c - 我如何让它解码(Perl cbc-crypt 到 C cbc_crypt 转换)

Question

我正在尝试能够解码使用 perl 脚本编码的编码字符串。我不能只更改 perl 脚本的原因是因为已经存在许多通过 perl 脚本保存的重要数据，用 perl 解码并以其他方式重新编码会太多。把东西放在原地(现在)更容易。然而，编译后的 perl 代码是 2MB。我想用 C 语言编写它，这样可执行文件的大小会更小。

我目前所拥有的如下。虽然它不会工作。它基本上给了我垃圾输出。我认为问题在于 perl 脚本使用了基于十六进制的加密。我该如何解码呢？谁能指出我哪里出错了？

/*
Test to decode perl-encrypted string.
NOTE: Not all code written by me. Function code is either written by or derived
      from code from other people in response to similar questions found on the
      internet.

Required Lib: crypt (-lcrypt)

Perl Code from existing script (that is being converted to C):

    use Crypt::CBC;
    use Crypt::DES;
    my $text = "thisisalongtest";
    my $salt_key = "fOagmJOKu2SF";
    my $cipher = Crypt::CBC->new( -key => $salt_key, -cipher => 'DES' -header => 'none');
    my $enc_text = $cipher->encrypt_hex($text);
Perl crypt functions require libcrypt-cbc-perl & libcrypt-des-perl

Data:

Original Text: thisisalongtest
Salt Key: fOagmJOKu2SF
Resulting Encrypted String: 53616c7465645f5f167ebac84042fe7ceac836e1d3e7d3aa1dfc27e0e8cad0f1

Resulting output:

Decrypted: (unprintable junk characters)
*/

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <rpc/des_crypt.h>

#define BUFFSIZE 420

int encrypt(char key[9], char salt[9], char pass[BUFFSIZE], int mode);
void enc_from_hex(const char* st, char ret_result[BUFFSIZE]);
int hex_to_int(char c);
int hex_to_ascii(char c, char d);

int main (int argc, char *argv[]) {

    int err;
    char passwd[BUFFSIZE];
    char result[BUFFSIZE];
    char key[13];

    sprintf(key,"fOagmJOKu2SF");

    /* Change this from hex pairs to ASCII */
    sprintf(passwd, "53616c7465645f5f167ebac84042fe7ceac836e1d3e7d3aa1dfc27e0e8cad0f1");
    enc_from_hex(passwd, result);

    /* Decrypt */
    err = encrypt(key, "", result, 1); /* DO NOT use 'NULL' for 2nd parameter! */
    if(err != 0) {
        printf("Error.\n");
    } else {
        printf("Decrypted: %s\n", result);
    }

    return 0;
}

/* Encryption */
int encrypt(char key[13], char salt[13], char pass[BUFFSIZE], int mode){
    char temp[13];
    strcpy(temp, salt);
    int buffsize;
    int errcode;

    des_setparity(key);
    buffsize = strlen(pass);

    /* Pad pass to ensure size is divisable by 8.*/
    while (buffsize % 8 && buffsize<BUFFSIZE) {
        pass[buffsize++] = '\0';
    }

    /* Determine Function */
    if(mode == 1) {
        errcode = cbc_crypt(key, pass, buffsize, DES_DECRYPT | DES_SW, temp);
    } else {
        errcode = cbc_crypt(key, pass, buffsize, DES_ENCRYPT | DES_SW, temp);
    }

    if (DES_FAILED(errcode) || strcmp(pass, "") == 0) {
        return errcode;
    }

    return errcode;
}

/* Hex conversion functions */
void enc_from_hex(const char* st, char ret_result[BUFFSIZE]) {
    char temp[2];

    int length = strlen(st);
    int i;
    char buf = 0;
    for(i = 0; i < length; i++) {
        if(i % 2 != 0) {
            sprintf(temp, "%c", hex_to_ascii(buf, st[i]));
            strcat(ret_result, temp);
        } else {
            buf = st[i];
        }
    }

}

int hex_to_int(char c) {
    int first = c / 16 - 3;
    int second = c % 16;
    int result = first*10 + second;
    if(result > 9) result--;
    return result;
}

int hex_to_ascii(char c, char d) {
    int high = hex_to_int(c) * 16;
    int low = hex_to_int(d);
    return high+low;
}

Answer 1

正如@ikegami 在评论中指出的那样，传递给 key Crypt::CBC 的值并不是真正的 key 。该值被传递给另一个函数，该函数将它与随机盐结合，然后对其进行哈希处理以生成真正的 key 和初始化 vector 。随机盐与密码文本一起保存，其想法是，如果您使用相同的 key 多次加密相同的数据，每次的输出都会不同。

如果将加密字符串转换为 ascii，您会注意到前八个字符拼写为 Salted__，这对应于 OpenSSL 使用的格式。

下面是一个使用 OpenSSL 的 EVP api 的粗略示例:

//
// compile with: gcc -o crypt crypt.c -lssl -lcrypto
//
#include <stdio.h>
#include <string.h>
#include <openssl/evp.h>

int main(int argc, char *argv[]){
  char pass[]="fOagmJOKu2SF";
  char text[]="53616c7465645f5f167ebac84042fe7ceac836e1d3e7d3aa1dfc27e0e8cad0f1";

  int i = 0;
  char *pos=text;
  while(*pos){ // converts hex string to binary in place
    sscanf(pos, "%2hhx", &text[i++]);
    pos += 2;
  } text[i]=0;

  EVP_CIPHER_CTX ctx;
  unsigned char key[8] = {0};
  unsigned char  iv[8] = {0};

  int len;
  char *clear = malloc(strlen(text)); 

  //                                             v-> First Charicter after 'Salted__' 
  EVP_BytesToKey(EVP_des_cbc(), EVP_md5(), &text[8], pass, strlen(pass), 1, key, iv);

  EVP_DecryptInit(&ctx, EVP_des_cbc(), key, iv);
  //                                          v-> Cypertext starts after salt
  EVP_DecryptUpdate(&ctx, clear, &len, &text[16], strlen(text)-15);
  EVP_DecryptFinal(&ctx, clear, &len);

  printf("%s\n", clear);
  return 0;
}

http://www.ict.griffith.edu.au/anthony/info/crypto/openssl.hints https://www.openssl.org/docs/manmaster/crypto/EVP_BytesToKey.html https://www.openssl.org/docs/manmaster/crypto/EVP_EncryptInit.html