1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163

// 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 serde::{Deserialize, Serialize};

use super::{
    chain_key::ChainKey,
    message_key::MessageKey,
    ratchet::{Ratchet, RatchetPublicKey, RemoteRatchetKey},
    receiver_chain::ReceiverChain,
    root_key::{RemoteRootKey, RootKey},
};
use crate::olm::{messages::Message, shared_secret::Shared3DHSecret};

#[derive(Serialize, Deserialize, Clone)]
#[serde(transparent)]
pub(super) struct DoubleRatchet {
    inner: DoubleRatchetState,
}

impl DoubleRatchet {
    pub fn next_message_key(&mut self) -> MessageKey {
        match &mut self.inner {
            DoubleRatchetState::Inactive(ratchet) => {
                let mut ratchet = ratchet.activate();

                let message_key = ratchet.next_message_key();
                self.inner = DoubleRatchetState::Active(ratchet);

                message_key
            }
            DoubleRatchetState::Active(ratchet) => ratchet.next_message_key(),
        }
    }

    pub fn encrypt(&mut self, plaintext: &str) -> Message {
        self.next_message_key().encrypt(plaintext.as_bytes())
    }

    pub fn active(shared_secret: Shared3DHSecret) -> Self {
        let (root_key, chain_key) = shared_secret.expand();

        let root_key = RootKey::new(root_key);
        let chain_key = ChainKey::new(chain_key);

        let ratchet = ActiveDoubleRatchet {
            active_ratchet: Ratchet::new(root_key),
            symmetric_key_ratchet: chain_key,
        };

        Self { inner: ratchet.into() }
    }

    #[cfg(feature = "libolm-compat")]
    pub fn from_ratchet_and_chain_key(ratchet: Ratchet, chain_key: ChainKey) -> Self {
        Self {
            inner: ActiveDoubleRatchet {
                active_ratchet: ratchet,
                symmetric_key_ratchet: chain_key,
            }
            .into(),
        }
    }

    pub fn inactive(root_key: RemoteRootKey, ratchet_key: RemoteRatchetKey) -> Self {
        let ratchet = InactiveDoubleRatchet { root_key, ratchet_key };

        Self { inner: ratchet.into() }
    }

    pub fn advance(&mut self, ratchet_key: RemoteRatchetKey) -> (DoubleRatchet, ReceiverChain) {
        let (ratchet, receiver_chain) = match &self.inner {
            DoubleRatchetState::Active(r) => r.advance(ratchet_key),
            DoubleRatchetState::Inactive(r) => {
                let ratchet = r.activate();
                // Advancing an inactive ratchet shouldn't be possible since the
                // other side did not yet receive our new ratchet key.
                //
                // This will likely end up in a decryption error but for
                // consistency sake and avoiding the leakage of our internal
                // state it's better to error out there.
                let ret = ratchet.advance(ratchet_key);

                self.inner = ratchet.into();

                ret
            }
        };

        (Self { inner: DoubleRatchetState::Inactive(ratchet) }, receiver_chain)
    }
}

#[derive(Serialize, Deserialize, Clone)]
#[serde(rename_all = "snake_case")]
#[serde(tag = "type")]
enum DoubleRatchetState {
    Inactive(InactiveDoubleRatchet),
    Active(ActiveDoubleRatchet),
}

impl From<InactiveDoubleRatchet> for DoubleRatchetState {
    fn from(r: InactiveDoubleRatchet) -> Self {
        Self::Inactive(r)
    }
}

impl From<ActiveDoubleRatchet> for DoubleRatchetState {
    fn from(r: ActiveDoubleRatchet) -> Self {
        Self::Active(r)
    }
}

#[derive(Serialize, Deserialize, Clone)]
struct InactiveDoubleRatchet {
    root_key: RemoteRootKey,
    ratchet_key: RemoteRatchetKey,
}

impl InactiveDoubleRatchet {
    fn activate(&self) -> ActiveDoubleRatchet {
        let (root_key, chain_key, ratchet_key) = self.root_key.advance(&self.ratchet_key);
        let active_ratchet = Ratchet::new_with_ratchet_key(root_key, ratchet_key);

        ActiveDoubleRatchet { active_ratchet, symmetric_key_ratchet: chain_key }
    }
}

#[derive(Serialize, Deserialize, Clone)]
struct ActiveDoubleRatchet {
    active_ratchet: Ratchet,
    symmetric_key_ratchet: ChainKey,
}

impl ActiveDoubleRatchet {
    fn advance(&self, ratchet_key: RemoteRatchetKey) -> (InactiveDoubleRatchet, ReceiverChain) {
        let (root_key, remote_chain) = self.active_ratchet.advance(ratchet_key);

        let ratchet = InactiveDoubleRatchet { root_key, ratchet_key };
        let receiver_chain = ReceiverChain::new(ratchet_key, remote_chain);

        (ratchet, receiver_chain)
    }

    fn ratchet_key(&self) -> RatchetPublicKey {
        RatchetPublicKey::from(self.active_ratchet.ratchet_key())
    }

    fn next_message_key(&mut self) -> MessageKey {
        self.symmetric_key_ratchet.create_message_key(self.ratchet_key())
    }
}