Wire

This repository is part of the source code of Wire. You can find more information at https://wire.com[wire.com] or by contacting opensource@wire.com.

You can find the published source code at https://github.com/wireapp[github.com/wireapp].

For licensing information, see the attached LICENSE file and the list of third-party licenses at https://wire.com/legal/licenses/[wire.com/legal/licenses/].

= Proteus

// Links :axolotl: https://github.com/trevp/axolotl/wiki :whisper: https://whispersystems.org/blog/asynchronous-security/ :sodium: https://github.com/jedisct1/libsodium :chacha: https://en.wikipedia.org/wiki/Salsa20#ChaCha_variant :curve25519: https://en.wikipedia.org/wiki/Curve25519 :hkdf-rfc: https://tools.ietf.org/html/rfc5869 :hkdf-impl: https://github.com/wireapp/hkdf :hmac: https://en.wikipedia.org/wiki/Hash-based_message_authentication_code :mpl: https://img.shields.io/badge/license-MPL_2.0-blue.svg :cbor: https://tools.ietf.org/html/rfc7049 :wiki: https://github.com/wireapp/proteus/wiki/Serialisation-format

Proteus is an implementation of the link:{axolotl}[axolotl protocol] (later renamed to Double Ratchet Algorithm) without header keys. It is suitable for use in asynchronous environments through its use of link:{whisper}[prekeys].

The roles of the axolotl protocol for a particular session are fixed through the use of prekeys:

- The side that obtains a prekey and uses it to initiate a session
  is _Alice_.
- The side that receives a prekey message and uses it to initiate a
  session is _Bob_.

All cryptographic primitives used in the implementation of the protocol are provided by link:{sodium}[libsodium]:

- Cipher: link:{chacha}[ChaCha20]
- MAC: link:{hmac}[HMAC-SHA256]
- Diffie-Hellman: link:{curve25519}[Curve25519]
- KDF: link:{hkdf-rfc}[HKDF] (link:{hkdf-impl}[implementation])

For serialisation of messages, sessions and keys, link:{cbor}[CBOR] is used. The precise serialisation format is described in the link:{wiki}[wiki].