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
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
// Copyright 2015-2017 Benjamin Fry <benjaminfry@me.com>
//
// Licensed under the Apache License, Version 2.0, <LICENSE-APACHE or
// http://apache.org/licenses/LICENSE-2.0> or the MIT license <LICENSE-MIT or
// http://opensource.org/licenses/MIT>, at your option. This file may not be
// copied, modified, or distributed except according to those terms.

//! TLSA records for storing TLS certificate validation information

use crate::error::*;
use crate::serialize::binary::*;

/// [RFC 6698, DNS-Based Authentication for TLS](https://tools.ietf.org/html/rfc6698#section-2.1)
///
/// ```text
/// 2.1.  TLSA RDATA Wire Format
///
///    The RDATA for a TLSA RR consists of a one-octet certificate usage
///    field, a one-octet selector field, a one-octet matching type field,
///    and the certificate association data field.
///
///                         1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3
///     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
///    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
///    |  Cert. Usage  |   Selector    | Matching Type |               /
///    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+               /
///    /                                                               /
///    /                 Certificate Association Data                  /
///    /                                                               /
///    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/// ```
#[derive(Debug, PartialEq, Eq, Hash, Clone)]
pub struct TLSA {
    cert_usage: CertUsage,
    selector: Selector,
    matching: Matching,
    cert_data: Vec<u8>,
}

/// [RFC 6698, DNS-Based Authentication for TLS](https://tools.ietf.org/html/rfc6698#section-2.1.1)
///
/// ```text
/// 2.1.1.  The Certificate Usage Field
///
///    A one-octet value, called "certificate usage", specifies the provided
///    association that will be used to match the certificate presented in
///    the TLS handshake.  This value is defined in a new IANA registry (see
///    Section 7.2) in order to make it easier to add additional certificate
///    usages in the future.  The certificate usages defined in this
///    document are:
///
///       0 -- CA
///
///       1 -- Service
///
///       2 -- TrustAnchor
///
///       3 -- DomainIssued
///
///    The certificate usages defined in this document explicitly only apply
///    to PKIX-formatted certificates in DER encoding [X.690].  If TLS
///    allows other formats later, or if extensions to this RRtype are made
///    that accept other formats for certificates, those certificates will
///    need their own certificate usage values.
/// ```
#[derive(Debug, PartialEq, Eq, Hash, Clone, Copy)]
pub enum CertUsage {
    /// ```text
    ///       0 -- Certificate usage 0 is used to specify a CA certificate, or
    ///       the public key of such a certificate, that MUST be found in any of
    ///       the PKIX certification paths for the end entity certificate given
    ///       by the server in TLS.  This certificate usage is sometimes
    ///       referred to as "CA constraint" because it limits which CA can be
    ///       used to issue certificates for a given service on a host.  The
    ///       presented certificate MUST pass PKIX certification path
    ///       validation, and a CA certificate that matches the TLSA record MUST
    ///       be included as part of a valid certification path.  Because this
    ///       certificate usage allows both trust anchors and CA certificates,
    ///       the certificate might or might not have the basicConstraints
    ///       extension present.
    /// ```
    CA,

    /// ```text
    ///       1 -- Certificate usage 1 is used to specify an end entity
    ///       certificate, or the public key of such a certificate, that MUST be
    ///       matched with the end entity certificate given by the server in
    ///       TLS.  This certificate usage is sometimes referred to as "service
    ///       certificate constraint" because it limits which end entity
    ///       certificate can be used by a given service on a host.  The target
    ///       certificate MUST pass PKIX certification path validation and MUST
    ///       match the TLSA record.
    /// ```
    Service,

    /// ```text
    ///       2 -- Certificate usage 2 is used to specify a certificate, or the
    ///       public key of such a certificate, that MUST be used as the trust
    ///       anchor when validating the end entity certificate given by the
    ///       server in TLS.  This certificate usage is sometimes referred to as
    ///       "trust anchor assertion" and allows a domain name administrator to
    ///       specify a new trust anchor -- for example, if the domain issues
    ///       its own certificates under its own CA that is not expected to be
    ///       in the end users' collection of trust anchors.  The target
    ///       certificate MUST pass PKIX certification path validation, with any
    ///       certificate matching the TLSA record considered to be a trust
    ///       anchor for this certification path validation.
    /// ```
    TrustAnchor,

    /// ```text
    ///       3 -- Certificate usage 3 is used to specify a certificate, or the
    ///       public key of such a certificate, that MUST match the end entity
    ///       certificate given by the server in TLS.  This certificate usage is
    ///       sometimes referred to as "domain-issued certificate" because it
    ///       allows for a domain name administrator to issue certificates for a
    ///       domain without involving a third-party CA.  The target certificate
    ///       MUST match the TLSA record.  The difference between certificate
    ///       usage 1 and certificate usage 3 is that certificate usage 1
    ///       requires that the certificate pass PKIX validation, but PKIX
    ///       validation is not tested for certificate usage 3.
    /// ```
    DomainIssued,

    /// Unassigned at the time of this implementation
    Unassigned(u8),

    /// Private usage
    Private,
}

impl From<u8> for CertUsage {
    fn from(usage: u8) -> Self {
        match usage {
            0 => CertUsage::CA,
            1 => CertUsage::Service,
            2 => CertUsage::TrustAnchor,
            3 => CertUsage::DomainIssued,
            4..=254 => CertUsage::Unassigned(usage),
            255 => CertUsage::Private,
        }
    }
}

impl From<CertUsage> for u8 {
    fn from(usage: CertUsage) -> u8 {
        match usage {
            CertUsage::CA => 0,
            CertUsage::Service => 1,
            CertUsage::TrustAnchor => 2,
            CertUsage::DomainIssued => 3,
            CertUsage::Unassigned(usage) => usage,
            CertUsage::Private => 255,
        }
    }
}

/// [RFC 6698, DNS-Based Authentication for TLS](https://tools.ietf.org/html/rfc6698#section-2.1.1)
///
/// ```text
/// 2.1.2.  The Selector Field
///
///    A one-octet value, called "selector", specifies which part of the TLS
///    certificate presented by the server will be matched against the
///    association data.  This value is defined in a new IANA registry (see
///    Section 7.3).  The selectors defined in this document are:
///
///       0 -- Full
///
///       1 -- Spki
///
///    (Note that the use of "selector" in this document is completely
///    unrelated to the use of "selector" in DomainKeys Identified Mail
///    (DKIM) [RFC6376].)
/// ```
#[derive(Debug, PartialEq, Eq, Hash, Clone, Copy)]
pub enum Selector {
    /// Full certificate: the Certificate binary structure as defined in [RFC5280]
    Full,

    /// SubjectPublicKeyInfo: DER-encoded binary structure as defined in [RFC5280]
    Spki,

    /// Unassigned at the time of this writing
    Unassigned(u8),

    /// Private usage
    Private,
}

impl From<u8> for Selector {
    fn from(selector: u8) -> Self {
        match selector {
            0 => Selector::Full,
            1 => Selector::Spki,
            2..=254 => Selector::Unassigned(selector),
            255 => Selector::Private,
        }
    }
}

impl From<Selector> for u8 {
    fn from(selector: Selector) -> u8 {
        match selector {
            Selector::Full => 0,
            Selector::Spki => 1,
            Selector::Unassigned(selector) => selector,
            Selector::Private => 255,
        }
    }
}

/// [RFC 6698, DNS-Based Authentication for TLS](https://tools.ietf.org/html/rfc6698#section-2.1.3)
///
/// ```text
/// 2.1.3.  The Matching Type Field
///
///    A one-octet value, called "matching type", specifies how the
///    certificate association is presented.  This value is defined in a new
///    IANA registry (see Section 7.4).  The types defined in this document
///    are:
///
///       0 -- Raw
///
///       1 -- Sha256
///
///       2 -- Sha512
///
///    If the TLSA record's matching type is a hash, having the record use
///    the same hash algorithm that was used in the signature in the
///    certificate (if possible) will assist clients that support a small
///    number of hash algorithms.
/// ```
#[derive(Debug, PartialEq, Eq, Hash, Clone, Copy)]
pub enum Matching {
    /// Exact match on selected content
    Raw,

    /// SHA-256 hash of selected content [RFC6234]
    Sha256,

    /// SHA-512 hash of selected content [RFC6234]
    Sha512,

    /// Unassigned at the time of this writing
    Unassigned(u8),

    /// Private usage
    Private,
}

impl From<u8> for Matching {
    fn from(matching: u8) -> Self {
        match matching {
            0 => Matching::Raw,
            1 => Matching::Sha256,
            2 => Matching::Sha512,
            3..=254 => Matching::Unassigned(matching),
            255 => Matching::Private,
        }
    }
}

impl From<Matching> for u8 {
    fn from(matching: Matching) -> u8 {
        match matching {
            Matching::Raw => 0,
            Matching::Sha256 => 1,
            Matching::Sha512 => 2,
            Matching::Unassigned(matching) => matching,
            Matching::Private => 255,
        }
    }
}

impl TLSA {
    /// Constructs a new TLSA
    ///
    /// [RFC 6698, DNS-Based Authentication for TLS](https://tools.ietf.org/html/rfc6698#section-2)
    ///
    /// ```text
    /// 2.  The TLSA Resource Record
    ///
    ///    The TLSA DNS resource record (RR) is used to associate a TLS server
    ///    certificate or public key with the domain name where the record is
    ///    found, thus forming a "TLSA certificate association".  The semantics
    ///    of how the TLSA RR is interpreted are given later in this document.
    ///
    ///    The type value for the TLSA RR type is defined in Section 7.1.
    ///
    ///    The TLSA RR is class independent.
    ///
    ///    The TLSA RR has no special Time to Live (TTL) requirements.
    /// ```
    pub fn new(
        cert_usage: CertUsage,
        selector: Selector,
        matching: Matching,
        cert_data: Vec<u8>,
    ) -> Self {
        TLSA {
            cert_usage,
            selector,
            matching,
            cert_data,
        }
    }

    /// Specifies the provided association that will be used to match the certificate presented in the TLS handshake
    pub fn cert_usage(&self) -> CertUsage {
        self.cert_usage
    }

    /// Specifies which part of the TLS certificate presented by the server will be matched against the association data
    pub fn selector(&self) -> Selector {
        self.selector
    }

    /// Specifies how the certificate association is presented
    pub fn matching(&self) -> Matching {
        self.matching
    }

    /// Binary data for validating the cert, see other members to understand format
    pub fn cert_data(&self) -> &[u8] {
        &self.cert_data
    }
}

/// Read the RData from the given Decoder
///
/// ```text
///                         1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3
///     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
///    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
///    |  Cert. Usage  |   Selector    | Matching Type |               /
///    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+               /
///    /                                                               /
///    /                 Certificate Association Data                  /
///    /                                                               /
///    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/// ```
pub fn read(decoder: &mut BinDecoder, rdata_length: Restrict<u16>) -> ProtoResult<TLSA> {
    let cert_usage = decoder.read_u8()?.unverified(/*CertUsage is verified*/).into();
    let selector = decoder.read_u8()?.unverified(/*Selector is verified*/).into();
    let matching = decoder.read_u8()?.unverified(/*Matching is verified*/).into();

    // the remaining data is for the cert
    let cert_len = rdata_length
        .map(|u| u as usize)
        .checked_sub(3)
        .map_err(|_| ProtoError::from("invalid rdata length in TLSA"))?
        .unverified(/*used purely as length safely*/);
    let cert_data = decoder.read_vec(cert_len)?.unverified(/*will fail in usage if invalid*/);

    Ok(TLSA {
        cert_usage,
        selector,
        matching,
        cert_data,
    })
}

/// Write the RData from the given Decoder
pub fn emit(encoder: &mut BinEncoder, tlsa: &TLSA) -> ProtoResult<()> {
    encoder.emit_u8(tlsa.cert_usage.into())?;
    encoder.emit_u8(tlsa.selector.into())?;
    encoder.emit_u8(tlsa.matching.into())?;
    encoder.emit_vec(&tlsa.cert_data)?;
    Ok(())
}

#[cfg(test)]
mod tests {
    #![allow(clippy::dbg_macro, clippy::print_stdout)]

    use super::*;

    #[test]
    fn read_cert_usage() {
        assert_eq!(CertUsage::CA, CertUsage::from(0));
        assert_eq!(CertUsage::Service, CertUsage::from(1));
        assert_eq!(CertUsage::TrustAnchor, CertUsage::from(2));
        assert_eq!(CertUsage::DomainIssued, CertUsage::from(3));
        assert_eq!(CertUsage::Unassigned(4), CertUsage::from(4));
        assert_eq!(CertUsage::Unassigned(254), CertUsage::from(254));
        assert_eq!(CertUsage::Private, CertUsage::from(255));

        assert_eq!(u8::from(CertUsage::CA), 0);
        assert_eq!(u8::from(CertUsage::Service), 1);
        assert_eq!(u8::from(CertUsage::TrustAnchor), 2);
        assert_eq!(u8::from(CertUsage::DomainIssued), 3);
        assert_eq!(u8::from(CertUsage::Unassigned(4)), 4);
        assert_eq!(u8::from(CertUsage::Unassigned(254)), 254);
        assert_eq!(u8::from(CertUsage::Private), 255);
    }

    #[test]
    fn read_selector() {
        assert_eq!(Selector::Full, Selector::from(0));
        assert_eq!(Selector::Spki, Selector::from(1));
        assert_eq!(Selector::Unassigned(2), Selector::from(2));
        assert_eq!(Selector::Unassigned(254), Selector::from(254));
        assert_eq!(Selector::Private, Selector::from(255));

        assert_eq!(u8::from(Selector::Full), 0);
        assert_eq!(u8::from(Selector::Spki), 1);
        assert_eq!(u8::from(Selector::Unassigned(2)), 2);
        assert_eq!(u8::from(Selector::Unassigned(254)), 254);
        assert_eq!(u8::from(Selector::Private), 255);
    }

    #[test]
    fn read_matching() {
        assert_eq!(Matching::Raw, Matching::from(0));
        assert_eq!(Matching::Sha256, Matching::from(1));
        assert_eq!(Matching::Sha512, Matching::from(2));
        assert_eq!(Matching::Unassigned(3), Matching::from(3));
        assert_eq!(Matching::Unassigned(254), Matching::from(254));
        assert_eq!(Matching::Private, Matching::from(255));

        assert_eq!(u8::from(Matching::Raw), 0);
        assert_eq!(u8::from(Matching::Sha256), 1);
        assert_eq!(u8::from(Matching::Sha512), 2);
        assert_eq!(u8::from(Matching::Unassigned(3)), 3);
        assert_eq!(u8::from(Matching::Unassigned(254)), 254);
        assert_eq!(u8::from(Matching::Private), 255);
    }

    fn test_encode_decode(rdata: TLSA) {
        let mut bytes = Vec::new();
        let mut encoder: BinEncoder = BinEncoder::new(&mut bytes);
        emit(&mut encoder, &rdata).expect("failed to emit tlsa");
        let bytes = encoder.into_bytes();

        println!("bytes: {:?}", bytes);

        let mut decoder: BinDecoder = BinDecoder::new(bytes);
        let read_rdata =
            read(&mut decoder, Restrict::new(bytes.len() as u16)).expect("failed to read back");
        assert_eq!(rdata, read_rdata);
    }

    #[test]
    fn test_encode_decode_tlsa() {
        test_encode_decode(TLSA::new(
            CertUsage::Service,
            Selector::Spki,
            Matching::Sha256,
            vec![1, 2, 3, 4, 5, 6, 7, 8],
        ));
        test_encode_decode(TLSA::new(
            CertUsage::CA,
            Selector::Full,
            Matching::Raw,
            vec![1, 2, 3, 4, 5, 6, 7, 8],
        ));
        test_encode_decode(TLSA::new(
            CertUsage::DomainIssued,
            Selector::Full,
            Matching::Sha512,
            vec![1, 2, 3, 4, 5, 6, 7, 8],
        ));
        test_encode_decode(TLSA::new(
            CertUsage::Unassigned(40),
            Selector::Unassigned(39),
            Matching::Unassigned(6),
            vec![1, 2, 3, 4, 5, 6, 7, 8],
        ));
    }
}