lakers  

An implementation of EDHOC (RFC 9528) in Rust.

What is EDHOC?

Ephemeral Diffie-Hellman Over COSE (EDHOC) is a new IETF standard that provides a very lightweight authenticated key exchange, ideal for usage in constrained scenarios, such as in Internet of Things environments.

EDHOC Features

• lightweight: full authenticated key exchange in as few as 101 bytes
• secure: mutual authentication, forward secrecy, and identity protection
• transport-agnostic: can be used on scenarios with or without IP connectivity; a common way to transport EDHOC is over reliable CoAP
• code re-use: achieved due to re-using technologies common in IoT scenarios, such as COSE, CBOR, and CoAP
• finally, a main use case of EDHOC is to establish an OSCORE security context

lakers features

• easy to use, typestated API for Initiator and Responder
• microcontroller-optimized: no_std, no heap allocations, zero-dependencies (other than crypto backends)
• configurable crypto backends
• bindings for C and Python
• support for EDHOC extensions, including zero-touch authorization

It currently supports authentication mode STAT-STAT and Cipher Suite 2 (AES-CCM-16-64-128, SHA-256, 8, P-256, ES256, AES-CCM-16-64-128, SHA-256).

Getting started

To use lakers in your Rust project, add it to your Cargo.toml using cargo add lakers.

Here's a quick look at the API for the Initiator role (for the Responder role, and more details, check the examples or the unit tests):

// perform the handshake
let initiator = EdhocInitiator::new(default_crypto());

let (initiator, message_1) = initiator.prepare_message_1(None, &None)?; // c_i and ead_1 are set to None

let (initiator, _c_r, id_cred_r, _ead_2) = initiator.parse_message_2(&message_2)?;
let valid_cred_r = credential_check_or_fetch(Some(CRED_R), id_cred_r)?; // CRED_R contains Responder's public key
let initiator = initiator.verify_message_2(I, cred_i, valid_cred_r)?; // I is Initiator's private key

let (mut initiator, message_3, i_prk_out) = initiator.prepare_message_3(CredentialTransfer::ByReference, &None)?; // no ead_3

// derive a secret to use with OSCORE
let oscore_secret = initiator.edhoc_exporter(0u8, &[], 16); // label is 0

// update the prk_out key (context taken from draft-ietf-lake-traces)
let context = &[0xa0, 0x11, 0x58, 0xfd, 0xb8, 0x20, 0x89, 0x0c, 0xd6, 0xbe, 0x16, 0x96, 0x02, 0xb8, 0xbc, 0xea];
let prk_out_new = initiator.edhoc_key_update(context);

C API

C-compatible static libraries and headers are available for download in the releases page.

Python API

lakers-python is available on PyPI, to install it run pip install lakers-python.

Development

To work on lakers itself, follow the instructions below:

1. Make sure you have Rust installed.

2. Download, compile, and run the tests:

git clone git@github.com:openwsn-berkeley/lakers.git && cd lakers
cargo build
cargo test

lakers can be compiled with different configurations depending on the enabled features. To learn what are the available features and how to select them for several configurations of build and test, check the Github Actions file.

Example: EDHOC over CoAP on native host

In one terminal, run an example CoAP server:

cargo run --bin coapserver

In another one, run the client:

cargo run --bin coapclient

In the output you should find the EDHOC handshake messages and the derived OSCORE secret/salt.

The source code for these examples is at examples/coap/src/bin.

Example: EDHOC on nRF52840 device with different crypto backends

To build an example application that works on the nrf52840dk, do as follows:

# head to the example `no_std` example
cd ./examples/lakers-no_std

# build using the cryptocell310 crypto backend (hardware-accelerated)
cargo build --target="thumbv7em-none-eabihf" --release

# build using the psa crypto backend (software-based)
cargo build --target="thumbv7em-none-eabihf" --no-default-features --features="crypto-psa, ead-none, rtt" --release

To build and flash to the board:

1. install cargo-embed
2. run one of the commands above, but use the command embed in place of build. For example: cargo embed --target="thumbv7em-none-eabihf"

Directory structure

This library is structured as a cargo workspace. Its main members are:

• lib: The main library providing the EDHOC implementation.
• crypto: Diferent cryptographic backends (e.g. psa, cryptocell310, rustcrypto).
• ead: Implementation of extensions to EDHOC via the External Authorization Data (EAD) field.
• shared: Defines shared structs and modules used throughout the workspace members.
• lakers-c: Provides a foreign function interface that enables using lakers from C code.
• lakers-python: API for using lakers in Python.
• examples: Example applications that demonstrate how to use the library.