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deayzl's blog

[VishwaCTF] 0 | 1 writeup 본문

CTF writeup/Others

[VishwaCTF] 0 | 1 writeup

deayzl 2023. 4. 2. 19:33

files: encrypt.c, isThisFileUseful.txt, justBinaries.txt, up_down.py

isThisFileUseful.txt:

1001010110001010100011001000101110011110100101001001101010000110

justBinaries.txt:

111101000001010101111111011100111110010011010000100011011011010011001011000001111111101001110001100000011000110111111111010000100011011011000101101001001011001111100001110111111110010010001010100101001000111000000101000100100011101100000111100110100000001001100100111001010000000101100110001111111000001000100010011010001001000010010110000110101010010010111010101010001110011000100010

up_down.py:

#Just a simple Python program. Isn't it??

k = "1010"
n = ""

for i in k:
    if i == '0':
        n += '1'

    else:
        n += '0'

print(n)

encrypt.c:

#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
#include <math.h>
#include <time.h>
 
int IP[] =
{
    58, 50, 42, 34, 26, 18, 10, 2,
    60, 52, 44, 36, 28, 20, 12, 4,
    62, 54, 46, 38, 30, 22, 14, 6,
    64, 56, 48, 40, 32, 24, 16, 8,
    57, 49, 41, 33, 25, 17,  9, 1,
    59, 51, 43, 35, 27, 19, 11, 3,
    61, 53, 45, 37, 29, 21, 13, 5,
    63, 55, 47, 39, 31, 23, 15, 7
};
 
int E[] =
{
    32,  1,  2,  3,  4,  5,
    4,  5,  6,  7,  8,  9,
    8,  9, 10, 11, 12, 13,
    12, 13, 14, 15, 16, 17,
    16, 17, 18, 19, 20, 21,
    20, 21, 22, 23, 24, 25,
    24, 25, 26, 27, 28, 29,
    28, 29, 30, 31, 32,  1
};
 
int P[] =
{
    16,  7, 20, 21,
    29, 12, 28, 17,
    1, 15, 23, 26,
    5, 18, 31, 10,
    2,  8, 24, 14,
    32, 27,  3,  9,
    19, 13, 30,  6,
    22, 11,  4, 25
};
 
int FP[] =
{
    40, 8, 48, 16, 56, 24, 64, 32,
    39, 7, 47, 15, 55, 23, 63, 31,
    38, 6, 46, 14, 54, 22, 62, 30,
    37, 5, 45, 13, 53, 21, 61, 29,
    36, 4, 44, 12, 52, 20, 60, 28,
    35, 3, 43, 11, 51, 19, 59, 27,
    34, 2, 42, 10, 50, 18, 58, 26,
    33, 1, 41,  9, 49, 17, 57, 25
};
 
int S1[4][16] =
{
        14,  4, 13,  1,  2, 15, 11,  8,  3, 10,  6, 12,  5,  9,  0,  7,
        0, 15,  7,  4, 14,  2, 13,  1, 10,  6, 12, 11,  9,  5,  3,  8,
        4,  1, 14,  8, 13,  6,  2, 11, 15, 12,  9,  7,  3, 10,  5,  0,
        15, 12,  8,  2,  4,  9,  1,  7,  5, 11,  3, 14, 10,  0,  6, 13
};
 
int S2[4][16] =
{
    15,  1,  8, 14,  6, 11,  3,  4,  9,  7,  2, 13, 12,  0,  5, 10,
    3, 13,  4,  7, 15,  2,  8, 14, 12,  0,  1, 10,  6,  9, 11,  5,
    0, 14,  7, 11, 10,  4, 13,  1,  5,  8, 12,  6,  9,  3,  2, 15,
    13,  8, 10,  1,  3, 15,  4,  2, 11,  6,  7, 12,  0,  5, 14,  9
};
 
int S3[4][16] =
{
    10,  0,  9, 14,  6,  3, 15,  5,  1, 13, 12,  7, 11,  4,  2,  8,
    13,  7,  0,  9,  3,  4,  6, 10,  2,  8,  5, 14, 12, 11, 15,  1,
    13,  6,  4,  9,  8, 15,  3,  0, 11,  1,  2, 12,  5, 10, 14,  7,
    1, 10, 13,  0,  6,  9,  8,  7,  4, 15, 14,  3, 11,  5,  2, 12
};
 
int S4[4][16] =
{
    7, 13, 14,  3,  0,  6,  9, 10,  1,  2,  8,  5, 11, 12,  4, 15,
    13,  8, 11,  5,  6, 15,  0,  3,  4,  7,  2, 12,  1, 10, 14,  9,
    10,  6,  9,  0, 12, 11,  7, 13, 15,  1,  3, 14,  5,  2,  8,  4,
    3, 15,  0,  6, 10,  1, 13,  8,  9,  4,  5, 11, 12,  7,  2, 14
};
 
int S5[4][16] =
{
    2, 12,  4,  1,  7, 10, 11,  6,  8,  5,  3, 15, 13,  0, 14,  9,
    14, 11,  2, 12,  4,  7, 13,  1,  5,  0, 15, 10,  3,  9,  8,  6,
    4,  2,  1, 11, 10, 13,  7,  8, 15,  9, 12,  5,  6,  3,  0, 14,
    11,  8, 12,  7,  1, 14,  2, 13,  6, 15,  0,  9, 10,  4,  5,  3
};
 
int S6[4][16] =
{
    12,  1, 10, 15,  9,  2,  6,  8,  0, 13,  3,  4, 14,  7,  5, 11,
    10, 15,  4,  2,  7, 12,  9,  5,  6,  1, 13, 14,  0, 11,  3,  8,
    9, 14, 15,  5,  2,  8, 12,  3,  7,  0,  4, 10,  1, 13, 11,  6,
    4,  3,  2, 12,  9,  5, 15, 10, 11, 14,  1,  7,  6,  0,  8, 13
};
 
int S7[4][16]=
{
    4, 11,  2, 14, 15,  0,  8, 13,  3, 12,  9,  7,  5, 10,  6,  1,
    13,  0, 11,  7,  4,  9,  1, 10, 14,  3,  5, 12,  2, 15,  8,  6,
    1,  4, 11, 13, 12,  3,  7, 14, 10, 15,  6,  8,  0,  5,  9,  2,
    6, 11, 13,  8,  1,  4, 10,  7,  9,  5,  0, 15, 14,  2,  3, 12
};
 
int S8[4][16]=
{
    13,  2,  8,  4,  6, 15, 11,  1, 10,  9,  3, 14,  5,  0, 12,  7,
    1, 15, 13,  8, 10,  3,  7,  4, 12,  5,  6, 11,  0, 14,  9,  2,
    7, 11,  4,  1,  9, 12, 14,  2,  0,  6, 10, 13, 15,  3,  5,  8,
    2,  1, 14,  7,  4, 10,  8, 13, 15, 12,  9,  0,  3,  5,  6, 11
};
 
int PC1[] =
{
    57, 49, 41, 33, 25, 17,  9,
    1, 58, 50, 42, 34, 26, 18,
    10,  2, 59, 51, 43, 35, 27,
    19, 11,  3, 60, 52, 44, 36,
    63, 55, 47, 39, 31, 23, 15,
    7, 62, 54, 46, 38, 30, 22,
    14,  6, 61, 53, 45, 37, 29,
    21, 13,  5, 28, 20, 12,  4
};
 
int PC2[] =
{
    14, 17, 11, 24,  1,  5,
    3, 28, 15,  6, 21, 10,
    23, 19, 12,  4, 26,  8,
    16,  7, 27, 20, 13,  2,
    41, 52, 31, 37, 47, 55,
    30, 40, 51, 45, 33, 48,
    44, 49, 39, 56, 34, 53,
    46, 42, 50, 36, 29, 32
};
 
int SHIFTS[] = { 1, 1, 2, 2, 2, 2, 2, 2, 1, 2, 2, 2, 2, 2, 2, 1 };
 
FILE* out;
int LEFT[17][32], RIGHT[17][32];
int IPtext[64];
int EXPtext[48];
int XORtext[48];
int X[8][6];
int X2[32];
int R[32];
int key56bit[56];
int key48bit[17][48];
int CIPHER[64];
int ENCRYPTED[64];
 
void expansion_function(int pos, int text)
{
    for (int i = 0; i < 48; i++)
    {
        if (E[i] == pos + 1) {
            EXPtext[i] = text;
        }
    }
}
 
int initialPermutation(int pos, int text)
{
    int i;
    for (i = 0; i < 64; i++)
    {
        if (IP[i] == pos + 1) {
            break;
        }
    }
    IPtext[i] = text;
}
 
int F1(int i)
{
    int r, c, b[6];
 
    for (int j = 0; j < 6; j++) {
        b[j] = X[i][j];
    }
 
    r = b[0] * 2 + b[5];
    c = 8 * b[1] + 4 * b[2] + 2 * b[3] + b[4];
 
    if (i == 0) {
        return S1[r][c];
    }
    else if (i == 1) {
        return S2[r][c];
    }
    else if (i == 2) {
        return S3[r][c];
    }
    else if (i == 3) {
        return S4[r][c];
    }
    else if (i == 4) {
        return S5[r][c];
    }
    else if (i == 5) {
        return S6[r][c];
    }
    else if (i == 6) {
        return S7[r][c];
    }
    else if (i == 7) {
        return S8[r][c];
    }
}
 
int XOR(int a, int b) {
    return (a ^ b);
}
 
int ToBits(int value)
{
    int k, j, m;
    static int i;
 
    if (i % 32 == 0) {
        i = 0;
    }
 
    for (j = 3; j >= 0; j--)
    {
        m = 1 << j;
        k = value & m;
        if (k == 0) {
            X2[3 - j + i] = '0' - 48;
        }
        else {
            X2[3 - j + i] = '1' - 48;
        }
    }
 
    i = i + 4;
}
 
int SBox(int XORtext[])
{
    int k = 0;
    for (int i = 0; i < 8; i++)
    {
        for (int j = 0; j < 6; j++) {
            X[i][j] = XORtext[k++];
        }
    }
 
    int value;
    for (int i = 0; i < 8; i++)
    {
        value = F1(i);
        ToBits(value);
    }
}
 
int PBox(int pos, int text)
{
    int i;
    for (i = 0; i < 32; i++)
    {
        if (P[i] == pos + 1) {
            break;
        }
    }
    R[i] = text;
}
 
void cipher(int Round, int mode)
{
    for (int i = 0; i < 32; i++) {
        expansion_function(i, RIGHT[Round - 1][i]);
    }
 
    for (int i = 0; i < 48; i++)
    {
        if (mode == 0) {
            XORtext[i] = XOR(EXPtext[i], key48bit[Round][i]);
        }
        else {
            XORtext[i] = XOR(EXPtext[i], key48bit[17 - Round][i]);
        }
    }
 
    SBox(XORtext);
 
    for (int i = 0; i < 32; i++) {
        PBox(i, X2[i]);
    }
 
    for (int i = 0; i < 32; i++) {
        RIGHT[Round][i] = XOR(LEFT[Round - 1][i], R[i]);
    }
}
 
void finalPermutation(int pos, int text)
{
    int i;
    for (i = 0; i < 64; i++)
    {
        if (FP[i] == pos + 1) {
            break;
        }
    }
    ENCRYPTED[i] = text;
}
 
void convertToBinary(int n)
{
    int k, m;
    for (int i = 7; i >= 0; i--)
    {
        m = 1 << i;
        k = n & m;
 
        if (k == 0) {
            fprintf(out, "0");
        }
        else {
            fprintf(out, "1");
        }
    }
}
 
int convertCharToBit(long int n)
{
    FILE* inp = fopen("flag.txt", "rb");
    out = fopen("bits.txt", "wb+");
    char ch;
    int i = n * 8;
 
    while (i)
    {
        ch = fgetc(inp);
        if (ch == -1) {
            break;
        }
        i--;
        convertToBinary(ch);
    }
    fclose(out);
    fclose(inp);
}
 
void Encryption(long int plain[])
{
    out = fopen("justBinaries.txt", "ab+");
    for (int i = 0; i < 64; i++) {
        initialPermutation(i, plain[i]);
    }
 
    for (int i = 0; i < 32; i++) {
        LEFT[0][i] = IPtext[i];
    }
 
    for (int i = 32; i < 64; i++) {
        RIGHT[0][i - 32] = IPtext[i];
    }
 
    for (int k = 1; k < 17; k++)
    {
        cipher(k, 0);
 
        for (int i = 0; i < 32; i++)
            LEFT[k][i] = RIGHT[k - 1][i];
    }
 
    for (int i = 0; i < 64; i++)
    {
        if (i < 32) {
            CIPHER[i] = RIGHT[16][i];
        }
        else {
            CIPHER[i] = LEFT[16][i - 32];
        }
        finalPermutation(i, CIPHER[i]);
    }
 
    for (int i = 0; i < 64; i++) {
        fprintf(out, "%d", ENCRYPTED[i]);
    }
    fclose(out);
}

void convertToBits(int ch[])
{
    int value = 0;
    for (int i = 7; i >= 0; i--) {
        value += (int)pow(2, i) * ch[7 - i];
    }
    fprintf(out, "%c", value);
}
 
int bittochar()
{
    out = fopen("result.txt", "ab+");
    for (int i = 0; i < 64; i = i + 8) {
        convertToBits(&ENCRYPTED[i]);
    }
    fclose(out);
}
 
void key56to48(int round, int pos, int text)
{
    int i;
    for (i = 0; i < 56; i++)
    {
        if (PC2[i] == pos + 1) {
            break;
        }
    }
    key48bit[round][i] = text;
}
 
int key64to56(int pos, int text)
{
    int i;
    for (i = 0; i < 56; i++)
    {
        if (PC1[i] == pos + 1) {
            break;
        }
    }
    key56bit[i] = text;
}
 
void key64to48(unsigned int key[])
{
    int k, backup[17][2];
    int CD[17][56];
    int C[17][28], D[17][28];
 
    for (int i = 0; i < 64; i++) {
        key64to56(i, key[i]);
    }
 
    for (int i = 0; i < 56; i++)
    {
        if (i < 28) {
            C[0][i] = key56bit[i];
        }
        else {
            D[0][i - 28] = key56bit[i];
        }
    }
 
    for (int x = 1; x < 17; x++)
    {
        int shift = SHIFTS[x - 1];
 
        for (int i = 0; i < shift; i++) {
            backup[x - 1][i] = C[x - 1][i];
        }
 
        for (int i = 0; i < (28 - shift); i++) {
            C[x][i] = C[x - 1][i + shift];
        }
 
        k = 0;
        for (int i = 28 - shift; i < 28; i++) {
            C[x][i] = backup[x - 1][k++];
        }
 
        for (int i = 0; i < shift; i++) {
            backup[x - 1][i] = D[x - 1][i];
        }
 
        for (int i = 0; i < (28 - shift); i++) {
            D[x][i] = D[x - 1][i + shift];
        }
 
        k = 0;
        for (int i = 28 - shift; i < 28; i++) {
            D[x][i] = backup[x - 1][k++];
        }
    }
 
    for (int j = 0; j < 17; j++)
    {
        for (int i = 0; i < 28; i++) {
            CD[j][i] = C[j][i];
        }
 
        for (int i = 28; i < 56; i++) {
            CD[j][i] = D[j][i - 28];
        }
    }
 
    for (int j = 1; j < 17; j++)
    {
        for (int i = 0; i < 56; i++) {
            key56to48(j, i, CD[j][i]);
        }
    }
}

void encrypt(long int n)
{
    FILE* in = fopen("bits.txt", "rb");
 
    long int plain[n * 64];
    int i = -1;
    char ch;
 
    while (!feof(in))
    {
        ch = getc(in);
        plain[++i] = ch - 48;
    }
 
    for (int i = 0; i < n; i++) {
        Encryption(plain + 64 * i);
    }
 
    fclose(in);
}
 
void create16Keys()
{
    FILE* pt = fopen("key.txt", "rb");
    unsigned int key[64];
    int i = 0, ch;
 
    while (!feof(pt))
    {
        ch = getc(pt);
        key[i++] = ch - 48;
    }
 
    key64to48(key);
    fclose(pt);
}
 
long int findFileSize()
{
    FILE* inp = fopen("flag.txt", "rb");
    long int size;
 
    if (fseek(inp, 0L, SEEK_END)) {
        perror("fseek() failed");
    }
    else {
        size = ftell(inp);
    }
    fclose(inp);
 
    return size;
}
 
int main()
{ 
    create16Keys();
 
    long int n = findFileSize() / 8;
    convertCharToBit(n);
 
    encrypt(n);
 
    return 0;
}

The code of "encrypt.c" is quite similar with this code.

https://github.com/dhuertas/DES/blob/master/des.c

GitHub - dhuertas/DES: DES algorithm implementation in C

DES algorithm implementation in C. Contribute to dhuertas/DES development by creating an account on GitHub.

github.com

void cipher(int Round, int mode)
{
    for (int i = 0; i < 32; i++) {
        expansion_function(i, RIGHT[Round - 1][i]);
    }
 
    for (int i = 0; i < 48; i++)
    {
        if (mode == 0) {
            XORtext[i] = XOR(EXPtext[i], key48bit[Round][i]);
        }
        else {
            XORtext[i] = XOR(EXPtext[i], key48bit[17 - Round][i]);
        }
    }
 
    SBox(XORtext);
 
    for (int i = 0; i < 32; i++) {
        PBox(i, X2[i]);
    }
 
    for (int i = 0; i < 32; i++) {
        RIGHT[Round][i] = XOR(LEFT[Round - 1][i], R[i]);
    }
}

void Encryption(long int plain[])
{
    out = fopen("justBinaries.txt", "ab+");
    for (int i = 0; i < 64; i++) {
        initialPermutation(i, plain[i]);
    }
 
    for (int i = 0; i < 32; i++) {
        LEFT[0][i] = IPtext[i];
    }
 
    for (int i = 32; i < 64; i++) {
        RIGHT[0][i - 32] = IPtext[i];
    }
 
    for (int k = 1; k < 17; k++)
    {
        cipher(k, 0);
 
        for (int i = 0; i < 32; i++)
            LEFT[k][i] = RIGHT[k - 1][i];
    }
 
    for (int i = 0; i < 64; i++)
    {
        if (i < 32) {
            CIPHER[i] = RIGHT[16][i];
        }
        else {
            CIPHER[i] = LEFT[16][i - 32];
        }
        finalPermutation(i, CIPHER[i]);
    }
 
    for (int i = 0; i < 64; i++) {
        fprintf(out, "%d", ENCRYPTED[i]);
    }
    fclose(out);
}

If you compare the code with des code, you can figure out that the code works as decryption when mode (which is the second parameter of the function "cipher") is 1.

So, you can make a Decryption function like this.

(you can change the names of arrays "plain" and "ENCRYPTED" to ones you want, if you want)

void Decryption(long int plain[])
{
    out = fopen("decryptedBinaries.txt", "ab+");
    for (int i = 0; i < 64; i++) {
        initialPermutation(i, plain[i]);
    }
 
    for (int i = 0; i < 32; i++) {
        LEFT[0][i] = IPtext[i];
    }
 
    for (int i = 32; i < 64; i++) {
        RIGHT[0][i - 32] = IPtext[i];
    }
 
    for (int k = 1; k < 17; k++)
    {
        cipher(k, 1);
 
        for (int i = 0; i < 32; i++)
            LEFT[k][i] = RIGHT[k - 1][i];
    }
 
    for (int i = 0; i < 64; i++)
    {
        if (i < 32) {
            CIPHER[i] = RIGHT[16][i];
        }
        else {
            CIPHER[i] = LEFT[16][i - 32];
        }
        finalPermutation(i, CIPHER[i]);
    }
 
    for (int i = 0; i < 64; i++) {
        fprintf(out, "%d", ENCRYPTED[i]);
        printf("%d", ENCRYPTED[i]);
    }
    fclose(out);
}

void decrypt(long int n)
{
    FILE* in = fopen("justBinaries.txt", "rb");
 
    long int plain[n * 64];
    int i = -1;
    char ch;
 
    while (!feof(in))
    {
        ch = getc(in);
        plain[++i] = ch - 48;
    }
 
    for (int i = 0; i < n; i++) {
        Decryption(plain + 64 * i);
    }
 
    fclose(in);
}

If you see the function "Encryption", you can find that the encrypted flag is in "justBinaries.txt".

The size of file "justBinaries.txt" is 384 bytes, so integer "n" (which is the first parameter of the function "decrypt") must be 6.

(Cause 6 x 8 x 8 = 384)

(+ The size of file "isThisFileUseful.txt" is 64 bytes which means length of the data is 64 bits. So you can guess that this data must be the key used to encrypt flag. Go fix the code "keys.txt" -> "isThisFileUseful.txt" in the function "create16Keys")

Considering that "up_down.py" exists, you need to flip bits of "justBinaries.txt" and "isThisFileUseful.txt".

content = ''
with open('justBinaries.txt', 'rt') as f:
    while True:
        a = f.read(1)
        if len(a) == 0:
            break
        if a == '1':
            content += '0'
        else:
            content += '1'
with open('justBinaries_inversed.txt', 'wt') as f:
    f.write(content)

Then decryption code must be like this.

#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
#include <math.h>
#include <time.h>
#include <string.h>
 
int IP[] =
{
    58, 50, 42, 34, 26, 18, 10, 2,
    60, 52, 44, 36, 28, 20, 12, 4,
    62, 54, 46, 38, 30, 22, 14, 6,
    64, 56, 48, 40, 32, 24, 16, 8,
    57, 49, 41, 33, 25, 17,  9, 1,
    59, 51, 43, 35, 27, 19, 11, 3,
    61, 53, 45, 37, 29, 21, 13, 5,
    63, 55, 47, 39, 31, 23, 15, 7
};
 
int E[] =
{
    32,  1,  2,  3,  4,  5,
    4,  5,  6,  7,  8,  9,
    8,  9, 10, 11, 12, 13,
    12, 13, 14, 15, 16, 17,
    16, 17, 18, 19, 20, 21,
    20, 21, 22, 23, 24, 25,
    24, 25, 26, 27, 28, 29,
    28, 29, 30, 31, 32,  1
};
 
int P[] =
{
    16,  7, 20, 21,
    29, 12, 28, 17,
    1, 15, 23, 26,
    5, 18, 31, 10,
    2,  8, 24, 14,
    32, 27,  3,  9,
    19, 13, 30,  6,
    22, 11,  4, 25
};
 
int FP[] =
{
    40, 8, 48, 16, 56, 24, 64, 32,
    39, 7, 47, 15, 55, 23, 63, 31,
    38, 6, 46, 14, 54, 22, 62, 30,
    37, 5, 45, 13, 53, 21, 61, 29,
    36, 4, 44, 12, 52, 20, 60, 28,
    35, 3, 43, 11, 51, 19, 59, 27,
    34, 2, 42, 10, 50, 18, 58, 26,
    33, 1, 41,  9, 49, 17, 57, 25
};
 
int S1[4][16] =
{
        14,  4, 13,  1,  2, 15, 11,  8,  3, 10,  6, 12,  5,  9,  0,  7,
        0, 15,  7,  4, 14,  2, 13,  1, 10,  6, 12, 11,  9,  5,  3,  8,
        4,  1, 14,  8, 13,  6,  2, 11, 15, 12,  9,  7,  3, 10,  5,  0,
        15, 12,  8,  2,  4,  9,  1,  7,  5, 11,  3, 14, 10,  0,  6, 13
};
 
int S2[4][16] =
{
    15,  1,  8, 14,  6, 11,  3,  4,  9,  7,  2, 13, 12,  0,  5, 10,
    3, 13,  4,  7, 15,  2,  8, 14, 12,  0,  1, 10,  6,  9, 11,  5,
    0, 14,  7, 11, 10,  4, 13,  1,  5,  8, 12,  6,  9,  3,  2, 15,
    13,  8, 10,  1,  3, 15,  4,  2, 11,  6,  7, 12,  0,  5, 14,  9
};
 
int S3[4][16] =
{
    10,  0,  9, 14,  6,  3, 15,  5,  1, 13, 12,  7, 11,  4,  2,  8,
    13,  7,  0,  9,  3,  4,  6, 10,  2,  8,  5, 14, 12, 11, 15,  1,
    13,  6,  4,  9,  8, 15,  3,  0, 11,  1,  2, 12,  5, 10, 14,  7,
    1, 10, 13,  0,  6,  9,  8,  7,  4, 15, 14,  3, 11,  5,  2, 12
};
 
int S4[4][16] =
{
    7, 13, 14,  3,  0,  6,  9, 10,  1,  2,  8,  5, 11, 12,  4, 15,
    13,  8, 11,  5,  6, 15,  0,  3,  4,  7,  2, 12,  1, 10, 14,  9,
    10,  6,  9,  0, 12, 11,  7, 13, 15,  1,  3, 14,  5,  2,  8,  4,
    3, 15,  0,  6, 10,  1, 13,  8,  9,  4,  5, 11, 12,  7,  2, 14
};
 
int S5[4][16] =
{
    2, 12,  4,  1,  7, 10, 11,  6,  8,  5,  3, 15, 13,  0, 14,  9,
    14, 11,  2, 12,  4,  7, 13,  1,  5,  0, 15, 10,  3,  9,  8,  6,
    4,  2,  1, 11, 10, 13,  7,  8, 15,  9, 12,  5,  6,  3,  0, 14,
    11,  8, 12,  7,  1, 14,  2, 13,  6, 15,  0,  9, 10,  4,  5,  3
};
 
int S6[4][16] =
{
    12,  1, 10, 15,  9,  2,  6,  8,  0, 13,  3,  4, 14,  7,  5, 11,
    10, 15,  4,  2,  7, 12,  9,  5,  6,  1, 13, 14,  0, 11,  3,  8,
    9, 14, 15,  5,  2,  8, 12,  3,  7,  0,  4, 10,  1, 13, 11,  6,
    4,  3,  2, 12,  9,  5, 15, 10, 11, 14,  1,  7,  6,  0,  8, 13
};
 
int S7[4][16]=
{
    4, 11,  2, 14, 15,  0,  8, 13,  3, 12,  9,  7,  5, 10,  6,  1,
    13,  0, 11,  7,  4,  9,  1, 10, 14,  3,  5, 12,  2, 15,  8,  6,
    1,  4, 11, 13, 12,  3,  7, 14, 10, 15,  6,  8,  0,  5,  9,  2,
    6, 11, 13,  8,  1,  4, 10,  7,  9,  5,  0, 15, 14,  2,  3, 12
};
 
int S8[4][16]=
{
    13,  2,  8,  4,  6, 15, 11,  1, 10,  9,  3, 14,  5,  0, 12,  7,
    1, 15, 13,  8, 10,  3,  7,  4, 12,  5,  6, 11,  0, 14,  9,  2,
    7, 11,  4,  1,  9, 12, 14,  2,  0,  6, 10, 13, 15,  3,  5,  8,
    2,  1, 14,  7,  4, 10,  8, 13, 15, 12,  9,  0,  3,  5,  6, 11
};
 
int PC1[] =
{
    57, 49, 41, 33, 25, 17,  9,
    1, 58, 50, 42, 34, 26, 18,
    10,  2, 59, 51, 43, 35, 27,
    19, 11,  3, 60, 52, 44, 36,
    63, 55, 47, 39, 31, 23, 15,
    7, 62, 54, 46, 38, 30, 22,
    14,  6, 61, 53, 45, 37, 29,
    21, 13,  5, 28, 20, 12,  4
};
 
int PC2[] =
{
    14, 17, 11, 24,  1,  5,
    3, 28, 15,  6, 21, 10,
    23, 19, 12,  4, 26,  8,
    16,  7, 27, 20, 13,  2,
    41, 52, 31, 37, 47, 55,
    30, 40, 51, 45, 33, 48,
    44, 49, 39, 56, 34, 53,
    46, 42, 50, 36, 29, 32
};
 
int SHIFTS[] = { 1, 1, 2, 2, 2, 2, 2, 2, 1, 2, 2, 2, 2, 2, 2, 1 };
 
FILE* out;
int LEFT[17][32], RIGHT[17][32];
int IPtext[64];
int EXPtext[48];
int XORtext[48];
int X[8][6];
int X2[32];
int R[32];
int key56bit[56];
int key48bit[17][48];
int CIPHER[64];
int ENCRYPTED[64];
 
void expansion_function(int pos, int text)
{
    for (int i = 0; i < 48; i++)
    {
        if (E[i] == pos + 1) {
            EXPtext[i] = text;
        }
    }
}
 
int initialPermutation(int pos, int text)
{
    int i;
    for (i = 0; i < 64; i++)
    {
        if (IP[i] == pos + 1) {
            break;
        }
    }
    IPtext[i] = text;
}
 
int F1(int i)
{
    int r, c, b[6];
 
    for (int j = 0; j < 6; j++) {
        b[j] = X[i][j];
    }
 
    r = b[0] * 2 + b[5];
    c = 8 * b[1] + 4 * b[2] + 2 * b[3] + b[4];
 
    if (i == 0) {
        return S1[r][c];
    }
    else if (i == 1) {
        return S2[r][c];
    }
    else if (i == 2) {
        return S3[r][c];
    }
    else if (i == 3) {
        return S4[r][c];
    }
    else if (i == 4) {
        return S5[r][c];
    }
    else if (i == 5) {
        return S6[r][c];
    }
    else if (i == 6) {
        return S7[r][c];
    }
    else if (i == 7) {
        return S8[r][c];
    }
}
 
int XOR(int a, int b) {
    return (a ^ b);
}
 
int ToBits(int value)
{
    int k, j, m;
    static int i;
 
    if (i % 32 == 0) {
        i = 0;
    }
 
    for (j = 3; j >= 0; j--)
    {
        m = 1 << j;
        k = value & m;
        if (k == 0) {
            X2[3 - j + i] = '0' - 48;
        }
        else {
            X2[3 - j + i] = '1' - 48;
        }
    }
 
    i = i + 4;
}
 
int SBox(int XORtext[])
{
    int k = 0;
    for (int i = 0; i < 8; i++)
    {
        for (int j = 0; j < 6; j++) {
            X[i][j] = XORtext[k++];
        }
    }
 
    int value;
    for (int i = 0; i < 8; i++)
    {
        value = F1(i);
        ToBits(value);
    }
}
 
int PBox(int pos, int text)
{
    int i;
    for (i = 0; i < 32; i++)
    {
        if (P[i] == pos + 1) {
            break;
        }
    }
    R[i] = text;
}
 
void cipher(int Round, int mode)
{
    for (int i = 0; i < 32; i++) {
        expansion_function(i, RIGHT[Round - 1][i]);
    }
 
    for (int i = 0; i < 48; i++)
    {
        if (mode == 0) {
            XORtext[i] = XOR(EXPtext[i], key48bit[Round][i]);
        }
        else {
            XORtext[i] = XOR(EXPtext[i], key48bit[17 - Round][i]);
        }
    }
 
    SBox(XORtext);
 
    for (int i = 0; i < 32; i++) {
        PBox(i, X2[i]);
    }
 
    for (int i = 0; i < 32; i++) {
        RIGHT[Round][i] = XOR(LEFT[Round - 1][i], R[i]);
    }
}
 
void finalPermutation(int pos, int text)
{
    int i;
    for (i = 0; i < 64; i++)
    {
        if (FP[i] == pos + 1) {
            break;
        }
    }
    ENCRYPTED[i] = text;
}
 
void convertToBinary(int n)
{
    int k, m;
    for (int i = 7; i >= 0; i--)
    {
        m = 1 << i;
        k = n & m;
 
        if (k == 0) {
            fprintf(out, "0");
        }
        else {
            fprintf(out, "1");
        }
    }
}

void convertToChar(int n)
{
    int k, m;
    for (int i = 7; i >= 0; i--)
    {
        m = 1 << i;
        k = n & m;
 
        if (k == 0) {
            fprintf(out, "0");
        }
        else {
            fprintf(out, "1");
        }
    }
}
 
int convertCharToBit(long int n)
{
    FILE* inp = fopen("flag.txt", "rb");
    out = fopen("bits.txt", "wb+");
    char ch;
    int i = n * 8;
 
    while (i)
    {
        ch = fgetc(inp);
        if (ch == -1) {
            break;
        }
        i--;
        convertToBinary(ch);
    }
    fclose(out);
    fclose(inp);
}
 
void Encryption(long int plain[])
{
    out = fopen("justBinaries.txt", "ab+");
    for (int i = 0; i < 64; i++) {
        initialPermutation(i, plain[i]);
    }
 
    for (int i = 0; i < 32; i++) {
        LEFT[0][i] = IPtext[i];
    }
 
    for (int i = 32; i < 64; i++) {
        RIGHT[0][i - 32] = IPtext[i];
    }
 
    for (int k = 1; k < 17; k++)
    {
        cipher(k, 0);
 
        for (int i = 0; i < 32; i++)
            LEFT[k][i] = RIGHT[k - 1][i];
    }
 
    for (int i = 0; i < 64; i++)
    {
        if (i < 32) {
            CIPHER[i] = RIGHT[16][i];
        }
        else {
            CIPHER[i] = LEFT[16][i - 32];
        }
        finalPermutation(i, CIPHER[i]);
    }
 
    for (int i = 0; i < 64; i++) {
        fprintf(out, "%d", ENCRYPTED[i]);
        printf("%d", ENCRYPTED[i]);
    }
    fclose(out);
}

void Decryption(long int plain[])
{
    out = fopen("decryptedBinaries.txt", "ab+");
    for (int i = 0; i < 64; i++) {
        initialPermutation(i, plain[i]);
    }
 
    for (int i = 0; i < 32; i++) {
        LEFT[0][i] = IPtext[i];
    }
 
    for (int i = 32; i < 64; i++) {
        RIGHT[0][i - 32] = IPtext[i];
    }
 
    for (int k = 1; k < 17; k++)
    {
        cipher(k, 1);
 
        for (int i = 0; i < 32; i++)
            LEFT[k][i] = RIGHT[k - 1][i];
    }
 
    for (int i = 0; i < 64; i++)
    {
        if (i < 32) {
            CIPHER[i] = RIGHT[16][i];
        }
        else {
            CIPHER[i] = LEFT[16][i - 32];
        }
        finalPermutation(i, CIPHER[i]);
    }
 
    for (int i = 0; i < 64; i++) {
        fprintf(out, "%d", ENCRYPTED[i]);
        printf("%d", ENCRYPTED[i]);
    }
    fclose(out);
}

void convertToBits(int ch[])
{
    int value = 0;
    for (int i = 7; i >= 0; i--) {
        value += (int)pow(2, i) * ch[7 - i];
    }
    fprintf(out, "%c", value);
}
 
int bittochar()
{
    out = fopen("result.txt", "ab+");
    for (int i = 0; i < 64; i = i + 8) {
        convertToBits(&ENCRYPTED[i]);
    }
    fclose(out);
}
 
void key56to48(int round, int pos, int text)
{
    int i;
    for (i = 0; i < 56; i++)
    {
        if (PC2[i] == pos + 1) {
            break;
        }
    }
    key48bit[round][i] = text;
}
 
int key64to56(int pos, int text)
{
    int i;
    for (i = 0; i < 56; i++)
    {
        if (PC1[i] == pos + 1) {
            break;
        }
    }
    key56bit[i] = text;
}
 
void key64to48(unsigned int key[])
{
    int k, backup[17][2];
    int CD[17][56];
    int C[17][28], D[17][28];
 
    for (int i = 0; i < 64; i++) {
        key64to56(i, key[i]);
    }
 
    for (int i = 0; i < 56; i++)
    {
        if (i < 28) {
            C[0][i] = key56bit[i];
        }
        else {
            D[0][i - 28] = key56bit[i];
        }
    }
 
    for (int x = 1; x < 17; x++)
    {
        int shift = SHIFTS[x - 1];
 
        for (int i = 0; i < shift; i++) {
            backup[x - 1][i] = C[x - 1][i];
        }
 
        for (int i = 0; i < (28 - shift); i++) {
            C[x][i] = C[x - 1][i + shift];
        }
 
        k = 0;
        for (int i = 28 - shift; i < 28; i++) {
            C[x][i] = backup[x - 1][k++];
        }
 
        for (int i = 0; i < shift; i++) {
            backup[x - 1][i] = D[x - 1][i];
        }
 
        for (int i = 0; i < (28 - shift); i++) {
            D[x][i] = D[x - 1][i + shift];
        }
 
        k = 0;
        for (int i = 28 - shift; i < 28; i++) {
            D[x][i] = backup[x - 1][k++];
        }
    }
 
    for (int j = 0; j < 17; j++)
    {
        for (int i = 0; i < 28; i++) {
            CD[j][i] = C[j][i];
        }
 
        for (int i = 28; i < 56; i++) {
            CD[j][i] = D[j][i - 28];
        }
    }
 
    for (int j = 1; j < 17; j++)
    {
        for (int i = 0; i < 56; i++) {
            key56to48(j, i, CD[j][i]);
        }
    }
}

void encrypt(long int n)
{
    FILE* in = fopen("bits.txt", "rb");
 
    long int plain[n * 64];
    int i = -1;
    char ch;
 
    while (!feof(in))
    {
        ch = getc(in);
        plain[++i] = ch - 48;
    }

    for (int i = 0; i < n * 64; i++) {
        printf("%ld", plain[i]);
    }
    putchar('\n');
 
    for (int i = 0; i < n; i++) {
        Encryption(plain + 64 * i);
    }
    putchar('\n');
 
    fclose(in);
}

void decrypt(long int n)
{
    FILE* in = fopen("justBinaries_inversed.txt", "rb");
 
    long int plain[n * 64];
    int i = -1;
    char ch;
 
    while (!feof(in))
    {
        ch = getc(in);
        plain[++i] = ch - 48;
    }
 
    for (int i = 0; i < n; i++) {
        Decryption(plain + 64 * i);
    }
 
    fclose(in);
}
 
void create16Keys()
{
    FILE* pt = fopen("isThisFileUseful_inversed.txt", "rb");
    unsigned int key[64];
    int i = 0, ch;
 
    while (!feof(pt))
    {
        ch = getc(pt);
        key[i++] = ch - 48;
    }
 
    key64to48(key);
    fclose(pt);
}
 
long int findFileSize()
{
    FILE* inp = fopen("flag.txt", "rb");
    long int size;
 
    if (fseek(inp, 0L, SEEK_END)) {
        perror("fseek() failed");
    }
    else {
        size = ftell(inp);
    }
    fclose(inp);
 
    return size;
}
 
int main()
{ 
    create16Keys();
    decrypt(6);

 
    return 0;
}

content = ''
with open('decryptedBinaries.txt', 'rt') as f:
    while True:
        a = f.read(1)
        if len(a) == 0:
            break
        content += a
        
    
for i in range(0, len(content), 8):
    tmp_byte = 0
    tmp = content[i:i+8]
    for j in range(7, -1, -1):
        tmp_byte |= int(tmp[7-j], 2) << j
    print(chr(tmp_byte), end='')
#flag:{n0w_y0u_423_d0n3_w17h_u58_f023n51c5} -> VishwaCTF{n0w_y0u_423_d0n3_w17h_u58_f023n51c5}

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