我们可以在不知道明文大小的情况下使用 C 中的 OpenSSL 解密(对称加密/解密)消息吗？

Question

我正在使用以下代码在使用 openssl 的 Windows 中使用 C 加密和解密二进制数据。如您所见，在这两个函数中，我都知道纯文本的大小。有什么方法可以在不知道纯文本大小的情况下解密消息？

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <openssl/des.h>
char * Encrypt(char *Key, char *Msg, int size)
    {
    static char*    Res;
    int             n = 0;
    DES_cblock      Key2;
    DES_key_schedule schedule;
    Res = (char *)malloc(size);
    /* Prepare the key for use with DES_cfb64_encrypt */
    memcpy(Key2, Key, 8);
    DES_set_odd_parity(&Key2);
    DES_set_key_checked(&Key2, &schedule);
    /* Encryption occurs here */
    DES_cfb64_encrypt((unsigned char *)Msg, (unsigned char *)Res,size, &schedule, &Key2, &n, DES_ENCRYPT);
    return (Res);
}
char * Decrypt(char *Key, char *Msg, int size)
{
    static char*    Res;
    int             n = 0;
    DES_cblock      Key2;
    DES_key_schedule schedule;
    Res = (char *)malloc(size);
    /* Prepare the key for use with DES_cfb64_encrypt */
    memcpy(Key2, Key, 8);
    DES_set_odd_parity(&Key2);
        DES_set_key_checked(&Key2, &schedule);
    /* Decryption occurs here */
    DES_cfb64_encrypt((unsigned char *)Msg, (unsigned char *)Res,size, &schedule, &Key2, &n, DES_DECRYPT);
    return (Res);
}
int _tmain(int argc, _TCHAR* argv[])
{
    char key[] = "password";
    char clear[] = "This is a secret message";
    char *decrypted;
    char *encrypted;
    encrypted = (char *)malloc(sizeof(clear));
    decrypted = (char *)malloc(sizeof(clear));
    printf("Clear text\t : %s : sizeof: %i\n", clear, strlen (clear));
    memcpy(encrypted, Encrypt(key, clear, sizeof(clear)), sizeof(clear));
    printf("Encrypted text\t : %s sizeof: %i\n", encrypted, strlen(encrypted));
    memcpy(decrypted, Decrypt(key, encrypted, sizeof(clear)), sizeof(clear));
    printf("Decrypted text\t : %s sizeof: %i\n", decrypted, strlen(decrypted));
    return 0;
}

Answer 1

只有密码反馈？当然，只要您知道 block 边界在哪里，您就是黄金(即您需要知道您在密文中的位置)。