Are there...one-way encryption algorithms

[Sidney Markowitz]

Enzo Michelangeli wrote:
> but the slight risk of collision,
> although practically negligible, is a bit irksome

If you quantify the "practically negligible" risk, it might be less 
irksome: SHA-1 is a 160 bit hash. The birthday paradox says that you 
would need to hash 2^80 different credit card numbers before you had a 
50% probability of having even one collision in your database keys. Very 
roughly that means you would need to have a trillion different credit 
card numbers in your database in order to get as much as a one in a 
trillion chance of a collision. You would probably find dealing with a 
trillion different credit card numbers more irksome than the negligible 
chance of a collision even that many would give you.

  -- sidney

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