Криптография: зашифровать исходный текст с помощью ключа, пропустить его через S-block и выдать шифр-текст - C (СИ)

#include <stdio.h>
 
int sbox[16] = {3, 14, 1, 10, 4, 9, 5, 6, 8, 11, 15, 2, 13, 12, 0, 7};
int sboxRev[16] = {14, 2, 11, 0, 4, 6, 7, 15, 8, 5, 3, 9, 13, 12, 1, 10};
int chars[16][16];

int roundFunc(int input, int key)
{
    return sbox[key ^ input];    
}
 
int encrypt(int input, int k0, int k1)
{
    int x0 = roundFunc(input, k0);
    return x0 ^ k1;        
}
 
void findDiffs()
{
    printf("\nCreating XOR differential table:\n");
    
    int c, d, e, f;
    
    for(c = 0; c < 16; c++)
        for(d = 0; d < 16; d++)
            chars[c ^ d][sbox[ c ] ^ sbox[d]]++;        
 
    for(c = 0; c < 16; c++)
    {
        for(d = 0; d < 16; d++)
            printf("  %x ", chars[ c ][d]);
        printf("\n");
    }
    
    printf("\nDisplaying most probable differentials:\n");
    
    for(c = 0; c < 16; c++)
        for(d = 0; d < 16; d++)
            if (chars[ c ][d] == 6)            
                printf("  6/16:   %i --> %i\n", c, d);  
}
 
int knownP0[10000];
int knownP1[10000];
int knownC0[10000];
int knownC1[10000];
 
int goodP0, goodP1, goodC0, goodC1;
 
int numPairs;
 
//int realk0, realk1;
 
int chardat0[16];
int chardatmax = 0;
 
void genCharData(int indiff, int outdiff)
{
            printf("\nGenerating possible intermediate values based on differential(%i --> %i):\n", indiff, outdiff);
    
            chardatmax = 0;
            int f;
            for(f = 0; f < 16; f++)
            {
                int myComp = f ^ indiff;
                
                if ((sbox[f] ^ sbox[myComp]) == outdiff)         
                {
                    printf("  Possibles:   %i + %i --> %i + %i\n", f, myComp, sbox[f], sbox[myComp]);
                    chardat0[chardatmax] = f;
                    chardatmax++;
                }
            }    
}
 
void genPairs(int indiff)
{
    printf("\nGenerating %i known pairs with input differential of %i.\n", numPairs, indiff);
    
    int realk0 = rand() % 16;                                                       //Create random subkey0
    int realk1 = rand() % 16;                                                       //Create random subkey0
    
    printf("  Real K0 = %i\n", realk0);
    printf("  Real K1 = %i\n", realk1);

    int c;
    for(c = 0; c < numPairs; c++)                                               //Create plaintext pairs with XOR difference of indiff
    {
        knownP0[ c ] = rand() % 16;
        knownP1[ c ] = knownP0[ c ] ^ indiff;
        knownC0[ c ] = encrypt(knownP0[ c ], realk0, realk1);
        knownC1[ c ] = encrypt(knownP1[ c ], realk0, realk1);
    }  
}
 
void findGoodPair(int outdiff)
{
    printf("\nSearching for good pair:\n");
    int c;
    for(c = 0; c < numPairs; c++)
        if ((knownC0[ c ] ^ knownC1[ c ]) == outdiff)                               //Does the ciphertext pair fit the characteristic?
        {   
            goodC0 = knownC0[ c ];
            goodC1 = knownC1[ c ];
            goodP0 = knownP0[ c ];
            goodP1 = knownP1[ c ];   
            printf("  FOUND GOOD PAIR: (P0 = %i, P1 = %i) --> (C0 = %i, C1 = %i)\n", goodP0, goodP1, goodC0, goodC1);        
            return;    
        }     
    printf("NO GOOD PAIR FOUND!\n");
}
 
int testKey(int testK0, int testK1)
{
    int c;
    int crap = 0;
    for(c = 0; c < numPairs; c++)
    {
        if ((encrypt(knownP0[ c ], testK0, testK1) != knownC0[ c ]) || (encrypt(knownP1[ c ], testK0, testK1) != knownC1[ c ]))
        {
            crap = 1;
            break;
        }        
    }
    
    if (crap == 0)
        return 1;     
    else   
        return 0;   
}
 
void crack()
{
    printf("\nBrute forcing reduced keyspace:\n");
    
    int f;
    for(f = 0; f < chardatmax; f++)                                             //Test each possible value based on characteristic
    {
        int testK0 = chardat0[f] ^ goodP0;
        int testK1 = sbox[chardat0[f]] ^ goodC0;
 
        if (testKey(testK0, testK1) == 1)
            printf("  KEY! (%i, %i)\n", testK0, testK1);
        else
            printf("       (%i, %i)\n", testK0, testK1);
    }  
}
 
int main()
{
    srand(time(NULL));                                                          //Randomize values per run
    
    findDiffs();                                                                //Find some good differentials in the S-Boxes
    
    numPairs = 8;                                                               //Define number of known pairs
    
    genCharData(4, 7);                                                          //Find inputs that lead a certain characteristic
    genPairs(4);                                                                //Generate chosen-plaintext pairs
    findGoodPair(7);                                                            //Choose a known pair that satisfies the characteristic
    crack();                                                                    //Use charData and "good pair" in find key                                                               
 
    while(1){}
    return 0;    
}