The 'payto' URI Scheme for Payments
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.
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 .
'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:
Invalid Example (authority missing):
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:
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:
- The description clearly defines the syntax and semantics of the
payment target and optional parameters if applicable.
- Relevant references are provided if they are available.
- The chosen name is appropriate for the payment target type, does
not conflict with well-known payment systems, and avoids potential to
confuse users.
- The payment system underlying the payment target type is not
fundamentally incompatible with the general options (such as positive
decimal amounts) in this specification.
- 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.
- 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.
- 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:
-
- 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:
-
- 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:
-
- 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:
-
- 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:
-
- 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:
-
- 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:
-
- 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
Codes for the representation of currencies
International Organization for
Standardization
Financial Services - Universal financial industry message
scheme
International Organization for
Standardization
2020 Nacha Operating Rules & Guidelines
Nacha
https://www.nacha.org/
Unicode Technical
Report #36: Unicode Security Considerations
markdavis@google.com
michel@suignard.com
Informative References
Bitcoin Improvement Proposal 21
Clickjacking: Attacks and Defenses
Unified Payment Interface - Common URL Specifications For
Deep
Linking And Proximity Integration
National Payments Corporation of
India
ILP Addresses - v2.0.0
Interledger
Banking -- Banking telecommunication messages -- Business
identifier code (BIC)
International Organization for
Standardization
GNUnet Assigned Numbers Authority (GANA)
GNUnet e.V.