Tag: encrypted

I got a challenge to brute force encrypted DB. I received zip file with: DB,DLL(encrypted) and exe.

I opened the exe with DnSpy to read the logic: it requires 4 digit pin code to Decrypt the DB and DLL.

The logic is this: the pin code must be in length of 4. After that the code hashes the pin 10 times, saves the value as str2. After that hashes str2 another 10 times and save as str3.

Now check if Text3 is equal to an hard coded MD5 hash :”2D3114BCC2E5C58BBAC77F04237723D9″, if yes then decrypt the encrypted files using str2 as key.

The problem is that I brute forced it with no success, no number from 0000-9999 if hashed 20 times is equal to the hardcoded value in the source code.

Then I thought maybe the challenge is harder and no 4 digit pin is equal to the hard coded hash (if hashed 20 times). I thought maybe brute forcing the dycryption? That way I’ll get 10,0000 files but how do I distinguish between the real DB and between file decrypted with the wrong key?

Thanks!

str = this.richTextBoxPinCode.Text;
    if (str.Length != 4)
    {
        this.richTextBoxPinCode.Text = "";
        return;
    }

    try
    {
        str2 = str;
        str3 = str;
        num = 0;
   
        while (true)
        {
            if (num >= 10)
            {
                num2 = 0;
           
                while (true)
                {
                    if (num2 >= 10)
                    {
                        if ("2D3114BCC2E5C58BBAC77F04237723D9" == str2)
                        {
                            buffer = StringToByteArray(str3);
                            this.DecryptFile(buffer, "ForceCoinTransactionSigner.dll.enc", "ForceCoinTransactionSigner.dll");
                            this.DecryptFile(buffer, "db.txt.enc", "db.txt");
                            base.Hide();
                            new AppForm().ShowDialog();
                            base.Close();
                        }
                        break;
                    }
                    str2 = this.DoMD5(str2);
                    num2 += 1;
                }
                break;
            }
            str2 = this.DoMD5(str2);
            str3 = this.DoMD5(str3);
            num += 1;
        }
    }