차분 공격 - 실습

Toy Cipher 를 대상으로 진행한 차분 공격 실습이다.

 

0. 평문쌍, 암호문쌍

 

평문쌍 코드

#define CRT_SECURE_NO_WARNINGS

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

int main()
{
    FILE *pA, *pB, *cA, *cB;
    uint32_t random = 0;
    uint32_t plain_a = 0x00, plain_b = 0x00;
	uint32_t cipher_a = 0x00, cipher_b = 0x00;
    uint32_t a = 0x00;
    
    //Write Plaintext
    pA = fopen("Plaintext_A.txt", "w");
    pB = fopen("Plaintext_B.txt", "w");
    srand((unsigned)time(NULL));
    
    for (int i = 0; i < 0x7ff; i++) {
        random = rand() % 0xffffffff;
        plain_a = random;
        a = !((random >> 24) & 0x1);
        plain_b = (plain_a & 0xfeffffff) | (a << 24);
        
        fprintf(pA, "%x\n", plain_a);
        fprintf(pB, "%x\n", plain_b);
    }
    
    fclose(pA);
    fclose(pB);

    return 0;
}

 

평문쌍, 암호문쌍 파일 (암호문쌍은 평문쌍의 Toy Cipher 를 적용시킨 결과이다)

Text.zip

0.04MB

 

1. 암호 알고리즘 : Toy Cipher

 

2. DDT

DDT

3. 입력차분 : 0x01000000, 출력차분 : 0x00001842

4. Propagation Ratio : 1 / 512

5. 차분 경로

6. 키복구 알고리즘 코드

#define CRT_SECURE_NO_WARNINGS
  
#include <stdio.h>
#include <stdlib.h>
#include <time.h>

uint8_t static SBOX[16] = { 1, 10, 4, 12, 6, 15, 3, 9, 2, 13, 11, 7, 5, 0, 8, 14 };
uint8_t static InvPT[32] = { 6, 9, 12, 3, 2, 5, 8, 31, 30, 1, 4, 27, 26, 29, 0, 23, 22, 25, 28, 19, 18, 21, 24, 15, 14, 17, 20, 11, 10, 13, 16, 7 };
uint8_t static InvSBOX[16] = { 13, 0, 8, 6, 2, 12, 4, 11, 14, 7, 1, 10, 3, 9, 15, 5 };
uint8_t static PT[32] = { 14, 9, 4, 3, 10, 5, 0, 31, 6, 1,
    28, 27, 2, 29, 24, 23, 30, 25, 20, 19,
    26, 21, 16, 15, 22, 17, 12, 11, 18, 13, 8, 7 };

uint32_t InversePermutation(uint32_t AX)
{	
	uint32_t AIP = 0x00;

	for (int k = 0; k < 32; k++)
		AIP |= ((AX >> k) & 0x1) << (InvPT[31 - k]);

	return AIP;
}	

uint32_t InverseSBOX(uint32_t APT)
{
	uint32_t ASB = 0x00;
	uint32_t tmp = 0x00;

	for (int k = 0; k < 8; k++) {
		tmp = (APT >> (28 - k * 4)) & 0xf;
		ASB |= InvSBOX[tmp] << (28 - k * 4); 
	}

	return ASB;
}

int main()
{
    FILE *cA = NULL, *cB = NULL;
	uint32_t ciphertext_A = 0x00, ciphertext_B = 0x00;
	uint32_t maxkey = 0x00;
	uint32_t AX_A = 0x00, APT_A = 0x00, ASB_A = 0x00;
	uint32_t AX_B = 0x00, APT_B = 0x00, ASB_B = 0x00;
	uint16_t check = 0x00;
	int cipher_A[2048] = { 0x00, };
	int cipher_B[2048] = { 0x00, };
	int count[0xffff] = { 0, };
	int max = 0;

    cA = fopen("Ciphertext_A.txt", "r");
    cB = fopen("Ciphertext_B.txt", "r");

	for (int i = 0; i < 2048; i++) {
		fscanf(cA, "%x", &cipher_A[i]);
		fscanf(cB, "%x", &cipher_B[i]);

		for (int j = 0; j < 0xffff; j++) {
			APT_A = InversePermutation(cipher_A[i]);
			APT_B = InversePermutation(cipher_B[i]);

			ASB_A = InverseSBOX(APT_A ^ j);
			ASB_B = InverseSBOX(APT_B ^ j);

			check = (ASB_A ^ ASB_B) & 0xffff;
			
			if (check == 0x1842)
				count[j]++;
		}
	}

	fclose(cA);
    fclose(cB);

    for (int i = 0; i < 0xffff; i++) {
		if (count[i] > max) {
			max = count[i];
			maxkey = i;
		}
	}

	printf("MAX : %d\n", max);
	printf("KEY : %x\n", maxkey);

	return 0;
}

7. 출력값