I think there are some standard header bytes, so the number of combinations of the interesting parts might be much smaller. Also I said less than 7 bytes, so it's actually 281474976710656 . If header bytes reduce 1 or 2 bytes, it will be 4294967296 - 1099511627776. 1099511627776 / 1000 / 60 / 60 / 24 / 365 is around 35 years.