I think this one is actually secure, because as far as I can see, it's impossible to decrypt it without the key, and you can't guess the next byte of the message without knowing the one before it. I can explain it if you have a question, but for now, here's the code:
public class Xorcryption
{
/**
Testing method
*/
public static void main(String args[])
{
String message = "This is an test message.";
String key = "00112233445566778899";
printStringHex(message); // Hex before encrypting
message = xorEncode(message, key);
printStringHex(message); // Hex after encrypting
message = xorDecode(message, key);
printStringHex(message); // Hex after decrypting
System.out.println(message);
}
/**
Prints a string in hex.
*/
private static void printStringHex(String s)
{
for(int i = 0; i < s.length(); i++)
{
System.out.print(Integer.toHexString((int)s.charAt(i)) + " ");
}
System.out.println();
}
/**
Encodes a string
@param data Data to encode
@param key Key to encode with
*/
public static String xorEncode(String data, String key)
{
byte m_cData[] = data.getBytes();
byte m_cKey [] = key .getBytes();
int keyPointer = 0;
for(int i = 0; i < m_cData.length; i++)
{
m_cData[i] ^= m_cKey[keyPointer];
keyPointer += m_cData[i];
keyPointer %= m_cKey.length;
}
return new String(m_cData);
}
/**
Decodes a string
@param data Data to decode
@param key Key to decode with
*/
public static String xorDecode(String data, String key)
{
byte m_cData[] = data.getBytes();
byte m_cKey [] = key .getBytes();
// This was a little interesting to code, because by the time
// we increase the keyPointer, what we have to increase it by
// is already destroyed by the line above it. Therefore, we
// have to set keyPointerAdd before we decrypt the byte that
// holds what's added to the pointer.
int keyPointer = 0;
byte keyPointerAdd = 0;
for(int i = 0; i < m_cData.length; i++)
{
keyPointerAdd = m_cData[i];
m_cData[i] ^= m_cKey[keyPointer];
keyPointer += keyPointerAdd;
keyPointer %= m_cKey.length;
}
return new String(m_cData);
}
}
Note: If you're actually going to use it, you can exclude main and printStringHex and use it all staticly (is that a word?).
