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
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
|
//! Padding for OpenPGP messages.
//!
//! To reduce the amount of information leaked via the message length,
//! encrypted OpenPGP messages (see [Section 11.3 of RFC 4880]) should
//! be padded.
//!
//! [Section 11.3 of RFC 4880]: https://tools.ietf.org/html/rfc4880#section-11.3
//!
//! To pad a message using the streaming serialization interface, the
//! [`Padder`] needs to be inserted into the writing stack between the
//! [`Encryptor`] and [`Signer`]. This is illustrated in this
//! [example].
//!
//! [`Encryptor`]: super::Encryptor
//! [`Signer`]: super::Signer
//! [example]: Padder#examples
//!
//! # Padding in OpenPGP
//!
//! There are a number of ways to pad messages within the boundaries
//! of the OpenPGP protocol, keeping an eye on backwards-compatibility
//! with common implementations:
//!
//! - Add a decoy notation to a signature packet (up to about 60k)
//!
//! - Add a signature with a private algorithm and store the decoy
//! traffic in the MPIs (up to 4 GB)
//!
//! - Use a compression container and store the decoy traffic in a
//! chunk that decompresses to the empty string (unlimited)
//!
//! - Use a bunch of marker packets, which are ignored (each packet:
//! 3 bytes for the body, 5 bytes for the header)
//!
//! - Apparently, GnuPG understands a comment packet (tag: 61),
//! which is not standardized (up to 64k)
//!
//! We believe that padding the compressed data stream is the best
//! option, because as far as OpenPGP is concerned, it is completely
//! transparent for the recipient (for example, no weird packets are
//! inserted).
//!
//! Unfortunately, [testing] discovered problems when the resulting
//! messages are consumed by (at the time of this writing) OpenPGP.js,
//! RNP, and GnuPG. If compatibility with these implementations is a
//! concern, using this padding method is not advisable.
//!
//! [testing]: https://tests.sequoia-pgp.org/#Packet_excess_consumption
//!
//! To be effective, the padding layer must be placed inside the
//! encryption container. To increase compatibility, the padding
//! layer must not be signed. That is to say, the message structure
//! should be `(encryption (padding ops literal signature))`, the
//! exact structure GnuPG emits by default.
use std::fmt;
use std::io::{self, Write};
use crate::{
Result,
packet::prelude::*,
};
use crate::packet::header::CTB;
use crate::serialize::{
Marshal,
stream::{
writer,
Cookie,
Message,
PartialBodyFilter,
},
};
use crate::types::{
CompressionAlgorithm,
CompressionLevel,
};
/// Pads a packet stream.
///
/// Writes a compressed data packet containing all packets written to
/// this writer, and pads it according to the given policy.
///
/// The policy is a `Fn(u64) -> u64`, that given the number of bytes
/// written to this writer `N`, computes the size the compression
/// container should be padded up to. It is an error to return a
/// number that is smaller than `N`.
///
/// # Compatibility
///
/// This implementation uses the [DEFLATE] compression format. The
/// packet structure contains a flag signaling the end of the stream
/// (see [Section 3.2.3 of RFC 1951]), and any data appended after
/// that is not part of the stream.
///
/// [DEFLATE]: https://tools.ietf.org/html/rfc1951
/// [Section 3.2.3 of RFC 1951]: https://tools.ietf.org/html/rfc1951#page-9
///
/// [Section 9.3 of RFC 4880] recommends that this algorithm should be
/// implemented, therefore support across various implementations
/// should be good.
///
/// [Section 9.3 of RFC 4880]: https://tools.ietf.org/html/rfc4880#section-9.3
///
/// # Examples
///
/// This example illustrates the use of `Padder` with the [Padmé]
/// policy. Note that for brevity, the encryption and signature
/// filters are omitted.
///
/// [Padmé]: padme()
///
/// ```
/// use std::io::Write;
/// use sequoia_openpgp as openpgp;
/// use openpgp::serialize::stream::{Message, LiteralWriter};
/// use openpgp::serialize::stream::padding::Padder;
/// use openpgp::types::CompressionAlgorithm;
/// # fn main() -> sequoia_openpgp::Result<()> {
///
/// let mut unpadded = vec![];
/// {
/// let message = Message::new(&mut unpadded);
/// // XXX: Insert Encryptor here.
/// // XXX: Insert Signer here.
/// let mut message = LiteralWriter::new(message).build()?;
/// message.write_all(b"Hello world.")?;
/// message.finalize()?;
/// }
///
/// let mut padded = vec![];
/// {
/// let message = Message::new(&mut padded);
/// // XXX: Insert Encryptor here.
/// let message = Padder::new(message).build()?;
/// // XXX: Insert Signer here.
/// let mut message = LiteralWriter::new(message).build()?;
/// message.write_all(b"Hello world.")?;
/// message.finalize()?;
/// }
/// assert!(unpadded.len() < padded.len());
/// # Ok(())
/// # }
pub struct Padder<'a> {
inner: writer::BoxStack<'a, Cookie>,
policy: fn(u64) -> u64,
}
assert_send_and_sync!(Padder<'_>);
impl<'a> Padder<'a> {
/// Creates a new padder with the given policy.
///
/// # Examples
///
/// This example illustrates the use of `Padder` with the [Padmé]
/// policy.
///
/// [Padmé]: padme()
///
/// The most useful filter to push to the writer stack next is the
/// [`Signer`] or the [`LiteralWriter`]. Finally, literal data
/// *must* be wrapped using the [`LiteralWriter`].
///
/// [`Signer`]: super::Signer
/// [`LiteralWriter`]: super::LiteralWriter
///
/// ```
/// # fn main() -> sequoia_openpgp::Result<()> {
/// use sequoia_openpgp as openpgp;
/// use openpgp::serialize::stream::padding::Padder;
///
/// # let message = openpgp::serialize::stream::Message::new(vec![]);
/// let message = Padder::new(message).build()?;
/// // Optionally add a `Signer` here.
/// // Add a `LiteralWriter` here.
/// # let _ = message;
/// # Ok(()) }
/// ```
pub fn new(inner: Message<'a>) -> Self {
Self {
inner: writer::BoxStack::from(inner),
policy: padme,
}
}
/// Sets padding policy, returning the padder.
///
/// # Examples
///
/// This example illustrates the use of `Padder` with an explicit policy.
///
/// ```
/// # fn main() -> sequoia_openpgp::Result<()> {
/// use sequoia_openpgp as openpgp;
/// use openpgp::serialize::stream::padding::{Padder, padme};
///
/// # let message = openpgp::serialize::stream::Message::new(vec![]);
/// let message = Padder::new(message).with_policy(padme).build()?;
/// // Optionally add a `Signer` here.
/// // Add a `LiteralWriter` here.
/// # let _ = message;
/// # Ok(()) }
/// ```
pub fn with_policy(mut self, p: fn(u64) -> u64) -> Self {
self.policy = p;
self
}
/// Builds the padder, returning the writer stack.
///
/// # Examples
///
/// This example illustrates the use of `Padder` with the [Padmé]
/// policy.
///
/// [Padmé]: padme()
///
/// The most useful filter to push to the writer stack next is the
/// [`Signer`] or the [`LiteralWriter`]. Finally, literal data
/// *must* be wrapped using the [`LiteralWriter`].
///
/// [`Signer`]: super::Signer
/// [`LiteralWriter`]: super::LiteralWriter
///
/// ```
/// # fn main() -> sequoia_openpgp::Result<()> {
/// use sequoia_openpgp as openpgp;
/// use openpgp::serialize::stream::padding::Padder;
///
/// # let message = openpgp::serialize::stream::Message::new(vec![]);
/// let message = Padder::new(message).build()?;
/// // Optionally add a `Signer` here.
/// // Add a `LiteralWriter` here.
/// # let _ = message;
/// # Ok(()) }
/// ```
pub fn build(mut self) -> Result<Message<'a>> {
let mut inner = self.inner;
let level = inner.cookie_ref().level + 1;
// Packet header.
CTB::new(Tag::CompressedData).serialize(&mut inner)?;
let mut inner: Message<'a>
= PartialBodyFilter::new(Message::from(inner),
Cookie::new(level));
// Compressed data header.
inner.as_mut().write_u8(CompressionAlgorithm::Zip.into())?;
// Create an appropriate filter.
self.inner =
writer::ZIP::new(inner, Cookie::new(level),
CompressionLevel::none()).into();
Ok(Message::from(Box::new(self)))
}
}
impl<'a> fmt::Debug for Padder<'a> {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
f.debug_struct("Padder")
.field("inner", &self.inner)
.finish()
}
}
impl<'a> io::Write for Padder<'a> {
fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
self.inner.write(buf)
}
fn flush(&mut self) -> io::Result<()> {
self.inner.flush()
}
}
impl<'a> writer::Stackable<'a, Cookie> for Padder<'a>
{
fn into_inner(self: Box<Self><
|