void des_ctr_decrypt(unsigned char *ciphertext, unsigned char *plaintext, long ciphertext_len, unsigned char *key, unsigned char *iv) { DES_key_schedule key_schedule; DES_set_key_checked(key, &key_schedule); unsigned char keystream[BLOCK_SIZE]; unsigned char block[BLOCK_SIZE]; int i, j; for (i = 0; i < ciphertext_len; i += BLOCK_SIZE) { DES_ecb_encrypt(iv, keystream, &key_schedule, DES_ENCRYPT); for (j = 0; j < BLOCK_SIZE; j++) { block[j] = ciphertext[i + j] ^ keystream[j]; plaintext[i + j] = block[j]; } increment_iv(iv); }}
时间: 2024-04-21 12:27:15 浏览: 15
这段代码实现了 DES 算法的 CTR 模式解密,其中参数 ciphertext 是待解密的密文,plaintext 是解密后的明文,ciphertext_len 是密文长度,key 是解密使用的密钥,iv 是初始化向量。该函数与上一个问题中的代码几乎相同,唯一的区别在于函数名和参数的名称不同。函数中使用 DES_set_key_checked 函数将密钥设置到 key_schedule 中,然后使用 ECB 模式对 iv 进行加密,得到的结果作为密钥流与密文异或得到明文。每次解密完成后,iv 需要按照一定规则进行递增。该函数也是一种对称加密算法,加密和解密使用的密钥是相同的。
相关问题
#include <stdio.h> #include <stdlib.h> #include <string.h> #include <openssl/des.h> #define BLOCK_SIZE 8 void increment_iv(unsigned char *iv) { int i; for (i = BLOCK_SIZE - 1; i >= 0; i--) { if (iv[i] == 0xff) { iv[i] = 0; } else { iv[i]++; break; } }} void des_ctr_encrypt(unsigned char *plaintext, unsigned char *ciphertext, long plaintext_len, unsigned char *key, unsigned char *iv) { DES_key_schedule key_schedule; DES_set_key_checked(key, &key_schedule); unsigned char keystream[BLOCK_SIZE]; unsigned char block[BLOCK_SIZE]; int i, j; for (i = 0; i < plaintext_len; i += BLOCK_SIZE) { DES_ecb_encrypt(iv, keystream, &key_schedule, DES_ENCRYPT); for (j = 0; j < BLOCK_SIZE; j++) { block[j] = plaintext[i + j] ^ keystream[j]; ciphertext[i + j] = block[j]; } increment_iv(iv); } } void des_ctr_decrypt(unsigned char *ciphertext, unsigned char *plaintext, long ciphertext_len, unsigned char *key, unsigned char *iv) { DES_key_schedule key_schedule; DES_set_key_checked(key, &key_schedule); unsigned char keystream[BLOCK_SIZE]; unsigned char block[BLOCK_SIZE]; int i, j; for (i = 0; i < ciphertext_len; i += BLOCK_SIZE) { DES_ecb_encrypt(iv, keystream, &key_schedule, DES_ENCRYPT); for (j = 0; j < BLOCK_SIZE; j++) { block[j] = ciphertext[i + j] ^ keystream[j]; plaintext[i + j] = block[j]; } increment_iv(iv); }} int main() { unsigned char key[] = "01234567"; unsigned char iv[] = "12345678"; unsigned char plaintext[] = "Hello, DES-CTR!"; long plaintext_len = strlen((char *) plaintext); unsigned char ciphertext[plaintext_len]; des_ctr_encrypt(plaintext, ciphertext, plaintext_len, key, iv); printf("Ciphertext: %s\n", ciphertext); unsigned char decrypted[plaintext_len]; des_ctr_decrypt(ciphertext, decrypted, plaintext_len, key, iv); printf("Plaintext: %s\n", decrypted); return 0;}
这段代码实现了基于 DES 算法的 CTR 模式加密和解密功能。CTR 模式是一种流密码模式,在加密过程中,明文按照固定的块长(这里是 8 字节)被分成若干块,每个块都会被加密。CTR 模式需要使用一个初始向量 IV 和密钥 key,通过 DES 算法将 IV 加密得到一个密钥流 keystream,然后将明文按块与 keystream 进行异或操作得到密文,同时 IV 也需要进行增量操作,保证下一次加密时使用的 IV 是不同的。解密过程与加密过程类似,只需要将密文按块与 keystream 进行异或操作得到明文即可。在这个例子中,输入的明文是 "Hello, DES-CTR!",输出的密文和解密后的明文会在命令行中显示。
DES-CTR模式C语言代码
以下为DES-CTR模式的C语言代码示例:
```c
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <openssl/des.h>
#define BLOCK_SIZE 8
void increment_iv(unsigned char *iv) {
int i;
for (i = BLOCK_SIZE - 1; i >= 0; i--) {
if (iv[i] == 0xff) {
iv[i] = 0;
} else {
iv[i]++;
break;
}
}
}
void des_ctr_encrypt(unsigned char *plaintext, unsigned char *ciphertext,
long plaintext_len, unsigned char *key,
unsigned char *iv) {
DES_key_schedule key_schedule;
DES_set_key_checked(key, &key_schedule);
unsigned char keystream[BLOCK_SIZE];
unsigned char block[BLOCK_SIZE];
int i, j;
for (i = 0; i < plaintext_len; i += BLOCK_SIZE) {
DES_ecb_encrypt(iv, keystream, &key_schedule, DES_ENCRYPT);
for (j = 0; j < BLOCK_SIZE; j++) {
block[j] = plaintext[i + j] ^ keystream[j];
ciphertext[i + j] = block[j];
}
increment_iv(iv);
}
}
void des_ctr_decrypt(unsigned char *ciphertext, unsigned char *plaintext,
long ciphertext_len, unsigned char *key,
unsigned char *iv) {
DES_key_schedule key_schedule;
DES_set_key_checked(key, &key_schedule);
unsigned char keystream[BLOCK_SIZE];
unsigned char block[BLOCK_SIZE];
int i, j;
for (i = 0; i < ciphertext_len; i += BLOCK_SIZE) {
DES_ecb_encrypt(iv, keystream, &key_schedule, DES_ENCRYPT);
for (j = 0; j < BLOCK_SIZE; j++) {
block[j] = ciphertext[i + j] ^ keystream[j];
plaintext[i + j] = block[j];
}
increment_iv(iv);
}
}
int main() {
unsigned char key[] = "01234567";
unsigned char iv[] = "12345678";
unsigned char plaintext[] = "Hello, DES-CTR!";
long plaintext_len = strlen((char *) plaintext);
unsigned char ciphertext[plaintext_len];
des_ctr_encrypt(plaintext, ciphertext, plaintext_len, key, iv);
printf("Ciphertext: %s\n", ciphertext);
unsigned char decrypted[plaintext_len];
des_ctr_decrypt(ciphertext, decrypted, plaintext_len, key, iv);
printf("Plaintext: %s\n", decrypted);
return 0;
}
```
注意:此处的DES算法使用了OpenSSL库。在使用此代码时需要在编译命令中添加-lcrypto选项。
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