Ideas to create a small (<10 digits), not (very) secure “hash”

Question

I\'m working on an online event ticketing system, where users will be able to self print his tickets and show up at the event where it will be scanned (barcode) and ideally

Answer 1

Consider a very simple scheme based on a Feistel network to permute, say, the ticket ID number. This message (which happens to be on the PostgreSQL lists but doesn't really have much to do with PostgreSQL) describes a simple Feistel network. On each ticket you could print a ticket ID number (sequentially chosen), then a "ticket secret code" that's the result of putting the ID number through a Feistel network. Possible variations include appending a check digit to the secret code, and basing the input to the Feistel network on more than just the sequentially generated number (number + 10,000 * event ID number, et cetera).