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From: Jeff Garzik <jgarzik@bitpay.com>
To: Mike Hearn <mike@plan99.net>
Cc: Bitcoin Dev <bitcoin-development@lists.sourceforge.net>,
	Andreas Schildbach <andreas@schildbach.de>
Subject: Re: [Bitcoin-development] BIP72 amendment proposal
Date: Fri, 12 Sep 2014 10:15:21 -0400	[thread overview]
Message-ID: <CAJHLa0Px985E7NyhHVPRpLxXD6XDGhd_WwsbHNBaQZVMQwxTwA@mail.gmail.com> (raw)
In-Reply-To: <CANEZrP1iTfZxY915hzoAEApz1+wd_S9j5RCwVJCNFqQ_+DNTSQ@mail.gmail.com>

Indeed -- Every byte added to the QR code makes it more difficult to
be used in restaurants, pubs and other low-light conditions.  BitPay
tested some of these scenarios.

Scannability is absolutely impacted.

On Fri, Sep 12, 2014 at 9:49 AM, Mike Hearn <mike@plan99.net> wrote:
> A few thoughts on this:
>
> (1) Base64 of SHA256 seems overkill. 256 bits of hash is a lot. The risk
> here is that a MITM intercepts the payment request, which will be typically
> requested just seconds after the QR code is vended. 80 bits of entropy would
> still be a lot and take a long time to brute force, whilst keeping QR codes
> more compact, which impacts scannability.
>
> (2) This should not be necessary in the common HTTPS context. The QR code
> itself is going to be fetched from some service, over HTTPS. I see no
> reasonable attacker that can MITM the request for the BIP70 message but not
> the request to get the QR code. Adding a hash makes QR codes more bloated
> and harder to scan, all on the assumption that HTTPS is broken in some odd
> way that we haven't actually ever seen in practice.
>
> (3) This can be useful in the Bluetooth context, but then again, we could
> also do things a different way by signing with the key in the first part of
> the URI, thus avoiding the need for a hash.
>
> I know I've been around the loop on this one with Andreas many times. But
> this BIP doesn't fix any actually existing problem in the previous spec. It
> exists because Andreas thinks SSL is useless. If SSL is useless we all have
> much bigger problems.
>
> ------------------------------------------------------------------------------
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> _______________________________________________
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>



-- 
Jeff Garzik
Bitcoin core developer and open source evangelist
BitPay, Inc.      https://bitpay.com/



  reply	other threads:[~2014-09-12 14:15 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <mailman.341412.1410515709.2178.bitcoin-development@lists.sourceforge.net>
2014-09-12 10:11 ` [Bitcoin-development] BIP72 amendment proposal Mark van Cuijk
2014-09-12 11:07   ` Andreas Schildbach
2014-09-12 13:49     ` Mike Hearn
2014-09-12 14:15       ` Jeff Garzik [this message]
2014-09-12 14:36       ` Andreas Schildbach
2014-09-12 15:25         ` Christophe Biocca
2014-09-12 15:33           ` Christophe Biocca
2014-09-12 15:37             ` Mike Hearn
2014-09-12 16:31               ` Mike Hearn
2014-09-12 18:43                 ` Aaron Voisine
2014-09-15  7:43                   ` Andreas Schildbach
2014-09-15  7:12                 ` Andreas Schildbach
2014-09-12 15:36         ` Mike Hearn
     [not found] <mailman.342174.1410547421.2163.bitcoin-development@lists.sourceforge.net>
2014-09-12 20:59 ` Mark van Cuijk
2014-09-13  8:53   ` Wladimir
2014-09-12  9:29 Andreas Schildbach
2014-09-12  9:55 ` Wladimir

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