Re: [81attendees] What is it at the bottom of restaurant receipts?

Ben Campbell <ben@estacado.net> Tue, 09 August 2011 17:31 UTC

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To: "Worley, Dale R (Dale)" <dworley@avaya.com>
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Subject: Re: [81attendees] What is it at the bottom of restaurant receipts?
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I asked a couple of waiters about them, and they had no idea what the dingbats were for. That tells me that they don't use them for anything. They use the barcodes for everything. That makes me wonder if the dingbats were put there for restaurants that didn't invest in the bar-code system, as some sort of alternative verification. Or maybe they're only used by auditors. Or in expense reimbursement. 

On Aug 9, 2011, at 12:20 PM, Worley, Dale R (Dale) wrote:

> Comparing a few receipts, I've so far discovered:
> 
> There are always 12 dingbats in the row.
> 
> There are never duplicates on a single receipt.  This suggests that the dingbats are not a direct transcription of information, but rather statistically random.
> 
> One can easily stack 5 receipts (60 dingbats) and see no duplicates.  This suggests (via the birthday paradox) that there are more than 60^2 = 3600 dingbats that are commonly used.
> 
> My current guess is that there are 4096 dingbats representing 12 bits each, and the line represents 12 * 12 = 144 bits that are either a hash or a digital signature of the data in the hash.  The dingbats are probably to be visually compared by a human with a similar display that is computed by a government device from the data on the receipt.
> 
> Curiously, on one receipt I have, the dingbat row consists of a sequence of 6 dingbats repeated twice, which seems to me to be very unlikely.
> 
> Dale
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