c语言实现des的ofb工作模式
时间: 2023-07-28 21:49:56 浏览: 55
OFB(Output Feedback)是一种常用的加密工作模式,它可以将块加密算法转化为流加密算法。下面是用 C 语言实现 DES 的 OFB 工作模式的示例代码:
```c
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdint.h>
#include <unistd.h>
#include <openssl/des.h>
#define BLOCK_SIZE 8
// 生成随机的初始向量
void generate_iv(uint8_t *iv, int len)
{
FILE *fp = fopen("/dev/urandom", "r");
if (!fp) {
perror("fopen");
exit(EXIT_FAILURE);
}
fread(iv, 1, len, fp);
fclose(fp);
}
// 输出十六进制字符串
void print_hex(uint8_t *buf, int len)
{
int i;
for (i = 0; i < len; i++) {
printf("%02x", buf[i]);
}
printf("\n");
}
// DES加密函数
void des_encrypt(uint8_t *in, uint8_t *out, int len, uint8_t *key, uint8_t *iv)
{
DES_key_schedule ks;
DES_set_key_checked(key, &ks);
uint8_t ivec[BLOCK_SIZE];
memcpy(ivec, iv, BLOCK_SIZE);
int i;
for (i = 0; i < len; i += BLOCK_SIZE) {
DES_ncbc_encrypt(&in[i], &out[i], BLOCK_SIZE, &ks, &ivec, DES_ENCRYPT);
}
}
// DES解密函数
void des_decrypt(uint8_t *in, uint8_t *out, int len, uint8_t *key, uint8_t *iv)
{
DES_key_schedule ks;
DES_set_key_checked(key, &ks);
uint8_t ivec[BLOCK_SIZE];
memcpy(ivec, iv, BLOCK_SIZE);
int i;
for (i = 0; i < len; i += BLOCK_SIZE) {
DES_ncbc_encrypt(&in[i], &out[i], BLOCK_SIZE, &ks, &ivec, DES_DECRYPT);
}
}
// OFB加密函数
void ofb_encrypt(uint8_t *in, uint8_t *out, int len, uint8_t *key, uint8_t *iv)
{
uint8_t ivec[BLOCK_SIZE];
memcpy(ivec, iv, BLOCK_SIZE);
uint8_t keystream[BLOCK_SIZE];
int i;
for (i = 0; i < len; i += BLOCK_SIZE) {
DES_ecb_encrypt(ivec, keystream, &((DES_key_schedule *)key), DES_ENCRYPT);
int j;
for (j = 0; j < BLOCK_SIZE; j++) {
out[i+j] = in[i+j] ^ keystream[j];
}
memcpy(ivec, keystream, BLOCK_SIZE);
}
}
int main(int argc, char *argv[])
{
// 明文
uint8_t plaintext[] = "hello world";
int len = strlen((char *)plaintext);
// 密钥
uint8_t key[BLOCK_SIZE] = {0x01, 0x23, 0x45, 0x67, 0x89, 0xab, 0xcd, 0xef};
// 生成随机的初始向量
uint8_t iv[BLOCK_SIZE];
generate_iv(iv, BLOCK_SIZE);
// 加密
uint8_t ciphertext[len];
ofb_encrypt(plaintext, ciphertext, len, key, iv);
printf("ciphertext: ");
print_hex(ciphertext, len);
// 解密
uint8_t plaintext2[len];
ofb_encrypt(ciphertext, plaintext2, len, key, iv);
printf("plaintext: %s\n", plaintext2);
return 0;
}
```
注:该示例代码使用了 OpenSSL 库中的 DES 函数。