Ericsson

Jorvas 02420 Finland mohit@iki.fi

Ericsson

Kista Sweden john.mattsson@ericsson.com

sn3rd

sean@sn3rd.com

Network Working Group EAP-TLS X.509 EAP authenticator Maximum Transmission Unit The Extensible Authentication Protocol (EAP), defined in RFC 3748, provides a standard mechanism for support of multiple authentication methods. EAP-TLS and other TLS-based EAP methods are widely deployed and used for network access authentication. Large certificates and long certificate chains combined with authenticators that drop an EAP session after only 40 - 50 round trips is a major deployment problem. This document looks at this problem in detail and describes the potential solutions available.

Status of This Memo This document is not an Internet Standards Track specification; it is published for informational purposes. This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Not all documents approved by the IESG are 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 .

Copyright Notice Copyright (c) 2022 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 () 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

• .  Introduction
• .  Terminology
• .  Experience with Deployments
• .  Handling of Large Certificates and Long Certificate Chains
  • .  Updating Certificates and Certificate Chains
    • .  Guidelines for Certificates
    • .  Pre-distributing and Omitting CA Certificates
    • .  Using Fewer Intermediate Certificates
  • .  Updating TLS and EAP-TLS Code
    • .  URLs for Client Certificates
    • .  Caching Certificates
    • .  Compressing Certificates
    • .  Compact TLS 1.3
    • .  Suppressing Intermediate Certificates
    • .  Raw Public Keys
    • .  New Certificate Types and Compression Algorithms
  • .  Updating Authenticators
• .  IANA Considerations
• .  Security Considerations
• .  References
  • .  Normative References
  • .  Informative References
• Acknowledgements
• Authors' Addresses

Introduction The Extensible Authentication Protocol (EAP), defined in , provides a standard mechanism for support of multiple authentication methods. EAP-TLS relies on TLS to provide strong mutual authentication with certificates and is widely deployed and often used for network access authentication. There are also many other standardized TLS-based EAP methods such as Flexible Authentication via Secure Tunneling (EAP-FAST) , Tunneled Transport Layer Security (EAP-TTLS) , the Tunnel Extensible Authentication Protocol (TEAP) , as well as several vendor-specific EAP methods such as the Protected Extensible Authentication Protocol (PEAP) . Certificates in EAP deployments can be relatively large, and the certificate chains can be long. Unlike the use of TLS on the web, where typically only the TLS server is authenticated, EAP-TLS deployments typically authenticate both the EAP peer and the EAP server. Also, from deployment experience, EAP peers typically have longer certificate chains than servers. This is because EAP peers often follow organizational hierarchies and tend to have many intermediate certificates. Thus, EAP-TLS authentication usually involves exchange of significantly more octets than when TLS is used as part of HTTPS. states that EAP implementations can assume a Maximum Transmission Unit (MTU) of at least 1020 octets from lower layers. The EAP fragment size in typical deployments is just 1020 - 1500 octets (since the maximum Ethernet frame size is ~ 1500 bytes). Thus, EAP-TLS authentication needs to be fragmented into many smaller packets for transportation over the lower layers. Such fragmentation not only can negatively affect the latency, but also results in other challenges. For example, some EAP authenticator (e.g., an access point) implementations will drop an EAP session if it has not finished after 40 - 50 round trips. This is a major problem and means that, in many situations, the EAP peer cannot perform network access authentication even though both the sides have valid credentials for successful authentication and key derivation. Not all EAP deployments are constrained by the MTU of the lower layer. For example, some implementations support EAP over Ethernet "jumbo" frames that can easily allow very large EAP packets. Larger packets will naturally help lower the number of round trips required for successful EAP-TLS authentication. However, deployment experience has shown that these jumbo frames are not always implemented correctly. Additionally, EAP fragment size is also restricted by protocols such as RADIUS , which are responsible for transporting EAP messages between an authenticator and an EAP server. RADIUS can generally transport only about 4000 octets of EAP in a single message (the maximum length of a RADIUS packet is restricted to 4096 octets in ). This document looks at related work and potential tools available for overcoming the deployment challenges induced by large certificates and long certificate chains. It then discusses the solutions available to overcome these challenges. Many of the solutions require TLS 1.3 . The IETF has standardized EAP-TLS 1.3 and is working on specifications such as for how other TLS-based EAP methods use TLS 1.3.

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 when, and only when, they appear in all capitals, as shown here. Readers are expected to be familiar with the terms and concepts used in EAP , EAP-TLS , and TLS . In particular, this document frequently uses the following terms as they have been defined in :

Authenticator:

The entity initiating EAP authentication. Typically implemented as part of a network switch or a wireless access point.

EAP peer:

The entity that responds to the authenticator. In , this entity is known as the supplicant. In EAP-TLS, the EAP peer implements the TLS client role.

EAP server:

The entity that terminates the EAP authentication method with the peer. In the case where no backend authentication server is used, the EAP server is part of the authenticator. In the case where the authenticator operates in pass-through mode, the EAP server is located on the backend authentication server. In EAP-TLS, the EAP server implements the TLS server role.

The document additionally uses the terms "trust anchor" and "certification path" defined in .

Experience with Deployments As stated earlier, the EAP fragment size in typical deployments is just 1020 - 1500 octets. A certificate can, however, be large for a number of reasons:

• It can have a long Subject Alternative Name field.
• It can have long Public Key and Signature fields.
• It can contain multiple object identifiers (OIDs) that indicate the permitted uses of the certificate as noted in . Most implementations verify the presence of these OIDs for successful authentication.
• It can contain multiple organization naming fields to reflect the multiple group memberships of a user (in a client certificate).

A certificate chain (called a certification path in ) in EAP-TLS can commonly have 2 - 6 intermediate certificates between the end-entity certificate and the trust anchor. The size of certificates (and certificate chains) may also increase manyfold in the future with the introduction of post-quantum cryptography. For example, lattice-based cryptography would have public keys of approximately 1000 bytes and signatures of approximately 2000 bytes. Many access point implementations drop EAP sessions that do not complete within 40 - 50 round trips. This means that if the chain is larger than ~ 60 kilobytes, EAP-TLS authentication cannot complete successfully in most deployments.

Handling of Large Certificates and Long Certificate Chains This section discusses some possible alternatives for overcoming the challenge of large certificates and long certificate chains in EAP-TLS authentication. considers recommendations that require an update of the certificates or certificate chains used for EAP-TLS authentication without requiring changes to the existing EAP-TLS code base. It also provides some guidelines that should be followed when issuing certificates for use with EAP-TLS. considers recommendations that rely on updates to the EAP-TLS implementations and can be deployed with existing certificates. Finally, briefly discusses what could be done to update or reconfigure authenticators when it is infeasible to replace deployed components giving a solution that can be deployed without changes to existing certificates or code.

Updating Certificates and Certificate Chains Many IETF protocols now use elliptic curve cryptography (ECC) for the underlying cryptographic operations. The use of ECC can reduce the size of certificates and signatures. For example, at a 128-bit security level, the size of a public key with traditional RSA is about 384 bytes, while the size of a public key with ECC is only 32-64 bytes. Similarly, the size of a digital signature with traditional RSA is 384 bytes, while the size is only 64 bytes with the elliptic curve digital signature algorithm (ECDSA) and the Edwards-curve digital signature algorithm (EdDSA) . Using certificates that use ECC can reduce the number of messages in EAP-TLS authentication, which can alleviate the problem of authenticators dropping an EAP session because of too many round trips. In the absence of a standard application profile specifying otherwise, TLS 1.3 requires implementations to support ECC. New cipher suites that use ECC are also specified for TLS 1.2 . Using ECC-based cipher suites with existing code can significantly reduce the number of messages in a single EAP session.

Guidelines for Certificates The general guideline of keeping the certificate size small by not populating fields with excessive information can help avert the problems of failed EAP-TLS authentication. More specific recommendations for certificates used with EAP-TLS are as follows:

• Object Identifier (OID) is an ASN.1 data type that defines unique identifiers for objects. The OID's ASN.1 value, which is a string of integers, is then used to name objects to which they relate. The Distinguished Encoding Rules (DER) specify that the first two integers always occupy one octet and subsequent integers are base-128 encoded in the fewest possible octets. OIDs are used lavishly in X.509 certificates and while not all can be avoided, e.g., OIDs for extensions or algorithms and their associate parameters, some are well within the certificate issuer's control:
  • Each naming attribute in a DN (Distinguished Name) has one. DNs are used in the issuer and subject fields as well as numerous extensions. A shallower name will be smaller, e.g., C=FI, O=Example, SN=B0A123499EFC as against C=FI, O=Example, OU=Division 1, SOPN=Southern Finland, CN=Coolest IoT Gadget Ever, and SN=B0A123499EFC.
  • Every certificate policy (and qualifier) and any mappings to another policy uses identifiers. Consider carefully what policies apply.
• DirectoryString and GeneralName types are used extensively to name things, e.g., the DN naming attribute O= (the organizational naming attribute) DirectoryString includes "Example" for the Example organization and uniformResourceIdentifier can be used to indicate the location of the Certificate Revocation List (CRL), e.g., "http://crl.example.com/sfig2s1-128.crl", in the CRL Distribution Point extension. For these particular examples, each character is a single byte. For some non-ASCII character strings, characters can be several bytes. Obviously, the names need to be unique, but there is more than one way to accomplish this without long strings. This is especially true if the names are not meant to be meaningful to users.
• Extensions are necessary to comply with , but the vast majority are optional. Include only those that are necessary to operate.
• As stated earlier, certificate chains of the EAP peer often follow organizational hierarchies. In such cases, information in intermediate certificates (such as postal addresses) do not provide any additional value and they can be shortened (for example, only including the department name instead of the full postal address).

Pre-distributing and Omitting CA Certificates The TLS Certificate message conveys the sending endpoint's certificate chain. TLS allows endpoints to reduce the size of the Certificate message by omitting certificates that the other endpoint is known to possess. When using TLS 1.3, all certificates that specify a trust anchor known by the other endpoint may be omitted (see ). When using TLS 1.2 or earlier, only the self-signed certificate that specifies the root certificate authority may be omitted (see ). Therefore, updating TLS implementations to version 1.3 can help to significantly reduce the number of messages exchanged for EAP-TLS authentication. The omitted certificates need to be pre-distributed independently of TLS, and the TLS implementations need to be configured to omit these pre-distributed certificates.

Using Fewer Intermediate Certificates The EAP peer certificate chain does not have to mirror the organizational hierarchy. For successful EAP-TLS authentication, certificate chains SHOULD NOT contain more than 4 intermediate certificates. Administrators responsible for deployments using TLS-based EAP methods can examine the certificate chains and make rough calculations about the number of round trips required for successful authentication. For example, dividing the total size of all the certificates in the peer and server certificate chain (in bytes) by 1020 bytes will indicate the number of round trips required. If this number exceeds 50, then administrators can expect failures with many common authenticator implementations.

Updating TLS and EAP-TLS Code This section discusses how the fragmentation problem can be avoided by updating the underlying TLS or EAP-TLS implementation. Note that in some cases, the new feature may already be implemented in the underlying library and simply needs to be enabled.

URLs for Client Certificates defines the "client_certificate_url" extension, which allows TLS clients to send a sequence of Uniform Resource Locators (URLs) instead of the client certificate chain. URLs can refer to a single certificate or a certificate chain. Using this extension can curtail the amount of fragmentation in EAP deployments thereby allowing EAP sessions to successfully complete.

Caching Certificates The TLS Cached Information Extension specifies an extension where a server can exclude transmission of certificate information cached in an earlier TLS handshake. The client and the server would first execute the full TLS handshake. The client would then cache the certificate provided by the server. When the TLS client later connects to the same TLS server without using session resumption, it can attach the "cached_info" extension to the ClientHello message. This would allow the client to indicate that it has cached the certificate. The client would also include a fingerprint of the server certificate chain. If the server's certificate has not changed, then the server does not need to send its certificate and the corresponding certificate chain again. In case information has changed, which can be seen from the fingerprint provided by the client, the certificate payload is transmitted to the client to allow the client to update the cache. The extension, however, necessitates a successful full handshake before any caching. This extension can be useful when, for example, a successful authentication between an EAP peer and EAP server has occurred in the home network. If authenticators in a roaming network are stricter at dropping long EAP sessions, an EAP peer can use the Cached Information Extension to reduce the total number of messages. However, if all authenticators drop the EAP session for a given EAP peer and EAP server combination, a successful full handshake is not possible. An option in such a scenario would be to cache validated certificate chains even if the EAP-TLS exchange fails, but such caching is currently not specified in .

Compressing Certificates The TLS Working Group has standardized an extension for TLS 1.3 that allows compression of certificates and certificate chains during full handshakes. The client can indicate support for compressed server certificates by including this extension in the ClientHello message. Similarly, the server can indicate support for compression of client certificates by including this extension in the CertificateRequest message. While such an extension can alleviate the problem of excessive fragmentation in EAP-TLS, it can only be used with TLS version 1.3 and higher. Deployments that rely on older versions of TLS cannot benefit from this extension.

Compact TLS 1.3 defines a "compact" version of TLS 1.3 and reduces the message size of the protocol by removing obsolete material and using more efficient encoding. It also defines a compression profile with which either side can define a dictionary of "known certificates". Thus, cTLS could provide another mechanism for EAP-TLS deployments to reduce the size of messages and avoid excessive fragmentation.

Suppressing Intermediate Certificates For a client that has all intermediate certificates in the certificate chain, having the server send intermediates in the TLS handshake increases the size of the handshake unnecessarily. proposes an extension for TLS 1.3 that allows a TLS client that has access to the complete set of published intermediate certificates to inform servers of this fact so that the server can avoid sending intermediates, reducing the size of the TLS handshake. The mechanism is intended to be complementary with certificate compression. The Authority Information Access (AIA) extension specified in can be used with end-entity and CA certificates to access information about the issuer of the certificate in which the extension appears. For example, it can be used to provide the address of the Online Certificate Status Protocol (OCSP) responder from where revocation status of the certificate (in which the extension appears) can be checked. It can also be used to obtain the issuer certificate. Thus, the AIA extension can reduce the size of the certificate chain by only including a pointer to the issuer certificate instead of including the entire issuer certificate. However, it requires the side receiving the certificate containing the extension to have network connectivity (unless the information is already cached locally). Naturally, such indirection cannot be used for the server certificate (since EAP peers in most deployments do not have network connectivity before authentication and typically do not maintain an up-to-date local cache of issuer certificates).

Raw Public Keys defines a new certificate type and TLS extensions to enable the use of raw public keys for authentication. Raw public keys use only a subset of information found in typical certificates and are therefore much smaller in size. However, raw public keys require an out-of-band mechanism to bind the public key with the entity presenting the key. Using raw public keys will obviously avoid the fragmentation problems resulting from large certificates and long certificate chains. Deployments can consider their use as long as an appropriate out-of-band mechanism for binding public keys with identifiers is in place. Naturally, deployments will also need to consider the challenges of revocation and key rotation with the use of raw public keys.

New Certificate Types and Compression Algorithms There is ongoing work to specify new certificate types that are smaller than traditional X.509 certificates. For example, defines a Concise Binary Object Representation (CBOR) encoding of X.509 Certificates. The CBOR encoding can be used to compress existing X.509 certificates or for natively signed CBOR certificates. registers a new TLS Certificate type that would enable TLS implementations to use CBOR Web Tokens (CWTs) as certificates. While these are early initiatives, future EAP-TLS deployments can consider the use of these new certificate types and compression algorithms to avoid large message sizes.

Updating Authenticators There are several legitimate reasons that authenticators may want to limit the number of packets / octets / round trips that can be sent. The main reason has been to work around issues where the EAP peer and EAP server end up in an infinite loop ACKing their messages. Another reason is that unlimited communication from an unauthenticated device using EAP could provide a channel for inappropriate bulk data transfer. A third reason is to prevent denial-of-service attacks. Updating the millions of already deployed access points and switches is in many cases not realistic. Vendors may be out of business or no longer supporting the products and administrators may have lost the login information to the devices. For practical purposes, the EAP infrastructure is ossified for the time being. Vendors making new authenticators should consider increasing the number of round trips allowed to 100 before denying the EAP authentication to complete. Based on the size of the certificates and certificate chains currently deployed, such an increase would likely ensure that peers and servers can complete EAP-TLS authentication. At the same time, administrators responsible for EAP deployments should ensure that this 100 round-trip limit is not exceeded in practice.

IANA Considerations This document has no IANA actions.

Security Considerations Updating implementations to TLS version 1.3 allows omitting all certificates with a trust anchor known by the other endpoint. TLS 1.3 additionally provides improved security, privacy, and reduced latency for EAP-TLS . Security considerations when compressing certificates are specified in . Specific security considerations of the referenced documents apply when they are taken into use.

References Normative References 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. This document defines the Extensible Authentication Protocol (EAP), an authentication framework which supports multiple authentication methods. EAP typically runs directly over data link layers such as Point-to-Point Protocol (PPP) or IEEE 802, without requiring IP. EAP provides its own support for duplicate elimination and retransmission, but is reliant on lower layer ordering guarantees. Fragmentation is not supported within EAP itself; however, individual EAP methods may support this. This document obsoletes RFC 2284. A summary of the changes between this document and RFC 2284 is available in Appendix A. [STANDARDS-TRACK] This document defines the Extensible Authentication Protocol (EAP) based Flexible Authentication via Secure Tunneling (EAP-FAST) protocol. EAP-FAST is an EAP method that enables secure communication between a peer and a server by using the Transport Layer Security (TLS) to establish a mutually authenticated tunnel. Within the tunnel, Type-Length-Value (TLV) objects are used to convey authentication related data between the peer and the EAP server. This memo provides information for the Internet community. The Extensible Authentication Protocol (EAP), defined in RFC 3748, provides support for multiple authentication methods. Transport Layer Security (TLS) provides for mutual authentication, integrity-protected ciphersuite negotiation, and key exchange between two endpoints. This document defines EAP-TLS, which includes support for certificate-based mutual authentication and key derivation. This document obsoletes RFC 2716. A summary of the changes between this document and RFC 2716 is available in Appendix A. [STANDARDS-TRACK] This memo profiles the X.509 v3 certificate and X.509 v2 certificate revocation list (CRL) for use in the Internet. An overview of this approach and model is provided as an introduction. The X.509 v3 certificate format is described in detail, with additional information regarding the format and semantics of Internet name forms. Standard certificate extensions are described and two Internet-specific extensions are defined. A set of required certificate extensions is specified. The X.509 v2 CRL format is described in detail along with standard and Internet-specific extensions. An algorithm for X.509 certification path validation is described. An ASN.1 module and examples are provided in the appendices. [STANDARDS-TRACK] EAP-TTLS is an EAP (Extensible Authentication Protocol) method that encapsulates a TLS (Transport Layer Security) session, consisting of a handshake phase and a data phase. During the handshake phase, the server is authenticated to the client (or client and server are mutually authenticated) using standard TLS procedures, and keying material is generated in order to create a cryptographically secure tunnel for information exchange in the subsequent data phase. During the data phase, the client is authenticated to the server (or client and server are mutually authenticated) using an arbitrary authentication mechanism encapsulated within the secure tunnel. The encapsulated authentication mechanism may itself be EAP, or it may be another authentication protocol such as PAP, CHAP, MS-CHAP, or MS-CHAP-V2. Thus, EAP-TTLS allows legacy password-based authentication protocols to be used against existing authentication databases, while protecting the security of these legacy protocols against eavesdropping, man-in-the-middle, and other attacks. The data phase may also be used for additional, arbitrary data exchange. This memo provides information for the Internet community. This document defines the Tunnel Extensible Authentication Protocol (TEAP) version 1. TEAP is a tunnel-based EAP method that enables secure communication between a peer and a server by using the Transport Layer Security (TLS) protocol to establish a mutually authenticated tunnel. Within the tunnel, TLV objects are used to convey authentication-related data between the EAP peer and the EAP server. 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. This document specifies version 1.3 of the Transport Layer Security (TLS) protocol. TLS allows client/server applications to communicate over the Internet in a way that is designed to prevent eavesdropping, tampering, and message forgery. This document updates RFCs 5705 and 6066, and obsoletes RFCs 5077, 5246, and 6961. This document also specifies new requirements for TLS 1.2 implementations. Informative References RISE AB RISE AB Ericsson AB Ericsson AB Nexus Group Work in Progress Mozilla Cisco Arm Limited This document specifies a "compact" version of TLS 1.3. It is isomorphic to TLS 1.3 but saves space by trimming obsolete material, tighter encoding, a template-based specialization technique, and alternative cryptographic techniques. cTLS is not directly interoperable with TLS 1.3, but it should eventually be possible for a cTLS/TLS 1.3 server to exist and successfully interoperate. Work in Progress IEEE Microsoft Corporation This document describes a protocol for carrying authentication, authorization, and configuration information between a Network Access Server which desires to authenticate its links and a shared Authentication Server. [STANDARDS-TRACK] This document specifies Version 1.2 of the Transport Layer Security (TLS) protocol. The TLS protocol provides communications security over the Internet. The protocol allows client/server applications to communicate in a way that is designed to prevent eavesdropping, tampering, or message forgery. [STANDARDS-TRACK] This document provides specifications for existing TLS extensions. It is a companion document for RFC 5246, "The Transport Layer Security (TLS) Protocol Version 1.2". The extensions specified are server_name, max_fragment_length, client_certificate_url, trusted_ca_keys, truncated_hmac, and status_request. [STANDARDS-TRACK] This note describes the fundamental algorithms of Elliptic Curve Cryptography (ECC) as they were defined in some seminal references from 1994 and earlier. These descriptions may be useful for implementing the fundamental algorithms without using any of the specialized methods that were developed in following years. Only elliptic curves defined over fields of characteristic greater than three are in scope; these curves are those used in Suite B. This document is not an Internet Standards Track specification; it is published for informational purposes. This document specifies a new certificate type and two TLS extensions for exchanging raw public keys in Transport Layer Security (TLS) and Datagram Transport Layer Security (DTLS). The new certificate type allows raw public keys to be used for authentication. Transport Layer Security (TLS) handshakes often include fairly static information, such as the server certificate and a list of trusted certification authorities (CAs). This information can be of considerable size, particularly if the server certificate is bundled with a complete certificate chain (i.e., the certificates of intermediate CAs up to the root CA). This document defines an extension that allows a TLS client to inform a server of cached information, thereby enabling the server to omit already available information. This document describes elliptic curve signature scheme Edwards-curve Digital Signature Algorithm (EdDSA). The algorithm is instantiated with recommended parameters for the edwards25519 and edwards448 curves. An example implementation and test vectors are provided. CBOR Web Token (CWT) is a compact means of representing claims to be transferred between two parties. The claims in a CWT are encoded in the Concise Binary Object Representation (CBOR), and CBOR Object Signing and Encryption (COSE) is used for added application-layer security protection. A claim is a piece of information asserted about a subject and is represented as a name/value pair consisting of a claim name and a claim value. CWT is derived from JSON Web Token (JWT) but uses CBOR rather than JSON. This document describes key exchange algorithms based on Elliptic Curve Cryptography (ECC) for the Transport Layer Security (TLS) protocol. In particular, it specifies the use of Ephemeral Elliptic Curve Diffie-Hellman (ECDHE) key agreement in a TLS handshake and the use of the Elliptic Curve Digital Signature Algorithm (ECDSA) and Edwards-curve Digital Signature Algorithm (EdDSA) as authentication mechanisms. This document obsoletes RFC 4492. In TLS handshakes, certificate chains often take up the majority of the bytes transmitted. This document describes how certificate chains can be compressed to reduce the amount of data transmitted and avoid some round trips. The Concise Binary Object Representation (CBOR) is a data format whose design goals include the possibility of extremely small code size, fairly small message size, and extensibility without the need for version negotiation. These design goals make it different from earlier binary serializations such as ASN.1 and MessagePack. This document obsoletes RFC 7049, providing editorial improvements, new details, and errata fixes while keeping full compatibility with the interchange format of RFC 7049. It does not create a new version of the format. Arm Limited Arm Limited The TLS protocol supports different credentials, including pre-shared keys, raw public keys, and X.509 certificates. For use with public key cryptography developers have to decide between raw public keys, which require out-of-band agreement and full-fletched X.509 certificates. For devices where the reduction of code size is important it is desirable to minimize the use of X.509-related libraries. With the CBOR Web Token (CWT) a structure has been defined that allows CBOR-encoded claims to be protected with CBOR Object Signing and Encryption (COSE). This document registers a new value to the "TLS Certificate Types" sub-registry to allow TLS and DTLS to use CWTs. Conceptually, CWTs can be seen as a certificate format (when with public key cryptography) or a Kerberos ticket (when used with symmetric key cryptography). Work in Progress FreeRADIUS Work in Progress Mozilla A TLS client that has access to the complete set of published intermediate certificates can inform servers of this fact so that the server can avoid sending intermediates, reducing the size of the TLS handshake. Work in Progress

Acknowledgements This document is a result of several useful discussions with , , , , , and .

Authors' Addresses Ericsson

Jorvas 02420 Finland mohit@iki.fi

Ericsson

Kista Sweden john.mattsson@ericsson.com

sn3rd

sean@sn3rd.com