Problems with converting char array to string

Question

I have a function in a small application that I'm writing to break a recycled one-time pad cypher. Having used VB.NET for most of my career I thought it would be interesting to implement the app in C#. However, I have encountered a problem due to my present unfamiliarity with C#.

The function takes in two strings (of binary digits), converts these strings to char arrays, and then performs an XOR on them and places the result in a third char array.

This is fine until I try to convert the third char array to a string. Instead of the string looking like "11001101" etc, I get the following result: " \0\0 \0 " i.e. the "1"s are being represented by spaces and the "0"s by "\0".

My code is as follows:

    public string calcXor(string a, string b)
    {
        char[] charAArray = a.ToCharArray();
        char[] charBArray = b.ToCharArray();

        int len = 0;

        // Set length to be the length of the shorter string
        if (a.Length > b.Length)
            len = b.Length - 1;
        else
            len = a.Length - 1;

        char[] result = new char[len];

        for (int i = 0; i < len; i++)
        {
            result[i] = (char)(charAArray[i] ^ charBArray[i]);
        }

        return new string(result);
    }

Should you not be XORing the binary data representing the characters, rather than the binary data representing the characters '1' and '0'? Tis a bit of a step back from what you're asking, but.. — Craig Graham
– Craig Graham, Commented Jan 28, 2014 at 13:45
I'm just waiting for my reputation to get to 15 and then I can up-vote the answers. — David Brower
– David Brower, Commented Jan 28, 2014 at 14:05

Dmitrii Bychenko · Accepted Answer · 2014-01-28 14:02:02Z

2

Your problem is in the line

  result[i] = (char)(charAArray[i] ^ charBArray[i]);

that should be

  // (Char) 1 is not '1'!
  result[i] = (char)((charAArray[i] ^ charBArray[i]) + '0');

More compact solution is to use StringBuilder, not arrays:

public string calcXor(String a, String b) {
  int len = (a.Length < b.Length) ? a.Length : b.Length;

  StringBuilder Sb = new StringBuilder();

  for (int i = 0; i < len; ++i) 
    // Sb.Append(CharToBinary(a[i] ^ b[i])); // <- If you want 0's and 1's  
    Sb.Append(a[i] ^ b[i]); // <- Just int, not in binary format as in your solution

  return Sb.ToString();
}

public static String CharToBinary(int value, Boolean useUnicode = false) {
  int size = useUnicode ? 16 : 8;

  StringBuilder Sb = new StringBuilder(size);

  Sb.Length = size;

  for (int i = size - 1; i >= 0; --i) {
    Sb[i] = value % 2 == 0 ? '0' : '1';
    value /= 2;
  }

  return Sb.ToString();
}

Your solution just computes xor's (e.g. "65") and put them into line (e.g. 65728...); if you want 0's and 1's representation, you should use formatting

edited Jan 28, 2014 at 14:02

answered Jan 28, 2014 at 13:43

Dmitrii Bychenko

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3 Comments

David Brower Over a year ago

Thanks you. That's it. +1 for the more compact solution.

Jeppe Stig Nielsen Over a year ago

Do you realize (in your "should be" section) that charAArray[i] ^ charBArray[i] + '0' means charAArray[i] ^ (charBArray[i] + '0'), so addition comes before (has higher priority or precedence) than bitwise XOR?

Dmitrii Bychenko Over a year ago

@Jeppe Stig Nielsen: Thank you! The subtle detail that priority of '^' is less than '+' slept from my mind.

steffan · Accepted Answer · 2014-01-28 13:41:44Z

0

Have a look at the ASCII Table. 0 is the Null character \0. You could try ToString()

answered Jan 28, 2014 at 13:41

steffan

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Comments

Master117 · Accepted Answer · 2014-01-28 13:55:52Z

0

Have you tried using binary / byte[]? It seems like the fastest way to me.

public string calcXor(string a, string b)
{
  //String to binary
  byte[] ab = ConvertToBinary(a);
  byte[] bb = ConvertToBinary(b);
  //(XOR)
  byte[] cb = a^b  

  return cb.ToString();
}

public static byte[] ConvertToBinary(string str)
{
  System.Text.ASCIIEncoding  encoding = new System.Text.ASCIIEncoding();
  return encoding.GetBytes(str);
}

answered Jan 28, 2014 at 13:55

Master117

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Comments

David Brower · Accepted Answer · 2014-01-31 16:31:32Z

0

I just wanted to add that the solution I eventually chose is as follows:

//Parameter binary is a bit string
public void someroutine(String binary) 
{
 var data = GetBytesFromBinaryString(binary);
 var text = Encoding.ASCII.GetString(data);
}

public Byte[] GetBytesFromBinaryString(String binary)
{
 var list = new List<Byte>();

 for (int i = 0; i < binary.Length; i += 8)
     {
     String t = binary.Substring(i, 8);
     list.Add(Convert.ToByte(t, 2));
     }

 return list.ToArray();
}

answered Jan 31, 2014 at 16:31

David Brower

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