compal-decrypt.c

compal-decrypt.c

/* 
Program for decrypting Compal CH7465LG private key

Compilation:
gcc -o compal-decrypt compal-decrypt.c -lcrypto

Running:
./compal-decrypt 
usage: ./compal-decrypt <infile> <outfile>
  
Author: Carlo Meijer <carlo@youcontent.nl> 
*/
   

#include <stdio.h>
#include <stdlib.h>
#include <sys/stat.h>
#include <string.h>
#include <openssl/des.h>

static unsigned char g_abKey[] = {
  0xBE, 0x26, 0x01, 0xC4, 0x52, 0x76, 0x84, 0x4C, 0x9C, 0xDE, 
  0x13, 0x4D, 0xE7, 0x60, 0x2B, 0xD1, 0xDC, 0xA3, 0xAB, 0x87, 
  0x9A
};

int sprinkle(unsigned char *a1, unsigned char *a2) // straight from IDA decompiler
{
  int result; // r0
  signed int v3; // r3
  int v4; // r2

  *a2 = *a1 & 0xFE;
  a2[1] = (*a1 << 7) + ((a1[1] >> 1) & 0x7E);
  a2[2] = (a1[1] << 6) + ((a1[2] >> 2) & 0x3E);
  a2[3] = 0x20 * a1[2] + ((a1[3] >> 3) & 0x1E);
  a2[4] = 0x10 * a1[3] + ((a1[4] >> 4) & 0xE);
  a2[5] = 8 * a1[4] + ((a1[5] >> 5) & 6);
  a2[6] = 4 * a1[5] + ((a1[6] >> 6) & 2);
  a2[7] = 2 * a1[6];
  result = 0;
  do
  {
    v3 = 1;
    v4 = (unsigned char)(a2[result] ^ 1);
    for ( a2[result] = v4; ; v4 = (unsigned char)a2[result] )
    {
      if ( (v4 >> v3) & 1 )
        a2[result] = v4 ^ 1;
      if ( ++v3 == 8 )
        break;
    }
    ++result;
  }
  while ( result != 8 );
  return result;
}

void des3ABC_CBC_decrypt(
    unsigned char *lpKey1,
    unsigned char *lpKey2,
    unsigned char *lpKey3,
    unsigned char *lpIv,
    unsigned char *lpInput,
    unsigned int dwLength,
    unsigned char *lpOutput
) {
  int v12; // r7
  int v13; // r2
  int v14; // r2
  unsigned char abKey1[8]; // [sp+8h] [bp-40h]
  unsigned char abKey2[8]; // [sp+10h] [bp-38h]
  unsigned char abKey3[8]; // [sp+18h] [bp-30h]
  char v18[40]; // [sp+20h] [bp-28h]
  DES_key_schedule stKey1, stKey2, stKey3;

  sprinkle(lpKey1, abKey1);
  sprinkle(lpKey2, abKey2);
  sprinkle(lpKey3, abKey3);

  DES_set_key((DES_cblock *)abKey1, &stKey1);
  DES_set_key((DES_cblock *)abKey2, &stKey2);
  DES_set_key((DES_cblock *)abKey3, &stKey3);

  if ( (dwLength + 7) >> 3 )
  {
    v12 = 0;
    do
    {
      DES_ecb3_encrypt((const_DES_cblock *)lpInput, (DES_cblock *)v18, &stKey1, &stKey2, &stKey3, DES_DECRYPT);
      v13 = 0;
      if ( v12 )
      {
        do
        {
          lpOutput[v13] = v18[v13] ^ lpInput[v13 - 8];
          ++v13;
        }
        while ( v13 != 8 );
      }
      else
      {
        do
        {
          lpOutput[v13] = v18[v13] ^ lpIv[v13];
          v14 = v13 + 1;
          if ( v14 == 8 )
            break;
          lpOutput[v14] = v18[v14] ^ lpIv[v14];
          v13 = v14 + 1;
        }
        while ( v13 != 8 );
      }
      ++v12;
      lpInput += 8;
      lpOutput += 8;
    }
    while ( (dwLength + 7) >> 3 != v12 );
  }
}

int main(int argc, char **argv) {
    if(argc != 3) {
        goto _usage;
    }

    struct stat stInfile;
    FILE *hInfile, *hOutfile;
    unsigned char *lpInput, *lpOutput;
    unsigned char abIv[8];
    memset(abIv, 0, 8);
    unsigned int dwLength, dwOutLength;

    hInfile = fopen(argv[1], "rb");
    if (hInfile == NULL) {
        perror(argv[1]);
        return 1;
    }

    fstat(fileno(hInfile), &stInfile);
    dwLength = stInfile.st_size;
    lpInput = malloc((dwLength + 7) & ~7);
    lpOutput = malloc((dwLength + 7) & ~7);
    fread(lpInput, dwLength, 1, hInfile);
    if (dwLength & 8) {
        memset(lpInput + dwLength, 0, 8 - (dwLength & 8));
    }

    des3ABC_CBC_decrypt(g_abKey, &g_abKey[7], &g_abKey[14], abIv, lpInput, dwLength, lpOutput);
    if (lpOutput[20] != 0x30 || lpOutput[21] != 0x82) {
        printf ("[-] invalid format\n");
        return 1;
    }
    dwOutLength = lpOutput[23] + 4 + (lpOutput[22] << 8);
    
    hOutfile = fopen(argv[2], "wb");
    if (hOutfile == NULL) {
        perror(argv[2]);
        return 1;
    }

    fwrite(lpOutput + 20, dwOutLength, 1, hOutfile);
    fclose(hInfile);
    fclose(hOutfile);
    free(lpInput);
    free(lpOutput);

    printf ("[+] success!\n");

    return 0;
_usage:
    printf("usage: %s <infile> <outfile>\n", argv[0]);
    return 0;
}

Thanks for your work.
Is it possible to make an encryption program using this method?
I'm interested in putting a non-encrypted private key from a different modem to this one.