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Vasco uses DES (I don't know the details).

I'm sorry, I already read this somewhere on the web; the term I should have used was "protocol": how do they use DES to create those numbers - do they encrypt a counter, or a time, or a shared secret - what? Does anybody know? [I assume they encrypt something based on 1) the serial number and 2) a time or a counter.] Plus, there are less than 24 (7 * 3.3) bits in 7 digits; how does it get these particular 24 out of the 64 in a block? Thanks for any help, Mark