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641 lines
23 KiB
C
641 lines
23 KiB
C
//
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// aes.c
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// Modified based on ideas from https://github.com/m3y54m/aes-in-c.git and FIPS 197
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// james.stine@okstate.edu 11 October 2024
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//
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#include <stdio.h>
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#include <stdlib.h>
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enum errorCode {
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SUCCESS = 0,
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ERROR_AES_UNKNOWN_KEYSIZE,
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ERROR_MEMORY_ALLOCATION_FAILED,
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};
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// Implementation: S-Box (page 14 FIPS 197 Table 4)
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unsigned char sbox[256] = {
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// 0 1 2 3 4 5 6 7 8 9 A B C D E F
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0x63, 0x7c, 0x77, 0x7b, 0xf2, 0x6b, 0x6f, 0xc5, 0x30, 0x01, 0x67, 0x2b, 0xfe, 0xd7, 0xab, 0x76, // 0
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0xca, 0x82, 0xc9, 0x7d, 0xfa, 0x59, 0x47, 0xf0, 0xad, 0xd4, 0xa2, 0xaf, 0x9c, 0xa4, 0x72, 0xc0, // 1
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0xb7, 0xfd, 0x93, 0x26, 0x36, 0x3f, 0xf7, 0xcc, 0x34, 0xa5, 0xe5, 0xf1, 0x71, 0xd8, 0x31, 0x15, // 2
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0x04, 0xc7, 0x23, 0xc3, 0x18, 0x96, 0x05, 0x9a, 0x07, 0x12, 0x80, 0xe2, 0xeb, 0x27, 0xb2, 0x75, // 3
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0x09, 0x83, 0x2c, 0x1a, 0x1b, 0x6e, 0x5a, 0xa0, 0x52, 0x3b, 0xd6, 0xb3, 0x29, 0xe3, 0x2f, 0x84, // 4
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0x53, 0xd1, 0x00, 0xed, 0x20, 0xfc, 0xb1, 0x5b, 0x6a, 0xcb, 0xbe, 0x39, 0x4a, 0x4c, 0x58, 0xcf, // 5
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0xd0, 0xef, 0xaa, 0xfb, 0x43, 0x4d, 0x33, 0x85, 0x45, 0xf9, 0x02, 0x7f, 0x50, 0x3c, 0x9f, 0xa8, // 6
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0x51, 0xa3, 0x40, 0x8f, 0x92, 0x9d, 0x38, 0xf5, 0xbc, 0xb6, 0xda, 0x21, 0x10, 0xff, 0xf3, 0xd2, // 7
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0xcd, 0x0c, 0x13, 0xec, 0x5f, 0x97, 0x44, 0x17, 0xc4, 0xa7, 0x7e, 0x3d, 0x64, 0x5d, 0x19, 0x73, // 8
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0x60, 0x81, 0x4f, 0xdc, 0x22, 0x2a, 0x90, 0x88, 0x46, 0xee, 0xb8, 0x14, 0xde, 0x5e, 0x0b, 0xdb, // 9
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0xe0, 0x32, 0x3a, 0x0a, 0x49, 0x06, 0x24, 0x5c, 0xc2, 0xd3, 0xac, 0x62, 0x91, 0x95, 0xe4, 0x79, // A
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0xe7, 0xc8, 0x37, 0x6d, 0x8d, 0xd5, 0x4e, 0xa9, 0x6c, 0x56, 0xf4, 0xea, 0x65, 0x7a, 0xae, 0x08, // B
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0xba, 0x78, 0x25, 0x2e, 0x1c, 0xa6, 0xb4, 0xc6, 0xe8, 0xdd, 0x74, 0x1f, 0x4b, 0xbd, 0x8b, 0x8a, // C
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0x70, 0x3e, 0xb5, 0x66, 0x48, 0x03, 0xf6, 0x0e, 0x61, 0x35, 0x57, 0xb9, 0x86, 0xc1, 0x1d, 0x9e, // D
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0xe1, 0xf8, 0x98, 0x11, 0x69, 0xd9, 0x8e, 0x94, 0x9b, 0x1e, 0x87, 0xe9, 0xce, 0x55, 0x28, 0xdf, // E
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0x8c, 0xa1, 0x89, 0x0d, 0xbf, 0xe6, 0x42, 0x68, 0x41, 0x99, 0x2d, 0x0f, 0xb0, 0x54, 0xbb, 0x16}; // F
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// inverse S-box used in the InvSubBytes() (page 23 FIPS 197 Table 6)
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unsigned char rsbox[256] =
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// 0 1 2 3 4 5 6 7 8 9 A B C D E F
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{0x52, 0x09, 0x6a, 0xd5, 0x30, 0x36, 0xa5, 0x38, 0xbf, 0x40, 0xa3, 0x9e, 0x81, 0xf3, 0xd7, 0xfb, // 0
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0x7c, 0xe3, 0x39, 0x82, 0x9b, 0x2f, 0xff, 0x87, 0x34, 0x8e, 0x43, 0x44, 0xc4, 0xde, 0xe9, 0xcb, // 1
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0x54, 0x7b, 0x94, 0x32, 0xa6, 0xc2, 0x23, 0x3d, 0xee, 0x4c, 0x95, 0x0b, 0x42, 0xfa, 0xc3, 0x4e, // 2
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0x08, 0x2e, 0xa1, 0x66, 0x28, 0xd9, 0x24, 0xb2, 0x76, 0x5b, 0xa2, 0x49, 0x6d, 0x8b, 0xd1, 0x25, // 3
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0x72, 0xf8, 0xf6, 0x64, 0x86, 0x68, 0x98, 0x16, 0xd4, 0xa4, 0x5c, 0xcc, 0x5d, 0x65, 0xb6, 0x92, // 4
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0x6c, 0x70, 0x48, 0x50, 0xfd, 0xed, 0xb9, 0xda, 0x5e, 0x15, 0x46, 0x57, 0xa7, 0x8d, 0x9d, 0x84, // 5
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0x90, 0xd8, 0xab, 0x00, 0x8c, 0xbc, 0xd3, 0x0a, 0xf7, 0xe4, 0x58, 0x05, 0xb8, 0xb3, 0x45, 0x06, // 6
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0xd0, 0x2c, 0x1e, 0x8f, 0xca, 0x3f, 0x0f, 0x02, 0xc1, 0xaf, 0xbd, 0x03, 0x01, 0x13, 0x8a, 0x6b, // 7
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0x3a, 0x91, 0x11, 0x41, 0x4f, 0x67, 0xdc, 0xea, 0x97, 0xf2, 0xcf, 0xce, 0xf0, 0xb4, 0xe6, 0x73, // 8
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0x96, 0xac, 0x74, 0x22, 0xe7, 0xad, 0x35, 0x85, 0xe2, 0xf9, 0x37, 0xe8, 0x1c, 0x75, 0xdf, 0x6e, // 9
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0x47, 0xf1, 0x1a, 0x71, 0x1d, 0x29, 0xc5, 0x89, 0x6f, 0xb7, 0x62, 0x0e, 0xaa, 0x18, 0xbe, 0x1b, // A
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0xfc, 0x56, 0x3e, 0x4b, 0xc6, 0xd2, 0x79, 0x20, 0x9a, 0xdb, 0xc0, 0xfe, 0x78, 0xcd, 0x5a, 0xf4, // B
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0x1f, 0xdd, 0xa8, 0x33, 0x88, 0x07, 0xc7, 0x31, 0xb1, 0x12, 0x10, 0x59, 0x27, 0x80, 0xec, 0x5f, // C
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0x60, 0x51, 0x7f, 0xa9, 0x19, 0xb5, 0x4a, 0x0d, 0x2d, 0xe5, 0x7a, 0x9f, 0x93, 0xc9, 0x9c, 0xef, // D
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0xa0, 0xe0, 0x3b, 0x4d, 0xae, 0x2a, 0xf5, 0xb0, 0xc8, 0xeb, 0xbb, 0x3c, 0x83, 0x53, 0x99, 0x61, // E
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0x17, 0x2b, 0x04, 0x7e, 0xba, 0x77, 0xd6, 0x26, 0xe1, 0x69, 0x14, 0x63, 0x55, 0x21, 0x0c, 0x7d}; // F
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// Implementation: Rcon (Round constants) - help introduce non-linearity and prevent symmetries
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// Rcon[i] = 0x02^(i-1) mod x^8 + x^4 + x^3 + x + 1
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unsigned char Rcon[255] = {
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0x8d, 0x01, 0x02, 0x04, 0x08, 0x10, 0x20, 0x40, 0x80, 0x1b, 0x36, 0x6c, 0xd8,
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0xab, 0x4d, 0x9a, 0x2f, 0x5e, 0xbc, 0x63, 0xc6, 0x97, 0x35, 0x6a, 0xd4, 0xb3,
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0x7d, 0xfa, 0xef, 0xc5, 0x91, 0x39, 0x72, 0xe4, 0xd3, 0xbd, 0x61, 0xc2, 0x9f,
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0x25, 0x4a, 0x94, 0x33, 0x66, 0xcc, 0x83, 0x1d, 0x3a, 0x74, 0xe8, 0xcb, 0x8d,
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0x01, 0x02, 0x04, 0x08, 0x10, 0x20, 0x40, 0x80, 0x1b, 0x36, 0x6c, 0xd8, 0xab,
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0x4d, 0x9a, 0x2f, 0x5e, 0xbc, 0x63, 0xc6, 0x97, 0x35, 0x6a, 0xd4, 0xb3, 0x7d,
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0xfa, 0xef, 0xc5, 0x91, 0x39, 0x72, 0xe4, 0xd3, 0xbd, 0x61, 0xc2, 0x9f, 0x25,
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0x4a, 0x94, 0x33, 0x66, 0xcc, 0x83, 0x1d, 0x3a, 0x74, 0xe8, 0xcb, 0x8d, 0x01,
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0x02, 0x04, 0x08, 0x10, 0x20, 0x40, 0x80, 0x1b, 0x36, 0x6c, 0xd8, 0xab, 0x4d,
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0x9a, 0x2f, 0x5e, 0xbc, 0x63, 0xc6, 0x97, 0x35, 0x6a, 0xd4, 0xb3, 0x7d, 0xfa,
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0xef, 0xc5, 0x91, 0x39, 0x72, 0xe4, 0xd3, 0xbd, 0x61, 0xc2, 0x9f, 0x25, 0x4a,
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0x94, 0x33, 0x66, 0xcc, 0x83, 0x1d, 0x3a, 0x74, 0xe8, 0xcb, 0x8d, 0x01, 0x02,
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0x04, 0x08, 0x10, 0x20, 0x40, 0x80, 0x1b, 0x36, 0x6c, 0xd8, 0xab, 0x4d, 0x9a,
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0x2f, 0x5e, 0xbc, 0x63, 0xc6, 0x97, 0x35, 0x6a, 0xd4, 0xb3, 0x7d, 0xfa, 0xef,
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0xc5, 0x91, 0x39, 0x72, 0xe4, 0xd3, 0xbd, 0x61, 0xc2, 0x9f, 0x25, 0x4a, 0x94,
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0x33, 0x66, 0xcc, 0x83, 0x1d, 0x3a, 0x74, 0xe8, 0xcb, 0x8d, 0x01, 0x02, 0x04,
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0x08, 0x10, 0x20, 0x40, 0x80, 0x1b, 0x36, 0x6c, 0xd8, 0xab, 0x4d, 0x9a, 0x2f,
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0x5e, 0xbc, 0x63, 0xc6, 0x97, 0x35, 0x6a, 0xd4, 0xb3, 0x7d, 0xfa, 0xef, 0xc5,
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0x91, 0x39, 0x72, 0xe4, 0xd3, 0xbd, 0x61, 0xc2, 0x9f, 0x25, 0x4a, 0x94, 0x33,
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0x66, 0xcc, 0x83, 0x1d, 0x3a, 0x74, 0xe8, 0xcb};
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unsigned char getRconValue(unsigned char num);
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// Implementation: Key Expansion
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enum keySize {
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SIZE_16 = 16,
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SIZE_24 = 24,
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SIZE_32 = 32
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};
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// AES Encryption Function Prototypes
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void subBytes(unsigned char *state);
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void shiftRows(unsigned char *state);
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void shiftRow(unsigned char *state, unsigned char nbr);
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void addRoundKey(unsigned char *state, unsigned char *roundKey);
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unsigned char galois_multiplication(unsigned char a, unsigned char b);
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void mixColumns(unsigned char *state);
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void mixColumn(unsigned char *column);
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void aes_cipher(unsigned char *state, unsigned char *roundKey);
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void createRoundKey(unsigned char *expandedKey, unsigned char *roundKey);
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void aes_main(unsigned char *state, unsigned char *expandedKey, int nbrRounds);
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char aes_encrypt(unsigned char *input, unsigned char *output, unsigned char *key, enum keySize size);
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// AES Decryption Function Prototypes
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void invSubBytes(unsigned char *state);
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void invShiftRows(unsigned char *state);
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void invShiftRow(unsigned char *state, unsigned char nbr);
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void invMixColumns(unsigned char *state);
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void invMixColumn(unsigned char *column);
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void aes_invRound(unsigned char *state, unsigned char *roundKey);
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void aes_invCipher(unsigned char *state, unsigned char *expandedKey, int nbrRounds);
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char aes_decrypt(unsigned char *input, unsigned char *output, unsigned char *key, enum keySize size);
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// Helper function to print AES state
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void printState(const unsigned char *state) {
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for (int col = 0; col < 4; col++) {
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printf("%02x %02x %02x %02x ",
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state[col], state[col + 4], state[col + 8], state[col + 12]);
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}
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printf("\n");
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}
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unsigned char getSBoxValue(unsigned char num) {
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return sbox[num];
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}
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unsigned char getSBoxInvert(unsigned char num) {
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return rsbox[num];
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}
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// left circular rotation (i.e., byte-wise rotate left) on a 4-byte word
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void rotate(unsigned char *word) {
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unsigned char temp = word[0];
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word[0] = word[1];
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word[1] = word[2];
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word[2] = word[3];
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word[3] = temp;
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}
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unsigned char getRconValue(unsigned char num) {
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return Rcon[num];
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}
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void KeySchedule(unsigned char *word, int iteration) {
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int i;
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// Key Schedule: RotWord → SubWord → XOR with Rcon
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// used during key expansion to transform the input word before XORing it with a
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// word from earlier in the expanded key array.
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// rotate the 32-bit word 8 bits to the left
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rotate(word);
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// apply S-Box substitution on all 4 parts of the 32-bit word
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for (i = 0; i < 4; ++i) {
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word[i] = getSBoxValue(word[i]);
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}
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// XOR the output of the rcon operation with i to the first part (leftmost) only
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word[0] = word[0] ^ getRconValue(iteration);
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}
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// Rijndael's key expansion: expands an 128, 192, 256 key into an 176, 208, 240 bytes key
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void KeyExpansion(unsigned char *expandedKey, unsigned char *key,
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enum keySize size, size_t expandedKeySize) {
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// current expanded keySize, in bytes
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int currentSize = 0;
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int rconIteration = 1;
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int i;
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unsigned char t[4] = {0}; // temporary 4-byte variable
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// set the 16, 24,32 bytes of the expanded key to the input key
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for (i = 0; i < size; i++)
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expandedKey[i] = key[i];
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currentSize += size;
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while (currentSize < expandedKeySize) {
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// assign the previous 4 bytes to the temporary value t
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for (i = 0; i < 4; i++) {
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t[i] = expandedKey[(currentSize - 4) + i];
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}
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// every 16, 24, 32 bytes we apply the core schedule to t
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// and increment rconIteration afterwards
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if (currentSize % size == 0) {
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KeySchedule(t, rconIteration++);
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}
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// For 256-bit keys, we add an extra sbox to the calculation
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if (size == SIZE_32 && ((currentSize % size) == 16)) {
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for (i = 0; i < 4; i++)
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t[i] = getSBoxValue(t[i]);
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}
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// We XOR t with the four-byte block 16, 24, 32 bytes before the new expanded key.
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// This becomes the next four bytes in the expanded key.
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for (i = 0; i < 4; i++) {
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expandedKey[currentSize] = expandedKey[currentSize - size] ^ t[i];
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currentSize++;
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}
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}
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}
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void subBytes(unsigned char *state) {
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for (int i = 0; i < 16; i++) {
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state[i] = getSBoxValue(state[i]);
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}
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}
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void shiftRows(unsigned char *state) {
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for (int row = 0; row < 4; row++) {
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shiftRow(state + row * 4, row);
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}
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}
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void shiftRow(unsigned char *state, unsigned char nbr) {
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unsigned char temp[4];
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// Perform rotation directly
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for (int i = 0; i < 4; i++) {
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temp[i] = state[(i + nbr) % 4];
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}
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// Copy result back to state
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for (int i = 0; i < 4; i++) {
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state[i] = temp[i];
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}
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}
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void addRoundKey(unsigned char *state, unsigned char *roundKey) {
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int i;
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for (i = 0; i < 16; i++)
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state[i] = state[i] ^ roundKey[i];
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}
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// Based on work by Tom St. Denis/Simon Johnson
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// https://www.amazon.com/Cryptography-Developers-Tom-St-Denis/dp/1597491047
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unsigned char gfmul(unsigned char a, unsigned char b) {
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unsigned char p = 0;
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for (unsigned char counter = 0; counter < 8; counter++) {
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if (b & 1)
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p ^= a;
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a = (a << 1) ^ ((a & 0x80) ? 0x1b : 0);
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b >>= 1;
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}
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return p;
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}
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// Section 5.1.3 of FIPS 197
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void mixColumns(unsigned char *state) {
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unsigned char column[4];
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for (int col = 0; col < 4; col++) {
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// Extract the column from the state
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for (int row = 0; row < 4; row++) {
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column[row] = state[row * 4 + col];
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}
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// Mix the column
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mixColumn(column);
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// Store the mixed column back into the state
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for (int row = 0; row < 4; row++) {
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state[row * 4 + col] = column[row];
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}
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}
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}
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void mixColumn(unsigned char *column) {
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unsigned char a[4], b[4];
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for (int i = 0; i < 4; i++) {
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a[i] = column[i];
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b[i] = gfmul(column[i], 2);
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}
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column[0] = b[0] ^ a[3] ^ a[2] ^ gfmul(a[1], 3);
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column[1] = b[1] ^ a[0] ^ a[3] ^ gfmul(a[2], 3);
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column[2] = b[2] ^ a[1] ^ a[0] ^ gfmul(a[3], 3);
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column[3] = b[3] ^ a[2] ^ a[1] ^ gfmul(a[0], 3);
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}
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// The rounds in the specifcation of CIPHER() are composed of the following 4 byte-oriented
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// transformations on the state (Section 5.1 of FIPS 197) - outputs hex after each step
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void aes_cipher(unsigned char *state, unsigned char *roundKey) {
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subBytes(state);
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printState(state);
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shiftRows(state);
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printState(state);
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mixColumns(state);
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printState(state);
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addRoundKey(state, roundKey);
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printf("\n"); // Optional: for spacing
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}
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void createRoundKey(unsigned char *expandedKey, unsigned char *roundKey) {
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int i, j;
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// iterate over the columns
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for (i = 0; i < 4; i++) {
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// iterate over the rows
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for (j = 0; j < 4; j++)
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roundKey[(i + (j * 4))] = expandedKey[(i * 4) + j];
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}
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}
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void aes_main(unsigned char *state, unsigned char *expandedKey, int nbrRounds) {
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unsigned char roundKey[16];
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// Initial round key
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createRoundKey(expandedKey, roundKey);
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printState(state);
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printf("\n");
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addRoundKey(state, roundKey);
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for (int i = 1; i < nbrRounds; i++) {
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createRoundKey(expandedKey + 16 * i, roundKey);
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printState(state);
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aes_cipher(state, roundKey); // includes printState calls inside if in debug mode
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}
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// Final round (no MixColumns)
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printState(state);
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createRoundKey(expandedKey + 16 * nbrRounds, roundKey);
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subBytes(state);
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printState(state);
|
||
|
||
shiftRows(state);
|
||
printState(state);
|
||
|
||
addRoundKey(state, roundKey);
|
||
printState(state);
|
||
}
|
||
|
||
char aes_encrypt(unsigned char *input, unsigned char *output,
|
||
unsigned char *key, enum keySize size) {
|
||
int nbrRounds;
|
||
int expandedKeySize;
|
||
unsigned char block[16];
|
||
unsigned char *expandedKey = NULL;
|
||
|
||
// Determine number of rounds based on key size
|
||
switch (size) {
|
||
case SIZE_16: nbrRounds = 10; break;
|
||
case SIZE_24: nbrRounds = 12; break;
|
||
case SIZE_32: nbrRounds = 14; break;
|
||
default: return ERROR_AES_UNKNOWN_KEYSIZE;
|
||
}
|
||
|
||
expandedKeySize = 16 * (nbrRounds + 1);
|
||
|
||
expandedKey = (unsigned char *)malloc(expandedKeySize);
|
||
if (expandedKey == NULL) {
|
||
return ERROR_MEMORY_ALLOCATION_FAILED;
|
||
}
|
||
|
||
// Map input (row-major to column-major for AES)
|
||
for (int row = 0; row < 4; row++) {
|
||
for (int col = 0; col < 4; col++) {
|
||
block[row + 4 * col] = input[4 * row + col];
|
||
}
|
||
}
|
||
|
||
// Expand the key
|
||
KeyExpansion(expandedKey, key, size, expandedKeySize);
|
||
|
||
// Encrypt the block
|
||
aes_main(block, expandedKey, nbrRounds);
|
||
|
||
// Map block back to output (column-major to row-major)
|
||
for (int row = 0; row < 4; row++) {
|
||
for (int col = 0; col < 4; col++) {
|
||
output[4 * row + col] = block[row + 4 * col];
|
||
}
|
||
}
|
||
|
||
// de-allocate memory for expandedKey
|
||
free(expandedKey);
|
||
return SUCCESS;
|
||
}
|
||
|
||
void invSubBytes(unsigned char *state) {
|
||
for (int i = 0; i < 16; i++) {
|
||
state[i] = getSBoxInvert(state[i]);
|
||
}
|
||
}
|
||
|
||
void invShiftRows(unsigned char *state) {
|
||
for (int row = 0; row < 4; row++) {
|
||
invShiftRow(state + row * 4, row);
|
||
}
|
||
}
|
||
|
||
void invShiftRow(unsigned char *state, unsigned char nbr) {
|
||
unsigned char temp[4];
|
||
|
||
// Perform rotation to the right by `nbr` positions
|
||
for (int i = 0; i < 4; i++) {
|
||
temp[i] = state[(i - nbr + 4) % 4];
|
||
}
|
||
|
||
// Copy back the rotated values
|
||
for (int i = 0; i < 4; i++) {
|
||
state[i] = temp[i];
|
||
}
|
||
}
|
||
|
||
void invMixColumns(unsigned char *state) {
|
||
unsigned char column[4];
|
||
|
||
for (int col = 0; col < 4; col++) {
|
||
// Extract one column (4 bytes from each row)
|
||
for (int row = 0; row < 4; row++) {
|
||
column[row] = state[row * 4 + col];
|
||
}
|
||
|
||
// Apply inverse MixColumn transformation
|
||
invMixColumn(column);
|
||
|
||
// Store transformed column back into the state
|
||
for (int row = 0; row < 4; row++) {
|
||
state[row * 4 + col] = column[row];
|
||
}
|
||
}
|
||
}
|
||
|
||
void invMixColumn(unsigned char *column) {
|
||
unsigned char a[4];
|
||
|
||
for (int i = 0; i < 4; i++)
|
||
a[i] = column[i];
|
||
|
||
unsigned char a0_14 = gfmul(a[0], 14);
|
||
unsigned char a1_11 = gfmul(a[1], 11);
|
||
unsigned char a2_13 = gfmul(a[2], 13);
|
||
unsigned char a3_9 = gfmul(a[3], 9);
|
||
|
||
unsigned char a0_9 = gfmul(a[0], 9);
|
||
unsigned char a1_14 = gfmul(a[1], 14);
|
||
unsigned char a2_11 = gfmul(a[2], 11);
|
||
unsigned char a3_13 = gfmul(a[3], 13);
|
||
|
||
unsigned char a0_13 = gfmul(a[0], 13);
|
||
unsigned char a1_9 = gfmul(a[1], 9);
|
||
unsigned char a2_14 = gfmul(a[2], 14);
|
||
unsigned char a3_11 = gfmul(a[3], 11);
|
||
|
||
unsigned char a0_11 = gfmul(a[0], 11);
|
||
unsigned char a1_13 = gfmul(a[1], 13);
|
||
unsigned char a2_9 = gfmul(a[2], 9);
|
||
unsigned char a3_14 = gfmul(a[3], 14);
|
||
|
||
column[0] = a0_14 ^ a1_11 ^ a2_13 ^ a3_9;
|
||
column[1] = a0_9 ^ a1_14 ^ a2_11 ^ a3_13;
|
||
column[2] = a0_13 ^ a1_9 ^ a2_14 ^ a3_11;
|
||
column[3] = a0_11 ^ a1_13 ^ a2_9 ^ a3_14;
|
||
}
|
||
|
||
void aes_invRound(unsigned char *state, unsigned char *roundKey) {
|
||
|
||
invShiftRows(state);
|
||
invSubBytes(state);
|
||
addRoundKey(state, roundKey);
|
||
invMixColumns(state);
|
||
}
|
||
|
||
void aes_invCipher(unsigned char *state, unsigned char *expandedKey, int nbrRounds) {
|
||
unsigned char roundKey[16];
|
||
|
||
// Initial round key for final round
|
||
createRoundKey(expandedKey + 16 * nbrRounds, roundKey);
|
||
addRoundKey(state, roundKey);
|
||
|
||
// Inverse rounds (excluding final round)
|
||
for (int round = nbrRounds - 1; round > 0; round--) {
|
||
createRoundKey(expandedKey + 16 * round, roundKey);
|
||
aes_invRound(state, roundKey);
|
||
}
|
||
|
||
// Final inverse round (no invMixColumns)
|
||
createRoundKey(expandedKey, roundKey);
|
||
invShiftRows(state);
|
||
invSubBytes(state);
|
||
addRoundKey(state, roundKey);
|
||
}
|
||
|
||
char aes_decrypt(unsigned char *input, unsigned char *output,
|
||
unsigned char *key, enum keySize size) {
|
||
int nbrRounds;
|
||
int expandedKeySize;
|
||
unsigned char block[16];
|
||
unsigned char *expandedKey = NULL;
|
||
|
||
// Determine the number of rounds based on key size
|
||
switch (size) {
|
||
case SIZE_16: nbrRounds = 10; break;
|
||
case SIZE_24: nbrRounds = 12; break;
|
||
case SIZE_32: nbrRounds = 14; break;
|
||
default: return ERROR_AES_UNKNOWN_KEYSIZE;
|
||
}
|
||
|
||
expandedKeySize = 16 * (nbrRounds + 1);
|
||
|
||
expandedKey = (unsigned char *)malloc(expandedKeySize);
|
||
if (expandedKey == NULL) {
|
||
return ERROR_MEMORY_ALLOCATION_FAILED;
|
||
}
|
||
|
||
// Transpose input (column-major block for AES)
|
||
for (int row = 0; row < 4; row++) {
|
||
for (int col = 0; col < 4; col++) {
|
||
block[row + 4 * col] = input[4 * row + col];
|
||
}
|
||
}
|
||
|
||
// Key expansion
|
||
KeyExpansion(expandedKey, key, size, expandedKeySize);
|
||
|
||
// Decrypt
|
||
aes_invCipher(block, expandedKey, nbrRounds);
|
||
|
||
// Transpose back into output (row-major)
|
||
for (int row = 0; row < 4; row++) {
|
||
for (int col = 0; col < 4; col++) {
|
||
output[4 * row + col] = block[row + 4 * col];
|
||
}
|
||
}
|
||
|
||
// de-allocate memory for expandedKey
|
||
free(expandedKey);
|
||
return SUCCESS;
|
||
}
|
||
|
||
int main(int argc, char *argv[]) {
|
||
|
||
// Rounds: Number of AES rounds
|
||
// Words/Key: Number of 32-bit words per round key (Nb = 4 for AES)
|
||
// Round Keys: Total words in expanded key = Nb × (Rounds + 1)
|
||
// KeyExp (B): Key expansion size in bytes = Round Keys × 4
|
||
// Block (B): Block size in bytes = 128 bits / 8 = 16
|
||
|
||
//+-----------+ Block Size | Rounds | Words/Key | Round Keys | KeyExp (B) | Block (B) |
|
||
//|-----------|------------|--------|-----------|------------|------------|-----------|
|
||
//| AES-128 | 128 bits | 10 | 4 | 44 | 176 | 16 |
|
||
//| AES-192 | 128 bits | 12 | 4 | 52 | 208 | 16 |
|
||
//| AES-256 | 128 bits | 14 | 4 | 60 | 240 | 16 |
|
||
//+-----------+------------+--------+-----------+------------+------------+-----------+
|
||
|
||
// the expanded keySize to store full set of round keys
|
||
int expandedKeySize = 240;
|
||
unsigned char expandedKey[expandedKeySize];
|
||
|
||
// the cipher key (FIPS 197 example (page 28) 128-bit Cipher Key in Appendix A)
|
||
//unsigned char key[16] = {0x2b, 0x7e, 0x15, 0x16, 0x28, 0xae, 0xd2, 0xa6,
|
||
// 0xab, 0xf7, 0x15, 0x88, 0x09, 0xcf, 0x4f, 0x3c};
|
||
// (FIPS 197 example (page 34) in Appendix B)
|
||
|
||
// AES uses an internal structure called the state, which is a 4x4 byte matrix (16 bytes total).
|
||
// AES operates on 128-bit blocks (16 bytes), always — regardless of key size (128, 192, 256).
|
||
//unsigned char plaintext[16] = {0x32, 0x43, 0xf6, 0xa8, 0x88, 0x5a, 0x30, 0x8d,
|
||
// 0x31, 0x31, 0x98, 0xa2, 0xe0, 0x37, 0x07, 0x34};
|
||
|
||
// the cipher key size defined on Line 86
|
||
enum keySize size = SIZE_32;
|
||
|
||
// These examples are in Appendix C of FIPS 197 starting on page 35 (2001 version)
|
||
// AES 128-bit key and plaintext input
|
||
unsigned char key[16] = {
|
||
0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07,
|
||
0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d, 0x0e, 0x0f
|
||
};
|
||
|
||
unsigned char plaintext[16] = {
|
||
0x00, 0x11, 0x22, 0x33, 0x44, 0x55, 0x66, 0x77,
|
||
0x88, 0x99, 0xaa, 0xbb, 0xcc, 0xdd, 0xee, 0xff
|
||
};
|
||
|
||
// AES-192 key and plaintext input
|
||
unsigned char key192[24] = {
|
||
0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07,
|
||
0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d, 0x0e, 0x0f,
|
||
0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17
|
||
};
|
||
|
||
unsigned char plaintext192[16] = {
|
||
0x00, 0x11, 0x22, 0x33, 0x44, 0x55, 0x66, 0x77,
|
||
0x88, 0x99, 0xaa, 0xbb, 0xcc, 0xdd, 0xee, 0xff
|
||
};
|
||
|
||
// AES-256 key and plaintext input
|
||
unsigned char key256[32] = {
|
||
0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07,
|
||
0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d, 0x0e, 0x0f,
|
||
0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17,
|
||
0x18, 0x19, 0x1a, 0x1b, 0x1c, 0x1d, 0x1e, 0x1f
|
||
};
|
||
|
||
unsigned char plaintext256[16] = {
|
||
0x00, 0x11, 0x22, 0x33, 0x44, 0x55, 0x66, 0x77,
|
||
0x88, 0x99, 0xaa, 0xbb, 0xcc, 0xdd, 0xee, 0xff
|
||
};
|
||
|
||
// the ciphertext
|
||
unsigned char ciphertext[16];
|
||
// the decrypted text
|
||
unsigned char decryptedtext[16];
|
||
int i;
|
||
|
||
printf("Implementation of the AES algorithm in C\n");
|
||
printf("\nCipher Key (hex format):\n");
|
||
for (i = 0; i < 16; i++) {
|
||
// Print characters in hex format, 16 chars per line
|
||
printf("%2.2x%c", key[i], ((i + 1) % 16) ? ' ' : '\n');
|
||
}
|
||
|
||
// Test the Key Expansion
|
||
KeyExpansion(expandedKey, key, size, expandedKeySize);
|
||
printf("\nExpanded Key (hex format):\n");
|
||
for (i = 0; i < expandedKeySize; i++) {
|
||
printf("%2.2x%c", expandedKey[i], ((i + 1) % 16) ? ' ' : '\n');
|
||
}
|
||
|
||
printf("\nPlaintext (hex format):\n");
|
||
for (i = 0; i < 16; i++) {
|
||
printf("%2.2x%c", plaintext[i], ((i + 1) % 16) ? ' ' : '\n');
|
||
}
|
||
|
||
// AES Encryption
|
||
aes_encrypt(plaintext, ciphertext, key, SIZE_32);
|
||
printf("\nCiphertext (hex format):\n");
|
||
for (i = 0; i < 16; i++) {
|
||
printf("%02x%c", ciphertext[i], ((i + 1) % 16) ? ' ' : '\n');
|
||
}
|
||
|
||
// AES Decryption
|
||
aes_decrypt(ciphertext, decryptedtext, key, SIZE_32);
|
||
printf("\nDecrypted text (hex format):\n");
|
||
for (i = 0; i < 16; i++) {
|
||
printf("%2.2x%c", decryptedtext[i], ((i + 1) % 16) ? ' ' : '\n');
|
||
}
|
||
|
||
return 0;
|
||
}
|