Handy code for dealing with keys.

git-svn-id: https://samskivert.googlecode.com/svn/trunk@1609 6335cc39-0255-0410-8fd6-9bcaacd3b74c

projects/samskivert/src/java/com/samskivert/util/KeyUtil.java

@@ -0,0 +1,104 @@
+//
+// samskivert library - useful routines for java programs
+// Copyright (C) 2001-2004 Michael Bayne
+//
+// This library is free software; you can redistribute it and/or modify it
+// under the terms of the GNU Lesser General Public License as published
+// by the Free Software Foundation; either version 2.1 of the License, or
+// (at your option) any later version.
+//
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+// Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public
+// License along with this library; if not, write to the Free Software
+// Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
+
+package com.samskivert.util;
+
+import java.lang.StringBuffer;
+import java.util.Random;
+
+/**
+ * Handy functions for dealing with license key creation and general key
+ * issues.
+ */
+public class KeyUtil
+{
+    /**
+     * Convenient function to make a random key of the specified total
+     * length, containing length - 1 random digits, that is verifiable
+     * using {@link verifyLuhn}.
+     */
+    public static String makeVerifiableKey (Random rand, int length)
+    {
+        return makeLuhnVerifiable(generateRandomKey(rand, length - 1));
+    }
+
+    /**
+     * Return a key of the given length that contains random numbers.
+     */
+    public static String generateRandomKey (Random rand, int length)
+    {
+        int numKeyChars = KEY_CHARS.length();
+        StringBuffer buf = new StringBuffer();
+        for (int ii = 0; ii < length; ii++) {
+            buf.append(KEY_CHARS.charAt(rand.nextInt(numKeyChars)));
+        }
+        return buf.toString();
+    }
+
+    /**
+     * Verify the key with the Luhn check.  If the key is all zeros,
+     * then the luhn check is true, but that is almost never what you want
+     * so explicitly check for zero and return false if it is.
+     */
+    public static boolean verifyLuhn (String key)
+    {
+        // If there is a non digit, or it is all zeros.
+        if (key.matches("\\D") || key.matches("^[0]+$")) {
+            return false;
+        }
+
+        return (getLuhnRemainder(key) == 0);
+    }
+
+    /**
+     * Takes a random string of digits and adds the appropriate check
+     * digit in order to make the whole string verifyable using {@link
+     * verifyLuhn}.
+     */
+    public static String makeLuhnVerifiable (String key)
+    {
+        String prekey = key + '0';
+        int rem = getLuhnRemainder(prekey);
+
+        return (rem == 0 ? prekey : key + (10 - rem));
+    }
+
+    /**
+     * Return the luhn remainder for the given key.
+     *
+     * {@see http://www.beachnet.com/~hstiles/cardtype.html }
+     * {@see http://www.google.com/search?q=luhn%20credit%20card }
+     */
+    public static int getLuhnRemainder (String key)
+    {
+        int len = key.length();
+        int sum = 0;
+        for (int multSeq = len % 2, ii=0; ii < len; ii++) {
+            int c = key.charAt(ii) - '0';
+            if (ii % 2 == multSeq) {
+                c *= 2;
+            }
+            sum += (c / 10) + (c % 10);
+        }
+
+        return sum % 10;
+    }
+
+    /** Characters used in creating key strings. */
+    protected static String KEY_CHARS = "0123456789";
+}