Best way to generate order numbers for an online store?

Question

Every order in my online store has a user-facing order number. I\'m wondering the best way to generate them. Criteria include:

• Short
• Easy to say over the

Answer 1

Something like this:

1. Get sequential order number. Or, maybe, an UNIX timestamp plus two or three random digits (when two orders are placed at the same moment) is fine too.
2. Bitwise-XOR it with some semi-secret value to make number appear "pseudo-random". This is primitive and won't stop those who really want to investigate how many orders you have, but for true "randomness" you need to keep a (large) permutation table. Or you'll need to have large random numbers, so you won't be hit by the birthday paradox.
3. Add checkdigit using Verhoeff algorithm (I'm not sure it will have such a good properties for base33, but it shouldn't be bad).
4. Convert the number to - for example - base 33 ("0-9A-Z", except for "O", "Q" and "L" which can be mistaken with "0" and "1") or something like that. Ease of pronouncation means excluding more letters.
5. Group the result in some visually readable pattern, like XXX-XXX-XX, so users won't have to track the position with their fingers or mouse pointers.