unique key generator

Hi i want to generate a unique key.
I want it to be made up of letters and numbers.

I have been looking at RC2 using the following code:

-----------------------------------
using System.Security.Cryptography;

static void Main(string[] args)
{
RC2 r = RC2.Create();
r.GenerateIV();
r.GenerateKey();

for (short i = 13; i < 200; i += 13)
{
byte[] data = BitConverter.GetBytes(i);
byte[] enc = r.CreateEncryptor().TransformFinalBlock(data, 0, 2);
Console.WriteLine("{0}\t= {1}", 13, Convert.ToBase64String(enc));
}
Console.ReadLine();
}

---------------------------------------------

The problem is that this generates a key that contains non alphanumeric characters:
i.e
/MQpLW6J+3o=  

----------------------------

so is there anything out there that will generate a unique alphanumeric key (Not a guid) about 10-12 characters.  something that will be unique across time.

thanks very much.
LVL 1
MrKevorkianAsked:
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Mike TomlinsonMiddle School Assistant TeacherCommented:
What's wrong with a GUID?...you could just remove the hypens and use Substring() to get the required number of characters from the left, middle, or right side...
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MrKevorkianAuthor Commented:
if i remove characters - whats the guarentee that it will be unique?
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MrKevorkianAuthor Commented:
i have had a look at RNGCryptoServiceProvider and that seems that it might be useful.  But doesnt  allow you to introduce a seed to it initially.
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Mike TomlinsonMiddle School Assistant TeacherCommented:
If you want to GUARANTEE that your number is unique then you would have to store every single number you've ever used in a database so you can search for previously used values.

Otherwise I'm pretty sure it doesn't matter what system you use to generate your "unique" key as you are at best simply "not likely" to get a repeat value.

But I'm no security expert...
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rdrunnerCommented:
Hello...

Du you want to include any other informations in your "key" or should it "just" be a number?

What you could do is to create a small function that will convert several bytes into a set of allowed characters.  This could be done along the lines of mime encoding. So basically you get your number as a byte array, then you take small chunks of it (in32 Values) and mod them through the number of allowed characters (This gets the remainder) and pick the nth Character out of your allowed set.. then you (Integer) divide them through the number of allowed chars and repeat the process until you are left with a '0'

To revert you can reverse the process and retrieve the number again.

Also this allows you to decide which letters are skipped (for example I/1 or O/0), so there wont be any characters that are hard to read...
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rdrunnerCommented:
Edit:
To achieve uniqueness, i would just store the numbers in the DB like suggested or use a (counter * key + counter) that will allways reach the desiered target-Number length. (e.g. if you know you need to generate "millions" then dont start the counter at "1" but use 1000000 as start for your counter.

The merging of those numbers could be more complex, depending on your need for this key.... But it will allow a unique number with each counter value, and it can be reproduced which counter was used to generate the key...
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