Double Ratchet Algorithm: Difference between revisions

Revision as of 00:29, 15 May 2023

Revision as of 14:17, 15 May 2023

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== Etymology ==

{{Unreferenced section|date=April 2020}}

"[[Axolotl]]" was in reference to the salamander's self-healing properties.

[[File:Ratchet example.gif|alt=A gif of a ratchet moving showing that the mechanism can only move in one direction|thumb|125px|A mechanical ratchet]]

"[[Axolotl]]" was in reference to the salamander's self-healing properties. The term "ratchet" in cryptography is used in analogy to a [[Ratchet (device)|mechanical ratchet]]. In the mechanical sense, a ratchet only allows advancement in one direction; a cryptographic ratchet only allows keys to be generated from the previous key. Unlike a circular ratchet, however, each state is unique.

== Origin ==

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== Properties ==

[[File:Ratchet example.gif|alt=A gif of a ratchet moving showing that the mechanism can only move in one direction|thumb|125px|A mechanical ratchet]]

The Double Ratchet Algorithm features properties that have been commonly available in end-to-end encryption systems for a long time: encryption of contents on the entire way of transport as well as [[authentication]] of the remote peer and protection against manipulation of messages. As a hybrid of [[Diffie–Hellman key exchange|DH]] and [[Key derivation function|KDF]] ratchets, it combines several desired features of both principles. From [[Off-the-Record Messaging|OTR]] messaging it takes the properties of [[forward secrecy]] and automatically reestablishing secrecy in case of compromise of a session key, forward secrecy with a compromise of the secret persistent main key, and [[deniable encryption|plausible deniability]] for the authorship of messages. Additionally, it enables session key renewal without interaction with the remote peer by using secondary KDF ratchets. An additional key-derivation step is taken to enable retaining session keys for out-of-order messages without endangering the following keys.