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

// Copyright 2021 The Matrix.org Foundation C.I.C.
//
// 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::sync::{Arc, Mutex};

use ruma::{
    api::client::backup::{EncryptedSessionDataInit, KeyBackupData, KeyBackupDataInit},
    serde::Base64,
};
use vodozemac::{pk_encryption::PkEncryption, Curve25519PublicKey};
use zeroize::Zeroizing;

use super::decryption::DecodeError;
use crate::{olm::InboundGroupSession, types::Signatures};

#[derive(Debug)]
struct InnerBackupKey {
    key: Curve25519PublicKey,
    signatures: Signatures,
    version: Mutex<Option<String>>,
}

/// The public part of a backup key.
#[derive(Clone)]
pub struct MegolmV1BackupKey {
    inner: Arc<InnerBackupKey>,
}

#[cfg(not(tarpaulin_include))]
impl std::fmt::Debug for MegolmV1BackupKey {
    fn fmt(&self, formatter: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        formatter
            .debug_struct("MegolmV1BackupKey")
            .field("key", &self.to_base64())
            .field("version", &self.backup_version())
            .finish()
    }
}

impl MegolmV1BackupKey {
    pub(super) fn new(key: Curve25519PublicKey, version: Option<String>) -> Self {
        Self {
            inner: InnerBackupKey {
                key,
                signatures: Default::default(),
                version: Mutex::new(version),
            }
            .into(),
        }
    }

    /// Get the full name of the backup algorithm this backup key supports.
    pub fn backup_algorithm(&self) -> &str {
        "m.megolm_backup.v1.curve25519-aes-sha2"
    }

    /// Get all the signatures of this `MegolmV1BackupKey`.
    pub fn signatures(&self) -> Signatures {
        self.inner.signatures.to_owned()
    }

    /// Try to create a new `MegolmV1BackupKey` from a base 64 encoded string.
    pub fn from_base64(public_key: &str) -> Result<Self, DecodeError> {
        let key = Curve25519PublicKey::from_base64(public_key)?;

        let inner =
            InnerBackupKey { key, signatures: Default::default(), version: Mutex::new(None) };

        Ok(MegolmV1BackupKey { inner: inner.into() })
    }

    /// Convert the [`MegolmV1BackupKey`] to a base 64 encoded string.
    pub fn to_base64(&self) -> String {
        self.inner.key.to_base64()
    }

    /// Get the backup version that this key is used with, if any.
    pub fn backup_version(&self) -> Option<String> {
        self.inner.version.lock().unwrap().clone()
    }

    /// Set the backup version that this `MegolmV1BackupKey` will be used with.
    ///
    /// The key won't be able to encrypt room keys unless a version has been
    /// set.
    pub fn set_version(&self, version: String) {
        *self.inner.version.lock().unwrap() = Some(version);
    }

    /// Export the given inbound group session, and encrypt the data, ready for
    /// writing to the backup.
    pub async fn encrypt(&self, session: InboundGroupSession) -> KeyBackupData {
        let pk = PkEncryption::from_key(self.inner.key);

        // The forwarding chains don't mean much, we only care whether we received the
        // session directly from the creator of the session or not.
        let forwarded_count = (session.has_been_imported() as u8).into();
        let first_message_index = session.first_known_index().into();

        // Convert our key to the backup representation.
        let key = session.to_backup().await;

        // The key gets zeroized in `BackedUpRoomKey` but we're creating a copy
        // here that won't, so let's wrap it up in a `Zeroizing` struct.
        let key =
            Zeroizing::new(serde_json::to_vec(&key).expect("Can't serialize exported room key"));

        let message = pk.encrypt(&key);

        let session_data = EncryptedSessionDataInit {
            ephemeral: Base64::new(message.ephemeral_key.to_vec()),
            ciphertext: Base64::new(message.ciphertext),
            mac: Base64::new(message.mac),
        }
        .into();

        KeyBackupDataInit {
            first_message_index,
            forwarded_count,
            // TODO: is this actually used anywhere? seems to be completely
            // useless and requires us to get the Device out of the store?
            // Also should this be checked at the time of the backup or at the
            // time of the room key receival?
            is_verified: false,
            session_data,
        }
        .into()
    }
}