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Generating Unique Keys in .Net

, 17 Jun 2006
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I need to create some unique IDs. GUIDs are great as they give Globally Unique identifier but they are big. I mean if you want to issue unique number in your application which you want to give as Booking Number or any reference number then GUIDs is obviously not a solution.


I have few applications where I need to create some unique IDs. GUIDs are great as they give Globally Unique identifier but they are big. I mean if you want to issue unique number in your application which you want to give as Booking Number or any reference number then GUIDs is obviously not a solution. Therefore, I need some simple Id which is unique too. For example when I send a request to my Credit Card Processor there's an ID that correlates my invoice with the transaction at the provider. A GUID isn't what I'd want here.

But one relatively simple solution is to create sequential ID which will be of appropriate size as well as it will guarantee uniqueness. Very Good and Simple solution!!! Isn’t it !! My answer would be NO !! Because it is security threat for your website. In case of Web Application where you can Retrieve your Order or Booking Details by just giving Order Reference number, you can easily BruteForce Sequential Reference numbers to retrieve records.

In this article I will discuss some of my research and techniques.

Using DateTime and HashCode:

Using DateTime for generating unique keys is very common practice. I have remixed this approach by inducing HashCode in it also. Like


It will give you some key like 496bffe0. At the first glance it seems to be satisfied Unique key as its using current time and hashing to generate key but GetHashCode() doesn’t procduce unique code everytime. Althought Microsoft is using Double Hashing algorithms with N Number of collision resolving double hash function but during my experimentation I found lot of collisions.

Using GUIDs and HashCode:

So then I tried


It gives key something like 649cf2e3

Somehow I don't think that this string representation at least is unique… 38 characters represented as 8? Ok 32 bits, but still it's 8 digits and characters limited to hex values and yes my doubt got right as I wrote program which generated 100,000 keys and checked it for collisions and found several keys duplicated.

Using RNGCryptoServiceProvider and Character Masking

The .net Framwork provides RNGCryptoServiceProvider class which Implements a cryptographic Random Number Generator (RNG) using the implementation provided by the cryptographic service provider (CSP). This class is usually used to generate random numbers. Although I can use this class to generate unique number in some sense but it is also not collision less. Moreover while generating key we can make key more complicated by making it as alpha numeric rather than numeric only. So, I used this class along with some character masking to generate unique key of fixed length. Below is code sample:

  private string GetUniqueKey()
  int maxSize  = 8 ;
  int minSize = 5 ;
  char[] chars = new char[62];
  string a;
  a = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890";
  chars = a.ToCharArray();
  int size  = maxSize ;
  byte[] data = new byte[1];
  RNGCryptoServiceProvider  crypto = new RNGCryptoServiceProvider();
  crypto.GetNonZeroBytes(data) ;
  size =  maxSize ;
  data = new byte[size];
  StringBuilder result = new StringBuilder(size) ;
  foreach(byte b in data )
  { result.Append(chars[__b % (chars.Length - )>); }
   <span class="code-keyword">return result.ToString();


For lab testing purposes, I created 10,00,000 unique keys by using above three procedures and found the following results :

Generation Method

Time Taken

Number of Generated Keys

Number of Duplicate Keys

All Fixed Length Keys


Using DateTime and HashCode

01.56 sec 





Using GUIDs and HashCode

04.45 sec





Using RNGCryptoServiceProvider and Character Masking


00.40 sec


0 (Wow!!)



The above analysis shows that RNGCrypto with Character Masking is best method to generate Unique keys.

Note: The above research is for study purpose only. Yes there can be another methods which are better than the ones mentioned above.



This article has no explicit license attached to it but may contain usage terms in the article text or the download files themselves. If in doubt please contact the author via the discussion board below.

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About the Author

Altaf Al-Amin

United Arab Emirates United Arab Emirates
Altaf Al-Amin Najvani
Project Manager
Commercial Bank Of Dubai

BS - Computer Science
Masters In Project Management
Masters In Business Administration
CISA - Certified Information Systems Auditor
ITIL (Foundation)
Microsoft Certified Technology Specialist (SQL Server 2005)
Microsoft Certified Technology Specialist (Web Applications)
Microsoft Certified Application Developer (.NET)
Microsoft Certified Solution Developer (.NET)

Comments and Discussions

General[My vote of 2] You are comparing different things Pinmember_groo_8-Oct-12 1:10 
GeneralMy vote of 5 PinmemberGedeonGP19-Jul-12 18:46 
GeneralMy vote of 1 Pinmembernetizenk18-Jul-12 9:31 
GeneralRe: My vote of 1 Pinmemberwout de zeeuw23-Sep-12 5:30 
SuggestionVB.Net version PinmemberMember 822886530-Jun-12 1:49 
Questionon using GUIDS as primary keys ... f.y.i. Pinmembergerry lowry13-Jun-12 6:58 
QuestionDuplicates, less frequently, do get created using the RNG technique too! Pinmembergerry lowry13-Jun-12 6:52 
GeneralMy vote of 5 Pinmembershoebass21-Feb-12 21:27 
GeneralProblem with the code Pinmemberlove_chopra127-Apr-11 2:01 
GeneralKeeping things simple PinmemberHarout Saryan23-Mar-11 15:54 
GeneralMy vote of 5 PinmemberNariman Marvi11-Aug-10 0:43 
GeneralMy execution times are different [modified] Pinmemberschuetz17-Aug-09 21:45 
GeneralMy vote of 2 PinmemberAntonio Herrero Lopes19-May-09 18:49 
GeneralThanks alot Pinmemberammarcs15-Mar-09 12:30 
GeneralRe: Thanks alot PinmemberAltaf Al-Amin15-Mar-09 18:52 
Generalthanks for youre helpful guide Pinmembersooarty18-Nov-08 1:51 
GeneralUniqueKey CS to VB Pinmemberjkirkerx17-Sep-08 8:59 
GeneralRe: UniqueKey CS to VB Pinmember800XL23-Nov-09 4:37 
GeneralRe: UniqueKey CS to VB Pinmemberjkirkerx23-Nov-09 7:25 
GeneralRe: UniqueKey CS to VB Pinmemberjkirkerx23-Nov-09 7:31 
GeneralThank you! PinmemberLarsHB25-Jun-08 21:09 
GeneralShort and instructive. PinmemberBugMeNot ACCOUNT10-Apr-08 7:10 
GeneralNice Article Pinmembershouvik969-Apr-08 5:09 
GeneralRe: Nice Article Pinmembersai_sss18-Jul-10 22:57 
QuestionCan u help me???? Pinmembershouvik968-Apr-08 1:01 

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