RFC 4785

Pre-Shared Key (PSK) Ciphersuites with NULL Encryption for Transport Layer Security (TLS)

📅 published January 2007, from ietf

RFC 4785 💖 Pre-Shared Key (PSK) Ciphersuites with NULL Encryption for Transport Layer Security (TLS)

okay bestie, this one is a Standards Track doc from the IETF, and it's giving practical, no-frills TLS 🦋

RFC number: 4785
Network Working Group, Standards Track
Authors: Uri Blumenthal and Purushottam Goel, both at Intel Corporation 🧚
Date: January 2007
Obsoletes / Updates: the header doesn't list any RFCs it obsoletes or updates ✨

Status of This Memo 📋

this doc is an Internet standards track protocol spec for the Internet community, and it's asking for discussion and suggestions for improvements 🗣️. for the current standardization state and status of this protocol, check the "Internet Official Protocol Standards" (STD 1). distribution of this memo is unlimited 🌸.

Copyright Notice ©️

Abstract 🌈

so this doc specifies authentication-only ciphersuites with no encryption for the Pre-Shared Key (PSK) based Transport Layer Security (TLS) protocol 🔐. they're useful when you want authentication and integrity protection but confidentiality isn't needed, or isn't allowed 🙈.

Table of Contents 🗂️

   1. Introduction ....................................................2
      1.1. Applicability Statement ....................................2
   2. Conventions Used in This Document ...............................2
   3. Cipher Usage ....................................................3
   4. Security Considerations .........................................3
   5. IANA Considerations .............................................3
   6. Acknowledgments .................................................3
   7. References ......................................................4
      7.1. Normative References .......................................4
      7.2. Informative References .....................................4

1. Introduction ✨

okay so the PSK TLS spec, [TLS-PSK], gives you ciphersuites for TLS using pre-shared symmetric keys 🔑. the catch is that every ciphersuite in [TLS-PSK] requires encryption. but there are situations where you only need authentication and integrity protection, and confidentiality just isn't needed 🤷‍♀️. there are also situations where confidentiality isn't permitted. for example, implementations that have to follow import restrictions in some countries 🌍. even with no encryption, these suites still let the client and server authenticate each other, and they still give you message integrity 💅.

this doc augments [TLS-PSK] by adding three more ciphersuites (PSK, DHE_PSK, RSA_PSK) that do authentication and integrity only, with no encryption 🎀. you're expected to already be familiar with the [TLS-PSK] standard before reading this one, so go read that first, bestie 📚.

1.1. Applicability Statement 🧁

the ciphersuites in this doc are meant for a pretty limited set of applications, usually with just a very small number of clients and servers 🥺. even in those environments, other alternatives might fit better 👀.

if the main goal is avoiding Public-key Infrastructures (PKIs), you could consider self-signed certificates with public key fingerprints 🪪. instead of manually setting up a shared secret in something like a config file, you could put a fingerprint (hash) of the other party's public key (or certificate) in there instead 💜.

you can also use the Secure Remote Password (SRP) ciphersuites for shared secret authentication [SRP] 🔒. SRP was designed to work with passwords, and it has protection against dictionary attacks baked in 🙌. the tradeoff is that it's computationally more expensive than the PSK ciphersuites in [TLS-PSK] 🐢.

2. Conventions Used in This Document 📝

the key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119] 🫶.

3. Cipher Usage 🍓

the three new ciphersuites here match the three cipher suites defined in [TLS-PSK], except that these ones use null encryption 🌸.

these ciphersuites use the following options for the key exchange and hash parts of the protocol 💅:

   CipherSuite                     Key Exchange   Cipher      Hash

   TLS_PSK_WITH_NULL_SHA           PSK            NULL        SHA
   TLS_DHE_PSK_WITH_NULL_SHA       DHE_PSK        NULL        SHA
   TLS_RSA_PSK_WITH_NULL_SHA       RSA_PSK        NULL        SHA

for what PSK means, check section 1 in [TLS-PSK]. for DHE, RSA, and SHA, check appendixes A.5 and B in [TLS] 📖.

4. Security Considerations 💀

⚠️ big deal section, don't skip it! ⚠️ as with every scheme that uses shared keys, you need to take special care to protect the shared values and to limit how long they're exposed 🔐. this doc augments [TLS-PSK], so everything in the Security Considerations section of [TLS-PSK] applies here too. on top of that, these cipher suites don't support confidentiality, so take care not to send sensitive information (like passwords) over connections protected by one of these ciphersuites 🚨.

5. IANA Considerations 🏷️

this doc defines three new ciphersuites, and their values live in the TLS Cipher Suite registry defined in [TLS] 📋.

   CipherSuite   TLS_PSK_WITH_NULL_SHA      = { 0x00, 0x2C };
   CipherSuite   TLS_DHE_PSK_WITH_NULL_SHA  = { 0x00, 0x2D };
   CipherSuite   TLS_RSA_PSK_WITH_NULL_SHA  = { 0x00, 0x2E };

6. Acknowledgments 🫂

the ciphersuites in this doc are an augmentation of, and based on, [TLS-PSK] 💜.

7. References 📚

7.1. Normative References 🌟

   [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
             Requirement Levels", BCP 14, RFC 2119, March 1997.

   [TLS]     Dierks, T. and E. Rescorla, "The Transport Layer Security
             (TLS) Protocol Version 1.1", RFC 4346, April 2006.

   [TLS-PSK] Eronen, P. and H. Tschofenig, "Pre-Shared Key Ciphersuites
             for Transport Layer Security (TLS)", RFC 4279, December
             2005.

7.2. Informative References 💭

   [SRP]     Taylor, D., Wu, T., Mavrogiannopoulos, N., and T. Perrin,
             "Using SRP for TLS Authentication", Work in Progress,
             December 2006.

Authors' Addresses 🧚‍♀️

   Uri Blumenthal
   Intel Corporation
   1515 State Route 10,
   PY2-1 10-4
   Parsippany, NJ 07054
   USA

   EMail: urimobile@optonline.net


   Purushottam Goel
   Intel Corporation
   2111 N.E. 25 Ave.
   JF3-414
   Hillsboro, OR 97124
   USA

   EMail: Purushottam.Goel@intel.com

Full Copyright Statement 🩵

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Acknowledgement ✨

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