Hashing a 10 digit number to a 2 digit alphanumeric

I need a function that does the following:

1. Takes a 10 digit number as input and creates a unique hash of that number
2. The hash should allow letters so that it can be shorter than the original number
3. The algorithm should be one-way (ie. irreversable)
4. I'm guessing by adding 26 letters (A to Z) with (0 to 9) will give 36 possibilities for each character. This means a 10 digit number can be hashed to a 2 digit alpha-numeric (?)

10^10 = 10000000000
2^36 = 68719476736

Eg. Hash(0374863796) returns A3 and no other 10 digit number (or < 10 digits) should produce A3.

Does anyone have any ideas about the algorithm to do such a thing. I've looked over the Net at hashing algs such as MD5, but it's not really suited for my purpose. I'm afraid I'm not much good at maths either...

I don't think you will be able to only use 2 characters and have any form of uniqueness, if you only use Alphanumeric characters you have a total of 36 characters to utilize:

So, ( 36 ^ 2 ) = 1296

That means there are only 1296 combinations of all of those characters when only 2 characters are used. No where near a 10 digit number...

Oops... err as I said, my maths skills are not much to be desired.

Ok, if we correct my mistake, and make the new number 8 digits

ie. 36^8 = 2821109907456

Which should cover a 10 digit number, yes?

After I correct this ahem discrepency with my original post, are there any suggestions as to a solution to such a problem?

Thanks in advance

Quote:

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Originally posted by headkaze
I need a function that does the following:

1. Takes a 10 digit number as input and creates a unique hash of that number
3. The algorithm should be one-way (ie. irreversable)

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These two points appear to be at odds - at least in my opinion.

Unique means that there is only "one" new pattern for every "original" values.

One-way means that many different "original" values become the same "new" pattern. That is how "one-way" is implemented - by having many "originals" flow into a single "new" pattern. That makes it impossible to reverse...