matrix_sdk_crypto/types/
qr_login.rs

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
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
// Copyright 2024 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.

//! Data types for the QR code login mechanism described in [MSC4108]
//!
//! [MSC4108]: https://github.com/matrix-org/matrix-spec-proposals/pull/4108

use std::{
    io::{Cursor, Read},
    str::{self, Utf8Error},
};

use byteorder::{BigEndian, ReadBytesExt};
use thiserror::Error;
use url::Url;
use vodozemac::{base64_decode, base64_encode, Curve25519PublicKey};

/// The version of the QR code data, currently only one version is specified.
const VERSION: u8 = 0x02;
/// The prefix that is used in the QR code data.
const PREFIX: &[u8] = b"MATRIX";

/// Error type for the decoding of the [`QrCodeData`].
#[derive(Debug, Error)]
#[cfg_attr(feature = "uniffi", derive(uniffi::Error), uniffi(flat_error))]
pub enum LoginQrCodeDecodeError {
    /// The QR code data is no long enough, it's missing some fields.
    #[error("The QR code data is missing some fields.")]
    NotEnoughData(#[from] std::io::Error),
    /// One of the URLs in the QR code data is not a valid UTF-8 encoded string.
    #[error("One of the URLs in the QR code data is not a valid UTF-8 string")]
    NotUtf8(#[from] Utf8Error),
    /// One of the URLs in the QR code data could not be parsed.
    #[error("One of the URLs in the QR code data could not be parsed: {0:?}")]
    UrlParse(#[from] url::ParseError),
    /// The QR code data contains an invalid mode, we expect the login (0x03)
    /// mode or the reciprocate mode (0x04).
    #[error(
        "The QR code data contains an invalid QR code login mode, expected 0x03 or 0x04, got {0}"
    )]
    InvalidMode(u8),
    /// The QR code data contains an unsupported version.
    #[error("The QR code data contains an unsupported version, expected {VERSION}, got {0}")]
    InvalidVersion(u8),
    /// The base64 encoded variant of the QR code data is not a valid base64
    /// string.
    #[error("The QR code data could not have been decoded from a base64 string: {0:?}")]
    Base64(#[from] vodozemac::Base64DecodeError),
    /// The QR code data doesn't contain the expected `MATRIX` prefix.
    #[error("The QR code data has an unexpected prefix, expected: {expected:?}, got {got:?}")]
    InvalidPrefix {
        /// The expected prefix.
        expected: &'static [u8],
        /// The prefix we received.
        got: [u8; 6],
    },
}

/// The mode-specific data for the QR code.
///
/// The QR code login mechanism supports both, the new device, as well as the
/// existing device to display the QR code.
///
/// Depending on which device is displaying the QR code, additional data will be
/// attached to the QR code.
#[derive(Debug, Clone, PartialEq, Eq)]
pub enum QrCodeModeData {
    /// Enum variant for the case where the new device is displaying the QR
    /// code.
    Login,
    /// Enum variant for the case where the existing device is displaying the QR
    /// code.
    Reciprocate {
        /// The homeserver the existing device is using. This will let the new
        /// device know which homeserver it should use as well.
        server_name: String,
    },
}

impl QrCodeModeData {
    /// Get the [`QrCodeMode`] which is associated to this [`QrCodeModeData`]
    /// instance.
    pub fn mode(&self) -> QrCodeMode {
        self.into()
    }
}

/// The mode of the QR code login.
///
/// The QR code login mechanism supports both, the new device, as well as the
/// existing device to display the QR code.
///
/// The different modes have an explicit one-byte identifier which gets added to
/// the QR code data.
#[derive(Debug, Clone, PartialEq, Eq)]
pub enum QrCodeMode {
    /// Enum variant for the case where the new device is displaying the QR
    /// code.
    Login = 0x03,
    /// Enum variant for the case where the existing device is displaying the QR
    /// code.
    Reciprocate = 0x04,
}

impl TryFrom<u8> for QrCodeMode {
    type Error = LoginQrCodeDecodeError;

    fn try_from(value: u8) -> Result<Self, Self::Error> {
        match value {
            0x03 => Ok(Self::Login),
            0x04 => Ok(Self::Reciprocate),
            mode => Err(LoginQrCodeDecodeError::InvalidMode(mode)),
        }
    }
}

impl From<&QrCodeModeData> for QrCodeMode {
    fn from(value: &QrCodeModeData) -> Self {
        match value {
            QrCodeModeData::Login => Self::Login,
            QrCodeModeData::Reciprocate { .. } => Self::Reciprocate,
        }
    }
}

/// Data for the QR code login mechanism.
///
/// The [`QrCodeData`] can be serialized and encoded as a QR code or it can be
/// decoded from a QR code.
#[derive(Debug, Clone, PartialEq, Eq)]
pub struct QrCodeData {
    /// The ephemeral Curve25519 public key. Can be used to establish a shared
    /// secret using the Diffie-Hellman key agreement.
    pub public_key: Curve25519PublicKey,
    /// The URL of the rendezvous session, can be used to exchange messages with
    /// the other device.
    pub rendezvous_url: Url,
    /// Mode specific data, may contain the homeserver URL.
    pub mode_data: QrCodeModeData,
}

impl QrCodeData {
    /// Attempt to decode a slice of bytes into a [`QrCodeData`] object.
    ///
    /// The slice of bytes would generally be returned by a QR code decoder.
    pub fn from_bytes(bytes: &[u8]) -> Result<Self, LoginQrCodeDecodeError> {
        // The QR data consists of the following values:
        // 1. The ASCII string MATRIX.
        // 2. One byte version, only 0x02 is supported.
        // 3. One byte intent/mode, either 0x03 or 0x04.
        // 4. 32 bytes for the ephemeral Curve25519 key.
        // 5. Two bytes for the length of the rendezvous URL, a u16 in big-endian
        //    encoding.
        // 6. The UTF-8 encoded string containing the rendezvous URL.
        // 7. If the intent/mode from point 3. is 0x04, then two bytes for the length of
        //    the homeserver URL, a u16 in big-endian encoding.
        // 8. If the intent/mode from point 3. is 0x04, then the UTF-8 encoded string
        //    containing the homeserver URL.
        let mut reader = Cursor::new(bytes);

        // 1. Let's get the prefix first and double check if this QR code is intended
        //    for the QR code login mechanism.
        let mut prefix = [0u8; PREFIX.len()];
        reader.read_exact(&mut prefix)?;

        if PREFIX != prefix {
            return Err(LoginQrCodeDecodeError::InvalidPrefix { expected: PREFIX, got: prefix });
        }

        // 2. Next up is the version, we continue only if the version matches.
        let version = reader.read_u8()?;
        if version == VERSION {
            // 3. The intent/mode is the next one to parse, we return an error imediatelly
            //    the intent isn't 0x03 or 0x04.
            let mode = QrCodeMode::try_from(reader.read_u8()?)?;

            // 4. Let's get the public key and convert it to our strongly typed
            // Curve25519PublicKey type.
            let mut public_key = [0u8; Curve25519PublicKey::LENGTH];
            reader.read_exact(&mut public_key)?;
            let public_key = Curve25519PublicKey::from_bytes(public_key);

            // 5. We read two bytes for the length of the rendezvous URL.
            let rendezvous_url_len = reader.read_u16::<BigEndian>()?;
            // 6. We read and parse the rendezvous URL itself.
            let mut rendezvous_url = vec![0u8; rendezvous_url_len.into()];
            reader.read_exact(&mut rendezvous_url)?;
            let rendezvous_url = Url::parse(str::from_utf8(&rendezvous_url)?)?;

            let mode_data = match mode {
                QrCodeMode::Login => QrCodeModeData::Login,
                QrCodeMode::Reciprocate => {
                    // 7. If the mode is 0x04, we attempt to read the two bytes for the length of
                    //    the homeserver URL.
                    let server_name_len = reader.read_u16::<BigEndian>()?;

                    // 8. We read and parse the homeserver URL.
                    let mut server_name = vec![0u8; server_name_len.into()];
                    reader.read_exact(&mut server_name)?;
                    let server_name = String::from_utf8(server_name).map_err(|e| e.utf8_error())?;

                    QrCodeModeData::Reciprocate { server_name }
                }
            };

            Ok(Self { public_key, rendezvous_url, mode_data })
        } else {
            Err(LoginQrCodeDecodeError::InvalidVersion(version))
        }
    }

    /// Encode the [`QrCodeData`] into a list of bytes.
    ///
    /// The list of bytes can be used by a QR code generator to create an image
    /// containing a QR code.
    pub fn to_bytes(&self) -> Vec<u8> {
        let rendezvous_url_len = (self.rendezvous_url.as_str().len() as u16).to_be_bytes();

        let encoded = [
            PREFIX,
            &[VERSION],
            &[self.mode_data.mode() as u8],
            self.public_key.as_bytes().as_slice(),
            &rendezvous_url_len,
            self.rendezvous_url.as_str().as_bytes(),
        ]
        .concat();

        if let QrCodeModeData::Reciprocate { server_name } = &self.mode_data {
            let server_name_len = (server_name.as_str().len() as u16).to_be_bytes();

            [encoded.as_slice(), &server_name_len, server_name.as_str().as_bytes()].concat()
        } else {
            encoded
        }
    }

    /// Attempt to decode a base64 encoded string into a [`QrCodeData`] object.
    pub fn from_base64(data: &str) -> Result<Self, LoginQrCodeDecodeError> {
        Self::from_bytes(&base64_decode(data)?)
    }

    /// Encode the [`QrCodeData`] into a list of bytes.
    ///
    /// The list of bytes can be used by a QR code generator to create an image
    /// containing a QR code.
    pub fn to_base64(&self) -> String {
        base64_encode(self.to_bytes())
    }

    /// Get the mode of this [`QrCodeData`] instance.
    pub fn mode(&self) -> QrCodeMode {
        self.mode_data.mode()
    }
}

#[cfg(test)]
mod test {
    use assert_matches2::assert_let;
    use similar_asserts::assert_eq;

    use super::*;

    // Test vector for the QR code data, copied from the MSC.
    const QR_CODE_DATA: &[u8] = &[
        0x4D, 0x41, 0x54, 0x52, 0x49, 0x58, 0x02, 0x03, 0xd8, 0x86, 0x68, 0x6a, 0xb2, 0x19, 0x7b,
        0x78, 0x0e, 0x30, 0x0a, 0x9d, 0x4a, 0x21, 0x47, 0x48, 0x07, 0x00, 0xd7, 0x92, 0x9f, 0x39,
        0xab, 0x31, 0xb9, 0xe5, 0x14, 0x37, 0x02, 0x48, 0xed, 0x6b, 0x00, 0x47, 0x68, 0x74, 0x74,
        0x70, 0x73, 0x3a, 0x2f, 0x2f, 0x72, 0x65, 0x6e, 0x64, 0x65, 0x7a, 0x76, 0x6f, 0x75, 0x73,
        0x2e, 0x6c, 0x61, 0x62, 0x2e, 0x65, 0x6c, 0x65, 0x6d, 0x65, 0x6e, 0x74, 0x2e, 0x64, 0x65,
        0x76, 0x2f, 0x65, 0x38, 0x64, 0x61, 0x36, 0x33, 0x35, 0x35, 0x2d, 0x35, 0x35, 0x30, 0x62,
        0x2d, 0x34, 0x61, 0x33, 0x32, 0x2d, 0x61, 0x31, 0x39, 0x33, 0x2d, 0x31, 0x36, 0x31, 0x39,
        0x64, 0x39, 0x38, 0x33, 0x30, 0x36, 0x36, 0x38,
    ];

    // Test vector for the QR code data, copied from the MSC, with the mode set to
    // reciprocate.
    const QR_CODE_DATA_RECIPROCATE: &[u8] = &[
        0x4D, 0x41, 0x54, 0x52, 0x49, 0x58, 0x02, 0x04, 0xd8, 0x86, 0x68, 0x6a, 0xb2, 0x19, 0x7b,
        0x78, 0x0e, 0x30, 0x0a, 0x9d, 0x4a, 0x21, 0x47, 0x48, 0x07, 0x00, 0xd7, 0x92, 0x9f, 0x39,
        0xab, 0x31, 0xb9, 0xe5, 0x14, 0x37, 0x02, 0x48, 0xed, 0x6b, 0x00, 0x47, 0x68, 0x74, 0x74,
        0x70, 0x73, 0x3a, 0x2f, 0x2f, 0x72, 0x65, 0x6e, 0x64, 0x65, 0x7a, 0x76, 0x6f, 0x75, 0x73,
        0x2e, 0x6c, 0x61, 0x62, 0x2e, 0x65, 0x6c, 0x65, 0x6d, 0x65, 0x6e, 0x74, 0x2e, 0x64, 0x65,
        0x76, 0x2f, 0x65, 0x38, 0x64, 0x61, 0x36, 0x33, 0x35, 0x35, 0x2d, 0x35, 0x35, 0x30, 0x62,
        0x2d, 0x34, 0x61, 0x33, 0x32, 0x2d, 0x61, 0x31, 0x39, 0x33, 0x2d, 0x31, 0x36, 0x31, 0x39,
        0x64, 0x39, 0x38, 0x33, 0x30, 0x36, 0x36, 0x38, 0x00, 0x0A, 0x6d, 0x61, 0x74, 0x72, 0x69,
        0x78, 0x2e, 0x6f, 0x72, 0x67,
    ];

    // Test vector for the QR code data in base64 format, self-generated.
    const QR_CODE_DATA_BASE64: &str =
        "TUFUUklYAgS0yzZ1QVpQ1jlnoxWX3d5jrWRFfELxjS2gN7pz9y+3PABaaHR0\
         cHM6Ly9zeW5hcHNlLW9pZGMubGFiLmVsZW1lbnQuZGV2L19zeW5hcHNlL2Ns\
         aWVudC9yZW5kZXp2b3VzLzAxSFg5SzAwUTFINktQRDQ3RUc0RzFUM1hHACVo\
         dHRwczovL3N5bmFwc2Utb2lkYy5sYWIuZWxlbWVudC5kZXYv";

    #[test]
    fn parse_qr_data() {
        let expected_curve_key =
            Curve25519PublicKey::from_base64("2IZoarIZe3gOMAqdSiFHSAcA15KfOasxueUUNwJI7Ws")
                .unwrap();

        let expected_rendezvous =
            Url::parse("https://rendezvous.lab.element.dev/e8da6355-550b-4a32-a193-1619d9830668")
                .unwrap();

        let data = QrCodeData::from_bytes(QR_CODE_DATA)
            .expect("We should be able to parse the QR code data");

        assert_eq!(
            expected_curve_key, data.public_key,
            "The parsed public key should match the expected one"
        );

        assert_eq!(
            expected_rendezvous, data.rendezvous_url,
            "The parsed rendezvous URL should match expected one",
        );

        assert_eq!(
            data.mode(),
            QrCodeMode::Login,
            "The mode in the test bytes vector should be Login"
        );

        assert_eq!(
            QrCodeModeData::Login,
            data.mode_data,
            "The parsed QR code mode should match expected one",
        );
    }

    #[test]
    fn parse_qr_data_reciprocate() {
        let expected_curve_key =
            Curve25519PublicKey::from_base64("2IZoarIZe3gOMAqdSiFHSAcA15KfOasxueUUNwJI7Ws")
                .unwrap();

        let expected_rendezvous =
            Url::parse("https://rendezvous.lab.element.dev/e8da6355-550b-4a32-a193-1619d9830668")
                .unwrap();

        let data = QrCodeData::from_bytes(QR_CODE_DATA_RECIPROCATE)
            .expect("We should be able to parse the QR code data");

        assert_eq!(
            expected_curve_key, data.public_key,
            "The parsed public key should match the expected one"
        );

        assert_eq!(
            expected_rendezvous, data.rendezvous_url,
            "The parsed rendezvous URL should match expected one",
        );

        assert_eq!(
            data.mode(),
            QrCodeMode::Reciprocate,
            "The mode in the test bytes vector should be Reciprocate"
        );

        assert_let!(
            QrCodeModeData::Reciprocate { server_name } = data.mode_data,
            "The parsed QR code mode should match the expected one",
        );

        assert_eq!(
            server_name, "matrix.org",
            "We should have correctly found the matrix.org homeserver in the QR code data"
        );
    }

    #[test]
    fn parse_qr_data_base64() {
        let expected_curve_key =
            Curve25519PublicKey::from_base64("tMs2dUFaUNY5Z6MVl93eY61kRXxC8Y0toDe6c/cvtzw")
                .unwrap();

        let expected_rendezvous =
            Url::parse("https://synapse-oidc.lab.element.dev/_synapse/client/rendezvous/01HX9K00Q1H6KPD47EG4G1T3XG")
                .unwrap();

        let expected_server_name = "https://synapse-oidc.lab.element.dev/";

        let data = QrCodeData::from_base64(QR_CODE_DATA_BASE64)
            .expect("We should be able to parse the QR code data");

        assert_eq!(
            expected_curve_key, data.public_key,
            "The parsed public key should match the expected one"
        );

        assert_eq!(
            data.mode(),
            QrCodeMode::Reciprocate,
            "The mode in the test bytes vector should be Reciprocate"
        );

        assert_eq!(
            expected_rendezvous, data.rendezvous_url,
            "The parsed rendezvous URL should match the expected one",
        );

        assert_let!(QrCodeModeData::Reciprocate { server_name } = data.mode_data);

        assert_eq!(
            server_name, expected_server_name,
            "The parsed server name should match the expected one"
        );
    }

    #[test]
    fn qr_code_encoding_roundtrip() {
        let data = QrCodeData::from_bytes(QR_CODE_DATA)
            .expect("We should be able to parse the QR code data");

        let encoded = data.to_bytes();

        assert_eq!(
            QR_CODE_DATA, &encoded,
            "Decoding and re-encoding the QR code data should yield the same bytes"
        );

        let data = QrCodeData::from_base64(QR_CODE_DATA_BASE64)
            .expect("We should be able to parse the QR code data");

        let encoded = data.to_base64();

        assert_eq!(
            QR_CODE_DATA_BASE64, &encoded,
            "Decoding and re-encoding the QR code data should yield the same base64 string"
        );
    }
}