A Lesson In Timing Attacks (see http://codahale.com/a-lesson-in-timing-attacks/)

constantTimeEquality.java

// Better
public static boolean isEqual(byte[] a, byte[] b) {
    if (a.length != b.length) {
        return false;
    }
    
    int result = 0;
    for (int i = 0; i < a.length; i++) {
      result |= a[i] ^ b[i]
    }
    return result == 0;
}

// worse
public static boolean isEqual(byte digesta[], byte digestb[]) {
    if (digesta.length != digestb.length)
        return false;

    for (int i = 0; i < digesta.length; i++) {
        if (digesta[i] != digestb[i]) {
            return false;
        }
    }
    return true;
}