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

Andrew Thurber <anthurbe@cisco.com> Tue, 09 August 2011 18:14 UTC

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From: Andrew Thurber <anthurbe@cisco.com>
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To: Paul Coverdale <coverdale@sympatico.ca>
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Subject: Re: [81attendees] What is it at the bottom of restaurant receipts?
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This appears to be mandated by the new Revenu Quebec SRM system required at all restaurants to eliminate "Zapper" style tax fraud, with the receipts encoding a digital signature and fingerprint using the bar code and character string.

The SRM literature I found specifically does NOT describe the generation, encoding or purpose of the fields in the footer, though it carefully describes all other aspects of the receipts.

I don't know the algorithm or how Revenu Quebec would use the data.

Andrew

On Aug 9, 2011, at 1:58 PM, Paul Coverdale wrote:

Just to add a bit more to the mystery, I had exactly the same lunch on 3
days. On each of the 3 receipts the row of 12 dingbats is completely
different, not even a repeat of any character.

Google doesn't help much. I did a search for "Quebec City" and "dingbats",
but it just came back with a listing of all the members of the National
Assembly... (that's a Canadian joke, by the way).

...Paul

> -----Original Message-----
> From: 81attendees-bounces@ietf.org [mailto:81attendees-bounces@ietf.org]
> On Behalf Of Worley, Dale R (Dale)
> Sent: Tuesday, August 09, 2011 1:20 PM
> To: 81attendees@ietf.org
> Subject: Re: [81attendees] What is it at the bottom of restaurant
> receipts?
> 
> 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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