Network Working Group D. Cridland Internet-Draft Intended status: Standards Track T. Molitor Expires: 5 June 2025 M. Wild A. Melnikov Isode Ltd 2 December 2024 Extensible Simple Authentication and Security Layer (SASL) draft-melnikov-sasl2-02 Abstract The Simple Authentication and Security Layer (SASL) is a framework for providing authentication and data security services in connection-oriented protocols via replaceable mechanisms. It provides a structured interface between protocols and mechanisms. The resulting framework allows new protocols to reuse existing mechanisms and allows old protocols to make use of new mechanisms. The framework also provides a protocol for securing subsequent protocol exchanges within a data security layer. This document describes how a SASL mechanism is structured, describes how protocols include support for SASL, and defines the protocol for carrying a data security layer over a connection. This document also defines how servers can request fulfillment of extra authentication related tasks, such as two factor authentication and/or password change. Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at https://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on 5 June 2025. Cridland, et al. Expires 5 June 2025 [Page 1] Internet-Draft Extended SASL December 2024 Copyright Notice Copyright (c) 2024 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/ license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Revised BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Conventions Used in This Document . . . . . . . . . . . . . . 4 3. Tasks . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 4. Channel Binding advertisement . . . . . . . . . . . . . . . . 6 5. Extra Protocol Requirements . . . . . . . . . . . . . . . . . 7 6. Extra Mechanism Requirements . . . . . . . . . . . . . . . . 8 7. Example of a Protocol fulfilling extra requirements . . . . . 8 8. Open Issues . . . . . . . . . . . . . . . . . . . . . . . . . 9 9. Security Considerations . . . . . . . . . . . . . . . . . . . 9 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 9 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 9 12.1. Normative References . . . . . . . . . . . . . . . . . . 9 12.2. Informative References . . . . . . . . . . . . . . . . . 10 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10 1. Introduction The Simple Authentication and Security Layer (SASL) is a framework for providing authentication and data security services in connection-oriented protocols via replaceable mechanisms. SASL provides a structured interface between protocols and mechanisms. SASL also provides a protocol for securing subsequent protocol exchanges within a data security layer. The data security layer can provide data integrity, data confidentiality, and other services. SASL's design is intended to allow new protocols to reuse existing mechanisms without requiring redesign of the mechanisms and allows existing protocols to make use of new mechanisms without redesign of protocols. Cridland, et al. Expires 5 June 2025 [Page 2] Internet-Draft Extended SASL December 2024 SASL is conceptually a framework that provides an abstraction layer between protocols and mechanisms as illustrated in the following diagram. SMTP LDAP XMPP Other protocols ... \ | | / \ | | / SASL abstraction layer / | | \ / | | \ EXTERNAL GSSAPI PLAIN Other mechanisms ... It is through the interfaces of this abstraction layer that the framework allows any protocol to utilize any mechanism. While this layer does generally hide the particulars of protocols from mechanisms and the particulars of mechanisms from protocols, this layer does not generally hide the particulars of mechanisms from protocol implementations. For example, different mechanisms require different information to operate, some of them use password-based authentication, some of then require realm information, others make use of Kerberos tickets, certificates, etc. Also, in order to perform authorization, server implementations generally have to implement identity mapping between authentication identities, whose form is mechanism specific, and authorization identities, whose form is application protocol specific. Section 2 discusses identity concepts. It is possible to design and implement this framework in ways that do abstract away particulars of similar mechanisms. Such a framework implementation, as well as mechanisms implementations, could be designed not only to be shared by multiple implementations of a particular protocol but to be shared by implementations of multiple protocols. Since the publication of [RFC4422] a number of shortcomings in the SASL framework were identified that are addressed in this document. [[Note that the current draft only shows changes from RFC 4422.]] This specification addresses a number of shortfalls in [RFC4422]: * Support for Two-factor authentication (2FA) or Multi-factor authentication (MFA) tasks. * Support for mandatory password change tasks. * Channel Binding advertisement. Cridland, et al. Expires 5 June 2025 [Page 3] Internet-Draft Extended SASL December 2024 * Shared key derivation after successful authentication. Extensions to SASL documented herein are primarily to allow for better capability discovery, and additional results beyond total success or abject failure. 2. Conventions Used in This Document 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. Character names in this document use the notation for code points and names from the Unicode Standard [Unicode]. For example, the letter "a" may be represented as either or . Note: a glossary of terms used in Unicode can be found in [Glossary]. Information on the Unicode character encoding model can be found in [CharModel]. Example lines prefaced by "C:" are sent by the client and ones prefaced by "S:" by the server. If a single "C:" or "S:" label applies to multiple lines, then the line breaks between those lines are for editorial clarity only, and are not part of the actual protocol exchange. 3. Tasks A protocol profile might have a way to indicate that while the SASL exchange was successful, it is insufficient to allow authentication at this time. We call this indicator a "continue outcome message". This can be used to indicate a need to execute extra task(s), for example, that the Client needs to perform a Second Factor Authentication ("2FA")and/or is required to change password (this list is not meant to be exhaustive in any way). These tasks are analogous to a SASL mechanism, but have a number of differences - they may never attempt to negotiate a new authorization identifier, nor a new security layer. Each task has a name ([[need to define syntax and maximum length]]) that SHOULD be registered with IANA. Cridland, et al. Expires 5 June 2025 [Page 4] Internet-Draft Extended SASL December 2024 A client MAY choose any one of the offered tasks; if multiple are required, once a task is successfully completed, the server will indicate that another one is required, and so on, until all mandatory tasks are complete. The continue outcome message MAY include SASL mechanism specific additional data, as the successful outcome message does. Finally, the continue outcome message MAY contain a textual data, which contains human-readable data explaining the nature of the step required. Example 1. Continue Required (using XMPP protocol) S: SSdtIGJvcmVkIG5vdy4= HOTP-EXAMPLE TOTP-EXAMPLE This account requires 2FA If any SASL security layer was negotiated, it takes effect after the final octet of the first continue outcome message. Clients respond with a task initiation message, which has a single mandatory parameter containing the selected task name, and MAY contain any task specific data. Each task MUST end either by the server sending a task failure indicator message, if the task failed, a continue outcome message, if the task was completed successfully and the server requests the client to perform a new task, or a successful outcome message, indicating that the task was completed successfully and no further tasks are needed. Cridland, et al. Expires 5 June 2025 [Page 5] Internet-Draft Extended SASL December 2024 Example 2. Fictional TOTP task SSd2ZSBydW4gb3V0IG9mIGlkZWFzIGhlcmUu 94d27acffa2e99a42ba7786162a9e73e7ab17b9d OTRkMjdhY2ZmYTJlOTlhNDJiYTc3ODYxNjJhOWU3M2U3YWIxN2I5ZAo= SGFkIHlvdSBnb2luZywgdGhlcmUsIGRpZG4ndCBJPw== juliet@montague.example 4. Channel Binding advertisement Most modern SASL mechanism are expected to support channel bindings [RFC5056]. Explicit advertisement of server supported channel binding types improves interoperability and is also necessary to prevent certain MITM attacks. Cridland, et al. Expires 5 June 2025 [Page 6] Internet-Draft Extended SASL December 2024 Example 3. Channel Binding Type advertisement in XMPP (XEP-0440). Note that the element is the new channel binding advertisement. EXTERNAL SCRAM-SHA-1-PLUS PLAIN 5. Extra Protocol Requirements [[Note that the item number continues the numbering of requirements from Section 4 of RFC 4422.]] [[Alexey: All of the features below are optional (in order to remain backward compatible with RFC 4422). However if any is implemented, all of them MUST be implemented in a protocol. This makes client implementations easier.]] 9) Facility to advertise the list of Channel Bindings that the server supports. See Section 4. 10) Facility to issue reuthentication tokens for SASL mechanisms that support them. 11) Detail any task negotiation facility that the protocol provides. [[Alexey: does this need to be done before authentication starts, or is it sufficient to discover these at the end of SASL mechanism exchange, when specific extra tasks are requested?]] A protocol MUST specify a facility through which the client may discover, the names of the SASL tasks that the server makes available to the client. This facility is typically provided through the protocol's extensions or capabilities discovery facility (so that the client can be made aware of which tasks might be required to complete authentication before starting any authentication), as well as provided at the end of a SASL authentication exchange. 12) Definition of the messages necessary for executing tasks, including the following: Cridland, et al. Expires 5 June 2025 [Page 7] Internet-Draft Extended SASL December 2024 a. A message to initiate execution of a task (see Section 3). This message MUST contain a field for carrying the name of the task selected by the client. This message MUST allow for an optional field for carrying an initial task related data. The specification MUST describe how messages with an empty initial task related data are distinguished from messages with no initial task related data. This field MUST be capable of carrying arbitrary sequences of octets (including zero-length sequences and sequences containing zero-valued octets). b. Messages to transfer task related data from server and from client (see Section 3). Each of these messages MUST be capable of carrying arbitrary sequences of octets (including zero-length sequences and sequences containing zero-valued octets). c. A message to indicate the outcome of the task execution and whether or not execution of further tasks is required by the server (see Section 3). This message MUST allow for an optional field for carrying additional data with a successful outcome. The specification MUST describe how messages with an empty additional data are distinguished from messages with no additional data. This field MUST be capable of carrying arbitrary sequences of octets (including zero- length sequences and sequences containing zero-valued octets). 6. Extra Mechanism Requirements [[Note that the number continues the numbering of requirements from Section 5 of RFC 4422.]] 6) Optional facility for SASL mechanism shared key derivation after a successful authentication. 7) Optional facility for SASL mechanism to generate reauthentication token after a successful authentication. 7. Example of a Protocol fulfilling extra requirements [[Ideally need 2 protocols. For example XMPP and IMAP. IMAP can have a new command for tasks.]] Cridland, et al. Expires 5 June 2025 [Page 8] Internet-Draft Extended SASL December 2024 8. Open Issues 9. Security Considerations TBD 10. IANA Considerations IANA is requested to create a new subregistry of "SASL tasks" for registering SASL tasks as specified in this document. The registration template is as follows: Task Name: Task Type: Pointer to specification text: Notes (optional): The registration procedure for the above registry is Expert Review. 11. Acknowledgements TBD. Thank you XSF for XEP-0388, XEP-0440 and XEP-scram-upgrade. 12. References 12.1. Normative References [CharModel] Whistler, K. and A. Freytag, "Unicode character encoding model", Unicode tr17, 11 November 2022, . [Glossary] Consortium, U., "Glossary of Unicode Terms", Unicode glossary, 2023, . [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . Cridland, et al. Expires 5 June 2025 [Page 9] Internet-Draft Extended SASL December 2024 [RFC4422] Melnikov, A., Ed. and K. Zeilenga, Ed., "Simple Authentication and Security Layer (SASL)", RFC 4422, DOI 10.17487/RFC4422, June 2006, . [RFC4949] Shirey, R., "Internet Security Glossary, Version 2", FYI 36, RFC 4949, DOI 10.17487/RFC4949, August 2007, . [RFC5056] Williams, N., "On the Use of Channel Bindings to Secure Channels", RFC 5056, DOI 10.17487/RFC5056, November 2007, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . [Unicode] Consortium, U., "Unicode 15.0.0", Unicode 15.0.0, 13 September 2022, . 12.2. Informative References [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, . Authors' Addresses Dave Cridland Email: dave@cridland.net Thilo Molitor Email: thilo+xmpp@eightysoft.de Matthew Wild Email: mwild1@gmail.com Alexey Melnikov Isode Ltd Email: Alexey.Melnikov@isode.com Cridland, et al. Expires 5 June 2025 [Page 10]