Taler Systems SA

7, rue de Mondorf Erpeldange 5421 Luxembourg dold@taler.net

Bern University of Applied Sciences

Quellgasse 21 Biel/Bienne 2501 Switzerland christian.grothoff@bfh.ch

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

Status of This Memo This document is not an Internet Standards Track specification; it is published for informational purposes. This is a contribution to the RFC Series, independently of any other RFC stream. The RFC Editor has chosen to publish this document at its discretion and makes no statement about its value for implementation or deployment. Documents approved for publication by the RFC Editor are not candidates for any level of Internet Standard; see Section 2 of RFC 7841. Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at .

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Table of Contents

• .  Introduction
  • .  Objective
  • .  Requirements Language
• .  Syntax of a 'payto' URI
• .  Semantics
• .  Examples
• .  Generic Options
• .  Internationalization and Character Encoding
• .  Tracking Payment Target Types
  • .  ACH Bank Account
  • .  Business Identifier Code
  • .  International Bank Account Number
  • .  Unified Payments Interface
  • .  Bitcoin Address
  • .  Interledger Protocol Address
  • .  Void Payment Target
• .  Security Considerations
• .  IANA Considerations
• . Payto Payment Target Types
• . References
  • .  Normative References
  • .  Informative References
• Authors' Addresses

Introduction This document defines the 'payto' Uniform Resource Identifier (URI) scheme for designating transfer form data for payments.

Objective A 'payto' URI always identifies the target of a payment. A 'payto' URI 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.

Requirements Language The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 when, and only when, they appear in all capitals, as shown here.

Syntax of a 'payto' URI This document uses the Augmented Backus-Naur Form (ABNF) of . payto-URI = "payto://" authority path-abempty [ "?" opts ] opts = opt *( "&" opt ) opt-name = generic-opt / authority-specific-opt opt-value = *pchar opt = opt-name "=" opt-value generic-opt = "amount" / "receiver-name" / "sender-name" / "message" / "instruction" authority-specific-opt = ALPHA *( ALPHA / DIGIT / "-" / "." ) authority = ALPHA *( ALPHA / DIGIT / "-" / "." ) 'path-abempty' is defined in . 'pchar' is defined in .

Semantics The authority component of a payment URI identifies the payment target type. The payment target types are defined in the "Payto Payment Target Types" registry (see ). 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 target type SHOULD accept the options defined in generic-opt. The default operation of applications that invoke a URI with the 'payto' scheme MUST 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 via 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 "Payto 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.

Examples Valid Example: payto://iban/DE75512108001245126199?amount=EUR:200.0&message=hello Invalid Example (authority missing): payto:iban/12345

Generic Options Applications MUST accept URIs with options in any order. The "amount" option MUST NOT occur more than once. Other options MAY be allowed multiple times, with further restrictions depending on the payment target type. The following options SHOULD be understood by every payment target type.

amount:

The amount to transfer. The format MUST be: amount = currency ":" unit [ "." fraction ] currency = 1*ALPHA unit = 1*(DIGIT / ",") fraction = 1*(DIGIT / ",") If a 3-letter 'currency' is used, it MUST be an alphabetic code. A payment target type MAY define semantics beyond ISO 4217 for currency codes that are not 3 characters. The 'unit' value MUST be smaller than 2^53. If present, the 'fraction' MUST consist of no more than 8 decimal digits. The use of commas is optional for readability, and they MUST be ignored.

receiver-name:

Name of the entity that receives the payment (creditor). The value of this option MAY be subject to lossy conversion, modification, and truncation (for example, due to line wrapping or character set conversion).

sender-name:

Name of the entity that makes the payment (debtor). The value of this option MAY be subject to lossy conversion, modification, and truncation (for example, due to line wrapping or character set conversion).

message:

A short message to identify the purpose of the payment. The value of this option MAY be subject to lossy conversion, modification, and truncation (for example, due to line wrapping or character set conversion).

instruction:

A short message giving payment reconciliation instructions to the recipient. An instruction that follows the character set and length limitation defined by the respective payment target type SHOULD NOT be subject to lossy conversion.

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 characters using either an encoding or a replacement table. This conversion process MAY be lossy, except for the instruction field. If the value of the instruction field would be subject to lossy conversion, modification, or truncation, the application SHOULD refuse further processing of the payment until a different value for the instruction is provided. To avoid special encoding rules for the payment target identifier, the userinfo component is disallowed in 'payto' URIs. Instead, the payment target identifier is given as an option, where encoding rules are uniform for all options. Defining a generic way of tagging the language of option fields containing natural language text (such as "receiver-name", "sender-name", and "message) is out of the scope of this document, as internationalization must accommodate the restrictions and requirements of the underlying banking system of the payment target type. The internationalization concerns SHOULD be individually defined by each payment target type.

Tracking Payment Target Types A registry of "Payto Payment Target Types" is described in . The registration policy for this registry is "First Come First Served", as described in . When requesting new entries, careful consideration of the following criteria is strongly advised:

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.

Documents that support requests for new registry entries should provide the following information for each entry:

Name:

The name of the payment target type (case-insensitive ASCII string, restricted to alphanumeric characters, dots, and dashes).

Description:

A description of the payment target type, including the semantics of the path in the URI if applicable.

Example:

At least one example URI to illustrate the payment target type.

Contact:

The contact information of a person to contact for further information.

References:

Optionally, references describing the payment target type (such as an RFC) and target-specific options or references describing the payment system underlying the payment target type.

This document populates the registry with seven entries as follows (see also ).

ACH Bank Account

Name:

ach

Description:

Automated Clearing House (ACH). The path consists of two components: the routing number and the account number. Limitations on the length and character set of option values are defined by the implementation of the handler. Language tagging and internationalization of options are not supported.

Example:

payto://ach/122000661/1234

Contact:

N/A

References:

, RFC 8905

Business Identifier Code

Name:

bic

Description:

Business Identifier Code (BIC). The path consists of just a BIC. This is used for wire transfers between banks. The registry for BICs is provided by the Society for Worldwide Interbank Financial Telecommunication (SWIFT). The path does not allow specifying a bank account number. Limitations on the length and character set of option values are defined by the implementation of the handler. Language tagging and internationalization of options are not supported.

Example:

payto://bic/SOGEDEFFXXX

Contact:

N/A

References:

, RFC 8905

International Bank Account Number

Name:

iban

Description:

International Bank Account Number (IBAN). Generally, the IBAN allows to unambiguously derive the associated Business Identifier Code (BIC) using a lookup in the respective proprietary translation table. However, some legacy applications process payments to the same IBAN differently based on the specified BIC. Thus, the path can consist of either a single component (the IBAN) or two components (BIC followed by IBAN). The "message" option of the 'payto' URI corresponds to the "unstructured remittance information" of Single Euro Payments Area (SEPA) credit transfers and is thus limited to 140 characters with character set limitations that differ according to the countries of the banks and payment processors involved in the payment. The "instruction" option of the 'payto' URI corresponds to the "end-to-end identifier" of SEPA credit transfers and is thus limited to, at most, 35 characters, which can be alphanumeric or from the allowed set of special characters, i.e., "+?/-:().,'". Language tagging and internationalization of options are not supported.

Examples:

payto://iban/DE75512108001245126199 payto://iban/SOGEDEFFXXX/DE75512108001245126199

Contact:

N/A

References:

, RFC 8905

Unified Payments Interface

Name:

upi

Description:

Unified Payment Interface (UPI). The path is an account alias. The amount and receiver-name options are mandatory for this payment target. Limitations on the length and character set of option values are defined by the implementation of the handler. Language tags and internationalization of options are not supported.

Example:

payto://upi/alice@example.com?receiver-name=Alice&amount=INR:200

Contact:

N/A

References:

, RFC 8905

Bitcoin Address

Name:

bitcoin

Description:

Bitcoin protocol. The path is a "bitcoinaddress", as per . Limitations on the length and character set of option values are defined by the implementation of the handler. Language tags and internationalization of options are not supported.

Example:

payto://bitcoin/12A1MyfXbW6RhdRAZEqofac5jCQQjwEPBu

Contact:

N/A

References:

, RFC 8905

Interledger Protocol Address

Name:

ilp

Description:

Interledger protocol (ILP). The path is an ILP address, as per . Limitations on the length and character set of option values are defined by the implementation of the handler. Language tagging and internationalization of options are not supported.

Example:

payto://ilp/g.acme.bob

Contact:

N/A

References:

, RFC 8905

Void Payment Target

Name:

void

Description:

The "void" payment target type allows specifying the parameters of an out-of-band payment (such as cash or other types of in-person transactions). The path is optional and interpreted as a comment. Limitations on the length and character set of option values are defined by the implementation of the handler. Language tags and internationalization of options are not supported.

Example:

payto://void/?amount=EUR:10.5

Contact:

N/A

References:

RFC 8905

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 . 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 , 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 URI. The authentication/authorization mechanisms and transport security services used to process a payment encoded in a 'payto' URI are handled by the application and are not in scope of this document. 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.

IANA Considerations IANA maintains the "Uniform Resource Identifier (URI) Schemes" registry, which contains an entry for the 'payto' URI scheme as follows. IANA has updated that entry to reference this document.

Scheme name:

payto

Status:

provisional

URI scheme syntax:

See of RFC 8905.

URI scheme semantics:

See of RFC 8905.

Applications/protocols that use this scheme name:

payto URIs are mainly used by financial software.

Contact:

<grothoff@gnu.org>

Change controller:

<grothoff@gnu.org>

References:

See of RFC 8905.

Payto Payment Target Types This document specifies a list of payment target types. It is possible that future work will need to specify additional payment target types. The GNUnet Assigned Numbers Authority (GANA) operates the "Payto Payment Target Types" registry to track the following information for each payment target type:

Name:

The name of the payment target type (case-insensitive ASCII string, restricted to alphanumeric characters, dots, and dashes)

Contact:

The contact information of a person to contact for further information

References:

Optionally, references describing the payment target type (such as an RFC) and target-specific options or references describing the payment system underlying the payment target type

The entries in the "Payto Payment Target Types" registry defined in this document are as follows:

Name	Contact	Reference
ach	N/A	RFC 8905
bic	N/A	RFC 8905
iban	N/A	RFC 8905
upi	N/A	RFC 8905
bitcoin	N/A	RFC 8905
ilp	N/A	RFC 8905
void	N/A	RFC 8905

References Normative References International Organization for Standardization International Organization for Standardization Nacha

https://www.nacha.org/

In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. A Uniform Resource Identifier (URI) is a compact sequence of characters that identifies an abstract or physical resource. This specification defines the generic URI syntax and a process for resolving URI references that might be in relative form, along with guidelines and security considerations for the use of URIs on the Internet. The URI syntax defines a grammar that is a superset of all valid URIs, allowing an implementation to parse the common components of a URI reference without knowing the scheme-specific requirements of every possible identifier. This specification does not define a generative grammar for URIs; that task is performed by the individual specifications of each URI scheme. [STANDARDS-TRACK] Internet technical specifications often need to define a formal syntax. Over the years, a modified version of Backus-Naur Form (BNF), called Augmented BNF (ABNF), has been popular among many Internet specifications. The current specification documents ABNF. It balances compactness and simplicity with reasonable representational power. The differences between standard BNF and ABNF involve naming rules, repetition, alternatives, order-independence, and value ranges. This specification also supplies additional rule definitions and encoding for a core lexical analyzer of the type common to several Internet specifications. [STANDARDS-TRACK] Many protocols make use of points of extensibility that use constants to identify various protocol parameters. To ensure that the values in these fields do not have conflicting uses and to promote interoperability, their allocations are often coordinated by a central record keeper. For IETF protocols, that role is filled by the Internet Assigned Numbers Authority (IANA). To make assignments in a given registry prudently, guidance describing the conditions under which new values should be assigned, as well as when and how modifications to existing values can be made, is needed. This document defines a framework for the documentation of these guidelines by specification authors, in order to assure that the provided guidance for the IANA Considerations is clear and addresses the various issues that are likely in the operation of a registry. This is the third edition of this document; it obsoletes RFC 5226. RFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings.

markdavis@google.com

michel@suignard.com

Informative References International Organization for Standardization GNUnet e.V. Interledger National Payments Corporation of India

Authors' Addresses Taler Systems SA

7, rue de Mondorf Erpeldange 5421 Luxembourg dold@taler.net

Bern University of Applied Sciences

Quellgasse 21 Biel/Bienne 2501 Switzerland christian.grothoff@bfh.ch