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Diffstat (limited to 'aes.c')
| -rw-r--r-- | aes.c | 338 |
1 files changed, 338 insertions, 0 deletions
@@ -0,0 +1,338 @@ +/* + +This is the implementation of the AES128 algorithm, specifically ECB mode. + +The implementation is verified against the test vectors in: + National Institute of Standards and Technology Special Publication 800-38A 2001 ED + +ECB-AES128 +---------- + + plain-text: + 6bc1bee22e409f96e93d7e117393172a + ae2d8a571e03ac9c9eb76fac45af8e51 + 30c81c46a35ce411e5fbc1191a0a52ef + f69f2445df4f9b17ad2b417be66c3710 + + key: + 2b7e151628aed2a6abf7158809cf4f3c + + resulting cipher + 50fe67cc996d32b6da0937e99bafec60 + d9a4dada0892239f6b8b3d7680e15674 + a78819583f0308e7a6bf36b1386abf23 + c6d3416d29165c6fcb8e51a227ba994e + + +Use aes_encrypt_string() to encrypt or decrypt a string + +NOTE: String length must be evenly divisible by 16byte (str_len % 16 == 0) + You should pad the end of the string with zeros if this is not the case. + +*/ + +#ifndef _AES_C_ +#define _AES_C_ + + +/*****************************************************************************/ +/* Includes: */ +/*****************************************************************************/ +#include <string.h> +#include <stdint.h> +#include "aes.h" + + +/*****************************************************************************/ +/* Defines: */ +/*****************************************************************************/ +// The number of columns comprising a state in AES. This is a constant in AES. Value=4 +#define Nb 4 +// The number of 32 bit words in a key. +#define Nk 4 +// Key length in bytes [128 bit] +#define keyln 16 +// The number of rounds in AES Cipher. +#define Nr 10 + + +/*****************************************************************************/ +/* Private variables: */ +/*****************************************************************************/ +// in - pointer to the CipherText to be decrypted. +// out - pointer to buffer to hold output of the decryption. +// state - array holding the intermediate results during decryption. +static uint8_t* in, *out, state[4][4]; + +// The array that stores the round keys. +static uint8_t RoundKey[176]; + +// The Key input to the AES Program +static uint8_t* Key; + +// Marked const so it can be placed in read-only storage instead of RAM +// The numbers below can be computed dynamically trading ROM for RAM - +// This can be useful in (embedded) bootloader applications, where ROM is often limited. + +static const uint8_t sbox[256] = { + //0 1 2 3 4 5 6 7 8 9 A B C D E F + 0x63, 0x7c, 0x77, 0x7b, 0xf2, 0x6b, 0x6f, 0xc5, 0x30, 0x01, 0x67, 0x2b, 0xfe, 0xd7, 0xab, 0x76, + 0xca, 0x82, 0xc9, 0x7d, 0xfa, 0x59, 0x47, 0xf0, 0xad, 0xd4, 0xa2, 0xaf, 0x9c, 0xa4, 0x72, 0xc0, + 0xb7, 0xfd, 0x93, 0x26, 0x36, 0x3f, 0xf7, 0xcc, 0x34, 0xa5, 0xe5, 0xf1, 0x71, 0xd8, 0x31, 0x15, + 0x04, 0xc7, 0x23, 0xc3, 0x18, 0x96, 0x05, 0x9a, 0x07, 0x12, 0x80, 0xe2, 0xeb, 0x27, 0xb2, 0x75, + 0x09, 0x83, 0x2c, 0x1a, 0x1b, 0x6e, 0x5a, 0xa0, 0x52, 0x3b, 0xd6, 0xb3, 0x29, 0xe3, 0x2f, 0x84, + 0x53, 0xd1, 0x00, 0xed, 0x20, 0xfc, 0xb1, 0x5b, 0x6a, 0xcb, 0xbe, 0x39, 0x4a, 0x4c, 0x58, 0xcf, + 0xd0, 0xef, 0xaa, 0xfb, 0x43, 0x4d, 0x33, 0x85, 0x45, 0xf9, 0x02, 0x7f, 0x50, 0x3c, 0x9f, 0xa8, + 0x51, 0xa3, 0x40, 0x8f, 0x92, 0x9d, 0x38, 0xf5, 0xbc, 0xb6, 0xda, 0x21, 0x10, 0xff, 0xf3, 0xd2, + 0xcd, 0x0c, 0x13, 0xec, 0x5f, 0x97, 0x44, 0x17, 0xc4, 0xa7, 0x7e, 0x3d, 0x64, 0x5d, 0x19, 0x73, + 0x60, 0x81, 0x4f, 0xdc, 0x22, 0x2a, 0x90, 0x88, 0x46, 0xee, 0xb8, 0x14, 0xde, 0x5e, 0x0b, 0xdb, + 0xe0, 0x32, 0x3a, 0x0a, 0x49, 0x06, 0x24, 0x5c, 0xc2, 0xd3, 0xac, 0x62, 0x91, 0x95, 0xe4, 0x79, + 0xe7, 0xc8, 0x37, 0x6d, 0x8d, 0xd5, 0x4e, 0xa9, 0x6c, 0x56, 0xf4, 0xea, 0x65, 0x7a, 0xae, 0x08, + 0xba, 0x78, 0x25, 0x2e, 0x1c, 0xa6, 0xb4, 0xc6, 0xe8, 0xdd, 0x74, 0x1f, 0x4b, 0xbd, 0x8b, 0x8a, + 0x70, 0x3e, 0xb5, 0x66, 0x48, 0x03, 0xf6, 0x0e, 0x61, 0x35, 0x57, 0xb9, 0x86, 0xc1, 0x1d, 0x9e, + 0xe1, 0xf8, 0x98, 0x11, 0x69, 0xd9, 0x8e, 0x94, 0x9b, 0x1e, 0x87, 0xe9, 0xce, 0x55, 0x28, 0xdf, + 0x8c, 0xa1, 0x89, 0x0d, 0xbf, 0xe6, 0x42, 0x68, 0x41, 0x99, 0x2d, 0x0f, 0xb0, 0x54, 0xbb, 0x16 }; + +// The round constant word array, Rcon[i], contains the values given by +// x to th e power (i-1) being powers of x (x is denoted as {02}) in the field GF(2^8) +// Note that i starts at 1, not 0). +static const uint8_t Rcon[255] = { + 0x8d, 0x01, 0x02, 0x04, 0x08, 0x10, 0x20, 0x40, 0x80, 0x1b, 0x36, 0x6c, 0xd8, 0xab, 0x4d, 0x9a, + 0x2f, 0x5e, 0xbc, 0x63, 0xc6, 0x97, 0x35, 0x6a, 0xd4, 0xb3, 0x7d, 0xfa, 0xef, 0xc5, 0x91, 0x39, + 0x72, 0xe4, 0xd3, 0xbd, 0x61, 0xc2, 0x9f, 0x25, 0x4a, 0x94, 0x33, 0x66, 0xcc, 0x83, 0x1d, 0x3a, + 0x74, 0xe8, 0xcb, 0x8d, 0x01, 0x02, 0x04, 0x08, 0x10, 0x20, 0x40, 0x80, 0x1b, 0x36, 0x6c, 0xd8, + 0xab, 0x4d, 0x9a, 0x2f, 0x5e, 0xbc, 0x63, 0xc6, 0x97, 0x35, 0x6a, 0xd4, 0xb3, 0x7d, 0xfa, 0xef, + 0xc5, 0x91, 0x39, 0x72, 0xe4, 0xd3, 0xbd, 0x61, 0xc2, 0x9f, 0x25, 0x4a, 0x94, 0x33, 0x66, 0xcc, + 0x83, 0x1d, 0x3a, 0x74, 0xe8, 0xcb, 0x8d, 0x01, 0x02, 0x04, 0x08, 0x10, 0x20, 0x40, 0x80, 0x1b, + 0x36, 0x6c, 0xd8, 0xab, 0x4d, 0x9a, 0x2f, 0x5e, 0xbc, 0x63, 0xc6, 0x97, 0x35, 0x6a, 0xd4, 0xb3, + 0x7d, 0xfa, 0xef, 0xc5, 0x91, 0x39, 0x72, 0xe4, 0xd3, 0xbd, 0x61, 0xc2, 0x9f, 0x25, 0x4a, 0x94, + 0x33, 0x66, 0xcc, 0x83, 0x1d, 0x3a, 0x74, 0xe8, 0xcb, 0x8d, 0x01, 0x02, 0x04, 0x08, 0x10, 0x20, + 0x40, 0x80, 0x1b, 0x36, 0x6c, 0xd8, 0xab, 0x4d, 0x9a, 0x2f, 0x5e, 0xbc, 0x63, 0xc6, 0x97, 0x35, + 0x6a, 0xd4, 0xb3, 0x7d, 0xfa, 0xef, 0xc5, 0x91, 0x39, 0x72, 0xe4, 0xd3, 0xbd, 0x61, 0xc2, 0x9f, + 0x25, 0x4a, 0x94, 0x33, 0x66, 0xcc, 0x83, 0x1d, 0x3a, 0x74, 0xe8, 0xcb, 0x8d, 0x01, 0x02, 0x04, + 0x08, 0x10, 0x20, 0x40, 0x80, 0x1b, 0x36, 0x6c, 0xd8, 0xab, 0x4d, 0x9a, 0x2f, 0x5e, 0xbc, 0x63, + 0xc6, 0x97, 0x35, 0x6a, 0xd4, 0xb3, 0x7d, 0xfa, 0xef, 0xc5, 0x91, 0x39, 0x72, 0xe4, 0xd3, 0xbd, + 0x61, 0xc2, 0x9f, 0x25, 0x4a, 0x94, 0x33, 0x66, 0xcc, 0x83, 0x1d, 0x3a, 0x74, 0xe8, 0xcb }; + + +/*****************************************************************************/ +/* Private functions: */ +/*****************************************************************************/ +static uint8_t getSBoxValue(uint8_t num) +{ + return sbox[num]; +} + +// This function produces Nb(Nr+1) round keys. The round keys are used in each round to decrypt the states. +static void KeyExpansion() +{ + uint8_t i, j, k; + uint8_t tempa[4]; // used for the column/row operations + + // The first round key is the key itself. + for(i = 0; i < Nk; ++i) + { + RoundKey[ i * 4 ] = Key[ i * 4 ]; + RoundKey[(i * 4) + 1] = Key[(i * 4) + 1]; + RoundKey[(i * 4) + 2] = Key[(i * 4) + 2]; + RoundKey[(i * 4) + 3] = Key[(i * 4) + 3]; + } + + // All other round keys are found from the previous round keys. + for(; (i < (Nb * Nr) + 1); ++i) + { + for(j = 0; j < 4; ++j) + { + tempa[j]=RoundKey[(i-1) * 4 + j]; + } + if (i % Nk == 0) + { + // This function rotates the 4 bytes in a word to the left once. + // [a0,a1,a2,a3] becomes [a1,a2,a3,a0] + + // Function RotWord() + { + k = tempa[0]; + tempa[0] = tempa[1]; + tempa[1] = tempa[2]; + tempa[2] = tempa[3]; + tempa[3] = k; + } + + // SubWord() is a function that takes a four-byte input word and + // applies the S-box to each of the four bytes to produce an output word. + + // Function Subword() + { + tempa[0] = getSBoxValue(tempa[0]); + tempa[1] = getSBoxValue(tempa[1]); + tempa[2] = getSBoxValue(tempa[2]); + tempa[3] = getSBoxValue(tempa[3]); + } + + tempa[0] = tempa[0] ^ Rcon[i/Nk]; + } + else if (Nk > 6 && i % Nk == 4) + { + // Function Subword() + { + tempa[0] = getSBoxValue(tempa[0]); + tempa[1] = getSBoxValue(tempa[1]); + tempa[2] = getSBoxValue(tempa[2]); + tempa[3] = getSBoxValue(tempa[3]); + } + } + RoundKey[ i * 4 ] = RoundKey[ i - Nk * 4 ] ^ tempa[0]; + RoundKey[(i * 4) + 1] = RoundKey[(i - Nk) * (4 + 1)] ^ tempa[1]; + RoundKey[(i * 4) + 2] = RoundKey[(i - Nk) * (4 + 2)] ^ tempa[2]; + RoundKey[(i * 4) + 3] = RoundKey[(i - Nk) * (4 + 3)] ^ tempa[3]; + } +} + +// This function adds the round key to state. +// The round key is added to the state by an XOR function. +static void AddRoundKey(uint8_t round) +{ + uint8_t i,j; + for(i=0;i<4;i++) + { + for(j = 0; j < 4; ++j) + { + state[j][i] ^= RoundKey[round * Nb * 4 + i * Nb + j]; + } + } +} + +// The SubBytes Function Substitutes the values in the +// state matrix with values in an S-box. +static void SubBytes() +{ + uint8_t i, j; + for(i = 0; i < 4; ++i) + { + for(j = 0; j < 4; ++j) + { + state[i][j] = getSBoxValue(state[i][j]); + } + } +} + +// The ShiftRows() function shifts the rows in the state to the left. +// Each row is shifted with different offset. +// Offset = Row number. So the first row is not shifted. +static void ShiftRows() +{ + uint8_t temp; + + // Rotate first row 1 columns to left + temp = state[1][0]; + state[1][0] = state[1][1]; + state[1][1] = state[1][2]; + state[1][2] = state[1][3]; + state[1][3] = temp; + + // Rotate second row 2 columns to left + temp = state[2][0]; + state[2][0] = state[2][2]; + state[2][2] = temp; + + temp = state[2][1]; + state[2][1] = state[2][3]; + state[2][3] = temp; + + // Rotate third row 3 columns to left + temp = state[3][0]; + state[3][0] = state[3][3]; + state[3][3] = state[3][2]; + state[3][2] = state[3][1]; + state[3][1] = temp; +} + +static uint8_t xtime(uint8_t x) +{ + return ((x<<1) ^ (((x>>7) & 1) * 0x1b)); +} + +// MixColumns function mixes the columns of the state matrix +static void MixColumns() +{ + uint8_t i; + uint8_t Tmp,Tm,t; + for(i = 0; i < 4; ++i) + { + t = state[0][i]; + Tmp = state[0][i] ^ state[1][i] ^ state[2][i] ^ state[3][i] ; + Tm = state[0][i] ^ state[1][i] ; Tm = xtime(Tm); state[0][i] ^= Tm ^ Tmp ; + Tm = state[1][i] ^ state[2][i] ; Tm = xtime(Tm); state[1][i] ^= Tm ^ Tmp ; + Tm = state[2][i] ^ state[3][i] ; Tm = xtime(Tm); state[2][i] ^= Tm ^ Tmp ; + Tm = state[3][i] ^ t ; Tm = xtime(Tm); state[3][i] ^= Tm ^ Tmp ; + } +} + +// Cipher is the main function that encrypts the PlainText. +static void Cipher() +{ + uint8_t i, j, round = 0; + + //Copy the input PlainText to state array. + for(i = 0; i < 4; ++i) + { + for(j = 0; j < 4 ; ++j) + { + state[j][i] = in[(i * 4) + j]; + } + } + + // Add the First round key to the state before starting the rounds. + AddRoundKey(0); + + // There will be Nr rounds. + // The first Nr-1 rounds are identical. + // These Nr-1 rounds are executed in the loop below. + for(round = 1; round < Nr; ++round) + { + SubBytes(); + ShiftRows(); + MixColumns(); + AddRoundKey(round); + } + + // The last round is given below. + // The MixColumns function is not here in the last round. + SubBytes(); + ShiftRows(); + AddRoundKey(Nr); + + // The encryption process is over. + // Copy the state array to output array. + + for(i = 0; i < 4; ++i) + { + for(j = 0; j < 4; ++j) + { + out[(i * 4) + j] = state[j][i]; + } + } +} + + +/*****************************************************************************/ +/* Public functions: */ +/*****************************************************************************/ + +void AES128_ECB(uint8_t* input, uint8_t* key, uint8_t *output) +{ + // Copy the Key and CipherText + Key = key; + in = input; + out = output; + + // The KeyExpansion routine must be called before encryption. + KeyExpansion(); + + // The next function call encrypts the PlainText with the Key using AES algorithm. + Cipher(); +} + + +#endif //_AES_C_ |