vodozemac/olm/messages/pre_key.rs
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// Copyright 2021 Damir Jelić
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
use std::fmt::Debug;
use prost::Message as ProstMessage;
use serde::{Deserialize, Serialize};
use super::Message;
use crate::{
olm::SessionKeys,
utilities::{base64_decode, base64_encode},
Curve25519PublicKey, DecodeError,
};
/// An encrypted Olm pre-key message.
///
/// Contains metadata that is required to establish a [`Session`] and a normal
/// Olm [`Message`].
///
/// [`Session`]: crate::olm::Session
#[derive(Clone, Debug, PartialEq, Eq)]
pub struct PreKeyMessage {
pub(crate) session_keys: SessionKeys,
pub(crate) message: Message,
}
impl PreKeyMessage {
const VERSION: u8 = 3;
/// The single-use key that was uploaded to a public key directory by the
/// receiver of the message. Should be used to establish a [`Session`].
///
/// [`Session`]: crate::olm::Session
pub const fn one_time_key(&self) -> Curve25519PublicKey {
self.session_keys.one_time_key
}
/// The base key, a single use key that was created just in time by the
/// sender of the message. Should be used to establish a [`Session`].
///
/// [`Session`]: crate::olm::Session
pub const fn base_key(&self) -> Curve25519PublicKey {
self.session_keys.base_key
}
/// The long term identity key of the sender of the message. Should be used
/// to establish a [`Session`]
///
/// [`Session`]: crate::olm::Session
pub const fn identity_key(&self) -> Curve25519PublicKey {
self.session_keys.identity_key
}
/// The collection of all keys required for establishing an Olm [`Session`]
/// from this pre-key message.
///
/// Other methods on this struct (like [`PreKeyMessage::identity_key()`])
/// can be used to retrieve individual keys from this collection.
///
/// [`Session`]: crate::olm::Session
pub const fn session_keys(&self) -> SessionKeys {
self.session_keys
}
/// Returns the globally unique session ID, in base64-encoded form.
///
/// This is a shorthand helper of the [`SessionKeys::session_id()`] method.
pub fn session_id(&self) -> String {
self.session_keys.session_id()
}
/// The actual message that contains the ciphertext.
pub const fn message(&self) -> &Message {
&self.message
}
/// Try to decode the given byte slice as a Olm [`Message`].
///
/// The expected format of the byte array is described in the
/// [`PreKeyMessage::to_bytes()`] method.
pub fn from_bytes(message: &[u8]) -> Result<Self, DecodeError> {
Self::try_from(message)
}
/// Encode the `PreKeyMessage` as an array of bytes.
///
/// Olm `PreKeyMessage`s consist of a one-byte version, followed by a
/// variable length payload.
///
/// ```text
/// +--------------+------------------------------------+
/// | Version Byte | Payload Bytes |
/// +--------------+------------------------------------+
/// ```
///
/// The payload uses a format based on the Protocol Buffers encoding. It
/// consists of the following key-value pairs:
///
/// **Name** |**Tag**|**Type**| **Meaning**
/// :----------:|:-----:|:------:|:----------------------------------------:
/// One-Time-Key| 0x0A | String |The public part of Bob's single-use key
/// Base-Key | 0x12 | String |The public part of Alice's single-use key
/// Identity-Key| 0x1A | String |The public part of Alice's identity key
/// Message | 0x22 | String |An embedded Olm message
///
/// The last key/value pair in a [`PreKeyMessage`] is a normal Olm
/// [`Message`].
pub fn to_bytes(&self) -> Vec<u8> {
let message = ProtoBufPreKeyMessage {
one_time_key: self.session_keys.one_time_key.as_bytes().to_vec(),
base_key: self.session_keys.base_key.as_bytes().to_vec(),
identity_key: self.session_keys.identity_key.as_bytes().to_vec(),
message: self.message.to_bytes(),
};
let mut output: Vec<u8> = vec![0u8; message.encoded_len() + 1];
output[0] = Self::VERSION;
message
.encode(&mut output[1..].as_mut())
.expect("Couldn't encode our message into a protobuf");
output
}
/// Try to decode the given string as a Olm [`PreKeyMessage`].
///
/// The string needs to be a base64 encoded byte array that follows the
/// format described in the [`PreKeyMessage::to_bytes()`] method.
pub fn from_base64(message: &str) -> Result<Self, DecodeError> {
Self::try_from(message)
}
/// Encode the [`PreKeyMessage`] as a string.
///
/// This method first calls [`PreKeyMessage::to_bytes()`] and then encodes
/// the resulting byte array as a string using base64 encoding.
pub fn to_base64(&self) -> String {
base64_encode(self.to_bytes())
}
/// Create a new pre-key message from the session keys and standard message.
#[cfg(feature = "low-level-api")]
pub const fn wrap(session_keys: SessionKeys, message: Message) -> Self {
PreKeyMessage::new(session_keys, message)
}
pub(crate) const fn new(session_keys: SessionKeys, message: Message) -> Self {
Self { session_keys, message }
}
}
impl Serialize for PreKeyMessage {
fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
where
S: serde::Serializer,
{
let message = self.to_base64();
serializer.serialize_str(&message)
}
}
impl<'de> Deserialize<'de> for PreKeyMessage {
fn deserialize<D: serde::Deserializer<'de>>(d: D) -> Result<Self, D::Error> {
let ciphertext = String::deserialize(d)?;
PreKeyMessage::from_base64(&ciphertext).map_err(serde::de::Error::custom)
}
}
impl TryFrom<&str> for PreKeyMessage {
type Error = DecodeError;
fn try_from(value: &str) -> Result<Self, Self::Error> {
let decoded = base64_decode(value)?;
Self::try_from(decoded)
}
}
impl TryFrom<Vec<u8>> for PreKeyMessage {
type Error = DecodeError;
fn try_from(value: Vec<u8>) -> Result<Self, Self::Error> {
Self::try_from(value.as_slice())
}
}
impl TryFrom<&[u8]> for PreKeyMessage {
type Error = DecodeError;
fn try_from(value: &[u8]) -> Result<Self, Self::Error> {
let version = *value.first().ok_or(DecodeError::MissingVersion)?;
if version != Self::VERSION {
Err(DecodeError::InvalidVersion(Self::VERSION, version))
} else {
let decoded = ProtoBufPreKeyMessage::decode(&value[1..value.len()])?;
let one_time_key = Curve25519PublicKey::from_slice(&decoded.one_time_key)?;
let base_key = Curve25519PublicKey::from_slice(&decoded.base_key)?;
let identity_key = Curve25519PublicKey::from_slice(&decoded.identity_key)?;
let message = decoded.message.try_into()?;
let session_keys = SessionKeys { one_time_key, identity_key, base_key };
Ok(Self { session_keys, message })
}
}
}
#[derive(Clone, ProstMessage)]
struct ProtoBufPreKeyMessage {
#[prost(bytes, tag = "1")]
one_time_key: Vec<u8>,
#[prost(bytes, tag = "2")]
base_key: Vec<u8>,
#[prost(bytes, tag = "3")]
identity_key: Vec<u8>,
#[prost(bytes, tag = "4")]
message: Vec<u8>,
}