Re: Get ASCII value for character when higher than 127

On 30 May 2007 03:55:32 -0700, ssetz@wxs.nl wrote:


OK, this is my C++ version of XOR function:

<CODE language="C++">
//
// Crypt a string using XOR.
//
// The result is stored into a char-array.
// The string terminating NUL character is not crypted and
// is not copied into the destination array.
//
typedef std::vector< char > CharArray;
CharArray XorStringCrypt(
    const std::string & value,
    const std::string & key )
{
    if ( value.empty() )
        throw std::invalid_argument(
            "XorStringCrypt: Input array is empty" );

    if ( key.empty() )
        throw std::invalid_argument(
            "XorStringCrypt: Key string is empty" );

    CharArray result;
    result.resize( value.length() );
    
    const size_t valueLengtht = value.length();
    const size_t keyLength = key.length();
    size_t keyIndex = 0;

    for ( size_t i = 0; i < valueLengtht; i++ )
    {
        result.at(i) = value.at(i) ^ key.at(keyIndex);

        keyIndex++;
        if ( keyIndex == keyLength )
            keyIndex = 0;
    }

    return result;
}

</CODE>

You can use the function like this:

    // Crypt the message
    std::string value = "The secret message";
    std::string key = "Ciao";
    CharArray result = XorStringCrypt( value, key );

    // Save the array to file
    std::ofstream out("c:\\crypt.test");
    for ( CharArray::const_iterator it = result.begin();
          it != result.end(); ++it )
    {
        out.put( *it );
    }

This is the C# side:

<CODE language="C#">

// Apply XOR to an array
private static byte[] XorArrayCrypt(byte[] encrypted, byte[] key)
{
    byte[] decrypted = new byte[ encrypted.Length ];

    int k = 0;
    int i = 0;
    for ( i = 0; i < encrypted.Length; i++ )
    {
        decrypted[i] = (byte) (encrypted[i] ^ key[k]);

        k++;
        if (k == key.Length)
            k = 0;
    }

    return decrypted;
}

// Decrypt a string stored in encrypted byte array, using XOR
private static string XorDecrypt(byte[] encrypted, string key)
{
    UTF8Encoding encoding = new UTF8Encoding();

    byte[] keyBytes = encoding.GetBytes(key);
    byte[] decryptedBytes = XorArrayCrypt(encrypted, keyBytes);

    return encoding.GetString(decryptedBytes);
}
</CODE>

You can use them as follow:

 // Test decrypt
 private void button1_Click(object sender, EventArgs e)
 {
    //
    // Read file data into memory
    //
    FileStream inputFile = new FileStream(@"C:\crypt.test",
                                          FileMode.Open);
    int bytesCount = (int)inputFile.Length;
    byte[] byteArray = new byte[bytesCount];
    inputFile.Read(byteArray, 0, bytesCount);
    inputFile.Close();

    //
    // Decrypt (key is "Ciao")
    //
    string decrypted = XorDecrypt(byteArray, "Ciao");
    MessageBox.Show(decrypted);
}

</CODE>

It works fine, displaying from C#: "The secret message".

HTH
MrAsm