// Copyright (c) Facebook, Inc. and its affiliates.
//
// This source code is licensed under the MIT license found in the
// LICENSE file in the root directory of this source tree.

//! An implementation of the OPAQUE asymmetric password authentication key exchange protocol
//!
//! Note: This implementation is in sync with [draft-irtf-cfrg-opaque-03](https://www.ietf.org/archive/id/draft-irtf-cfrg-opaque-03.html),
//! but this specification is subject to change, until the final version published by the IETF.
//!
//! # Overview
//!
//! OPAQUE is a protocol between a client and a server. They must first agree on a collection of primitives
//! to be kept consistent throughout protocol execution. These include:
//! * a finite cyclic group along with a point representation,
//! * a key exchange protocol,
//! * a hashing function, and
//! * a slow hashing function.
//!
//! We will use the following choices in this example:
//! ```
//! use opaque_ke::ciphersuite::CipherSuite;
//! struct Default;
//! impl CipherSuite for Default {
//!     type Group = curve25519_dalek::ristretto::RistrettoPoint;
//!     type KeyExchange = opaque_ke::key_exchange::tripledh::TripleDH;
//!     type Hash = sha2::Sha512;
//!     type SlowHash = opaque_ke::slow_hash::NoOpHash;
//! }
//! ```
//! See [examples/simple_login.rs](https://github.com/novifinancial/opaque-ke/blob/master/examples/simple_login.rs)
//! for a working example of a simple password-based login using OPAQUE.
//!
//! Note that our choice of slow hashing function in this example, `NoOpHash`, is selected only to ensure
//! that the tests execute quickly. A real application should use an actual slow hashing function, such as `scrypt`,
//! which can be enabled through the `slow-hash` feature.
//!
//! ## Setup
//! To set up the protocol, the server begins by generating a static keypair:
//! ```
//! # use opaque_ke::errors::ProtocolError;
//! # use opaque_ke::ciphersuite::CipherSuite;
//! # struct Default;
//! # impl CipherSuite for Default {
//! #     type Group = curve25519_dalek::ristretto::RistrettoPoint;
//! #     type KeyExchange = opaque_ke::key_exchange::tripledh::TripleDH;
//! #     type Hash = sha2::Sha512;
//! #     type SlowHash = opaque_ke::slow_hash::NoOpHash;
//! # }
//! use rand::{rngs::OsRng, RngCore};
//! let mut rng = OsRng;
//! let server_kp = Default::generate_random_keypair(&mut rng);
//! # Ok::<(), ProtocolError>(())
//! ```
//! The server must persist this keypair for the registration and login steps, where the public component will be
//! used by the client during both registration and login, and the private component will be used by the server during login.
//!
//! ## Registration
//! The registration protocol between the client and server consists of four steps along with three messages:
//! [RegistrationRequest], [RegistrationResponse], and [RegistrationUpload]. A successful execution of the registration protocol results in the
//! server producing a password file corresponding to the password provided by
//! the client. This password file is typically stored server-side, and retrieved upon future login attempts made by the client.
//!
//! ### Client Registration Start
//! In the first step of registration, the client chooses as input a registration password. The client runs [ClientRegistration::start]
//! to produce a [ClientRegistrationStartResult], which consists of a [RegistrationRequest] to be sent to the server and
//! a [ClientRegistration] which must be persisted on the client for the final step of client registration.
//! ```
//! # use opaque_ke::{
//! #   errors::ProtocolError,
//! #   ServerRegistration,
//! #   slow_hash::NoOpHash,
//! # };
//! # use opaque_ke::ciphersuite::CipherSuite;
//! # struct Default;
//! # impl CipherSuite for Default {
//! #     type Group = curve25519_dalek::ristretto::RistrettoPoint;
//! #     type KeyExchange = opaque_ke::key_exchange::tripledh::TripleDH;
//! #     type Hash = sha2::Sha512;
//! #     type SlowHash = opaque_ke::slow_hash::NoOpHash;
//! # }
//! use opaque_ke::ClientRegistration;
//! use rand::{rngs::OsRng, RngCore};
//! let mut client_rng = OsRng;
//! let client_registration_start_result = ClientRegistration::<Default>::start(
//!     &mut client_rng,
//!     b"password",
//! )?;
//! # Ok::<(), ProtocolError>(())
//! ```
//!
//! ### Server Registration Start
//! In the second step of registration, the server takes as input the instance of [RegistrationRequest] from the client, and
//! the server's public key `server_kp.public()`.
//! The server runs [ServerRegistration::start] to produce an a [ServerRegistrationStartResult], which consists of
//! a [RegistrationResponse] to be returned to the client and
//! a [ServerRegistration] which must be persisted on the server for the final step of server registration.
//! ```
//! # use opaque_ke::{
//! #   errors::ProtocolError,
//! #   ClientRegistration,
//! #   slow_hash::NoOpHash,
//! # };
//! # use opaque_ke::ciphersuite::CipherSuite;
//! # struct Default;
//! # impl CipherSuite for Default {
//! #     type Group = curve25519_dalek::ristretto::RistrettoPoint;
//! #     type KeyExchange = opaque_ke::key_exchange::tripledh::TripleDH;
//! #     type Hash = sha2::Sha512;
//! #     type SlowHash = opaque_ke::slow_hash::NoOpHash;
//! # }
//! # use rand::{rngs::OsRng, RngCore};
//! # let mut client_rng = OsRng;
//! # let client_registration_start_result = ClientRegistration::<Default>::start(
//! #     &mut client_rng,
//! #     b"password",
//! # )?;
//! use opaque_ke::ServerRegistration;
//! let mut server_rng = OsRng;
//! let server_kp = Default::generate_random_keypair(&mut server_rng);
//! let server_registration_start_result = ServerRegistration::<Default>::start(
//!     &mut server_rng,
//!     client_registration_start_result.message,
//!     server_kp.public(),
//! )?;
//! # Ok::<(), ProtocolError>(())
//! ```
//!
//! ### Client Registration Finish
//! In the third step of registration, the client takes as input
//! a [RegistrationResponse] from the server, and
//! a [ClientRegistration] from the first step of registration.
//! The client runs [ClientRegistration::finish] to produce a [ClientRegistrationFinishResult], which consists of a [RegistrationUpload]
//! to be sent to the server and an `export_key` field which can be used optionally as described in the [Export Key](#export-key) section.
//! ```
//! # use opaque_ke::{
//! #   errors::ProtocolError,
//! #   ClientRegistration, ClientRegistrationFinishParameters, ServerRegistration,
//! #   slow_hash::NoOpHash,
//! # };
//! # use opaque_ke::ciphersuite::CipherSuite;
//! # struct Default;
//! # impl CipherSuite for Default {
//! #     type Group = curve25519_dalek::ristretto::RistrettoPoint;
//! #     type KeyExchange = opaque_ke::key_exchange::tripledh::TripleDH;
//! #     type Hash = sha2::Sha512;
//! #     type SlowHash = opaque_ke::slow_hash::NoOpHash;
//! # }
//! # use rand::{rngs::OsRng, RngCore};
//! # let mut client_rng = OsRng;
//! # let client_registration_start_result = ClientRegistration::<Default>::start(
//! #     &mut client_rng,
//! #     b"password",
//! # )?;
//! # let mut server_rng = OsRng;
//! # let server_kp = Default::generate_random_keypair(&mut server_rng);
//! # let server_registration_start_result = ServerRegistration::<Default>::start(&mut server_rng, client_registration_start_result.message, server_kp.public())?;
//! let client_registration_finish_result = client_registration_start_result.state.finish(
//!     &mut client_rng,
//!     server_registration_start_result.message,
//!     ClientRegistrationFinishParameters::default(),
//! )?;
//! # Ok::<(), ProtocolError>(())
//! ```
//!
//! ### Server Registration Finish
//! In the fourth step of registration, the server takes as input
//! a [RegistrationUpload] from the client, and
//! a [ServerRegistration] from the second step.
//! The server runs [ServerRegistration::finish] to produce a finalized [ServerRegistration].
//! At this point, the client can be considered as successfully registered, and the server can invoke
//! [ServerRegistration::serialize] to store the password file for use during the login protocol.
//! ```
//! # use opaque_ke::{
//! #   errors::ProtocolError,
//! #   ClientRegistration, ClientRegistrationFinishParameters, ServerRegistration,
//! #   slow_hash::NoOpHash,
//! # };
//! # use opaque_ke::ciphersuite::CipherSuite;
//! # struct Default;
//! # impl CipherSuite for Default {
//! #     type Group = curve25519_dalek::ristretto::RistrettoPoint;
//! #     type KeyExchange = opaque_ke::key_exchange::tripledh::TripleDH;
//! #     type Hash = sha2::Sha512;
//! #     type SlowHash = opaque_ke::slow_hash::NoOpHash;
//! # }
//! # use rand::{rngs::OsRng, RngCore};
//! # let mut client_rng = OsRng;
//! # let client_registration_start_result = ClientRegistration::<Default>::start(
//! #     &mut client_rng,
//! #     b"password",
//! # )?;
//! # let mut server_rng = OsRng;
//! # let server_kp = Default::generate_random_keypair(&mut server_rng);
//! # let server_registration_start_result = ServerRegistration::<Default>::start(&mut server_rng, client_registration_start_result.message, server_kp.public())?;
//! # let client_registration_finish_result = client_registration_start_result.state.finish(&mut client_rng, server_registration_start_result.message, ClientRegistrationFinishParameters::default())?;
//! let password_file = server_registration_start_result.state.finish(
//!     client_registration_finish_result.message,
//! )?;
//! # Ok::<(), ProtocolError>(())
//! ```
//!
//! ## Login
//! The login protocol between a client and server also consists of four steps along with three messages:
//! [CredentialRequest], [CredentialResponse], [CredentialFinalization]. The server is expected to have access to the password file
//! corresponding to an output of the registration phase. The login protocol will execute successfully only if the same password
//! was used in the registration phase that produced the password file that the server is testing against.
//!
//! ### Client Login Start
//! In the first step of login, the client chooses as input a login password.
//! The client runs [ClientLogin::start] to produce an output consisting of
//! a [CredentialRequest] to be sent to the server, and
//! a [ClientLogin] which must be persisted on the client for the final step of client login.
//! ```
//! # use opaque_ke::{
//! #   errors::ProtocolError,
//! #   ClientRegistration, ServerRegistration, ServerLogin, CredentialFinalization,
//! #   slow_hash::NoOpHash,
//! # };
//! # use opaque_ke::ciphersuite::CipherSuite;
//! # struct Default;
//! # impl CipherSuite for Default {
//! #     type Group = curve25519_dalek::ristretto::RistrettoPoint;
//! #     type KeyExchange = opaque_ke::key_exchange::tripledh::TripleDH;
//! #     type Hash = sha2::Sha512;
//! #     type SlowHash = opaque_ke::slow_hash::NoOpHash;
//! # }
//! # use rand::{rngs::OsRng, RngCore};
//! use opaque_ke::{ClientLogin, ClientLoginStartParameters};
//! let mut client_rng = OsRng;
//! let client_login_start_result = ClientLogin::<Default>::start(
//!   &mut client_rng,
//!   b"password",
//!   ClientLoginStartParameters::default(),
//! )?;
//! # Ok::<(), ProtocolError>(())
//! ```
//!
//! ### Server Login Start
//! In the second step of login, the server takes as input
//! a [CredentialRequest] from the client,
//! the server's private key `server_kp.private()`, and
//! the password file output from registration.
//! The server runs [ServerLogin::start] to produce an output consisting of
//! a [CredentialResponse] which is returned to the client, and
//! a [ServerLogin] which must be persisted on the server for the final step of login.
//! ```
//! # use opaque_ke::{
//! #   errors::ProtocolError,
//! #   ClientRegistration, ClientRegistrationFinishParameters, ServerRegistration, ClientLogin, ClientLoginStartParameters, CredentialFinalization,
//! #   slow_hash::NoOpHash,
//! # };
//! # use opaque_ke::ciphersuite::CipherSuite;
//! # struct Default;
//! # impl CipherSuite for Default {
//! #     type Group = curve25519_dalek::ristretto::RistrettoPoint;
//! #     type KeyExchange = opaque_ke::key_exchange::tripledh::TripleDH;
//! #     type Hash = sha2::Sha512;
//! #     type SlowHash = opaque_ke::slow_hash::NoOpHash;
//! # }
//! # use rand::{rngs::OsRng, RngCore};
//! # let mut client_rng = OsRng;
//! # let client_registration_start_result = ClientRegistration::<Default>::start(
//! #     &mut client_rng,
//! #     b"password",
//! # )?;
//! # let mut server_rng = OsRng;
//! # let server_kp = Default::generate_random_keypair(&mut server_rng);
//! # let server_registration_start_result = ServerRegistration::<Default>::start(&mut server_rng, client_registration_start_result.message, server_kp.public())?;
//! # let client_registration_finish_result = client_registration_start_result.state.finish(&mut client_rng, server_registration_start_result.message, ClientRegistrationFinishParameters::default())?;
//! # let password_file_bytes = server_registration_start_result.state.finish(client_registration_finish_result.message)?.serialize();
//! # let client_login_start_result = ClientLogin::<Default>::start(
//! #   &mut client_rng,
//! #   b"password",
//! #   ClientLoginStartParameters::default(),
//! # )?;
//! use opaque_ke::{ServerLogin, ServerLoginStartParameters};
//! let password_file = ServerRegistration::<Default>::deserialize(&password_file_bytes[..])?;
//! let mut server_rng = OsRng;
//! let server_login_start_result = ServerLogin::start(
//!     &mut server_rng,
//!     password_file,
//!     &server_kp.private(),
//!     client_login_start_result.message,
//!     ServerLoginStartParameters::default(),
//! )?;
//! # Ok::<(), ProtocolError>(())
//! ```
//!
//! ### Client Login Finish
//! In the third step of login, the client takes as input a [CredentialResponse] from the server.
//! The client runs [ClientLogin::finish] and produces an output consisting of
//! a [CredentialFinalization] to be sent to the server to complete the protocol,
//! the `session_key` sequence of bytes which will match the server's session key upon a successful login.
//! ```
//! # use opaque_ke::{
//! #   errors::ProtocolError,
//! #   ClientRegistration, ClientRegistrationFinishParameters, ServerRegistration, ClientLogin, ClientLoginStartParameters, ClientLoginFinishParameters, ServerLogin, ServerLoginStartParameters, CredentialFinalization,
//! #   slow_hash::NoOpHash,
//! # };
//! # use opaque_ke::ciphersuite::CipherSuite;
//! # struct Default;
//! # impl CipherSuite for Default {
//! #     type Group = curve25519_dalek::ristretto::RistrettoPoint;
//! #     type KeyExchange = opaque_ke::key_exchange::tripledh::TripleDH;
//! #     type Hash = sha2::Sha512;
//! #     type SlowHash = opaque_ke::slow_hash::NoOpHash;
//! # }
//! # use rand::{rngs::OsRng, RngCore};
//! # let mut client_rng = OsRng;
//! # let client_registration_start_result = ClientRegistration::<Default>::start(
//! #     &mut client_rng,
//! #     b"password",
//! # )?;
//! # let mut server_rng = OsRng;
//! # let server_kp = Default::generate_random_keypair(&mut server_rng);
//! # let server_registration_start_result = ServerRegistration::<Default>::start(&mut server_rng, client_registration_start_result.message, server_kp.public())?;
//! # let client_registration_finish_result = client_registration_start_result.state.finish(&mut client_rng, server_registration_start_result.message, ClientRegistrationFinishParameters::default())?;
//! # let password_file_bytes = server_registration_start_result.state.finish(client_registration_finish_result.message)?.serialize();
//! # let client_login_start_result = ClientLogin::<Default>::start(
//! #     &mut client_rng,
//! #     b"password",
//! #     ClientLoginStartParameters::default(),
//! # )?;
//! # let password_file =
//! #   ServerRegistration::<Default>::deserialize(
//! #     &password_file_bytes[..],
//! #   )?;
//! # let server_login_start_result =
//! #     ServerLogin::start(&mut server_rng, password_file, &server_kp.private(), client_login_start_result.message, ServerLoginStartParameters::default())?;
//! let client_login_finish_result = client_login_start_result.state.finish(
//!     server_login_start_result.message,
//!     ClientLoginFinishParameters::default(),
//! )?;
//! # Ok::<(), ProtocolError>(())
//! ```
//!
//! ### Server Login Finish
//! In the fourth step of login, the server takes as input a [CredentialFinalization] from the client and runs [ServerLogin::finish] to
//! produce an output consisting of the `session_key` sequence of bytes which will match the client's session key upon a successful login.
//! ```
//! # use opaque_ke::{
//! #   errors::ProtocolError,
//! #   ClientRegistration, ClientRegistrationFinishParameters, ServerRegistration, ClientLogin, ClientLoginStartParameters, ClientLoginFinishParameters, ServerLogin, ServerLoginStartParameters, CredentialFinalization,
//! #   slow_hash::NoOpHash,
//! # };
//! # use opaque_ke::ciphersuite::CipherSuite;
//! # struct Default;
//! # impl CipherSuite for Default {
//! #     type Group = curve25519_dalek::ristretto::RistrettoPoint;
//! #     type KeyExchange = opaque_ke::key_exchange::tripledh::TripleDH;
//! #     type Hash = sha2::Sha512;
//! #     type SlowHash = opaque_ke::slow_hash::NoOpHash;
//! # }
//! # use rand::{rngs::OsRng, RngCore};
//! # let mut client_rng = OsRng;
//! # let client_registration_start_result = ClientRegistration::<Default>::start(
//! #     &mut client_rng,
//! #     b"password",
//! # )?;
//! # let mut server_rng = OsRng;
//! # let server_kp = Default::generate_random_keypair(&mut server_rng);
//! # let server_registration_start_result = ServerRegistration::<Default>::start(&mut server_rng, client_registration_start_result.message, server_kp.public())?;
//! # let client_registration_finish_result = client_registration_start_result.state.finish(&mut client_rng, server_registration_start_result.message, ClientRegistrationFinishParameters::default())?;
//! # let password_file_bytes = server_registration_start_result.state.finish(client_registration_finish_result.message)?.serialize();
//! # let client_login_start_result = ClientLogin::<Default>::start(
//! #   &mut client_rng,
//! #   b"password",
//! #   ClientLoginStartParameters::default(),
//! # )?;
//! # let password_file =
//! #   ServerRegistration::<Default>::deserialize(
//! #     &password_file_bytes[..],
//! #   )?;
//! # let server_login_start_result =
//! #     ServerLogin::start(&mut server_rng, password_file, &server_kp.private(), client_login_start_result.message, ServerLoginStartParameters::default())?;
//! # let client_login_finish_result = client_login_start_result.state.finish(
//! #   server_login_start_result.message,
//! #   ClientLoginFinishParameters::default(),
//! # )?;
//! let server_login_finish_result = server_login_start_result.state.finish(
//!     client_login_finish_result.message,
//! )?;
//!
//! assert_eq!(
//!    client_login_finish_result.session_key,
//!    server_login_finish_result.session_key,
//! );
//! # Ok::<(), ProtocolError>(())
//! ```
//! If the protocol completes successfully, then the server obtains a `server_login_finish_result.session_key` which is guaranteed to
//! match `client_login_finish_result.session_key` (see the [Session Key](#session-key) section).
//! Otherwise, on failure, the [ServerLogin::finish] algorithm outputs the error [InvalidLoginError](errors::PakeError::InvalidLoginError).
//!
//! # Advanced Usage
//!
//! This implementation offers support for several optional features of OPAQUE, described below. They are not critical to the
//! execution of the main protocol, but can provide additional security benefits which can be suitable for various applications that rely on
//! OPAQUE for authentication.
//!
//! ## Session Key
//!
//! Upon a successful completion of the OPAQUE protocol (the client runs login with the same password used during registration),
//! the client and server have access to a session key, which is a pseudorandomly distributed 32-byte string which only the client
//! and server know. Multiple login runs using the same password for the same client will produce different session keys, distributed
//! as uniformly random strings. Thus, the session key can be used to establish a secure channel between the client and server.
//!
//! The session key can be accessed from the `session_key` field of [ClientLoginFinishResult] and [ServerLoginFinishResult]. See
//! the combination of [Client Login Finish](#client-login-finish) and [Server Login Finish](#server-login-finish) for example usage.
//!
//! ## Checking Server Consistency
//!
//! A [ClientLoginFinishResult] contains the `server_s_pk` field, which is represents the static public key of the server that is established
//! during the setup phase. This can be used by the client to verify the authenticity of the server it engages with during the login phase. In particular,
//! the client can check that the static public key of the server supplied during registration matches this field during login.
//! ```
//! # use opaque_ke::{
//! #   errors::ProtocolError,
//! #   ClientRegistration, ClientRegistrationFinishParameters, ServerRegistration, ClientLogin, ClientLoginStartParameters, ClientLoginFinishParameters, ServerLogin, ServerLoginStartParameters, CredentialFinalization,
//! #   slow_hash::NoOpHash,
//! # };
//! # use opaque_ke::ciphersuite::CipherSuite;
//! # struct Default;
//! # impl CipherSuite for Default {
//! #     type Group = curve25519_dalek::ristretto::RistrettoPoint;
//! #     type KeyExchange = opaque_ke::key_exchange::tripledh::TripleDH;
//! #     type Hash = sha2::Sha512;
//! #     type SlowHash = opaque_ke::slow_hash::NoOpHash;
//! # }
//! # use rand::{rngs::OsRng, RngCore};
//! # let mut client_rng = OsRng;
//! # let client_registration_start_result = ClientRegistration::<Default>::start(
//! #     &mut client_rng,
//! #     b"password",
//! # )?;
//! # let mut server_rng = OsRng;
//! // During setup, server generates its static keypair
//! let server_kp = Default::generate_random_keypair(&mut server_rng);
//! # let server_registration_start_result = ServerRegistration::<Default>::start(&mut server_rng, client_registration_start_result.message, server_kp.public())?;
//!
//! // During setup or registration, the server transmits its static public key to the client
//! let server_s_pk = server_kp.public(); // obtained from the server
//! # let client_registration_finish_result = client_registration_start_result.state.finish(&mut client_rng, server_registration_start_result.message, ClientRegistrationFinishParameters::default())?;
//! # let password_file_bytes = server_registration_start_result.state.finish(client_registration_finish_result.message)?.serialize();
//! # let client_login_start_result = ClientLogin::<Default>::start(
//! #     &mut client_rng,
//! #     b"password",
//! #     ClientLoginStartParameters::default(),
//! # )?;
//! # let password_file =
//! #   ServerRegistration::<Default>::deserialize(
//! #     &password_file_bytes[..],
//! #   )?;
//! # let server_login_start_result =
//! #     ServerLogin::start(&mut server_rng, password_file, &server_kp.private(), client_login_start_result.message, ServerLoginStartParameters::default())?;
//!
//! // And then later, during login...
//! let client_login_finish_result = client_login_start_result.state.finish(
//!     server_login_start_result.message,
//!     ClientLoginFinishParameters::default(),
//! )?;
//!
//! // Check that the server's static public key matches what was obtained during
//! // setup or registration
//! assert_eq!(
//!     &client_login_finish_result.server_s_pk,
//!     server_s_pk,
//! );
//! # Ok::<(), ProtocolError>(())
//! ```
//!
//! Note that without this check over the consistency of the server's static public key, a malicious actor could impersonate the registration server if it were able to copy the password
//! file output during registration! Therefore, it is recommended to perform the following check in the application layer if the client can obtain a copy of the server's static
//! public key beforehand.
//!
//!
//! ## Export Key
//!
//! The export key is a pseudorandomly distributed 32-byte string output by both the
//! [Client Registration Finish](#client-registration-finish) and [Client Login Finish](#client-login-finish) steps.
//! The same export key string will be output by both functions only if the exact same password is passed to [ClientRegistration::start] and [ClientLogin::start].
//!
//! The export key retains as much secrecy as the password itself, and is similarly derived through an evaluation of the slow hashing function. Hence, only the parties which
//! know the password the client uses during registration and login can recover this secret, as it is never exposed to the server. As a result, the export key
//! can be used (separately from the OPAQUE protocol) to provide confidentiality and integrity to other data which only the client should be able to process.
//! For instance, if the server is expected to maintain any client-side secrets which require a password to access, then this export key can be used to encrypt
//! these secrets so that they remain hidden from the server (see [examples/digital_locker.rs](https://github.com/novifinancial/opaque-ke/blob/master/examples/digital_locker.rs)
//! for a working example).
//!
//! You can access the export key from the `export_key` field of [ClientRegistrationFinishResult] and [ClientLoginFinishResult].
//!
//! ```
//! # use opaque_ke::{
//! #   errors::ProtocolError,
//! #   ClientRegistration, ClientRegistrationFinishParameters, ServerRegistration, ClientLogin, ClientLoginStartParameters, ClientLoginFinishParameters, ServerLogin, ServerLoginStartParameters, CredentialFinalization,
//! #   slow_hash::NoOpHash,
//! # };
//! # use opaque_ke::ciphersuite::CipherSuite;
//! # struct Default;
//! # impl CipherSuite for Default {
//! #     type Group = curve25519_dalek::ristretto::RistrettoPoint;
//! #     type KeyExchange = opaque_ke::key_exchange::tripledh::TripleDH;
//! #     type Hash = sha2::Sha512;
//! #     type SlowHash = opaque_ke::slow_hash::NoOpHash;
//! # }
//! # use rand::{rngs::OsRng, RngCore};
//! # let mut client_rng = OsRng;
//! # let client_registration_start_result = ClientRegistration::<Default>::start(
//! #     &mut client_rng,
//! #     b"password",
//! # )?;
//! # let mut server_rng = OsRng;
//! # let server_kp = Default::generate_random_keypair(&mut server_rng);
//! # let server_registration_start_result = ServerRegistration::<Default>::start(&mut server_rng, client_registration_start_result.message, server_kp.public())?;
//! // During registration...
//! let client_registration_finish_result = client_registration_start_result.state.finish(
//!     &mut client_rng,
//!     server_registration_start_result.message,
//!     ClientRegistrationFinishParameters::default()
//! )?;
//! # let password_file_bytes = server_registration_start_result.state.finish(client_registration_finish_result.message)?.serialize();
//! # let client_login_start_result = ClientLogin::<Default>::start(
//! #     &mut client_rng,
//! #     b"password",
//! #     ClientLoginStartParameters::default(),
//! # )?;
//! # let password_file =
//! #   ServerRegistration::<Default>::deserialize(
//! #     &password_file_bytes[..],
//! #   )?;
//! # let server_login_start_result =
//! #     ServerLogin::start(&mut server_rng, password_file, &server_kp.private(), client_login_start_result.message, ServerLoginStartParameters::default())?;
//!
//! // And then later, during login...
//! let client_login_finish_result = client_login_start_result.state.finish(
//!     server_login_start_result.message,
//!     ClientLoginFinishParameters::default(),
//! )?;
//!
//! assert_eq!(
//!     client_registration_finish_result.export_key,
//!     client_login_finish_result.export_key,
//! );
//! # Ok::<(), ProtocolError>(())
//! ```
//!
//! ## Custom Identifiers
//!
//! Typically when applications use OPAQUE to authenticate a client to a server, the client has a registered "username" which is sent to the server to
//! identify the corresponding password file established during registration. The server may also have an identifier corresponding to an entity (e.g. facebook.com).
//! By default, neither of these public identifiers need to be supplied to the OPAQUE protocol.
//!
//! But, for applications that wish to cryptographically bind these identities to
//! the registered password file as well as the session key output by the login phase, these custom identifiers can be specified through
//! [ClientRegistrationFinishParameters::WithIdentifiers] in [Client Registration Finish](#client-registration-finish):
//! ```
//! # use opaque_ke::{
//! #   errors::ProtocolError,
//! #   ClientRegistration, ClientRegistrationFinishParameters, ServerRegistration,
//! #   slow_hash::NoOpHash,
//! # };
//! # use opaque_ke::ciphersuite::CipherSuite;
//! # struct Default;
//! # impl CipherSuite for Default {
//! #     type Group = curve25519_dalek::ristretto::RistrettoPoint;
//! #     type KeyExchange = opaque_ke::key_exchange::tripledh::TripleDH;
//! #     type Hash = sha2::Sha512;
//! #     type SlowHash = opaque_ke::slow_hash::NoOpHash;
//! # }
//! # use rand::{rngs::OsRng, RngCore};
//! # let mut client_rng = OsRng;
//! # let client_registration_start_result = ClientRegistration::<Default>::start(
//! #     &mut client_rng,
//! #     b"password",
//! # )?;
//! # let mut server_rng = OsRng;
//! # let server_kp = Default::generate_random_keypair(&mut server_rng);
//! # let server_registration_start_result = ServerRegistration::<Default>::start(&mut server_rng, client_registration_start_result.message, server_kp.public())?;
//! let client_registration_finish_result = client_registration_start_result.state.finish(
//!     &mut client_rng,
//!     server_registration_start_result.message,
//!     ClientRegistrationFinishParameters::WithIdentifiers(
//!         b"username".to_vec(),
//!         b"facebook.com".to_vec(),
//!     ),
//! )?;
//! # Ok::<(), ProtocolError>(())
//! ```
//!
//! The same identifiers must also be supplied using [ServerLoginStartParameters::WithIdentifiers] in [Server Login Start](#server-login-start):
//! ```
//! # use opaque_ke::{
//! #   errors::ProtocolError,
//! #   ClientRegistration, ClientRegistrationFinishParameters, ServerRegistration, ClientLogin, ClientLoginStartParameters, CredentialFinalization,
//! #   slow_hash::NoOpHash,
//! # };
//! # use opaque_ke::ciphersuite::CipherSuite;
//! # struct Default;
//! # impl CipherSuite for Default {
//! #     type Group = curve25519_dalek::ristretto::RistrettoPoint;
//! #     type KeyExchange = opaque_ke::key_exchange::tripledh::TripleDH;
//! #     type Hash = sha2::Sha512;
//! #     type SlowHash = opaque_ke::slow_hash::NoOpHash;
//! # }
//! # use rand::{rngs::OsRng, RngCore};
//! # let mut client_rng = OsRng;
//! # let client_registration_start_result = ClientRegistration::<Default>::start(
//! #     &mut client_rng,
//! #     b"password",
//! # )?;
//! # let mut server_rng = OsRng;
//! # let server_kp = Default::generate_random_keypair(&mut server_rng);
//! # let server_registration_start_result = ServerRegistration::<Default>::start(&mut server_rng, client_registration_start_result.message, server_kp.public())?;
//! # let client_registration_finish_result = client_registration_start_result.state.finish(&mut client_rng, server_registration_start_result.message, ClientRegistrationFinishParameters::WithIdentifiers(b"username".to_vec(), b"facebook.com".to_vec()))?;
//! # let password_file_bytes = server_registration_start_result.state.finish(client_registration_finish_result.message)?.serialize();
//! # let client_login_start_result = ClientLogin::<Default>::start(
//! #   &mut client_rng,
//! #   b"password",
//! #   ClientLoginStartParameters::default(),
//! # )?;
//! # use opaque_ke::{ServerLogin, ServerLoginStartParameters};
//! # let password_file = ServerRegistration::<Default>::deserialize(&password_file_bytes[..])?;
//! # let mut server_rng = OsRng;
//! let server_login_start_result = ServerLogin::start(
//!     &mut server_rng,
//!     password_file,
//!     &server_kp.private(),
//!     client_login_start_result.message,
//!     ServerLoginStartParameters::WithIdentifiers(
//!         b"username".to_vec(),
//!         b"facebook.com".to_vec(),
//!     ),
//! )?;
//! # Ok::<(), ProtocolError>(())
//! ```
//!
//! as well as [ClientLoginFinishParameters::WithIdentifiers] in [Client Login Finish](#client-login-finish):
//! ```
//! # use opaque_ke::{
//! #   errors::ProtocolError,
//! #   ClientRegistration, ClientRegistrationFinishParameters, ServerRegistration, ClientLogin, ClientLoginStartParameters, ClientLoginFinishParameters, ServerLogin, ServerLoginStartParameters, CredentialFinalization,
//! #   slow_hash::NoOpHash,
//! # };
//! # use opaque_ke::ciphersuite::CipherSuite;
//! # struct Default;
//! # impl CipherSuite for Default {
//! #     type Group = curve25519_dalek::ristretto::RistrettoPoint;
//! #     type KeyExchange = opaque_ke::key_exchange::tripledh::TripleDH;
//! #     type Hash = sha2::Sha512;
//! #     type SlowHash = opaque_ke::slow_hash::NoOpHash;
//! # }
//! # use rand::{rngs::OsRng, RngCore};
//! # let mut client_rng = OsRng;
//! # let client_registration_start_result = ClientRegistration::<Default>::start(
//! #     &mut client_rng,
//! #     b"password",
//! # )?;
//! # let mut server_rng = OsRng;
//! # let server_kp = Default::generate_random_keypair(&mut server_rng);
//! # let server_registration_start_result = ServerRegistration::<Default>::start(&mut server_rng, client_registration_start_result.message, server_kp.public())?;
//! # let client_registration_finish_result = client_registration_start_result.state.finish(&mut client_rng, server_registration_start_result.message, ClientRegistrationFinishParameters::WithIdentifiers(b"username".to_vec(), b"facebook.com".to_vec()))?;
//! # let password_file_bytes = server_registration_start_result.state.finish(client_registration_finish_result.message)?.serialize();
//! # let client_login_start_result = ClientLogin::<Default>::start(
//! #     &mut client_rng,
//! #     b"password",
//! #     ClientLoginStartParameters::default(),
//! # )?;
//! # let password_file =
//! #   ServerRegistration::<Default>::deserialize(
//! #     &password_file_bytes[..],
//! #   )?;
//! # let server_login_start_result =
//! #     ServerLogin::start(&mut server_rng, password_file, &server_kp.private(), client_login_start_result.message, ServerLoginStartParameters::WithIdentifiers(b"username".to_vec(), b"facebook.com".to_vec()))?;
//! let client_login_finish_result = client_login_start_result.state.finish(
//!     server_login_start_result.message,
//!     ClientLoginFinishParameters::WithIdentifiers(
//!         b"username".to_vec(),
//!         b"facebook.com".to_vec(),
//!     ),
//! )?;
//! # Ok::<(), ProtocolError>(())
//! ```
//! Failing to supply the same pair of custom identifiers in any of the three steps above will result in an error in attempting to complete
//! the protocol!
//!
//! ## Key Exchange Additional Data
//!
//! A key exchange protocol typically supports the passing of data between the two parties before the exchange is complete, so as to bind the integrity
//! and/or confidentiality of application-specific data to the security of the key exchange. During the login phase, the client and server can pass
//! additional data alongside the first two messages of the protocol, with confidential data being supported for the second message.
//!
//! The following three messages support passing of additional data:
//! - The first login message, where the client can populate [ClientLoginStartParameters::WithInfo] with plaintext additional data, and
//! the server can retrieve using the `plain_info` field of [ServerLoginStartResult].
//! - The second login message, where the server can populate [ServerLoginStartParameters::WithInfo] with confidential additional data,
//! and the client can retrieve using the `confidential_info` field of [ClientLoginFinishResult].
//!
//! For the second login message, the `WithInfoAndIdentifiers` variant can be used to specify these fields in addition to
//! [custom identifiers](#custom-identifiers), with the ordering of the fields as `WithInfoAndIdentifiers(confidential_info, username, server_name)`.
//!
//!

#![cfg_attr(not(feature = "bench"), deny(missing_docs))]
#![deny(unsafe_code)]

#[cfg(not(any(feature = "u64_backend", feature = "u32_backend",)))]
compile_error!(
    "no dalek arithmetic backend cargo feature enabled! \
     please enable one of: u64_backend, u32_backend"
);

// Error types
pub mod errors;

// High-level API
mod opaque;

mod messages;

pub mod ciphersuite;
mod envelope;
pub mod hash;

pub mod group;

pub mod map_to_curve;

pub mod key_exchange;
pub mod keypair;

#[cfg(feature = "bench")]
pub mod oprf;
#[cfg(not(feature = "bench"))]
mod oprf;

pub mod slow_hash;

mod serialization;

#[cfg(test)]
mod tests;

// Exports

pub use rand;

pub use crate::messages::{
    CredentialFinalization, CredentialRequest, CredentialResponse, RegistrationRequest,
    RegistrationResponse, RegistrationUpload,
};
pub use crate::opaque::{ClientLogin, ClientRegistration, ServerLogin, ServerRegistration};
pub use crate::opaque::{
    ClientLoginFinishParameters, ClientLoginStartParameters, ClientRegistrationFinishParameters,
    ServerLoginStartParameters,
};
pub use crate::opaque::{
    ClientLoginFinishResult, ClientLoginStartResult, ClientRegistrationFinishResult,
    ClientRegistrationStartResult, ServerLoginFinishResult, ServerLoginStartResult,
    ServerRegistrationStartResult,
};