Network Working Group I. Y. Eroglu
Internet-Draft independent
Intended status: Informational 17 February 2025
Expires: 21 August 2025
Usage specification of the otpauth URI format for TOTP and HOTP token
generators
draft-linuxgemini-otpauth-uri-02
Abstract
This document describes a foundational schema for the otpauth URI,
utilized by TOTP (and/or HOTP) based authenticators.
Status of This Memo
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This Internet-Draft will expire on 21 August 2025.
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Table of Contents
1. Discussion . . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2.1. Conventions and Terminology . . . . . . . . . . . . . . . 3
3. Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3.1. TYPE entry (REQUIRED) . . . . . . . . . . . . . . . . . . 4
3.2. LABEL entry (REQUIRED) . . . . . . . . . . . . . . . . . 4
3.3. PARAMETERS entry (REQUIRED) . . . . . . . . . . . . . . . 5
3.3.1. secret parameter (REQUIRED) . . . . . . . . . . . . . 5
3.3.2. algorithm parameter (OPTIONAL) . . . . . . . . . . . 5
3.3.3. digits parameter (OPTIONAL) . . . . . . . . . . . . . 5
3.3.4. counter parameter (REQUIRED if HOTP) . . . . . . . . 5
3.3.5. period parameter (OPTIONAL, only TOTP) . . . . . . . 6
3.3.6. issuer parameter (OPTIONAL) . . . . . . . . . . . . . 6
3.3.7. Other parameters (OPTIONAL) . . . . . . . . . . . . . 6
4. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 6
5. Security Considerations . . . . . . . . . . . . . . . . . . . 6
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
7.1. Normative References . . . . . . . . . . . . . . . . . . 6
7.2. Informative References . . . . . . . . . . . . . . . . . 7
Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 8
Appendix B. Document History . . . . . . . . . . . . . . . . . . 8
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 8
1. Discussion
This note is to be removed before publishing as an RFC.
Source for this draft and an issue tracker can be found at
https://github.com/linuxgemini/otpauth-spec-draft
(https://github.com/linuxgemini/otpauth-spec-draft).
2. Introduction
The otpauth URI is used for easy addition of accounts to Time-Based
One-Time Password (TOTP) and/or HMAC-based One-Time Password (HOTP)
authenticators with various options
[Google.Authenticator.OSS.Wiki.Key.Format].
Although available as a provisional scheme at IANA
[IANA.URISchemes.Prov.otpauth], there are many deviations of the
specification usage per authenticator hardware and software
[Edent.Blog.Post].
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This document aims to provide foundational boundaries for the URI
format and standardize the secret sharing of One-Time Password (OTP)
tokens.
2.1. Conventions and Terminology
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 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
This specification uses the Augmented Backus-Naur Form (ABNF)
notation of [RFC5234].
This specification uses terms "TOTP" defined by [RFC6238] and "HOTP"
defined by [RFC4226]. Both RFCs also mention "secret", "issuer", and
"account".
The term "URI" is imported from [RFC3986]. Mentions of "query
string" in this document references the "Query" parameter (in section
3.4) of this RFC.
The Base16, Base32, and Base64 Data Encodings mentioned here are
imported from [RFC4648] with the same name.
3. Syntax
The URI MUST be formatted like below:
otpauth://TYPE/LABEL?PARAMETERS
An approximate ABNF representation of this is like below:
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otpauth-uri = "otpauth://" uri-type "/" uri-label "?" uri-parameters
uri-type = "totp" / "hotp"
uri-label = *VCHAR
uri-parameters = "secret=" *base-32 [ *uri-opt-parameters ]
uri-opt-parameters = ("&algorithm=" otp-algorithm)
uri-opt-parameters =/ ("&digits=" otp-digits)
uri-opt-parameters =/ ("&counter=" *DIGIT) / ("&period=" *DIGIT)
uri-opt-parameters =/ ("&issuer=" *VCHAR) / ("&" *VCHAR "=" *VCHAR)
; Please refer to RFC3986 for handling
; complex names
otp-algorithm = "SHA1" / "SHA256" / "SHA512"
otp-digits = %x36-38
; 6-8
base-32 = %x41-5A / %x32-37
; A-Z2-7
DIGIT = %x30-39
; 0-9
VCHAR = %x21-7E
; visible (printing) characters
3.1. TYPE entry (REQUIRED)
The type entry MUST be one of totp or hotp, depending on the One-Time
Password (OTP) type.
3.2. LABEL entry (REQUIRED)
The label entry MUST be an identifier representing the user. For
example, can be a username, nickname or a person's name.
The label entry MUST be considered as a Path per section 3.3. of
[RFC3986].
Although the Authenticator Team at Google recommends including the
secret issuer to be prepended to the label with the colon character
(: or %3A) as a separator in
[Google.Authenticator.OSS.Wiki.Key.Format], the authors of this
document believe that the issuer should only be appended as a
separate parameter (see next division).
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3.3. PARAMETERS entry (REQUIRED)
This entry is a URI query string. Each parameter MUST be separated
by the & character and SHOULD BE "URI Safe" (see section 2.2.
Reserved Characters in [RFC3986]).
The following parameters SHOULD BE included:
3.3.1. secret parameter (REQUIRED)
The secret of the OTP MUST be provided within this parameter. The
secret MUST be encoded in Base32. The padding specified in [RFC4648]
section 3.2 is not required and SHOULD BE omitted.
For example:
otpauth://totp/ietfuser?secret=NBSWY3DPFQQHO33SNRSAU
3.3.2. algorithm parameter (OPTIONAL)
The algorithm used for TOTP or HOTP tokens SHOULD BE provided in this
parameter. When not provided, SHA1 is assumed by default.
The ABNF representation is defined below:
otp-algorithm = "SHA1" / "SHA256" / "SHA512"
Some authenticators at the time of writing this document ignore this
parameter. The authors of this document believe that this parameter
MUST be supported in all cases.
3.3.3. digits parameter (OPTIONAL)
The number of digits in the output for TOTP or HOTP tokens SHOULD BE
provided in this parameter. This value MUST be between 6 and 8.
When not provided, 6 digits is assumed by default.
Some authenticators at the time of writing this document ignore this
parameter. The authors of this document believe that this parameter
MUST be supported in all cases.
3.3.4. counter parameter (REQUIRED if HOTP)
The provisioning counter for HOTP tokens MUST BE provided in this
parameter.
This parameter is ignored if the token type is TOTP.
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3.3.5. period parameter (OPTIONAL, only TOTP)
The refresh period (in seconds) for TOTP tokens SHOULD BE provided in
this parameter. When not provided, 30 seconds is assumed by default.
Some authenticators at the time of writing this document ignore this
parameter. The authors of this document believe that this parameter
MUST BE supported in all cases.
This parameter is ignored if the token type is HOTP.
3.3.6. issuer parameter (OPTIONAL)
The issuer name of TOTP or HOTP tokens SHOULD BE provided in this
parameter.
3.3.7. Other parameters (OPTIONAL)
Vendors MAY include other parameters in their issued otpauth URIs.
These parameters are OPTIONAL for the function of TOTP or HOTP tokens
and not necessary to be included in this document.
4. Examples
otpauth://totp/ietfuser?secret=NBSWY3DP
otpauth://hotp/13tfus3r?secret=NBSWY3DP&counter=192
otpauth://totp/big?issuer=IETF&secret=NBSWY3DP&period=5&algorithm=SHA256
5. Security Considerations
This URI format does not in itself pose a security threat. However,
the Security Considerations of [RFC3986] SHOULD BE followed.
6. IANA Considerations
This format is already available as a provisional entry
[IANA.URISchemes.Prov.otpauth]. IANA is asked to change the
provisional URI scheme to reference [[this RFC]].
7. References
7.1. Normative References
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[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[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,
<https://www.rfc-editor.org/info/rfc3986>.
[RFC4226] M'Raihi, D., Bellare, M., Hoornaert, F., Naccache, D., and
O. Ranen, "HOTP: An HMAC-Based One-Time Password
Algorithm", RFC 4226, DOI 10.17487/RFC4226, December 2005,
<https://www.rfc-editor.org/info/rfc4226>.
[RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data
Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006,
<https://www.rfc-editor.org/info/rfc4648>.
[RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234,
DOI 10.17487/RFC5234, January 2008,
<https://www.rfc-editor.org/info/rfc5234>.
[RFC6238] M'Raihi, D., Machani, S., Pei, M., and J. Rydell, "TOTP:
Time-Based One-Time Password Algorithm", RFC 6238,
DOI 10.17487/RFC6238, May 2011,
<https://www.rfc-editor.org/info/rfc6238>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
7.2. Informative References
[Edent.Blog.Post]
"Why is there no formal specification for otpauth URls?",
<https://shkspr.mobi/blog/2022/05/why-is-there-no-formal-
specification-for-otpauth-urls/>.
[Edent.Mastodon.Post]
"Fediverse post for "Why is there no formal specification
for otpauth URls?"",
<https://mastodon.social/@Edent/108266107975107228>.
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[Google.Authenticator.OSS.Wiki.Key.Format]
Google, "Google Authenticator Key Uri Format",
<https://github.com/google/google-authenticator/wiki/Key-
Uri-Format>.
[IANA.URISchemes.Prov.otpauth]
IANA, "Provisional scheme for the otpauth URI",
<https://www.iana.org/assignments/uri-schemes/prov/
otpauth>.
Appendix A. Acknowledgements
We would like to thank Q Misell, Terence Eden, The Google
Authenticator Team at Google, Eugene Fox, Seonghyeon Cho, and others
(please let us know, if you've been mistakenly omitted) for their
valuable input, feedback and general support of this work.
This document originated from discussions at the Fediverse initially
written by Terence Eden [Edent.Mastodon.Post].
Appendix B. Document History
[[ To be removed from the final specification ]]
-02
* various typo corrections
* various phrasing changes
-01
* corrected Terence's name
* corrected parameter confusion between TOTP and HOTP
-00
* first draft
Author's Address
Ilteris Yagiztegin Eroglu
independent
/Ankara
Türkiye
Email: ietf@linuxgemini.space
URI: https://linuxgemini.space
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