Crate hpke

hpke

WARNING: This code has not been audited. Use at your own discretion.

This is a pure Rust implementation of the HPKE hybrid encryption scheme. The purpose of hybrid encryption is to use allow someone to send secure messages to an entity whose public key they know. Here's an example of Alice and Bob, where Alice knows Bob's public key:

// These types define the ciphersuite Alice and Bob will be using
type Kem = X25519HkdfSha256;
type Aead = ChaCha20Poly1305;
type Kdf = HkdfSha384;

let mut csprng = StdRng::from_entropy();

// This is a description string for the session. Both Alice and Bob need to know this value.
// It's not secret.
let info_str = b"Alice and Bob's weekly chat";

// Alice initiates a session with Bob. OpModeS::Base means that Alice is not authenticating
// herself at all. If she had a public key herself, or a pre-shared secret that Bob also
// knew, she'd be able to authenticate herself. See the OpModeS and OpModeR types for more
// detail.
let (encapsulated_key, mut encryption_context) =
    hpke::setup_sender::<Aead, Kdf, Kem, _>(&OpModeS::Base, &bob_pk, info_str, &mut csprng)
        .expect("invalid server pubkey!");

// Alice encrypts a message to Bob. msg gets encrypted in place, and aad is authenticated
// associated data that is not encrypted.
let mut msg = *b"fronthand or backhand?";
let aad = b"a gentleman's game";
let auth_tag = encryption_context
    .seal(&mut msg, aad)
    .expect("encryption failed!");
// The msg was encrypted in-place. So rename it for clarity
let ciphertext = msg;

// ~~~
// Alice sends the encapsulated key, message ciphertext, AAD, and auth tag to Bob over the
// internet. Alice doesn't care if it's an insecure connection, because only Bob can read
// her ciphertext.
// ~~~

// Somewhere far away, Bob receives the data and makes a decryption session
let mut decryption_context =
    hpke::setup_receiver::<Aead, Kdf, Kem>(
        &OpModeR::Base,
        &bob_sk,
        &encapsulated_key,
        info_str,
    ).expect("failed to set up receiver!");
decryption_context.open(&mut ciphertext, aad, &auth_tag).expect("invalid ciphertext!");
// The ciphertext was decrypted in-place. So rename it for clarity
let plaintext = ciphertext;

assert_eq!(&plaintext, b"fronthand or backhand?");

Re-exports

pub use generic_array;

Modules

aead
kdf
kem
kex
op_mode
setup
single_shot

Structs

AeadCtxR	The HPKE receiver's context. This is what you use to open ciphertexts.
AeadCtxS	The HPKE senders's context. This is what you use to seal plaintexts.
EncappedKey	Holds the content of an encapsulated secret. This is what the receiver uses to derive the shared secret.
PskBundle	Contains preshared key bytes and an identifier. This is intended to go inside an OpModeR or OpModeS struct.

Enums

HpkeError	Describes things that can go wrong when trying to seal or open a ciphertext
OpModeR	The operation mode of the HPKE session (receiver's view). This is how the sender authenticates their identity to the receiver. This authentication information can include a preshared key, the identity key of the sender, both, or neither. Base is the only mode that does not provide any kind of sender identity authentication.
OpModeS	The operation mode of the HPKE session (sender's view). This is how the sender authenticates their identity to the receiver. This authentication information can include a preshared key, the identity key of the sender, both, or neither. Base is the only mode that does not provide any kind of sender identity authentication.

Traits

Deserializable	Implemented by types that can be deserialized from byte representation
Kem	Defines a combination of key exchange mechanism and a KDF, which together form a KEM
Serializable	Implemented by types that have a fixed-length byte representation

Functions

setup_receiver	Initiates a decryption context given a private key sk_recip and an encapsulated key which was encapsulated to sk_recip's corresponding public key
setup_sender	Initiates an encryption context to the given recipient public key
single_shot_open	Does a setup_receiver and AeadCtx::open in one shot. That is, it does a key decapsulation for the specified recipient and decrypts the provided ciphertext in-place. See setup::setup_reciever and AeadCtx::open for more detail.
single_shot_seal	Does a setup_sender and AeadCtx::seal in one shot. That is, it does a key encapsulation to the specified recipient and encrypts the provided plaintext in place. See setup::setup_sender and AeadCtx::seal for more detail.