Keyspace on the back of an envelope

One question that always plagues me: should I use 32-bit or 64-bit keys. I can never make a firm decision on this point. But I’ve just done some back of the envelope calculations in thinking about it.

If you issued one identity per second, every second of every day, it would take 136 years to exhaust the keyspace.

If you issued one thousand identities per second, it would take 50 days to exhaust the keyspace.


I found myself reminiscing about my implementation of Blowfish today. It earned me the great honour of being listed on Bruce Schneier’s web page. My implementation made Blowfish compatible across 32-bit signed ints, 64-bit signed ints, and 64-bit floats. I wrote this code coming up on 12 years ago… how time flies.