BIP 0020

  BIP: 20
  Title: URI Scheme
  Author: Luke Dashjr <luke+bip@dashjr.org>
          Nils Schneider <nils.schneider@gmail.com>
  Status: Final
  Type: Standards Track
  Created: 10-01-2011

Abstract

This BIP proposes a URI scheme for making Bitcoin payments.

Motivation

The purpose of this URI scheme is to enable users to easily make payments by simply clicking links on webpages or scanning QR Codes.

Specification

General rules for handling (important!)

Bitcoin clients MUST NOT act on URIs without getting the user's authorization. They SHOULD require the user to manually approve each payment individually, though in some cases they MAY allow the user to automatically make this decision.

Operating system integration

Graphical bitcoin clients SHOULD register themselves as the handler for the "bitcoin:" URI scheme by default, if no other handler is already registered. If there is already a registered handler, they MAY prompt the user to change it once when they first run the client.

BNF grammar

(See also a simpler representation of syntax)

bitcoinurn      = "bitcoin:" bitcoinaddress [ ";version=" bitcoinversion ] [ "?" bitcoinparams ]
bitcoinaddress  = base58 *base58
bitcoinversion  = "1.0"
bitcoinparams   = *bitcoinparam
bitcoinparam    = amountparam | labelparam | messageparam | sendparam | 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
otherparam      = pchar *pchar "=" *pchar

Query Keys

• label: Label for that address (e.g. name of receiver)
• address: bitcoin address
• message: message that shown to the user after scanning the QR code
• size: amount of base bitcoin units (see below)
• send: used to send bitcoin, rather than to request them
• (others): optional, for future extensions

Transfer amount/size

If an amount is provided, it may be specified either in decimal or, when prefixed with a single "x" character, hexadecimal. The number SHOULD be followed by "X" <digits> to signify an exponent to the base multiplier. Thus, "X8" multiplies your number by 100,000,000. For decimal values, this means the standard BTC unit. For hexadecimal values, this means ᵇTBC units (which are equivalent to 42.94967296 BTC). If exponent is omitted, implementations SHOULD assume X8 for decimal numbers, and X4 for hexadecimal numbers. I.e. amount=50.00 is treated as 50 BTC, and amount=x40 is treated as 40 TBC. When specifying bitcoin base units, "X0" SHOULD be used.

Bitcoin clients MAY display the amount in any format that is not intended to deceive the user. They SHOULD choose a format that is foremost least confusing, and only after that most reasonable given the amount requested. For example, so long as the majority of users work in BTC units, values should always be displayed in BTC by default, even if mBTC or TBC would otherwise be a more logical interpretation of the amount.

Rationale

Payment identifiers, not person identifiers

Current best practices are that a unique address should be used for every transaction. Therefore, a URI scheme should not represent an exchange of personal information, but a one-time payment.

Accessibility (URI scheme name)

Should someone from the outside happen to see such a URI, the URI scheme name already gives a description. A quick search should then do the rest to help them find the resources needed to make their payment. Other proposed names sound much more cryptic; the chance that someone googles that out of curiosity are much slimmer. Also, very likely, what he will find are mostly technical specifications - not the best introduction to bitcoin.

Forward compatibility

We want URIs generated in 2011 to still work in 2036: think about extensibility. Of course we can make only educated guesses about the future, but don't act as if there is none. This should be the best we can do, but it should not be seen as set in stone. Make it possible for later generations to improve our work, to mend our errors, without breaking the URIs created now. Version incompatibility is the easiest thing to drive users crazy: "I just upgraded to this shiny new version. What? It doesn't support the old format? AAAAAAARRRGH!"

Appendix

Simpler syntax

This section is non-normative and does not cover all possible syntax. Please see the BNF grammar above for the normative syntax.

[foo] means optional, <bar> are placeholders

bitcoin:<address>[;version=1.0][?amount=<amount>][?label=<label>][?message=<message>][?send=<private key>]

Examples

Just the address:

bitcoin:1NS17iag9jJgTHD1VXjvLCEnZuQ3rJED9L

Address with name:

bitcoin:1NS17iag9jJgTHD1VXjvLCEnZuQ3rJED9L?label=Luke-Jr

Request 20.30 BTC to "Luke-Jr":

bitcoin:1NS17iag9jJgTHD1VXjvLCEnZuQ3rJED9L?amount=20.3X8&label=Luke-Jr

Request 400 TBC:

bitcoin:1NS17iag9jJgTHD1VXjvLCEnZuQ3rJED9L?amount=x400X4

Request 4000 TBC:

bitcoin:1NS17iag9jJgTHD1VXjvLCEnZuQ3rJED9L?amount=x4X7

Request 5 uBTC:

bitcoin:1NS17iag9jJgTHD1VXjvLCEnZuQ3rJED9L?amount=5X2

Request 50 BTC with message:

bitcoin:1NS17iag9jJgTHD1VXjvLCEnZuQ3rJED9L?amount=50X8&label=Luke-Jr&message=Donation%20for%20project%20xyz

Send 1 BTC:

bitcoin:1NS17iag9jJgTHD1VXjvLCEnZuQ3rJED9L?amount=1X8&send=S4b3N3oGqDqR5jNuxEvDwf

Characters must be URI encoded properly.

Sending money via private key

To send a payment to someone else first construct a new keypair. You may want to use a mini private key format, or you may also use a full private key for more security depending on the amount being sent and how long you expect to pass before a claim. Now create and publish a transaction with an output of the amount you wish to send. Use this script in that output:

<pubkey> OP_CHECKSIG

Construct an address from the public key. Encode the URI as below:

bitcoin:<address>?send=<base 58 encoded private key>

You may optionally include amount or message fields as well. In a wallet to claim money sent this way search for an incoming transaction with the output script form above, where <address> matches the public key in the script. When you find the transaction create a claim transaction with an input script of this form:

<sig>

This claims the money you were sent. Until your claim transaction has confirmed the sender may take their money back.

Reference Implementations

Bitcoin clients

• Spesmilo supports all valid Bitcoin URIs, with Windows and KDE integration

Parsing amount

ECMAScript

reAmount = /^(([\d.]+)(X(\d+))?|x([\da-f]*)(\.([\da-f]*))?(X([\da-f]+))?)$/i;
function parseAmount(txt) {
	var m = txt.match(reAmount);
	return m[5] ? (
		(
			parseInt(m[5], 16) +
			(m[7] ? (parseInt(m[7], 16) * Math.pow(16, -(m[7].length))) : 0)
		) * (
			m[9] ? Math.pow(16, parseInt(m[9], 16)) : 0x10000
		)
	) : (
			m[2]
		*
			(m[4] ? Math.pow(10, m[4]) : 1e8)
	);
}

Python

m = re.match(r'^(([\d.]+)(X(\d+))?|x([\da-f]*)(\.([\da-f]*))?(X([\da-f]+))?)$', amount, re.IGNORECASE)
if m.group(5):
    amount = float(int(m.group(5), 16))
    if m.group(7):
        amount += float(int(m.group(7), 16)) * pow(16, -(len(m.group(7))))
    if m.group(9):
        amount *= pow(16, int(m.group(9), 16))
    else:
        amount *= 0x10000
else:
    amount = Decimal(m.group(2))
    if m.group(4):
        amount *= 10 ** int(m.group(4))
    else:
        amount *= 100000000

C#

Regex amountExpression = new Regex(@"^(([\d.]+)(X(\d+))?|x([\da-f]*)(\.([\da-f]*))?(X([\da-f]+))?)$", RegexOptions.IgnoreCase);
Match match = amountExpression.Match(value);
if (match.Success)
{
    if (match.Groups[5].Success)
    {
        long hexDecimal = 0;
        if (match.Groups[7].Success)
            hexDecimal = Convert.ToInt64(match.Groups[7].Value, 16) * (long)Math.Pow(16, -match.Groups[7].Length);

        long hexExponent = 0x10000;
        if (match.Groups[9].Success)
            hexExponent = (long)Math.Pow(16, Convert.ToInt32(match.Groups[9].Value, 16));

        Amount = (Convert.ToInt64(match.Groups[5].Value, 16) + hexDecimal) * hexExponent;
    }
    else
    {
        long decimalExponent = 100000000;
        if (match.Groups[4].Success)
            decimalExponent = (long)Math.Pow(10, int.Parse(match.Groups[4].Value));
        Amount = (long)(decimal.Parse(match.Groups[2].Value) * decimalExponent);
    }
}