// AES Implementation by X-N2O
// Started:  15:41:35 - 18 Nov 2009
// Finished: 20:03:59 - 21 Nov 2009
// Logarithm, S-Box, and RCON tables are not hardcoded
// Instead they are generated when the program starts
// All of the code below is based from the AES specification
// You can find it at http://csrc.nist.gov/publications/fips/fips197/fips-197.pdf
// You may use this code as you wish, but do not remove this comment
// This is only a proof of concept, and should not be considered as the most efficient implementation

#include <stdlib.h>
#include <string.h>
#include <stdio.h>

#define AES_RPOL      0x011b // reduction polynomial (x^8 + x^4 + x^3 + x + 1)
#define AES_GEN    0x03   // gf(2^8) generator  (x + 1)
#define AES_SBOX_CC   0x63   // S-Box C constant

#define KEY_128 (128/8)
#define KEY_192 (192/8)
#define KEY_256 (256/8)

#define aes_mul(a, b) ((a)&&(b)?g_aes_ilogt[(g_aes_logt[(a)]+g_aes_logt[(b)])%0xff]:0)
#define aes_inv(a)  ((a)?g_aes_ilogt[0xff-g_aes_logt[(a)]]:0)

unsigned char g_aes_logt[256], g_aes_ilogt[256];
unsigned char g_aes_sbox[256], g_aes_isbox[256];

typedef struct {
    unsigned char state[4][4];
    int kcol;
    size_t rounds;
    unsigned long keysched[0];
} aes_ctx_t;

void aes_init();
aes_ctx_t *aes_alloc_ctx(unsigned char *key, size_t keyLen);
inline unsigned long aes_subword(unsigned long w);
inline unsigned long aes_rotword(unsigned long w);
void aes_keyexpansion(aes_ctx_t *ctx);

inline unsigned char aes_mul_manual(unsigned char a, unsigned char b); // use aes_mul instead

void aes_subbytes(aes_ctx_t *ctx);
void aes_shiftrows(aes_ctx_t *ctx);
void aes_mixcolumns(aes_ctx_t *ctx);
void aes_addroundkey(aes_ctx_t *ctx, int round);
void aes_encrypt(aes_ctx_t *ctx, unsigned char input[16], unsigned char output[16]);

void aes_invsubbytes(aes_ctx_t *ctx);
void aes_invshiftrows(aes_ctx_t *ctx);
void aes_invmixcolumns(aes_ctx_t *ctx);
void aes_decrypt(aes_ctx_t *ctx, unsigned char input[16], unsigned char output[16]);

void aes_free_ctx(aes_ctx_t *ctx);

void init_aes()
{
    int i;
    unsigned char gen;

    // build logarithm table and it's inverse
    gen = 1;
    for(i = 0; i < 0xff; i++) {
        g_aes_logt[gen]  = i;
        g_aes_ilogt[i]   = gen;
        gen = aes_mul_manual(gen, AES_GEN);
    }

    // build S-Box and it's inverse
    for(i = 0; i <= 0xff; i++) {
        char bi;
        unsigned char inv = aes_inv(i);

        g_aes_sbox[i] = 0;
        for(bi = 0; bi < 8; bi++) {
            // based on transformation 5.1
            // could also be done with a loop based on the matrix
            g_aes_sbox[i] |= ((inv & (1<<bi)?1:0)
                        ^ (inv & (1 << ((bi+4) & 7))?1:0)
                        ^ (inv & (1 << ((bi+5) & 7))?1:0)
                        ^ (inv & (1 << ((bi+6) & 7))?1:0)
                        ^ (inv & (1 << ((bi+7) & 7))?1:0)
                        ^ (AES_SBOX_CC & (1 << bi)?1:0)
            ) << bi;
        }
        g_aes_isbox[g_aes_sbox[i]] = i;
    }
    // warning: quickhack
    g_aes_sbox[1] = 0x7c;
    g_aes_isbox[0x7c] = 1;
    g_aes_isbox[0x63] = 0;
}

aes_ctx_t *aes_alloc_ctx(unsigned char *key, size_t keyLen)
{
    aes_ctx_t *ctx;
    size_t rounds;
    size_t ks_size;

    switch(keyLen) {
        case 16: // 128-bit key
            rounds = 10;
            break;

        case 24: // 192-bit key
            rounds = 12;
            break;

        case 32: // 256-bit key
            rounds = 14;
            break;

        defaut:
            return NULL;
    }

    ks_size = 4*(rounds+1)*sizeof(unsigned long);
    ctx = malloc(sizeof(aes_ctx_t)+ks_size);
    if(ctx) {
        ctx->rounds = rounds;
        ctx->kcol = keyLen/4;
        memcpy(ctx->keysched, key, keyLen);
        ctx->keysched[43] = 0;
        aes_keyexpansion(ctx);
    }

    return ctx;
}

inline unsigned long aes_subword(unsigned long w)
{
    return g_aes_sbox[w & 0x000000ff] |
        (g_aes_sbox[(w & 0x0000ff00) >> 8] << 8) |
        (g_aes_sbox[(w & 0x00ff0000) >> 16] << 16) |
        (g_aes_sbox[(w & 0xff000000) >> 24] << 24);
}

inline unsigned long aes_rotword(unsigned long w)
{
    // May seem a bit different from the spec
    // It was changed because unsigned long is represented with little-endian convention on x86
    // Should not depend on architecture, but this is only a POC
    return ((w & 0x000000ff) << 24) |
        ((w & 0x0000ff00) >> 8) |
        ((w & 0x00ff0000) >> 8) |
        ((w & 0xff000000) >> 8);
}

void aes_keyexpansion(aes_ctx_t *ctx)
{
    unsigned long temp;
    unsigned long rcon;
    register int i;

    rcon = 0x00000001;
    for(i = ctx->kcol; i < (4*(ctx->rounds+1)); i++) {
        temp = ctx->keysched[i-1];
        if(!(i%ctx->kcol)) {
            temp = aes_subword(aes_rotword(temp)) ^ rcon;
            rcon = aes_mul(rcon, 2);
        } else if(ctx->kcol > 6 && i%ctx->kcol == 4)
            temp = aes_subword(temp);
        ctx->keysched[i] = ctx->keysched[i-ctx->kcol] ^ temp;
    }
}

inline unsigned char aes_mul_manual(unsigned char a, unsigned char b)
{
    register unsigned short ac;
    register unsigned char ret;

    ac = a;
    ret = 0;
    while(b) {
        if(b & 0x01)
            ret ^= ac;
        ac <<= 1;
        b >>= 1;
        if(ac & 0x0100)
            ac ^= AES_RPOL;
    }

    return ret;
}

void aes_subbytes(aes_ctx_t *ctx)
{
    int i;

    for(i = 0; i < 16; i++) {
        int x, y;

        x = i & 0x03;
        y = i >> 2;
        ctx->state[x][y] = g_aes_sbox[ctx->state[x][y]];
    }
}

void aes_shiftrows(aes_ctx_t *ctx)
{
    unsigned char nstate[4][4];
    int i;

    for(i = 0; i < 16; i++) {
        int x, y;

        x = i & 0x03;
        y = i >> 2;
        nstate[x][y] = ctx->state[x][(y+x) & 0x03];
    }

    memcpy(ctx->state, nstate, sizeof(ctx->state));
}

void aes_mixcolumns(aes_ctx_t *ctx)
{
    unsigned char nstate[4][4];
    int i;

    for(i = 0; i < 4; i++) {
        nstate[0][i] = aes_mul(0x02, ctx->state[0][i]) ^
                aes_mul(0x03, ctx->state[1][i]) ^
                ctx->state[2][i] ^
                ctx->state[3][i];
        nstate[1][i] = ctx->state[0][i] ^
                aes_mul(0x02, ctx->state[1][i]) ^
                aes_mul(0x03, ctx->state[2][i]) ^
                ctx->state[3][i];
        nstate[2][i] = ctx->state[0][i] ^
                ctx->state[1][i] ^
                aes_mul(0x02, ctx->state[2][i]) ^
                aes_mul(0x03, ctx->state[3][i]);
        nstate[3][i] = aes_mul(0x03, ctx->state[0][i]) ^
                ctx->state[1][i] ^
                ctx->state[2][i] ^
                aes_mul(0x02, ctx->state[3][i]);
    }

    memcpy(ctx->state, nstate, sizeof(ctx->state));
}

void aes_addroundkey(aes_ctx_t *ctx, int round)
{
    int i;

    for(i = 0; i < 16; i++) {
        int x, y;

        x = i & 0x03;
        y = i >> 2;
        ctx->state[x][y] = ctx->state[x][y] ^
            ((ctx->keysched[round*4+y] & (0xff << (x*8))) >> (x*8));
    }
}

void aes_encrypt(aes_ctx_t *ctx, unsigned char input[16], unsigned char output[16])
{
    int i;

    // copy input to state
    for(i = 0; i < 16; i++)
        ctx->state[i & 0x03][i >> 2] = input[i];

    aes_addroundkey(ctx, 0);

    for(i = 1; i < ctx->rounds; i++) {
        aes_subbytes(ctx);
        aes_shiftrows(ctx);
        aes_mixcolumns(ctx);
        aes_addroundkey(ctx, i);
    }

    aes_subbytes(ctx);
    aes_shiftrows(ctx);
    aes_addroundkey(ctx, ctx->rounds);

    // copy state to output
    for(i = 0; i < 16; i++)
        output[i] = ctx->state[i & 0x03][i >> 2];
}

void aes_invshiftrows(aes_ctx_t *ctx)
{
    unsigned char nstate[4][4];
    int i;

    for(i = 0; i < 16; i++) {
        int x, y;

        x = i & 0x03;
        y = i >> 2;
        nstate[x][(y+x) & 0x03] = ctx->state[x][y];
    }

    memcpy(ctx->state, nstate, sizeof(ctx->state));
}

void aes_invsubbytes(aes_ctx_t *ctx)
{
    int i;

    for(i = 0; i < 16; i++) {
        int x, y;

        x = i & 0x03;
        y = i >> 2;
        ctx->state[x][y] = g_aes_isbox[ctx->state[x][y]];
    }
}

void aes_invmixcolumns(aes_ctx_t *ctx)
{
    unsigned char nstate[4][4];
    int i;

    for(i = 0; i < 4; i++) {
        nstate[0][i] = aes_mul(0x0e, ctx->state[0][i]) ^
                aes_mul(0x0b, ctx->state[1][i]) ^
                aes_mul(0x0d, ctx->state[2][i]) ^
                aes_mul(0x09, ctx->state[3][i]);
        nstate[1][i] = aes_mul(0x09, ctx->state[0][i]) ^
                aes_mul(0x0e, ctx->state[1][i]) ^
                aes_mul(0x0b, ctx->state[2][i]) ^
                aes_mul(0x0d, ctx->state[3][i]);
        nstate[2][i] = aes_mul(0x0d, ctx->state[0][i]) ^
                aes_mul(0x09, ctx->state[1][i]) ^
                aes_mul(0x0e, ctx->state[2][i]) ^
                aes_mul(0x0b, ctx->state[3][i]);
        nstate[3][i] = aes_mul(0x0b, ctx->state[0][i]) ^
                aes_mul(0x0d, ctx->state[1][i]) ^
                aes_mul(0x09, ctx->state[2][i]) ^
                aes_mul(0x0e, ctx->state[3][i]);
    }

    memcpy(ctx->state, nstate, sizeof(ctx->state));
}

void aes_decrypt(aes_ctx_t *ctx, unsigned char input[16], unsigned char output[16])
{
    int i, j;

    // copy input to state
    for(i = 0; i < 16; i++)
        ctx->state[i & 0x03][i >> 2] = input[i];

    aes_addroundkey(ctx, ctx->rounds);
    for(i = ctx->rounds-1; i >= 1; i--) {
        aes_invshiftrows(ctx);
        aes_invsubbytes(ctx);
        aes_addroundkey(ctx, i);
        aes_invmixcolumns(ctx);
    }

    aes_invshiftrows(ctx);
    aes_invsubbytes(ctx);
    aes_addroundkey(ctx, 0);

    // copy state to output
    for(i = 0; i < 16; i++)
        output[i] = ctx->state[i & 0x03][i >> 2];
}

void aes_free_ctx(aes_ctx_t *ctx)
{
    free(ctx);
}

int main(int argc, char *argv[])
{
    unsigned char key[KEY_128] = "uber strong key!";
    unsigned char ptext[16] = "Attack at dawn!";
    unsigned char ctext[16];
    unsigned char decptext[16];
    aes_ctx_t *ctx;

    init_aes();
    ctx = aes_alloc_ctx(key, sizeof(key));
    if(!ctx) {
        perror("aes_alloc_ctx");
        return EXIT_FAILURE;
    }
    aes_encrypt(ctx, ptext, ctext);
    aes_decrypt(ctx, ctext, decptext);
    puts(decptext);

    aes_free_ctx(ctx);
    return EXIT_SUCCESS;
}

/*
C:\Users\Heavy\Desktop>cl main.cpp
Microsoft (R) C/C++ Optimizing Compiler Version 17.00.50727.1 for x64
Copyright (C) Microsoft Corporation.  All rights reserved.

main.cpp
main.cpp(119) : error C2440: '=' : cannot convert from 'void *' to 'aes_ctx_t *'

        Conversion from 'void*' to pointer to non-'void' requires an explicit ca
st
main.cpp(371) : error C2117: 'key' : array bounds overflow
        main.cpp(371) : see declaration of 'key'
        main.cpp(371) : see declaration of 'key'
main.cpp(385) : error C2664: 'puts' : cannot convert parameter 1 from 'unsigned
char [16]' to 'const char *'
        Types pointed to are unrelated; conversion requires reinterpret_cast, C-
style cast or function-style cast

C:\Users\Heavy\Desktop>
*/