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https://github.com/dalek-cryptography/x25519-dalek

X25519 elliptic curve Diffie-Hellman key exchange in pure-Rust, using curve25519-dalek.
https://github.com/dalek-cryptography/x25519-dalek

cryptography curve25519 elliptic-curve-diffie-hellman keyexchange rust

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X25519 elliptic curve Diffie-Hellman key exchange in pure-Rust, using curve25519-dalek.

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README 

        
# ARCHIVED



This repo has been [moved](https://github.com/dalek-cryptography/curve25519-dalek). Please direct all issues and pull requests to the new repo.



This repo will remain here in a read-only state for historical purposes.



---



# x25519-dalek  [![](https://img.shields.io/crates/v/x25519-dalek.svg)](https://crates.io/crates/x25519-dalek) [![](https://docs.rs/x25519-dalek/badge.svg)](https://docs.rs/x25519-dalek) [![](https://travis-ci.org/dalek-cryptography/x25519-dalek.svg?branch=master)](https://travis-ci.org/dalek-cryptography/x25519-dalek)



A pure-Rust implementation of x25519 elliptic curve Diffie-Hellman key exchange,

with curve operations provided by

[curve25519-dalek](https://github.com/dalek-cryptography/curve25519-dalek).



This crate provides two levels of API: a bare byte-oriented `x25519`

function which matches the function specified in [RFC7748][rfc7748], as

well as a higher-level Rust API for static and ephemeral Diffie-Hellman.



## Examples










Alice and Bob are two adorable kittens who have lost their mittens, and they

wish to be able to send secret messages to each other to coordinate finding

them, otherwise—if their caretaker cat finds out—they will surely be called

naughty kittens and be given no pie!



But the two kittens are quite clever.  Even though their paws are still too big

and the rest of them is 90% fuzziness, these clever kittens have been studying

up on modern public key cryptography and have learned a nifty trick called

*elliptic curve Diffie-Hellman key exchange*.  With the right incantations, the

kittens will be able to secretly organise to find their mittens, and then spend

the rest of the afternoon nomming some yummy pie!



First, Alice uses `EphemeralSecret::random()` and then

`PublicKey::from()` to produce her secret and public keys:



```ignore

use x25519_dalek::{EphemeralSecret, PublicKey};



let alice_secret = EphemeralSecret::random();

let alice_public = PublicKey::from(&alice_secret);

```



Bob does the same:



```ignore

# use x25519_dalek::{EphemeralSecret, PublicKey};

let bob_secret = EphemeralSecret::random();

let bob_public = PublicKey::from(&bob_secret);

```



Alice meows across the room, telling `alice_public` to Bob, and Bob

loudly meows `bob_public` back to Alice.  Alice now computes her

shared secret with Bob by doing:



```rust

# use rand_core::OsRng;

# use x25519_dalek::{EphemeralSecret, PublicKey};

# let alice_secret = EphemeralSecret::new(OsRng);

# let alice_public = PublicKey::from(&alice_secret);

# let bob_secret = EphemeralSecret::new(OsRng);

# let bob_public = PublicKey::from(&bob_secret);

let alice_shared_secret = alice_secret.diffie_hellman(&bob_public);

```



Similarly, Bob computes a shared secret by doing:



```rust

# use rand_core::OsRng;

# use x25519_dalek::{EphemeralSecret, PublicKey};

# let alice_secret = EphemeralSecret::new(OsRng);

# let alice_public = PublicKey::from(&alice_secret);

# let bob_secret = EphemeralSecret::new(OsRng);

# let bob_public = PublicKey::from(&bob_secret);

let bob_shared_secret = bob_secret.diffie_hellman(&alice_public);

```



These secrets are the same:



```rust

# use rand_core::OsRng;

# use x25519_dalek::{EphemeralSecret, PublicKey};

# let alice_secret = EphemeralSecret::new(OsRng);

# let alice_public = PublicKey::from(&alice_secret);

# let bob_secret = EphemeralSecret::new(OsRng);

# let bob_public = PublicKey::from(&bob_secret);

# let alice_shared_secret = alice_secret.diffie_hellman(&bob_public);

# let bob_shared_secret = bob_secret.diffie_hellman(&alice_public);

assert_eq!(alice_shared_secret.as_bytes(), bob_shared_secret.as_bytes());

```



Voilà!  Alice and Bob can now use their shared secret to encrypt their

meows, for example, by using it to generate a key and nonce for an

authenticated-encryption cipher.



This example used the ephemeral DH API, which ensures that secret keys

cannot be reused; Alice and Bob could instead use the static DH API

and load a long-term secret key.



# Installation



To install, add the following to your project's `Cargo.toml`:



```toml

[dependencies]

x25519-dalek = "2.0.0-rc.3"

```



# MSRV



Current MSRV is 1.60.



# Documentation



Documentation is available [here](https://docs.rs/x25519-dalek).



# Performance and backend selection



Performance is a secondary goal behind correctness, safety, and clarity, but we aim to be competitive with other implementations. To this end, we allow users to choose their _backend_, i.e., the underlying implementation of elliptic curve and scalar arithmetic. Different backends have different use cases. For example, if you demand formally verified code, you want to use the `fiat` backend (as it was generated from [Fiat Crypto][fiat]).



Further instructions and details regarding backends can be found in the [curve25519-dalek docs](https://github.com/dalek-cryptography/curve25519-dalek#backends).



# Note



This code matches the [RFC7748][rfc7748] test vectors.

The elliptic curve

operations are provided by `curve25519-dalek`, which makes a best-effort

attempt to prevent software side-channels.



"Secret Messages" cover image and [zine](https://shop.bubblesort.io/products/secret-messages-zine)

copyright © Amy Wibowo ([@sailorhg](https://twitter.com/sailorhg))



[rfc7748]: https://tools.ietf.org/html/rfc7748



# See also



- [crypto_box]: pure Rust public-key authenticated encryption compatible with

  the NaCl family of encryption libraries (libsodium, TweetNaCl) which uses

  `x25519-dalek` for key agreement



[fiat]: https://github.com/mit-plv/fiat-crypto

[crypto_box]: https://github.com/RustCrypto/nacl-compat/tree/master/crypto_box