User ID obfuscation

Question

I expect this\'s been asked before but haven\'t really found an appropriate answer here and also don\'t have the time to come up with my own solution...

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Answer 1

1. Use UUIDs

2. Make another column in the user table for, e.g. 64 bit integers, and fill it with a random number (each time a new user registered - generate it and check it's unique). A number looks better than UUID, however a bit more coding required.

3. Use maths. ;) You could generate pair of numbers X, Y such as X*Y = 1 (mod M). E.g. X=10000000019L, Y=1255114267L, and M=2^30. Then, you will have two simple functions:

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long encode(long id)
{  return (id * X) & M; }

long decode(long encodedId)
{  return (encodedId * Y) & M; }

It will produce nearly random encoded ids. It's easy, but hackable. If someone would bother to hack it, he will be able to guess your numbers and see encoded values too. However, I am not completely sure which complexity it is, but as I remember it's not very easy to hack.