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BUIP086: bitcoinash: URI format update
Propser: Brendan Lee <brendanjlee@protonmail.com>
Sponsored by: Gal Guki (@torusJKL)
Submitted on: 2018-02-05
Status: passed

Abstract

This BUIP describes a revision of the bitcoin: URI scheme (BIP 20/BIP21)
to enable the creation of Bitcoin transactions with multiple and complex
outputs including scripts and data. New features proposed to be added in
version 2.0 include: Creating a new URI format allowing multiple outputs
to be defined in a single URI Adding functionality to allow multiple
URLs to be scanned together and condensed into a single transaction
Create mechanisms that allow scripts and smart contracts to be applied
within the standard URI formatting guidelines

Motivation

This revision allows merchants to create more flexible transaction URIs
that can split single payments into multiple outputs. For example, a
merchant may have an agreement to pay some part of all gross revenue to
a landlord, some part to a franchise organisation and some part as
GST/VAT/Sales tax. This BUIP allows these additional transactions to be
handled instantaneously as part of the merchant’s regular commercial
operations, thereby simplifying their accounting and reporting
processes. It also enables the third parties to receive their payments
instantaneously rather than waiting until monthly or quarterly
accounting processes can be undertaken. This revision also allows users
to condense multiple URIs into a single set of outputs by scanning them
consecutively before executing the transaction. For example, a merchant
could attach QR codes to each item in the store directing the wallet to
pay different amounts to a single common address. The new
‘multiscanparam’ allows a compatible SPV wallet to enter multiple URLs
together to create a smart contract. Smart contracts can be used to
perform token passing using coloured coins, or through OP_RETURN
outputs. The addition of the ability to create unique scripts for each
output in the URI gives merchants and users a high degree of flexibility
and allows new application layers to be built and executed using methods
already widely used for bitcoin transactions.

Specification

The “bitcoincash:” URI scheme is updated to version 2.0. This new
version allows multiple new features including:

- Nesting of multiple transaction outputs within a single URI

- Addition of optional transaction outputs

- Processing of multiple URIs into a single transaction

- Specification of unique redeem scripts for each output defined in the
transaction

The URI scheme maintains compatibility with version 1.0 through the use
of compatible labels, but re-structures the URI outputs into a set of
transaction data arrays which contain information relating to each
transaction. Separate arrays exist for each transaction parameter
(bitcoinaddress, amountparam, messageparam, labelparam), with the
elements of each array being linked to the corresponding transaction
(e.g. amount[1], label[1] and message[1] would all relate to
transaction[1]).

- Additional parameters are added to the scheme including:

- multiscanparam – Boolean value allowing a merchant to allow payers to
merge multiple URIs into a single transaction

- bitcoinscript[ ] – An array containing script data for each output

- txidparam[ ] and voutparam[ ] – arrays used by scripts to
identify specific UTXO that the script is trying to spend

Note:

To maintain compatibility with URI standards, all reserved characters
must be transmitted as percent encoded values. E.g.
%5B = [ and %5D = ]. For further information on reserved characters,
see the following link:
https://tools.ietf.org/html/rfc3986#section-2.2

For the purposes of readability, this specification uses the reserved
symbols, however all examples have been represented using RFC3986
compliant notation.

Parameters

The URI and its parameters are defined as follows:

Bitcoincashurn = "bitcoincash:" bitcoinaddress [ ";version=" bitcoinversion ] [ "?" bitcoinparam ] [ "?" bitcoinparam[] ] [ "?" otherparam ]
bitcoinaddress = cashaddress | legacyaddress
cashaddress = cashadd  *cashaddr
legacyaddress = base58 *base58
bitcoinversion = "2.0"
bitcoinparam = amountparam | labelparam | messageparam | sendparam | multiscanorderparam | otherparam
amountparam = "amount=" *amount
amount = amountdecimal | amounthex
amountdecimal = *digit [ "." *digit ] [ "X" *digit ]
amounthex = "x" *hexdigit [ "." *hexdigit ] [ "X" *hexdigit ]
labelparam = "label=" *pchar
messageparam = "message" *pchar
sendparam = "send=" *pchar
multiscanorderparam = "order[?]=" *char
otherparam = pchar *pchar "=" *pchar
bitcoinparam[] = bitcoinaddress[] | amountparam[] | labelparam[] | messageparam[] | bitcoinscrip[]
bitcoinaddress[] = "address[?]=" cashaddress | legacyaddress
cashaddress = cashaddr  *cashaddr
legacyaddress = base58 *base58
bitcoinaddress[0] = bitcoinaddresss
amountparam[] = "amount[?]=" amount
amountparam[?] = amountdecimal | amounthex
amountdecimal = *digit [ "." *digit ] [ "X" *digit ]
amounthex = "x" *hexdigit [ "." *hexdigit ] [ "X" *hexdigit ]
amountparam[0] = amountparam
labelparam[] = "label[?]=" *pchar
labelparam[0] = labelparam
messageparam[] = "message[?]=" *pchar
messageparam[0] = messageparam
txscript[] = "txscript[?]=' *pchar
bitcoinscript[] = "script[?]=" *pchar
bitcoinscript[0] =  bitcoinscript
bitcoinscript[] = "script[?]=" *pchar
bitcoinscript[0] =  bitcoinscript
txidparam[] = "txid[?]=" *base64
voutparam[] = "vout[?]=" *digit

Compressed Labels

Due to the size constraints of some URL presentation methods the
following compressed labels will also be considered valid for
transaction construction:

"v" = "version"
"ad" = "address"
"am" = "amount"
"l" = "label"
"m" = "message"
"o" = "order"
"ts" = "txscript"
"bs" = "bitcoinscript"
"tx" = "txid"
"v" = "vout"

Compatibility

The new URI format maintains compatibility with the current version 1.0
format through the inclusion of the bitcoinparam labels used in
version1.0. This means that POS systems that do not need features
associated with version2.0 URLs do not need to upgrade to be compatible
with wallets that support version2.0 Capabilities The version 2.0 format
allows merchants to create structured URIs that can send multiple
complex outputs where each output can contain a non-default redeem
script and be sent to a unique destination. This is achieved by using
the bitcoinparam[ ] array structures.

The minimum amount of information needed by a wallet to add an output to
a transaction is a bitcoin address. For each output being requested, the
URI must add a bitcoin address to a position in the bitcoinaddress[ ]
array. The position of the address in the bitcoinaddress[ ] array
determines the position of the ancillary data in the amountparam[ ],
labelparam[ ], messageparam[ ], scriptparam[ ] and txid[ ]
arrays. E.g. amount data for the output to the address located in
bitcoinaddress[1], is entered into the amountparam[1],
messageparam[1] and labelparam[1] array positions.

A URI that defines more than one element in any bitcoinparam[N] field
would be rejected as invalid. E.g. if a URI defines an amount in the
amount field and then defines a conflicting amount in the amount[0]
array position, the URI would be rejected as invalid. Similarly, if
there are two separate values attached to the amount[2] label, the URI
would be rejected as invalid. For tokens and sidechains, a script can
identify a particular UTXO which is to be spent using the txidparam[ ]
and voutparam[ ] arrays. This can be used to specify a UTXO which is
known to contain a coloured coins or a certain script. For the
transaction to be valid, the selected UTXO

Requirements for URL reader

The URI provides a medium through which complex transaction structures
can be defined between two parties. For a transaction to be completed,
the seller must meet all the requirements stipulated in the URL. Where
amount[N] is defined, the wallet can assume that the requested value
is agreed upon between sender and receiver. It is up to the user’s
wallet to determine how best to structure that payment using the funds
has access to. Where script[N] is the wallet can assume that any
outputs sent to that address that do not contain the correct redeem
script will not meet the requirements of the contract and will not
complete the transaction. It is up to the sending wallet to ensure that
amounts and scripting requirements imposed by the receiver are met.

Multiscan contracts

The intent of the Multiscan function is to allow for the creation of a
new type of smart contract. A customer assembles a contract by using
their SPV wallet to scans URLs that include a contract order. A
multiscan contract is started when a wallet receives a URL with a
non-zero value in the multiscanorderparam field. The wallet sees this
and goes into multiscan mode. In multiscan mode, the wallet should allow
the user to enter multiple different URLs. URLs do not need to be
scanned in order however the wallet user will not be able to terminate
the contract without a URL labelled order[FF]. The order[FF] URL may
contain financial transactions and parameters. If OP_GROUP is used in
this Script[0], any URLs that are part of the contract will be able to
use coloured coins as well.

When the wallet assembles the transaction, the transactions in
addres[X>0] of the order[FF] URL, ascending transaction numbers
from zero will be set up to be the first when the contract is executed.
Scripts in the remaining URLs will be appended in ascending order. Once
all the URLs have been concatenated, the transactions with
address[X<0] as a parameter in the order[FF] URL are appended in
ascending order.

Any URLs that have the same multiscanorderparam must be concatentated in
no particular order. If a zero value transaction Where there are
multiple transactions directed to a particular address in the contract,
from multiple URLs with the same multiscanorderparam, those amounts can
be aggregated. Where they are contained in multiple levels of the
contract, the amount at each level can either be paid in a separate
output or added together. – NEED FEEDBACK ON THIS IDEA When additional
URLs are scanned, the wallet will expect multiscanparam to be non-zero.
If a URL without a non-zero multiscanparam is scanned, it is either
rejected from the contract, or the contract is terminated.

Example: Alice visits Bobmart to buy a few things.

When alice arrives, she can choose three baskets. Blue, green and red.
Each has a NFC chip in the handle containing an order[FF] URL. Alice
picks the blue basket and scans the handle with her phone. Its zero
script sets up the transaction to support colored coins using OP_GROUP.
Her basket will now reward her with 1 Bobpoint for every bit she spends.
Her phone now goes into scan mode. The green basket’s zero script sets
up the transaction to use the Bob’s charities colored coin system. Any
transactions would carry discounts that apply to Bobmart Rewards
members, but instead of receiving Bob’s her BobPoints, Bobmart gives 1
satoshi to a local charity. The red basket has no points or charity, and
is a basic payment script. Alice buys some fruit, (order[12]),
milk(order[2]), cheese (order[2]) and bread (order[10]), scanning
the code on each as she puts them in her basket. walks to the packing
area and hits ‘Pay Now’. Her wallet sets up a contract that applies
bob’s rewards to be automatically applied to her wallet. The transaction
then pays 500 bits to the dairy who made the milk and cheese, 250 to the
Bob’s dairy transport and storage, 1200 bits to various orchards for the
fruit and 1000 bits to bob’s fruit department and 500 bits to Bob’s
bakery. The wallet can send this onto the network and Bob and all of his
suppliers are paid at once.

Bitcoinscript

The version2.0 URI format allows URLs to be created which fully or
partially define complex smart contracts. By using the bitcoinscript[]
parameters, a URL can be constructed that defines smart contract scripts
to be applied to some or all of the outputs in the transaction. This can
be used to apply non-default redeem scrips such as timelocks,
tokenisation scripts or evaluation of multiple signatures to outputs
containing funds, or it can be used to define the contents of an
OP_RETURN output that needs to be included in the transaction. It is up
to the sending wallet to ensure that scripting requirements specified in
the URL are met.

Appendix

Version 1.0 Syntax

The version 2.0 implementation is still fully compatible with version
1.0 wallets. POS providers should ensure to always specify version=2.0
in situation where version 2.0 URLs are being presented. Otherwise a
version 1.0 compatible wallet will look only at the parameters in the
bitcoinparam fields and drop all other data.

Examples

Example 1: Bar transaction

Satoshi’s Tavern employs roving servers who take orders from patrons and
retrieve drinks from an automated dispensing robot. Servers use an app
to assemble orders for patrons who then pay the server directly.

Bob orders two beers and a Margarita from Alice who enters the order in
her app. The app creates the following URI and presents it as a QR code
(Line breaks added for clarity):

bitcoincash:qr2se9wy2egettFxPbmn99cK8v5AFq55Lx?version=2.0
&amount=1X6
&label=Satoshis%20Tavern:%20Server%20–%20Alice
&message=Order%20-%202%20x%20Sierra%20Nevada%20Pale%20Ale%2c%201%20x%20Margarita
&address%5B1%5D=qnttFxPbmn2se9wy2egAFq55Lxe99cK8v5
&amount%5B1%5D=1X5
&message%5B1%5D=Sales%20Tax
&address%5B2%5D=qn2se9nttFxPbmxwy2egFcK8v5q55Lxe99?
&label%5B2%5D=Tip
&message%5B2%5D=Tip
&receipt=true

If Bob’s wallet is compatible with the extension, Bob scans the QR code
with his hot wallet and is first presented with a prompt labelled ‘Tip’
and a numerical entry field where he can enter in an amount to tip
Alice. Bob enters a tip of 0.002BCH and the wallet creates a transaction
with outputs as follows:

0.01BCH to qr2se9wy2egettFxPbmn99cK8v5AFq55Lx
0.001BCH to qnttFxPbmn2se9wy2egAFq55Lxe99cK8v5
0.002BCH to qn2se9nttFxPbmxwy2egFcK8v5q55Lxe99
OP_RETURN: 'Satoshi's Tavern: Server – Alice; Order - 2 x Sierra Nevada Pale Ale, 1 x Margarita, 0.011BCH; Sales tax, 0.01BCH; Tip, 0.002BCH'
Change Output

and the following memo:

"Label: Satoshi's Tavern <carriage return>
2 x Sierra Nevada Pale Ale, 1 x Margarita 0.01BCH <carriage return>
Sales Tax 0.001BCH <carriage return>
Tip 0.002BCH"

The memo is stored locally in Bob’s wallet and may be uploaded to a
wallet provider’s systems in-case Bob’s wallet needs to be restored on a
new device, however it is not recorded on-chain and is not considered
immutable or appropriate for the storage of important transaction
records. The OP_RETURN output is recorded on-chain and represents an
immutable record of the transaction. When Bob sends the transaction, the
bar recognises that it has received a payment and looks for an output
with information encoded using an OP_RETURN opcode. Using this
information it automatically assembles the order and places it on a tray
for Alice to pick up and deliver to Bob. The government jurisdiction in
which Satoshi’s tavern operates instantaneously receives a sales tax
transaction of 0.001BCH, and Alice receives a tip payment of 0.002BCH
directly to her personal wallet. Bob’s wallet shows a transaction with 5
outputs and a memo detailing his purchase. Bob can also go on-chain and
see the transaction information encoded in the OP_RETURN output. If
Bob’s wallet is not compatible with the extension, his wallet recognises
that bitcoinparam version=2.0 and will reject the transaction. Alice’s
app should incorporate the ability to provide a Version1.0 compatible
transaction however this would be up to the POS app provider and is not
part of this specification.

Example 2: Online Content

Bchncontent.com accepts online payments for content including fiction
and non-fiction articles, music and video. Bob puts the following in his
cart: The album ‘Hex on you’ by Alice On-Chains, priced at 0.00012BCH An
e-book ‘A technical guide to URIs’ by Donald Drumpf priced at 0.00002BCH
A web comic ‘Driving with Fiat’ by Bill Burnie which is released under
creative commons. Any money given to Bill Burnie would be considered a
donation and is therefore tax exempt. Bob lives in a jurisdiction that
applies a 10% sales tax on top of the price of the items. When Bob
clicks ‘Purchase’, the bchncontent.com cart creates the following URI
and presents it as a QR code:

bitcoincash:qtFxPbmn99cK8r2se9wy2egetv5AFq55Lx?version=2.0
&amount=14X3
&label=BCHncontent.com
&message=Album%20–%20Hex%20on%20you%2c%20Alice%20On-Chains%2c%20 0.00012BCH;%20eBook%20–%20A%20technical%20guide%20to%20URIs%2c%20Donald Drumpf%2c%202X3BCH
&address%5B1%5D=qnttFxPbmn2se9wy2egAFq55Lxe99cK8v5
&amount%5B1%5D=14X2
&message%5B1%5D=Sales%20Tax
&address%5B2%5D=qse9wy2egAFq55Lxe99cK8nttFxPbmn2v5
&label%5B2%5D=Driving%20with%20Fiat%2c%20Bill%20Burnie
&message%5B2%5D=Creative%20Commons%20Comic%20–%20Driving%20with%20Fiat%2c%20Bill%20Burnie
&receipt=false

If Bob’s wallet is compatible with the extension, Bob scans the QR code
with his hot wallet. First, Bob is presented with a prompt labelled
‘Driving with Fiat, Bill Burnie’ where he can enter in an amount that he
wishes to donate to Bill Burnie. Bob enters an amount of 0.0002BCH.
Next, Bob is presented with a prompt asking him if he wishes to create
an invoice on-chain. Bob selects ‘Yes’.

Bob’s wallet creates a transaction with outputs as follows:

0.00014BCH to qtFxPbmn99cK8r2se9wy2egetv5AFq55Lx
0.000014BCH to qnttFxPbmn2se9wy2egAFq55Lxe99cK8v5
0.0002BCH to qse9wy2egAFq55Lxe99cK8nttFxPbmn2v5
OP_RETURN: 'BCHncontent.com: Album – Hex On You, Alice On-Chains, 0.00012BCH; eBook – A technical guide to URIs, Donald Drumpf, 0.00002BCH; Sales tax: 0.0014BCH; Creative Commons Comic – Driving with Fiat, Bill Burnie, 0.0002BCH donation'
Change output

and the following memo:

"Label: BCHncontent.com <carriage return>
Album – Hex on you, Alice On-Chains, 0.00012BCH; eBook – A technical guide to URIs, Donald Drumpf, 0.00002BCH <carriage return>
Sales Tax 0.000014BCH <carriage return>
Driving with Fiat, Bill Burnie, 0.0002BCH"

The memo is stored locally on his wallet, and may be uploaded to a
wallet provider’s systems in-case Bob’s wallet needs to be restored on a
new device, however it is not recorded on-chain and is not considered
immutable or appropriate for the storage of important transaction
records. The OP_RETURN output is recorded on-chain and represents an
immutable record of the transaction. When Bob sends the transaction, the
bchncontent.com SPV wallet recognises that it has received Bob’s payment
and sends Bob the instructions needed to access his content. The
government jurisdiction in which Bob lives instantaneously receives a
sales tax transaction of 0.000014BCH, and Bill Burnie receives a
donation of 0.0002BCH. Bob’s wallet shows a transaction with 5 outputs
and a memo detailing his purchase. Bob can also go on-chain and see the
transaction information encoded in the OP_RETURN output. If Bob’s
wallet is not compatible with version 2.0 transactions, it would see
parameter version = 2.0 and would reject the transaction as invalid. For
Bob to continue, the online merchant would need to provide a backwards
transaction method for Bob to use.

Example 3: Market Stall

Nutmeg Greg runs a market stall. He sells nutmeg and nutmeg related
goods. Bob walks into Nutmeg Greg’s stall and opens up a Version2.0
compatible app on his phone. Bob selects a jar of premium nutmeg off the
shelf and scans the QR code on the label which returns the following
(line breaks added for clarity only):

bitcoincash:qt9wy2egetv5AFxPbmn99cK8r2seFq55Lx?version=2.0
&amount=25X3
&label=Nutmeg%20Greg
&message=Premium%20Nutmeg%2c%200.00025BCH
&address%5B1%5D=qnttFxPbmn2se9wy2egAFq55Lxe99cK8v5
&amount%5B1%5D=25X2
&message%5B1%5D=Market%20Fee
&Multiscan=true
&receipt=true

Bob’s wallet starts creating a transaction with two outputs, one for
0.00025BCH to qt9wy2egetv5AFxPbmn99cK8r2seFq55Lx and another to
qnttFxPbmn2se9wy2egAFq55Lxe99cK8v5 for 0.000025BCH. The wallet then asks
Bob if he would like to add more items to the transaction. Bob selects
‘YES’. Bob selects a bag of nutmeg candy and scans the QR code on the
label which returns the following (line breaks added for clarity only):

bitcoincash:qt9wy2egetv5AFxPbmn99cK8r2seFq55Lx?version=2.0
&amount=3X4
&label=Nutmeg%20Greg
&message=Nutmeg%20Candy%2c%200.0003BCH
&address%5B1%5D=qnttFxPbmn2se9wy2egAFq55Lxe99cK8v5
&amount%5B1%5D=3X3
&message%5B1%5D=Market%20Fee
&Multiscan=true
&receipt=true

Bob’s wallet looks at the transaction it has already started creating
and sees common output addresses for each of the new outputs. It updates
the output to qt9wy2egetv5AFxPbmn99cK8r2seFq55Lx to 0.00055BCH and the
one to qnttFxPbmn2se9wy2egAFq55Lxe99cK8v5 to 0.000055BCH. The wallet
then asks Bob if he would like to add more items to the transaction. Bob
selects ‘No’. The wallet then asks Bob if he would like a receipt to be
recorded on-chain. Bob selects ‘No’. Bob’s wallet finalises the
transaction with outputs as follows:

0.00055BCH to qt9wy2egetv5AFxPbmn99cK8r2seFq55Lx
0.000055BCH to qnttFxPbmn2se9wy2egAFq55Lxe99cK8v5
OP_RETURN: 'Nutmeg Greg: Premium Nutmeg, 0.00025BCH; Nutmeg Greg: Nutmeg Candy, 0.0003BCH, Market Fee, 0.000055BCH'
Change output

and the following memo:

"Label: Nutmeg Greg <carriage return>
Premium Nutmeg, 0.00025BCH
Nutmeg Candy, 0.0003BCH
Market fee, 0.000055BCH
Change output

The memo is stored locally in Bob’s wallet, and may be uploaded to a
wallet provider’s systems in-case Bob’s wallet needs to be restored on a
new device, however it is not recorded on-chain and is not considered
immutable or appropriate for the storage of important transaction
records. When Bob sends the transaction, Nutmeg Greg’s SPV wallet sees
the transaction and displays the amount on Greg’s screen. Greg’s wallet
also displays the contents of the OP_RETURN output which he uses to
confirm Bob’s purchase. The market where Greg’s stall is located
instantaneously receives a fee transaction of 0.000055BCH. Bob’s wallet
shows a transaction with 4 outputs and a memo detailing his purchase.
Bob can also go on-chain and see the transaction information encoded in
the OP_RETURN output. If Bob’s wallet is not compatible with version
2.0 transactions, it would see parameter version = 2.0 and would reject
the transaction as invalid. For Bob to continue, Greg would need to
provide separate labels with version 1.0 compatible URI’s.