Double Ratchet Algorithm: Difference between revisions

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{{short description|Cryptographic key management algorithm}}

{{Redirect|Double ratchet|the hand tool|Wrench}}

[[File:Double Ratchet Algorithm.png|350px|thumb|right|TheFull ratchet step in the double ratchet algorithm. The Key Derivation Function (KDF) provides the ratcheting mechanism. The first "ratchet" is applied to the symmetric root key, the second ratchet to the asymmetric Diffie Hellman (DH) key.<ref>Trevor Perrin (editor), Moxie Marlinspike, "[https://signal.org/docs/specifications/doubleratchet/ The Double Ratchet Algorithm]. Revision 1, 2016-11-20</ref>]]

In [[cryptography]], the '''Double Ratchet Algorithm''' (previously referred to as the '''Axolotl Ratchet'''<ref name="Perrin-2016-03-30">{{cite web|last1=Perrin|first1=Trevor|title=Compare Revisions|url=https://github.com/trevp/double_ratchet/wiki/Home/_compare/6fa4a516b01327d736df1f52014d8b561a18189a...ab41721f9ed7ca0bdac3e24ce9fc573750e0614d|website=GitHub|access-date=9 April 2016|date=30 March 2016}}</ref><ref name="signal-inside-and-out">{{cite web|last1=Marlinspike|first1=Moxie|title=Signal on the outside, Signal on the inside|url=https://whispersystems.org/blog/signal-inside-and-out/|publisher=Open Whisper Systems|access-date=31 March 2016|date=30 March 2016}}</ref>) is a [[Key (cryptography)|key]] management [[algorithm]] that was developed by [[Trevor Perrin]] and [[Moxie Marlinspike]] in 2013. It can be used as part of a [[cryptographic protocol]] to provide [[end-to-end encryption]] for [[instant messaging]]. After an initial [[key-agreement protocol|key exchange]] it manages the ongoing renewal and maintenance of short-lived session keys. It combines a cryptographic so-called "ratchet" based on the [[Diffie–Hellman key exchange]] (DH) and a ratchet based on a [[key derivation function]] (KDF), such as a [[hash function]], and is therefore called a double ratchet.

The algorithm provides forward secrecy for messages, and implicit renegotiation of forward keys; properties for which the protocol is named.<ref>{{cite book|last1=Cohn-Gordon|first1=K.|last2=Cremers|first2=C.|last3=Garratt|first3=L.|title=2016 IEEE 29th Computer Security Foundations Symposium (CSF) |chapter=On Post-compromise Security |year=2016|pages=164–178|doi=10.1109/CSF.2016.19|isbn=978-1-5090-2607-4|s2cid=5703986|chapter-url=https://ora.ox.ac.uk/objects/uuid:241da365-1c73-4b6a-826c-f122c4c1e1b8}}</ref>

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* [[Conversations (software)|Conversations]]{{efn|name=OMEMO|Via the [[OMEMO]] protocol}}

* [[Cryptocat]]{{efn|name=OMEMO}}<ref>{{Cite web|url=https://crypto.cat/security.html|title=Security|publisher=Cryptocat|access-date=14 July 2016|archive-url=https://web.archive.org/web/20160407125207/https://crypto.cat/security.html|archive-date=7 April 2016|url-status=dead}}</ref>

* [[Messenger (software)|Facebook Messenger]]{{efn|Only in "secret conversations"}}{{efn|name=SIGNAL|Via the [[Signal Protocol]]}}<ref>{{cite magazine|last1=Greenberg|first1=Andy|url=https://www.wired.com/2016/10/facebook-completely-encrypted-messenger-update-now/|title=You Can All Finally Encrypt Facebook Messenger, So Do It|magazine=Wired|publisher=Condé Nast|access-date=5 October 2016|date=4 October 2016}}</ref>

* [[G Data CyberDefense|G Data]] Secure Chat{{efn|name=SIGNAL}}<ref name="G Data"/><ref>{{cite web|title=SecureChat|url=https://github.com/GDATASoftwareAG/SecureChat|website=GitHub|publisher=G Data|access-date=14 July 2016}}</ref>

* [[Gajim]]{{efn|name=OMEMO}}

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* [http://git.matrix.org/git/olm/about/docs/olm.rst Olm]: C++ implementation under the [[Apache license|Apache 2.0 license]]

* [https://matrix-org.github.io/vodozemac/vodozemac/index.html Vodozemac]: Rust implementation of the Olm variation, under the [[Apache license|Apache 2.0 license]]

* {{YouTube|id=7uEeE3TUqmU|title=Double ratchet algorithm: The ping-pong game encrypting Signal and WhatsApp}} (exposition)

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