DoubleRatchet

This is a mostly complete implementation of the Encrypted Header variant of the The Double Ratchet Algorithm designed by Open Whisper Systems.

WARNING: This implementation was created for learning purposes and should not be used outside of a development environment. Any concerns or suggestions are very welcome.

This implementation was built using the NodeJS crypto library as its only dependency. I decided to do this as Electron is the intended usage. However, it would be trivial to abstract the crypto provider in order to make this library browser friendly.

$3

``js
const Ratchet = require('doubleratchet').Ratchet

const pskRoot = ... // a shared secret between alice and bob
const pskHeader = ... // a shared secret between alice and bob
const pskNextHeader = ... // a shared secret between alice and bob

const alice = new Ratchet(pskRoot, pskHeader, pskNextHeader)
const bob = new Ratchet(pskRoot, pskNextHeader, pskHeader)

alice.acceptHandshake( bob.makeHandshake() )

bob.decrypt( alice.encrypt('hello bob') ) // "hello bob"
alice.decrypt( bob.encrypt('hello alice') ) // "hello alice"
`

See examples directory for more.

$3


`
git clone https://github.com/jowy/doubleratchet.git
cd doubleratchet
yarn install
yarn build
`

$3

| Parameter | Implementation |
| -------- | -------- |
| Ratchet ECDH Curve | secp521r1 |
| HMAC-KDF (HKDF) | SHA256 |
| Header Cipher | AES256 CBC Mode |
| Header Key Derivation | Salted HKDF |
| Header Key Length | 32 Bytes (Truncated) |
| Header IV Derivation | Salted HKDF |
| Message Cipher | AES256 CBC Mode |
| Message Key Derivation | Salted HKDF |
| Message Key Length | 32 Bytes (Truncated) |
| Message IV Derivation | Salted HKDF |
| Auth Tag Derivation | Salted HKDF |
| Auth Key Length | 32 Bytes (Truncated) |
| Auth Tag Length | 16 Bytes (Truncated) |
| Skipped Message Key Expire Method | Ratchet Invocation |
| Skipped Message Key TTL | 20 |

$3

- flow typing
- comments
- tests
- clean up KDF flow
- clean up Key and CipherKey initialization and handling
- clean up buffer handling
- state (de)serialization
- ~~fix header & nextHeader initialization and flow~~
- proper handling of input & output encoding
- revise CipherKey` kdf
- error handling for various things
- throw properly typed errors
- rollback chain state on failure
- ~~more examples demonstrating various features of the protocol~~
- API outline