Short, case-insensitive string obfuscation strategy

Question

I am looking for a way to identify (i.e. encode and decode) a set of Java strings with one token. The identification should not involve DB persistence. So far I

Answer 1

I have spent some time on this and I have a good solution for you.

Encode as base64 then as a custom base32 that uses 0-9a-v. Essentially, you lay out the bits 6 at a time (your chars are 0-9a-zA-Z) then encode them 5 at a time. This leads to hardly any extra space. For example, ABCXYZdefxyz123789 encodes as i9crnsuj9ov1h8o4433i14

Here's an implementation that works, including some test code that proves it is case-insensitive:

// Note: You can add 1 more char to this if you want to
static String chars = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";

private static String decodeToken(String encoded) {
    // Lay out the bits 5 at a time
    StringBuilder sb = new StringBuilder();
    for (byte b : encoded.toLowerCase().getBytes())
        sb.append(asBits(chars.indexOf(b), 5));

    sb.setLength(sb.length() - (sb.length() % 6));

    // Consume it 6 bits at a time
    int length = sb.length();
    StringBuilder result = new StringBuilder();
    for (int i = 0; i < length; i += 6)
        result.append(chars.charAt(Integer.parseInt(sb.substring(i, i + 6), 2)));

    return result.toString();
}

private static String generateToken(String x) {
    StringBuilder sb = new StringBuilder();
    for (byte b : x.getBytes())
        sb.append(asBits(chars.indexOf(b), 6));

    // Round up to 5 bit multiple
    // Consume it 5 bits at a time
    int length = sb.length();
    sb.append("00000".substring(0, length % 5));
    StringBuilder result = new StringBuilder();
    for (int i = 0; i < length; i += 5)
        result.append(chars.charAt(Integer.parseInt(sb.substring(i, i + 5), 2)));

    return result.toString();
}

private static String asBits(int index, int width) {
    String bits = "000000" + Integer.toBinaryString(index);
    return bits.substring(bits.length() - width);
}

public static void main(String[] args) {
    String input = "ABCXYZdefxyz123789";
    String token = generateToken(input);
    System.out.println(input + " ==> " + token);
    Assert.assertEquals("mixed", input, decodeToken(token));
    Assert.assertEquals("lower", input, decodeToken(token.toLowerCase()));
    Assert.assertEquals("upper", input, decodeToken(token.toUpperCase()));
    System.out.println("pass");
}