Independent Stream F. Dold
Internet-Draft Taler Systems SA
Intended status: Informational C. Grothoff
Expires: January 22, 2020 BFH
July 21, 2019

The 'payto' URI scheme for payments


This document defines the 'payto' Uniform Resource Identifier (URI) scheme for designating targets for payments.

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Table of Contents

1. Introduction

This document defines the 'payto' Uniform Resource Identifier (URI) [RFC3986] scheme for designating transfer form data for payments. In particular, it always identifies the target of a payment. A 'payto' URL consists of a payment target type, a target identifier and optional parameters such as an amount or a payment reference.

The interpretation of the target identifier is defined by the payment target type, and typically represents either a bank account or an (unsettled) transaction.

A unified URI scheme for all payment target types allows applications to offer user interactions with URIs that represent payment targets, simplifying the introduction of new payment systems and applications.

2. Syntax of a 'payto' URL

This document uses the Augmented Backus-Naur Form (ABNF) of [RFC5234].

  payto-URI = "payto" "://" authority path-abempty [ "?" opts ]
  opts = opt *( "&" opt )
  opt = (generic-opt / authority-specific-opt) "=" *( pchar )
  generic-opt = "amount" / "receiver-name" / "sender-name" /
                "message" / "instruction"
  authority = ALPHA *( ALPHA / DIGIT / "-" / "." )
  path-abempty = <path-abempty, see [RFC3986], Section 3.3>
  pchar = <pchar, see [RFC3986], Appendix A.>


3. Semantics

The authority component of a payment URI identifies the payment target type. The payment target types are defined in the "Payment Target Types" registry, see Section 8.2. The path component of the URI identifies the target for a payment as interpreted by the respective payment target type. The query component of the URI can provide additional parameters for a payment. Every payment method SHOULD accept the options defined in generic-opt. The default operation of applications that invoke a URI with the payto scheme SHOULD be to launch an application (if available) associated with the payment target type that can initiate a payment. If multiple handlers are registered for the same payment target type, the user SHOULD be able to choose which application to launch. This allows users with multiple bank accounts (each accessed the respective bank's banking application) to choose which account to pay with. An application SHOULD allow dereferencing a payto URI even if the payment target type of that URI is not registered in the "Payment Target Types" registry. Details of the payment MUST be taken from the path and options given in the URI. The user SHOULD be allowed to modify these details before confirming a payment.

4. Examples


  INVALID (authority missing):  payto:iban/12345


5. Generic Options

Applications MUST accept URIs with options in any order. The "amount" option MUST only occur at most once. Other options MAY be allowed multiple times, with further restrictions depending on the payment method. The following options SHOULD be understood by every payment method.

  amount = [ currency ":" ] unit [ "." fraction ]
  currency = 1*ALPHA
  unit = 1*(DIGIT / ",")
  fraction = 1*(DIGIT / ",")

amount: The amount to transfer, including currency information if applicable. The format MUST be:

receiver-name: Name of the entity that receives the payment (creditor).

sender-name: Name of the entity that makes the payment (debtor).

message: A short message to identify the purpose of the payment, which MAY be subject to lossy conversions (for example, due to character set encoding limitations).

instruction: A short message giving instructions to the recipient, which MUST NOT be subject to lossy conversions. Character set limitations allowed for such instructions depend on the payment method.

6. Internationalization and Character Encoding

Various payment systems use restricted character sets. An application that processes 'payto' URIs MUST convert characters that are not allowed by the respective payment systems into allowable character using either an encoding or a replacement table. This conversion process MAY be lossy, except for the instruction field.

To avoid special encoding rules for the payment target identifier, the userinfo component [RFC3986] is disallowed in payto URIs. Instead, the payment target identifier is given as an option, where encoding rules are uniform for all options.

7. Security Considerations

Interactive applications handling the payto URI scheme MUST NOT initiate any financial transactions without prior review and confirmation from the user, and MUST take measures to prevent clickjacking [HMW12].

Unless a payto URI is received over a trusted, authenticated channel, a user might not be able to identify the target of a payment. In particular due to homographs [unicode-tr36], a payment target type SHOULD NOT use human-readable names in combination with unicode in the target account specification, as it could give the user the illusion of being able to identify the target account from the URL.

To avoid unnecessary data collection, payment target types SHOULD NOT include personally identifying information about the sender of a payment that is not essential for an application to conduct a payment.

8. IANA Considerations

8.1. URI Scheme Registration

The "payto" URI scheme is already registered in the "Provisional URI Schemes" registry [RFC7595].

8.2. Payment Target Type Registry

This document defines a registry for payment methods. The name of the registry is "Payment Target Types".

The registry shall record for each entry: [RFC5226]. When requesting new entries, careful consideration of the following criteria is strongly advised:

The registration policy for this registry is "First Come First Served", as described in

  1. The description clearly defines the syntax and semantics of the payment target and optional parameters if applicable.
  2. Relevant references are provided if they are available.
  3. The chosen name is appropriate for the payment target type, does not conflict with well-known payment systems, and avoids potential to confuse users.
  4. The payment system underlying the payment target type is not fundamentally incompatible with the general options (such as positive decimal amounts) in this specification.
  5. The payment target type is not a vendor-specific version of a payment target type that could be described more generally by a vendor-neutral payment target type.
  6. The specification of the new payment target type remains within the scope of payment transfer form data. In particular specifying complete invoices is not in scope. Neither are processing instructions to the payment processor or bank beyond a simple payment.
  7. The payment target and the options do not contain the payment sender's account details.

8.2.1. ACH Bank Account

8.2.2. Business Identifier Code

8.2.3. International Bank Account Number

8.2.4. Unified Payments Interface

8.2.5. Bitcoin Address

8.2.6. Interledger Protocol Address

9. References

9.1. Normative References

[ISO20022] International Organization for Standardization, "ISO 20022 Financial Services - Universal financial industry message scheme", May 2013.
[NACHA] NACHA, "NACHA Operating Rules & Guidelines", January 2017.
[RFC3986] Berners-Lee, T., Fielding, R. and L. Masinter, "Uniform Resource Identifier (URI): Generic Syntax", STD 66, RFC 3986, DOI 10.17487/RFC3986, January 2005.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA Considerations Section in RFCs", RFC 5226, DOI 10.17487/RFC5226, May 2008.
[RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax Specifications: ABNF", STD 68, RFC 5234, January 2008.
[RFC7595] Thaler, D., Hansen, T. and T. Hardie, "Guidelines and Registration Procedures for URI Schemes", BCP 35, RFC 7595, DOI 10.17487/RFC7595, June 2015.
[unicode-tr36] Davis, M. and M. Suignard, "Unicode Technical Report #36: Unicode Security Considerations", September 2014.

9.2. Informational References

[BIC] International Organization for Standardization, "ISO 9362:2014 Business Identifier Code (BIC)", March 2019.
[BIP0021] Schneider, N. and M. Corallo, "Bitcoin Improvement Proposal 21", January 2012.
[HMW12] Huang, L., Moshchuk, A., Wang, H., Schecter, S. and C. Jackson, "Clickjacking: Attacks and Defenses", January 2012.
[ILP-ADDR] Interledger Team, "ILP Addresses - v2.0.0", September 2018.
[UPILinking] National Payment Corporation of India, "Unified Payment Interface - Common URL Specifications For Deep Linking And Proximity Integration", May 2016.

Authors' Addresses

Florian Dold Taler Systems SA 7, rue de Mondorf Erpeldange, L-5421 LU EMail:
Christian Grothoff BFH Höheweg 80 Biel/Bienne, CH-2501 CH EMail: