It's been a few days since we've done the Code Snippet Of the Day, so in lieu of Alex's normal article, here's your mid-day CodeSOD edited by Michael Casadevall ...

J.S. Bangs sends us today's snippit located deep within a Java codebase he's maintaining. The function, getRandomBits() returns a 32-byte array of random bites for security purposes. Since Java provides a Random method, this should be easy; in fact a proper implementation can be writting in five lines:

public static byte[] getRandomBits() {
  byte[] random = new byte[32];
  Random.nextBytes(random);
  return random;
}

Of course, J.S.'s predecessor found a more interesting way to do things. His version of getRandomBits did its job by:

* Enumerate all of the System properties
* Create an MD4 hash of all of the property key/value pairs
* Do a bitwise-XOR of the various hashes
* Throw in an MD4 hash of the current system time so that the value isn't always the same
* Bitwise-XOR that in there as well
* Return the result

The best thing J.S. could say about this code was "at least it's commented". I don't believe it within my ability however to do this code justice, so without futher to do:

    public static byte[] innerGetRandomBits() {
        int pos = 0;
        int iters = 0;

        bits = new byte[(nbits + 7) / 8];



        for (int i = 0; i < bits.length; i++)
            bits[i] = (byte) 0;

        

        Enumeration e = null;
        try {
            e = System.getProperties().propertyNames();
        } catch (Exception ex) {
            // no need to do anything
        }


        MD4 hash = new MD4();
        int hash_count = 0;
        int hash_bytes = 0;


        long ms = System.currentTimeMillis();
        byte[] bytes = new byte[12];
        for (int i = 0; i < 8; i++) {
            bytes[i] = (byte) (ms & 0xffL);
            ms = ms >> 8;
        }
        int hn = System.identityHashCode(bytes);
        for (int i = 0; i < 4; i++) {
            bytes[i + 8] = (byte) (hn & 0xffL);
            hn = hn >> 8;
        }


        if (e != null)
            while (e.hasMoreElements()) {
                String key = (String) e.nextElement();
                if (key != null) {
                    String val = System.getProperty(key);
                    if (val != null) {

                        String pair = key + val;
                        bytes = pair.getBytes();
                        hash.engineUpdate(bytes, 0, bytes.length);
                        hash_bytes += bytes.length;

                        // when the hash input size is large enough ...
                        if (hash_bytes >= 128) {
                            hash_count++;
                            hash_bytes = 0;

                            // ... produce a digest and ...
                            byte[] digest = hash.engineDigest();
                            for (int i = 0; i < digest.length; i++) {

                                // ...fold it into the bit buffer
                                bits[pos] = (byte) (bits[pos] ^ digest[i]);
                                pos++;
                                if (pos == bits.length) {
                                    pos = 0;
                                    iters++;
                                }
                            } // end for
                        } // end if hash_bytes
                    } // end if val non null
                } // end if key non null
            } // end while e.hasMoreElements

        while (iters < 2) {
            for (int j = 512 / 8; j > 0; j--) {
                Thread.yield();
                ms = System.currentTimeMillis();
                for (int i = 0; i < 8; i++) {
                    bytes[i] = (byte) (ms & 0xffL);
                    ms = ms >> 8;
                }
                hash.engineUpdate(bytes, 0, 8);
                hash_bytes += 8;

                // when the hash input size is large enough ...
                if (hash_bytes >= 128) {
                    hash_count++;
                    hash_bytes = 0;

                    // ... produce a digest and ...
                    byte[] digest = hash.engineDigest();
                    for (int i = 0; i < digest.length; i++) {

                        // ...fold it into the bit buffer
                        bits[pos] = (byte) (bits[pos] ^ digest[i]);
                        pos++;
                        if (pos == bits.length) {
                            pos = 0;
                            iters++;
                        }
                    } // end for
                } // end if hash_bytes
            } // end for
        } // end while iters

        return bits;
    }
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