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Closes #59. The doc examples have code interspersed with text explaining the API. Because each doctest executes independently, when these code examples are run as doctests, they have to include parts of the previous examples with # lines. These lines are hidden from Rustdoc output and do not appear in the rendered docs, but they do appear when viewing the README.md on Github. In order to hide these on Github, the code blocks were made non-executable, with their content moved to a unit test. However, this meant that the example API usage was not tested, and so when the unit test was updated to remove the deprecated `rand_os`, there was no check that the examples stayed in sync with the test, causing #59. To prevent this from reocurring in the future, go back to executable tests of the API examples.
130 lines
4.8 KiB
Markdown
130 lines
4.8 KiB
Markdown
# x25519-dalek [](https://crates.io/crates/x25519-dalek) [](https://docs.rs/x25519-dalek) [](https://travis-ci.org/dalek-cryptography/x25519-dalek)
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A pure-Rust implementation of x25519 elliptic curve Diffie-Hellman key exchange,
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with curve operations provided by
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[curve25519-dalek](https://github.com/dalek-cryptography/curve25519-dalek).
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This crate provides two levels of API: a bare byte-oriented `x25519`
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function which matches the function specified in [RFC7748][rfc7748], as
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well as a higher-level Rust API for static and ephemeral Diffie-Hellman.
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## Examples
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<a href="https://shop.bubblesort.io">
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<img
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style="float: right; width: auto; height: 300px;"
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src="https://raw.githubusercontent.com/dalek-cryptography/x25519-dalek/master/res/bubblesort-zines-secret-messages-cover.jpeg"/>
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</a>
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Alice and Bob are two adorable kittens who have lost their mittens, and they
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wish to be able to send secret messages to each other to coordinate finding
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them, otherwise—if their caretaker cat finds out—they will surely be called
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naughty kittens and be given no pie!
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But the two kittens are quite clever. Even though their paws are still too big
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and the rest of them is 90% fuzziness, these clever kittens have been studying
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up on modern public key cryptography and have learned a nifty trick called
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*elliptic curve Diffie-Hellman key exchange*. With the right incantations, the
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kittens will be able to secretly organise to find their mittens, and then spend
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the rest of the afternoon nomming some yummy pie!
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First, Alice uses `EphemeralSecret::new()` and then
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`PublicKey::from()` to produce her secret and public keys:
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```rust
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use rand_core::OsRng;
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use x25519_dalek::{EphemeralSecret, PublicKey};
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let alice_secret = EphemeralSecret::new(OsRng);
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let alice_public = PublicKey::from(&alice_secret);
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```
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Bob does the same:
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```rust
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# use rand_core::OsRng;
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# use x25519_dalek::{EphemeralSecret, PublicKey};
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let bob_secret = EphemeralSecret::new(OsRng);
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let bob_public = PublicKey::from(&bob_secret);
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```
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Alice meows across the room, telling `alice_public` to Bob, and Bob
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loudly meows `bob_public` back to Alice. Alice now computes her
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shared secret with Bob by doing:
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```rust
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# use rand_core::OsRng;
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# use x25519_dalek::{EphemeralSecret, PublicKey};
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# let alice_secret = EphemeralSecret::new(OsRng);
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# let alice_public = PublicKey::from(&alice_secret);
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# let bob_secret = EphemeralSecret::new(OsRng);
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# let bob_public = PublicKey::from(&bob_secret);
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let alice_shared_secret = alice_secret.diffie_hellman(&bob_public);
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```
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Similarly, Bob computes a shared secret by doing:
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```rust
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# use rand_core::OsRng;
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# use x25519_dalek::{EphemeralSecret, PublicKey};
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# let alice_secret = EphemeralSecret::new(OsRng);
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# let alice_public = PublicKey::from(&alice_secret);
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# let bob_secret = EphemeralSecret::new(OsRng);
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# let bob_public = PublicKey::from(&bob_secret);
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let bob_shared_secret = bob_secret.diffie_hellman(&alice_public);
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```
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These secrets are the same:
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```rust
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# use rand_core::OsRng;
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# use x25519_dalek::{EphemeralSecret, PublicKey};
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# let alice_secret = EphemeralSecret::new(OsRng);
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# let alice_public = PublicKey::from(&alice_secret);
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# let bob_secret = EphemeralSecret::new(OsRng);
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# let bob_public = PublicKey::from(&bob_secret);
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# let alice_shared_secret = alice_secret.diffie_hellman(&bob_public);
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# let bob_shared_secret = bob_secret.diffie_hellman(&alice_public);
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assert_eq!(alice_shared_secret.as_bytes(), bob_shared_secret.as_bytes());
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```
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Voilá! Alice and Bob can now use their shared secret to encrypt their
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meows, for example, by using it to generate a key and nonce for an
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authenticated-encryption cipher.
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This example used the ephemeral DH API, which ensures that secret keys
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cannot be reused; Alice and Bob could instead use the static DH API
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and load a long-term secret key.
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# Installation
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To install, add the following to your project's `Cargo.toml`:
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```toml
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[dependencies.x25519-dalek]
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version = "0.6"
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```
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# Documentation
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Documentation is available [here](https://docs.rs/x25519-dalek).
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# Note
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This code matches the [RFC7748][rfc7748] test vectors.
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The elliptic curve
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operations are provided by `curve25519-dalek`, which makes a best-effort
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attempt to prevent software side-channels.
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"Secret Messages" cover image and [zine](https://shop.bubblesort.io/products/secret-messages-zine)
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copyright © Amy Wibowo ([@sailorhg](https://twitter.com/sailorhg))
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[rfc7748]: https://tools.ietf.org/html/rfc7748
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# See also
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- [crypto_box]: pure Rust public-key authenticated encryption compatible with
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the NaCl family of encryption libraries (libsodium, TweetNaCl) which uses
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`x25519-dalek` for key agreement
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[crypto_box]: https://github.com/RustCrypto/AEADs/tree/master/crypto_box
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