Record Size Limit Extension for TLS
RFC 8449
Document | Type |
RFC - Proposed Standard
(August 2018; No errata)
Updates RFC 6066
|
|
---|---|---|---|
Author | Martin Thomson | ||
Last updated | 2018-12-19 | ||
Replaces | draft-thomson-tls-record-limit | ||
Stream | IETF | ||
Formats | plain text html pdf htmlized bibtex | ||
Reviews | |||
Stream | WG state | Submitted to IESG for Publication | |
Document shepherd | Sean Turner | ||
Shepherd write-up | Show (last changed 2018-02-01) | ||
IESG | IESG state | RFC 8449 (Proposed Standard) | |
Consensus Boilerplate | Yes | ||
Telechat date | |||
Responsible AD | Benjamin Kaduk | ||
Send notices to | Sean Turner <sean@sn3rd.com> | ||
IANA | IANA review state | IANA OK - Actions Needed | |
IANA action state | RFC-Ed-Ack |
Internet Engineering Task Force (IETF) M. Thomson Request for Comments: 8449 Mozilla Updates: 6066 August 2018 Category: Standards Track ISSN: 2070-1721 Record Size Limit Extension for TLS Abstract An extension to Transport Layer Security (TLS) is defined that allows endpoints to negotiate the maximum size of protected records that each will send the other. This replaces the maximum fragment length extension defined in RFC 6066. Status of This Memo This is an Internet Standards Track document. 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). Further information on Internet Standards is available in 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 https://www.rfc-editor.org/info/rfc8449. Copyright Notice Copyright (c) 2018 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 Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Thomson Standards Track [Page 1] RFC 8449 TLS Record Limit August 2018 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Conventions and Definitions . . . . . . . . . . . . . . . . . 3 3. Limitations of the "max_fragment_length" Extension . . . . . 3 4. The "record_size_limit" Extension . . . . . . . . . . . . . . 4 4.1. Record Expansion Limits . . . . . . . . . . . . . . . . . 6 5. Deprecating "max_fragment_length" . . . . . . . . . . . . . . 6 6. Security Considerations . . . . . . . . . . . . . . . . . . . 7 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 7 8.1. Normative References . . . . . . . . . . . . . . . . . . 7 8.2. Informative References . . . . . . . . . . . . . . . . . 8 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 8 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 8 1. Introduction Implementing Transport Layer Security (TLS) [TLS] or Datagram TLS (DTLS) [DTLS] for constrained devices can be challenging. However, recent improvements to the design and implementation of cryptographic algorithms have made TLS accessible to some highly limited devices (see, for example, [RFC7925]). Receiving large protected records can be particularly difficult for a device with limited operating memory. TLS versions 1.2 [RFC5246] and earlier permit senders to generate records 16384 octets in size, plus any expansion from compression and protection up to 2048 octets (though typically this expansion is only 16 octets). TLS 1.3 reduces the allowance for expansion to 256 octets. Allocating up to 18K of memory for ciphertext is beyond the capacity of some implementations. An Authentication Encryption with Additional Data (AEAD) cipher (see [RFC5116]) API requires that an entire record be present to decrypt and authenticate it. Similarly, other ciphers cannot produce authenticated data until the entire record is present. Incremental processing of records exposes endpoints to the risk of forged data. The "max_fragment_length" extension [RFC6066] was designed to enable constrained clients to negotiate a lower record size. However, "max_fragment_length" suffers from several design problems (see Section 3). This document defines a "record_size_limit" extension (Section 4). This extension replaces "max_fragment_length" [RFC6066], which this document deprecates. This extension is valid in all versions of TLS. Thomson Standards Track [Page 2] RFC 8449 TLS Record Limit August 2018 A smaller protected record size is just one of many problems that a constrained implementation might need to address. The "record_size_limit" extension only addresses the memory allocation problem; it does not address limits of code size, processingShow full document text