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Date: Tue, 21 Jul 2015 16:58:39 +0200
From: Thomas Voegtlin <thomasv@electrum.org>
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Subject: Re: [bitcoin-dev] QR code alternatives (was: Proposal: extend bip70
	with OpenAlias)
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Le 20/07/2015 16:40, Mike Hearn a =C3=A9crit :
>=20
> If we accept a single payment address i.e. no clever tricks around merg=
e
> avoidance, such a QR code could look like this:
>=20
> bitcoin:1aBcD1234....?x=3Dserialized_payment_request
>=20
> However this requires text mode and wastes bytes at the front for the U=
RI
> type.
>=20

It is possible to be both backward-compatible and to avoid wasting space
in URIs, if we simply assume that the payment request is a single
standard output + amount (that scenario will probably cover 99% of the
cases, and the few other cases may not need QR codes). We generate a
serialized bip70 PR from the parameters found in the URI, sign that
string, and add the signature to the URI.

Example:

bitcoin:1H14AiSc4PqkK9VTmeutZU3edSy3HS5HL8?amount=3D1&message=3Dhere%20is=
%20a%20test&time=3D1437489571&exp=3D604800&name=3Decdsa.net&sig=3D3Quot6m=
2RsR43NgV8VQQx3Ngf5u8wZY18mu523x3ViLrA3WLwSoQum2Znw3gRsTgfADpHuEiyyjnpxCL=
KWrkR4RQM

'time' is the timestamp of the request
'exp' is the duration of validity, 1 week here
(it saves a few bits to express it that way)

'name' is the domain name of the signer
'sig' is the signature

The QR code derived from that URI is perfectly scannable with a phone.