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copied!<p>When generating voucher codes - you should consider whether having a sequence which is predictable is really what you want. </p> <p>For example, Voucher Codes: ABC101, ABC102, ABC103 etc are fairly predictable. A user could quite easily guess voucher codes. </p> <p>To protect against this - you need some way of preventing random guesses from working. </p> <p>Two approaches: </p> <ul> <li><p>Embed a checksum in your voucher codes. </p> <p>The last number on a credit card is a checksum (Check digit) - when you add up the other numbers in a certain way, lets you ensure someone has entered a number correctly. See: <a href="http://www.beachnet.com/~hstiles/cardtype.html" rel="noreferrer">http://www.beachnet.com/~hstiles/cardtype.html</a> (first link out of google) for how this is done for credit cards. </p></li> <li><p>Have a large key-space, that is only sparsely populated.</p> <p>For example, if you want to generate 1,000 vouchers - then a key-space of 1,000,000 means you should be able to use random-generation (with duplicate and sequential checking) to ensure it's difficult to guess another voucher code. </p></li> </ul> <p>Here's a sample app using the large key-space approach: </p> <pre><code> static Random random = new Random(); static void Main(string[] args) { int vouchersToGenerate = 10; int lengthOfVoucher = 10; List<string> generatedVouchers = new List<string>(); char[] keys = "ABCDEFGHIJKLMNOPQRSTUVWXYZ01234567890".ToCharArray(); Console.WriteLine("Vouchers: "); while(generatedVouchers.Count < vouchersToGenerate) { var voucher = GenerateVoucher(keys, lengthOfVoucher); if (!generatedVouchers.Contains(voucher)) { generatedVouchers.Add(voucher); Console.WriteLine("\t[#{0}] {1}", generatedVouchers.Count, voucher); } } Console.WriteLine("done"); Console.ReadLine(); } private static string GenerateVoucher(char[] keys, int lengthOfVoucher) { return Enumerable .Range(1, lengthOfVoucher) // for(i.. ) .Select(k => keys[random.Next(0, keys.Length - 1)]) // generate a new random char .Aggregate("", (e, c) => e + c); // join into a string } </code></pre>

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