i, j;
andrewboyson 20:197c3e6e8b8d 163 for (i = 0; i < 4; ++i)
andrewboyson 19:f22327e8be7b 164 {
andrewboyson 20:197c3e6e8b8d 165 for (j = 0; j < 4; ++j)
andrewboyson 20:197c3e6e8b8d 166 {
andrewboyson 20:197c3e6e8b8d 167 *(state + j*4 + i) = sbox[*(state + j*4 + i)];
andrewboyson 20:197c3e6e8b8d 168 }
andrewboyson 19:f22327e8be7b 169 }
andrewboyson 19:f22327e8be7b 170 }
andrewboyson 19:f22327e8be7b 171
andrewboyson 19:f22327e8be7b 172 // The ShiftRows() function shifts the rows in the state to the left.
andrewboyson 19:f22327e8be7b 173 // Each row is shifted with different offset.
andrewboyson 19:f22327e8be7b 174 // Offset = Row number. So the first row is not shifted.
andrewboyson 20:197c3e6e8b8d 175 static void shiftRows(uint8_t* state)
andrewboyson 19:f22327e8be7b 176 {
andrewboyson 20:197c3e6e8b8d 177 uint8_t temp;
andrewboyson 20:197c3e6e8b8d 178
andrewboyson 20:197c3e6e8b8d 179 // Rotate first row 1 columns to left
andrewboyson 20:197c3e6e8b8d 180 temp = *(state + 4*0 + 1);
andrewboyson 20:197c3e6e8b8d 181 *(state + 4*0 + 1) = *(state + 4*1 + 1);
andrewboyson 20:197c3e6e8b8d 182 *(state + 4*1 + 1) = *(state + 4*2 + 1);
andrewboyson 20:197c3e6e8b8d 183 *(state + 4*2 + 1) = *(state + 4*3 + 1);
andrewboyson 20:197c3e6e8b8d 184 *(state + 4*3 + 1) = temp;
andrewboyson 20:197c3e6e8b8d 185
andrewboyson 20:197c3e6e8b8d 186 // Rotate second row 2 columns to left
andrewboyson 20:197c3e6e8b8d 187 temp = *(state + 4*0 + 2);
andrewboyson 20:197c3e6e8b8d 188 *(state + 4*0 + 2) = *(state + 4*2 + 2);
andrewboyson 20:197c3e6e8b8d 189 *(state + 4*2 + 2) = temp;
andrewboyson 20:197c3e6e8b8d 190
andrewboyson 20:197c3e6e8b8d 191 temp = *(state + 4*1 + 2);
andrewboyson 20:197c3e6e8b8d 192 *(state + 4*1 + 2) = *(state + 4*3 + 2);
andrewboyson 20:197c3e6e8b8d 193 *(state + 4*3 + 2) = temp;
andrewboyson 20:197c3e6e8b8d 194
andrewboyson 20:197c3e6e8b8d 195 // Rotate third row 3 columns to left
andrewboyson 20:197c3e6e8b8d 196 temp = *(state + 4*0 + 3);
andrewboyson 20:197c3e6e8b8d 197 *(state + 4*0 + 3) = *(state + 4*3 + 3);
andrewboyson 20:197c3e6e8b8d 198 *(state + 4*3 + 3) = *(state + 4*2 + 3);
andrewboyson 20:197c3e6e8b8d 199 *(state + 4*2 + 3) = *(state + 4*1 + 3);
andrewboyson 20:197c3e6e8b8d 200 *(state + 4*1 + 3) = temp;
andrewboyson 19:f22327e8be7b 201 }
andrewboyson 19:f22327e8be7b 202
andrewboyson 19:f22327e8be7b 203 static uint8_t xtime(uint8_t x)
andrewboyson 19:f22327e8be7b 204 {
andrewboyson 20:197c3e6e8b8d 205 return ((x<<1) ^ (((x>>7) & 1) * 0x1b));
andrewboyson 19:f22327e8be7b 206 }
andrewboyson 19:f22327e8be7b 207
andrewboyson 19:f22327e8be7b 208 // MixColumns function mixes the columns of the state matrix
andrewboyson 20:197c3e6e8b8d 209 static void mixColumns(uint8_t* state)
andrewboyson 19:f22327e8be7b 210 {
andrewboyson 20:197c3e6e8b8d 211 uint8_t i;
andrewboyson 20:197c3e6e8b8d 212 uint8_t tmp, tm, t;
andrewboyson 20:197c3e6e8b8d 213 for (i = 0; i < 4; ++i)
andrewboyson 20:197c3e6e8b8d 214 {
andrewboyson 20:197c3e6e8b8d 215 t = *(state + 4*i + 0);
andrewboyson 20:197c3e6e8b8d 216 tmp = *(state + 4*i + 0) ^ *(state + 4*i + 1) ^ *(state + 4*i + 2) ^ *(state + 4*i + 3);
andrewboyson 20:197c3e6e8b8d 217 tm = *(state + 4*i + 0) ^ *(state + 4*i + 1) ; tm = xtime(tm); *(state + 4*i + 0) ^= tm ^ tmp ;
andrewboyson 20:197c3e6e8b8d 218 tm = *(state + 4*i + 1) ^ *(state + 4*i + 2) ; tm = xtime(tm); *(state + 4*i + 1) ^= tm ^ tmp ;
andrewboyson 20:197c3e6e8b8d 219 tm = *(state + 4*i + 2) ^ *(state + 4*i + 3) ; tm = xtime(tm); *(state + 4*i + 2) ^= tm ^ tmp ;
andrewboyson 20:197c3e6e8b8d 220 tm = *(state + 4*i + 3) ^ t ; tm = xtime(tm); *(state + 4*i + 3) ^= tm ^ tmp ;
andrewboyson 20:197c3e6e8b8d 221 }
andrewboyson 19:f22327e8be7b 222 }
andrewboyson 19:f22327e8be7b 223
andrewboyson 20:197c3e6e8b8d 224 static uint8_t multiply(uint8_t x, uint8_t y)
andrewboyson 19:f22327e8be7b 225 {
andrewboyson 20:197c3e6e8b8d 226 return (((y>>0 & 1) * x) ^
andrewboyson 20:197c3e6e8b8d 227 ((y>>1 & 1) * xtime(x)) ^
andrewboyson 20:197c3e6e8b8d 228 ((y>>2 & 1) * xtime(xtime(x))) ^
andrewboyson 20:197c3e6e8b8d 229 ((y>>3 & 1) * xtime(xtime(xtime(x)))) ^
andrewboyson 20:197c3e6e8b8d 230 ((y>>4 & 1) * xtime(xtime(xtime(xtime(x)))))); /* this last call to xtime() can be omitted */
andrewboyson 20:197c3e6e8b8d 231 }
andrewboyson 19:f22327e8be7b 232
andrewboyson 19:f22327e8be7b 233 // MixColumns function mixes the columns of the state matrix.
andrewboyson 19:f22327e8be7b 234 // The method used to multiply may be difficult to understand for the inexperienced.
andrewboyson 19:f22327e8be7b 235 // Please use the references to gain more information.
andrewboyson 20:197c3e6e8b8d 236 static void invMixColumns(uint8_t* state)
andrewboyson 19:f22327e8be7b 237 {
andrewboyson 20:197c3e6e8b8d 238 int i;
andrewboyson 20:197c3e6e8b8d 239 uint8_t a, b, c, d;
andrewboyson 20:197c3e6e8b8d 240 for (i = 0; i < 4; ++i)
andrewboyson 20:197c3e6e8b8d 241 {
andrewboyson 20:197c3e6e8b8d 242 a = *(state + 4*i + 0);
andrewboyson 20:197c3e6e8b8d 243 b = *(state + 4*i + 1);
andrewboyson 20:197c3e6e8b8d 244 c = *(state + 4*i + 2);
andrewboyson 20:197c3e6e8b8d 245 d = *(state + 4*i + 3);
andrewboyson 19:f22327e8be7b 246
andrewboyson 20:197c3e6e8b8d 247 *(state + 4*i + 0) = multiply(a, 0x0e) ^ multiply(b, 0x0b) ^ multiply(c, 0x0d) ^ multiply(d, 0x09);
andrewboyson 20:197c3e6e8b8d 248 *(state + 4*i + 1) = multiply(a, 0x09) ^ multiply(b, 0x0e) ^ multiply(c, 0x0b) ^ multiply(d, 0x0d);
andrewboyson 20:197c3e6e8b8d 249 *(state + 4*i + 2) = multiply(a, 0x0d) ^ multiply(b, 0x09) ^ multiply(c, 0x0e) ^ multiply(d, 0x0b);
andrewboyson 20:197c3e6e8b8d 250 *(state + 4*i + 3) = multiply(a, 0x0b) ^ multiply(b, 0x0d) ^ multiply(c, 0x09) ^ multiply(d, 0x0e);
andrewboyson 20:197c3e6e8b8d 251 }
andrewboyson 19:f22327e8be7b 252 }
andrewboyson 19:f22327e8be7b 253
andrewboyson 19:f22327e8be7b 254
andrewboyson 19:f22327e8be7b 255 // The SubBytes Function Substitutes the values in the
andrewboyson 19:f22327e8be7b 256 // state matrix with values in an S-box.
andrewboyson 20:197c3e6e8b8d 257 static void invSubBytes(uint8_t* state)
andrewboyson 19:f22327e8be7b 258 {
andrewboyson 20:197c3e6e8b8d 259 uint8_t i, j;
andrewboyson 20:197c3e6e8b8d 260 for (i = 0; i < 4; ++i)
andrewboyson 19:f22327e8be7b 261 {
andrewboyson 20:197c3e6e8b8d 262 for (j = 0; j < 4; ++j)
andrewboyson 20:197c3e6e8b8d 263 {
andrewboyson 20:197c3e6e8b8d 264 *(state + 4*j + i) = rsbox[*(state + 4*j + i)];
andrewboyson 20:197c3e6e8b8d 265 }
andrewboyson 19:f22327e8be7b 266 }
andrewboyson 19:f22327e8be7b 267 }
andrewboyson 19:f22327e8be7b 268
andrewboyson 20:197c3e6e8b8d 269 static void invShiftRows(uint8_t* state)
andrewboyson 19:f22327e8be7b 270 {
andrewboyson 20:197c3e6e8b8d 271 uint8_t temp;
andrewboyson 20:197c3e6e8b8d 272
andrewboyson 20:197c3e6e8b8d 273 // Rotate first row 1 columns to right
andrewboyson 20:197c3e6e8b8d 274 temp = *(state + 4*3 + 1);
andrewboyson 20:197c3e6e8b8d 275 *(state + 4*3 + 1) = *(state + 4*2 + 1);
andrewboyson 20:197c3e6e8b8d 276 *(state + 4*2 + 1) = *(state + 4*1 + 1);
andrewboyson 20:197c3e6e8b8d 277 *(state + 4*1 + 1) = *(state + 4*0 + 1);
andrewboyson 20:197c3e6e8b8d 278 *(state + 4*0 + 1) = temp;
andrewboyson 20:197c3e6e8b8d 279
andrewboyson 20:197c3e6e8b8d 280 // Rotate second row 2 columns to right
andrewboyson 20:197c3e6e8b8d 281 temp = *(state + 4*0 + 2);
andrewboyson 20:197c3e6e8b8d 282 *(state + 4*0 + 2) = *(state + 4*2 + 2);
andrewboyson 20:197c3e6e8b8d 283 *(state + 4*2 + 2) = temp;
andrewboyson 20:197c3e6e8b8d 284
andrewboyson 20:197c3e6e8b8d 285 temp = *(state + 4*1 + 2);
andrewboyson 20:197c3e6e8b8d 286 *(state + 4*1 + 2) = *(state + 4*3 + 2);
andrewboyson 20:197c3e6e8b8d 287 *(state + 4*3 + 2) = temp;
andrewboyson 20:197c3e6e8b8d 288
andrewboyson 20:197c3e6e8b8d 289 // Rotate third row 3 columns to right
andrewboyson 20:197c3e6e8b8d 290 temp = *(state + 4*0 + 3);
andrewboyson 20:197c3e6e8b8d 291 *(state + 4*0 + 3) = *(state + 4*1 + 3);
andrewboyson 20:197c3e6e8b8d 292 *(state + 4*1 + 3) = *(state + 4*2 + 3);
andrewboyson 20:197c3e6e8b8d 293 *(state + 4*2 + 3) = *(state + 4*3 + 3);
andrewboyson 20:197c3e6e8b8d 294 *(state + 4*3 + 3) = temp;
andrewboyson 19:f22327e8be7b 295 }
andrewboyson 19:f22327e8be7b 296
andrewboyson 19:f22327e8be7b 297 // Cipher is the main function that encrypts the PlainText.
andrewboyson 20:197c3e6e8b8d 298 static void cipher(uint8_t* state, const uint8_t* roundKey)
andrewboyson 19:f22327e8be7b 299 {
andrewboyson 20:197c3e6e8b8d 300 uint8_t round = 0;
andrewboyson 20:197c3e6e8b8d 301
andrewboyson 20:197c3e6e8b8d 302 // Add the First round key to the state before starting the rounds.
andrewboyson 20:197c3e6e8b8d 303 addRoundKey(0, state, roundKey);
andrewboyson 20:197c3e6e8b8d 304
andrewboyson 20:197c3e6e8b8d 305 // There will be Nr rounds.
andrewboyson 20:197c3e6e8b8d 306 // The first Nr-1 rounds are identical.
andrewboyson 20:197c3e6e8b8d 307 // These Nr-1 rounds are executed in the loop below.
andrewboyson 20:197c3e6e8b8d 308 for (round = 1; round < NR; ++round)
andrewboyson 20:197c3e6e8b8d 309 {
andrewboyson 20:197c3e6e8b8d 310 subBytes(state);
andrewboyson 20:197c3e6e8b8d 311 shiftRows(state);
andrewboyson 20:197c3e6e8b8d 312 mixColumns(state);
andrewboyson 20:197c3e6e8b8d 313 addRoundKey(round, state, roundKey);
andrewboyson 20:197c3e6e8b8d 314 }
andrewboyson 20:197c3e6e8b8d 315
andrewboyson 20:197c3e6e8b8d 316 // The last round is given below.
andrewboyson 20:197c3e6e8b8d 317 // The MixColumns function is not here in the last round.
andrewboyson 20:197c3e6e8b8d 318 subBytes(state);
andrewboyson 20:197c3e6e8b8d 319 shiftRows(state);
andrewboyson 20:197c3e6e8b8d 320 addRoundKey(NR, state, roundKey);
andrewboyson 19:f22327e8be7b 321 }
andrewboyson 19:f22327e8be7b 322
andrewboyson 20:197c3e6e8b8d 323 static void invCipher(uint8_t* state, const uint8_t* roundKey)
andrewboyson 19:f22327e8be7b 324 {
andrewboyson 20:197c3e6e8b8d 325 uint8_t round = 0;
andrewboyson 20:197c3e6e8b8d 326
andrewboyson 20:197c3e6e8b8d 327 // Add the First round key to the state before starting the rounds.
andrewboyson 20:197c3e6e8b8d 328 addRoundKey(NR, state, roundKey);
andrewboyson 20:197c3e6e8b8d 329
andrewboyson 20:197c3e6e8b8d 330 // There will be Nr rounds.
andrewboyson 20:197c3e6e8b8d 331 // The first Nr-1 rounds are identical.
andrewboyson 20:197c3e6e8b8d 332 // These Nr-1 rounds are executed in the loop below.
andrewboyson 20:197c3e6e8b8d 333 for (round = (NR - 1); round > 0; --round)
andrewboyson 20:197c3e6e8b8d 334 {
andrewboyson 20:197c3e6e8b8d 335 invShiftRows(state);
andrewboyson 20:197c3e6e8b8d 336 invSubBytes(state);
andrewboyson 20:197c3e6e8b8d 337 addRoundKey(round, state, roundKey);
andrewboyson 20:197c3e6e8b8d 338 invMixColumns(state);
andrewboyson 20:197c3e6e8b8d 339 }
andrewboyson 20:197c3e6e8b8d 340
andrewboyson 20:197c3e6e8b8d 341 // The last round is given below.
andrewboyson 20:197c3e6e8b8d 342 // The MixColumns function is not here in the last round.
andrewboyson 20:197c3e6e8b8d 343 invShiftRows(state);
andrewboyson 20:197c3e6e8b8d 344 invSubBytes(state);
andrewboyson 20:197c3e6e8b8d 345 addRoundKey(0, state, roundKey);
andrewboyson 19:f22327e8be7b 346 }
andrewboyson 19:f22327e8be7b 347
andrewboyson 19:f22327e8be7b 348 /*****************************************************************************/
andrewboyson 19:f22327e8be7b 349 /* Public functions: */
andrewboyson 19:f22327e8be7b 350 /*****************************************************************************/
andrewboyson 19:f22327e8be7b 351
andrewboyson 19:f22327e8be7b 352 void Aes128CbcEncrypt(const uint8_t* key, const uint8_t* iv, uint8_t* buf, uint32_t length)
andrewboyson 19:f22327e8be7b 353 {
andrewboyson 20:197c3e6e8b8d 354 uint8_t ctxRoundKey[176];
andrewboyson 20:197c3e6e8b8d 355 keyExpansion(ctxRoundKey, key);
andrewboyson 20:197c3e6e8b8d 356
andrewboyson 20:197c3e6e8b8d 357 const uint8_t* prevIv = iv;
andrewboyson 20:197c3e6e8b8d 358 for (int i = 0; i < length; i += AES128CBC_BLOCK_SIZE)
andrewboyson 20:197c3e6e8b8d 359 {
andrewboyson 20:197c3e6e8b8d 360 for (int j = 0; j < AES128CBC_BLOCK_SIZE; ++j) buf[j] ^= prevIv[j];
andrewboyson 20:197c3e6e8b8d 361 cipher(buf, ctxRoundKey);
andrewboyson 20:197c3e6e8b8d 362 prevIv = buf;
andrewboyson 20:197c3e6e8b8d 363 buf += AES128CBC_BLOCK_SIZE;
andrewboyson 20:197c3e6e8b8d 364 }
andrewboyson 19:f22327e8be7b 365 }
andrewboyson 19:f22327e8be7b 366 void Aes128CbcDecrypt(const uint8_t* key, const uint8_t* iv, uint8_t* buf, uint32_t length)
andrewboyson 19:f22327e8be7b 367 {
andrewboyson 20:197c3e6e8b8d 368 uint8_t ctxRoundKey[176];
andrewboyson 20:197c3e6e8b8d 369 keyExpansion(ctxRoundKey, key);
andrewboyson 20:197c3e6e8b8d 370
andrewboyson 20:197c3e6e8b8d 371 uint8_t ctxIv[AES128CBC_BLOCK_SIZE];
andrewboyson 20:197c3e6e8b8d 372 memcpy (ctxIv, iv, AES128CBC_BLOCK_SIZE);
andrewboyson 20:197c3e6e8b8d 373
andrewboyson 20:197c3e6e8b8d 374 uint8_t storeNextIv[AES128CBC_BLOCK_SIZE];
andrewboyson 20:197c3e6e8b8d 375 for (int i = 0; i < length; i += AES128CBC_BLOCK_SIZE)
andrewboyson 20:197c3e6e8b8d 376 {
andrewboyson 20:197c3e6e8b8d 377 memcpy(storeNextIv, buf, AES128CBC_BLOCK_SIZE);
andrewboyson 20:197c3e6e8b8d 378 invCipher(buf, ctxRoundKey);
andrewboyson 20:197c3e6e8b8d 379 for (int j = 0; j < AES128CBC_BLOCK_SIZE; ++j) buf[j] ^= ctxIv[j];
andrewboyson 20:197c3e6e8b8d 380 memcpy(ctxIv, storeNextIv, AES128CBC_BLOCK_SIZE);
andrewboyson 20:197c3e6e8b8d 381 buf += AES128CBC_BLOCK_SIZE;
andrewboyson 20:197c3e6e8b8d 382 }
andrewboyson 19:f22327e8be7b 383 }