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
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
// Copyright 2015-2016 Brian Smith.
//
// Permission to use, copy, modify, and/or distribute this software for any
// purpose with or without fee is hereby granted, provided that the above
// copyright notice and this permission notice appear in all copies.
//
// THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHORS DISCLAIM ALL WARRANTIES
// WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
// MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY
// SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
// WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
// OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
// CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.

use super::PUBLIC_KEY_PUBLIC_MODULUS_MAX_LEN;
use crate::{bits, digest, error, io::der};

#[cfg(feature = "alloc")]
use crate::rand;

/// Common features of both RSA padding encoding and RSA padding verification.
pub trait Padding: 'static + Sync + crate::sealed::Sealed + core::fmt::Debug {
    // The digest algorithm used for digesting the message (and maybe for
    // other things).
    fn digest_alg(&self) -> &'static digest::Algorithm;
}

/// An RSA signature encoding as described in [RFC 3447 Section 8].
///
/// [RFC 3447 Section 8]: https://tools.ietf.org/html/rfc3447#section-8
#[cfg(feature = "alloc")]
pub trait RsaEncoding: Padding {
    #[doc(hidden)]
    fn encode(
        &self,
        m_hash: &digest::Digest,
        m_out: &mut [u8],
        mod_bits: bits::BitLength,
        rng: &dyn rand::SecureRandom,
    ) -> Result<(), error::Unspecified>;
}

/// Verification of an RSA signature encoding as described in
/// [RFC 3447 Section 8].
///
/// [RFC 3447 Section 8]: https://tools.ietf.org/html/rfc3447#section-8
pub trait Verification: Padding {
    fn verify(
        &self,
        m_hash: &digest::Digest,
        m: &mut untrusted::Reader,
        mod_bits: bits::BitLength,
    ) -> Result<(), error::Unspecified>;
}

/// PKCS#1 1.5 padding as described in [RFC 3447 Section 8.2].
///
/// See "`RSA_PSS_*` Details\" in `ring::signature`'s module-level
/// documentation for more details.
///
/// [RFC 3447 Section 8.2]: https://tools.ietf.org/html/rfc3447#section-8.2
#[derive(Debug)]
pub struct PKCS1 {
    digest_alg: &'static digest::Algorithm,
    digestinfo_prefix: &'static [u8],
}

impl crate::sealed::Sealed for PKCS1 {}

impl Padding for PKCS1 {
    fn digest_alg(&self) -> &'static digest::Algorithm {
        self.digest_alg
    }
}

#[cfg(feature = "alloc")]
impl RsaEncoding for PKCS1 {
    fn encode(
        &self,
        m_hash: &digest::Digest,
        m_out: &mut [u8],
        _mod_bits: bits::BitLength,
        _rng: &dyn rand::SecureRandom,
    ) -> Result<(), error::Unspecified> {
        pkcs1_encode(&self, m_hash, m_out);
        Ok(())
    }
}

impl Verification for PKCS1 {
    fn verify(
        &self,
        m_hash: &digest::Digest,
        m: &mut untrusted::Reader,
        mod_bits: bits::BitLength,
    ) -> Result<(), error::Unspecified> {
        // `mod_bits.as_usize_bytes_rounded_up() <=
        //      PUBLIC_KEY_PUBLIC_MODULUS_MAX_LEN` is ensured by `verify_rsa_()`.
        let mut calculated = [0u8; PUBLIC_KEY_PUBLIC_MODULUS_MAX_LEN];
        let calculated = &mut calculated[..mod_bits.as_usize_bytes_rounded_up()];
        pkcs1_encode(&self, m_hash, calculated);
        if m.read_bytes_to_end() != *calculated {
            return Err(error::Unspecified);
        }
        Ok(())
    }
}

// Implement padding procedure per EMSA-PKCS1-v1_5,
// https://tools.ietf.org/html/rfc3447#section-9.2. This is used by both
// verification and signing so it needs to be able to handle moduli of the
// minimum and maximum sizes for both operations.
fn pkcs1_encode(pkcs1: &PKCS1, m_hash: &digest::Digest, m_out: &mut [u8]) {
    let em = m_out;

    let digest_len = pkcs1.digestinfo_prefix.len() + pkcs1.digest_alg.output_len;

    // The specification requires at least 8 bytes of padding. Since we
    // disallow keys smaller than 1024 bits, this should always be true.
    assert!(em.len() >= digest_len + 11);
    let pad_len = em.len() - digest_len - 3;
    em[0] = 0;
    em[1] = 1;
    for i in 0..pad_len {
        em[2 + i] = 0xff;
    }
    em[2 + pad_len] = 0;

    let (digest_prefix, digest_dst) = em[3 + pad_len..].split_at_mut(pkcs1.digestinfo_prefix.len());
    digest_prefix.copy_from_slice(pkcs1.digestinfo_prefix);
    digest_dst.copy_from_slice(m_hash.as_ref());
}

macro_rules! rsa_pkcs1_padding {
    ( $PADDING_ALGORITHM:ident, $digest_alg:expr, $digestinfo_prefix:expr,
      $doc_str:expr ) => {
        #[doc=$doc_str]
        pub static $PADDING_ALGORITHM: PKCS1 = PKCS1 {
            digest_alg: $digest_alg,
            digestinfo_prefix: $digestinfo_prefix,
        };
    };
}

rsa_pkcs1_padding!(
    RSA_PKCS1_SHA1_FOR_LEGACY_USE_ONLY,
    &digest::SHA1_FOR_LEGACY_USE_ONLY,
    &SHA1_PKCS1_DIGESTINFO_PREFIX,
    "PKCS#1 1.5 padding using SHA-1 for RSA signatures."
);
rsa_pkcs1_padding!(
    RSA_PKCS1_SHA256,
    &digest::SHA256,
    &SHA256_PKCS1_DIGESTINFO_PREFIX,
    "PKCS#1 1.5 padding using SHA-256 for RSA signatures."
);
rsa_pkcs1_padding!(
    RSA_PKCS1_SHA384,
    &digest::SHA384,
    &SHA384_PKCS1_DIGESTINFO_PREFIX,
    "PKCS#1 1.5 padding using SHA-384 for RSA signatures."
);
rsa_pkcs1_padding!(
    RSA_PKCS1_SHA512,
    &digest::SHA512,
    &SHA512_PKCS1_DIGESTINFO_PREFIX,
    "PKCS#1 1.5 padding using SHA-512 for RSA signatures."
);

macro_rules! pkcs1_digestinfo_prefix {
    ( $name:ident, $digest_len:expr, $digest_oid_len:expr,
      [ $( $digest_oid:expr ),* ] ) => {
        static $name: [u8; 2 + 8 + $digest_oid_len] = [
            der::Tag::Sequence as u8, 8 + $digest_oid_len + $digest_len,
                der::Tag::Sequence as u8, 2 + $digest_oid_len + 2,
                    der::Tag::OID as u8, $digest_oid_len, $( $digest_oid ),*,
                    der::Tag::Null as u8, 0,
                der::Tag::OctetString as u8, $digest_len,
        ];
    }
}

pkcs1_digestinfo_prefix!(
    SHA1_PKCS1_DIGESTINFO_PREFIX,
    20,
    5,
    [0x2b, 0x0e, 0x03, 0x02, 0x1a]
);

pkcs1_digestinfo_prefix!(
    SHA256_PKCS1_DIGESTINFO_PREFIX,
    32,
    9,
    [0x60, 0x86, 0x48, 0x01, 0x65, 0x03, 0x04, 0x02, 0x01]
);

pkcs1_digestinfo_prefix!(
    SHA384_PKCS1_DIGESTINFO_PREFIX,
    48,
    9,
    [0x60, 0x86, 0x48, 0x01, 0x65, 0x03, 0x04, 0x02, 0x02]
);

pkcs1_digestinfo_prefix!(
    SHA512_PKCS1_DIGESTINFO_PREFIX,
    64,
    9,
    [0x60, 0x86, 0x48, 0x01, 0x65, 0x03, 0x04, 0x02, 0x03]
);

/// RSA PSS padding as described in [RFC 3447 Section 8.1].
///
/// See "`RSA_PSS_*` Details\" in `ring::signature`'s module-level
/// documentation for more details.
///
/// [RFC 3447 Section 8.1]: https://tools.ietf.org/html/rfc3447#section-8.1
#[derive(Debug)]
pub struct PSS {
    digest_alg: &'static digest::Algorithm,
}

impl crate::sealed::Sealed for PSS {}

// Maximum supported length of the salt in bytes.
// In practice, this is constrained by the maximum digest length.
const MAX_SALT_LEN: usize = digest::MAX_OUTPUT_LEN;

impl Padding for PSS {
    fn digest_alg(&self) -> &'static digest::Algorithm {
        self.digest_alg
    }
}

impl RsaEncoding for PSS {
    // Implement padding procedure per EMSA-PSS,
    // https://tools.ietf.org/html/rfc3447#section-9.1.
    fn encode(
        &self,
        m_hash: &digest::Digest,
        m_out: &mut [u8],
        mod_bits: bits::BitLength,
        rng: &dyn rand::SecureRandom,
    ) -> Result<(), error::Unspecified> {
        let metrics = PSSMetrics::new(self.digest_alg, mod_bits)?;

        // The `m_out` this function fills is the big-endian-encoded value of `m`
        // from the specification, padded to `k` bytes, where `k` is the length
        // in bytes of the public modulus. The spec says "Note that emLen will
        // be one less than k if modBits - 1 is divisible by 8 and equal to k
        // otherwise." In other words we might need to prefix `em` with a
        // leading zero byte to form a correct value of `m`.
        let em = if metrics.top_byte_mask == 0xff {
            m_out[0] = 0;
            &mut m_out[1..]
        } else {
            m_out
        };
        assert_eq!(em.len(), metrics.em_len);

        // Steps 1 and 2 are done by the caller to produce `m_hash`.

        // Step 3 is done by `PSSMetrics::new()` above.

        // Step 4.
        let mut salt = [0u8; MAX_SALT_LEN];
        let salt = &mut salt[..metrics.s_len];
        rng.fill(salt)?;

        // Step 5 and 6.
        let h_hash = pss_digest(self.digest_alg, m_hash, salt);

        // Re-order steps 7, 8, 9 and 10 so that we first output the db mask
        // into `em`, and then XOR the value of db.

        // Step 9. First output the mask into the out buffer.
        let (mut masked_db, digest_terminator) = em.split_at_mut(metrics.db_len);
        mgf1(self.digest_alg, h_hash.as_ref(), &mut masked_db)?;

        {
            // Steps 7.
            let masked_db = masked_db.iter_mut();
            // `PS` is all zero bytes, so skipping `ps_len` bytes is equivalent
            // to XORing `PS` onto `db`.
            let mut masked_db = masked_db.skip(metrics.ps_len);

            // Step 8.
            *(masked_db.next().ok_or(error::Unspecified)?) ^= 0x01;

            // Step 10.
            for (masked_db_b, salt_b) in masked_db.zip(salt) {
                *masked_db_b ^= *salt_b;
            }
        }

        // Step 11.
        masked_db[0] &= metrics.top_byte_mask;

        // Step 12.
        digest_terminator[..metrics.h_len].copy_from_slice(h_hash.as_ref());
        digest_terminator[metrics.h_len] = 0xbc;

        Ok(())
    }
}

impl Verification for PSS {
    // RSASSA-PSS-VERIFY from https://tools.ietf.org/html/rfc3447#section-8.1.2
    // where steps 1, 2(a), and 2(b) have been done for us.
    fn verify(
        &self,
        m_hash: &digest::Digest,
        m: &mut untrusted::Reader,
        mod_bits: bits::BitLength,
    ) -> Result<(), error::Unspecified> {
        let metrics = PSSMetrics::new(self.digest_alg, mod_bits)?;

        // RSASSA-PSS-VERIFY Step 2(c). The `m` this function is given is the
        // big-endian-encoded value of `m` from the specification, padded to
        // `k` bytes, where `k` is the length in bytes of the public modulus.
        // The spec. says "Note that emLen will be one less than k if
        // modBits - 1 is divisible by 8 and equal to k otherwise," where `k`
        // is the length in octets of the RSA public modulus `n`. In other
        // words, `em` might have an extra leading zero byte that we need to
        // strip before we start the PSS decoding steps which is an artifact of
        // the `Verification` interface.
        if metrics.top_byte_mask == 0xff {
            if m.read_byte()? != 0 {
                return Err(error::Unspecified);
            }
        };
        let em = m;

        // The rest of this function is EMSA-PSS-VERIFY from
        // https://tools.ietf.org/html/rfc3447#section-9.1.2.

        // Steps 1 and 2 are done by the caller to produce `m_hash`.

        // Step 3 is done by `PSSMetrics::new()` above.

        // Step 5, out of order.
        let masked_db = em.read_bytes(metrics.db_len)?;
        let h_hash = em.read_bytes(metrics.h_len)?;

        // Step 4.
        if em.read_byte()? != 0xbc {
            return Err(error::Unspecified);
        }

        // Step 7.
        let mut db = [0u8; PUBLIC_KEY_PUBLIC_MODULUS_MAX_LEN];
        let db = &mut db[..metrics.db_len];

        mgf1(self.digest_alg, h_hash.as_slice_less_safe(), db)?;

        masked_db.read_all(error::Unspecified, |masked_bytes| {
            // Step 6. Check the top bits of first byte are zero.
            let b = masked_bytes.read_byte()?;
            if b & !metrics.top_byte_mask != 0 {
                return Err(error::Unspecified);
            }
            db[0] ^= b;

            // Step 8.
            for i in 1..db.len() {
                db[i] ^= masked_bytes.read_byte()?;
            }
            Ok(())
        })?;

        // Step 9.
        db[0] &= metrics.top_byte_mask;

        // Step 10.
        let ps_len = metrics.ps_len;
        for i in 0..ps_len {
            if db[i] != 0 {
                return Err(error::Unspecified);
            }
        }
        if db[metrics.ps_len] != 1 {
            return Err(error::Unspecified);
        }

        // Step 11.
        let salt = &db[(db.len() - metrics.s_len)..];

        // Step 12 and 13.
        let h_prime = pss_digest(self.digest_alg, m_hash, salt);

        // Step 14.
        if h_hash != *h_prime.as_ref() {
            return Err(error::Unspecified);
        }

        Ok(())
    }
}

struct PSSMetrics {
    #[cfg_attr(not(feature = "alloc"), allow(dead_code))]
    em_len: usize,
    db_len: usize,
    ps_len: usize,
    s_len: usize,
    h_len: usize,
    top_byte_mask: u8,
}

impl PSSMetrics {
    fn new(
        digest_alg: &'static digest::Algorithm,
        mod_bits: bits::BitLength,
    ) -> Result<PSSMetrics, error::Unspecified> {
        let em_bits = mod_bits.try_sub_1()?;
        let em_len = em_bits.as_usize_bytes_rounded_up();
        let leading_zero_bits = (8 * em_len) - em_bits.as_usize_bits();
        debug_assert!(leading_zero_bits < 8);
        let top_byte_mask = 0xffu8 >> leading_zero_bits;

        let h_len = digest_alg.output_len;

        // We require the salt length to be equal to the digest length.
        let s_len = h_len;

        // Step 3 of both `EMSA-PSS-ENCODE` is `EMSA-PSS-VERIFY` requires that
        // we reject inputs where "emLen < hLen + sLen + 2". The definition of
        // `emBits` in RFC 3447 Sections 9.1.1 and 9.1.2 says `emBits` must be
        // "at least 8hLen + 8sLen + 9". Since 9 bits requires two bytes, these
        // two conditions are equivalent. 9 bits are required as the 0x01
        // before the salt requires 1 bit and the 0xbc after the digest
        // requires 8 bits.
        let db_len = em_len.checked_sub(1 + s_len).ok_or(error::Unspecified)?;
        let ps_len = db_len.checked_sub(h_len + 1).ok_or(error::Unspecified)?;

        debug_assert!(em_bits.as_usize_bits() >= (8 * h_len) + (8 * s_len) + 9);

        Ok(PSSMetrics {
            em_len,
            db_len,
            ps_len,
            s_len,
            h_len,
            top_byte_mask,
        })
    }
}

// Mask-generating function MGF1 as described in
// https://tools.ietf.org/html/rfc3447#appendix-B.2.1.
fn mgf1(
    digest_alg: &'static digest::Algorithm,
    seed: &[u8],
    mask: &mut [u8],
) -> Result<(), error::Unspecified> {
    let digest_len = digest_alg.output_len;

    // Maximum counter value is the value of (mask_len / digest_len) rounded up.
    let ctr_max = (mask.len() - 1) / digest_len;
    assert!(ctr_max <= u32::max_value() as usize);
    for (i, mask_chunk) in mask.chunks_mut(digest_len).enumerate() {
        let mut ctx = digest::Context::new(digest_alg);
        ctx.update(seed);
        ctx.update(&u32::to_be_bytes(i as u32));
        let digest = ctx.finish();
        let mask_chunk_len = mask_chunk.len();
        mask_chunk.copy_from_slice(&digest.as_ref()[..mask_chunk_len]);
    }

    Ok(())
}

fn pss_digest(
    digest_alg: &'static digest::Algorithm,
    m_hash: &digest::Digest,
    salt: &[u8],
) -> digest::Digest {
    // Fixed prefix.
    const PREFIX_ZEROS: [u8; 8] = [0u8; 8];

    // Encoding step 5 and 6, Verification step 12 and 13.
    let mut ctx = digest::Context::new(digest_alg);
    ctx.update(&PREFIX_ZEROS);
    ctx.update(m_hash.as_ref());
    ctx.update(salt);
    ctx.finish()
}

macro_rules! rsa_pss_padding {
    ( $PADDING_ALGORITHM:ident, $digest_alg:expr, $doc_str:expr ) => {
        #[doc=$doc_str]
        pub static $PADDING_ALGORITHM: PSS = PSS {
            digest_alg: $digest_alg,
        };
    };
}

rsa_pss_padding!(
    RSA_PSS_SHA256,
    &digest::SHA256,
    "RSA PSS padding using SHA-256 for RSA signatures.\n\nSee
                 \"`RSA_PSS_*` Details\" in `ring::signature`'s module-level
                 documentation for more details."
);
rsa_pss_padding!(
    RSA_PSS_SHA384,
    &digest::SHA384,
    "RSA PSS padding using SHA-384 for RSA signatures.\n\nSee
                 \"`RSA_PSS_*` Details\" in `ring::signature`'s module-level
                 documentation for more details."
);
rsa_pss_padding!(
    RSA_PSS_SHA512,
    &digest::SHA512,
    "RSA PSS padding using SHA-512 for RSA signatures.\n\nSee
                 \"`RSA_PSS_*` Details\" in `ring::signature`'s module-level
                 documentation for more details."
);

#[cfg(test)]
mod test {
    use super::*;
    use crate::{digest, error, test};
    use alloc::vec;

    #[test]
    fn test_pss_padding_verify() {
        test::run(
            test_file!("rsa_pss_padding_tests.txt"),
            |section, test_case| {
                assert_eq!(section, "");

                let digest_name = test_case.consume_string("Digest");
                let alg = match digest_name.as_ref() {
                    "SHA256" => &RSA_PSS_SHA256,
                    "SHA384" => &RSA_PSS_SHA384,
                    "SHA512" => &RSA_PSS_SHA512,
                    _ => panic!("Unsupported digest: {}", digest_name),
                };

                let msg = test_case.consume_bytes("Msg");
                let msg = untrusted::Input::from(&msg);
                let m_hash = digest::digest(alg.digest_alg(), msg.as_slice_less_safe());

                let encoded = test_case.consume_bytes("EM");
                let encoded = untrusted::Input::from(&encoded);

                // Salt is recomputed in verification algorithm.
                let _ = test_case.consume_bytes("Salt");

                let bit_len = test_case.consume_usize_bits("Len");
                let is_valid = test_case.consume_string("Result") == "P";

                let actual_result =
                    encoded.read_all(error::Unspecified, |m| alg.verify(&m_hash, m, bit_len));
                assert_eq!(actual_result.is_ok(), is_valid);

                Ok(())
            },
        );
    }

    // Tests PSS encoding for various public modulus lengths.
    #[cfg(feature = "alloc")]
    #[test]
    fn test_pss_padding_encode() {
        test::run(
            test_file!("rsa_pss_padding_tests.txt"),
            |section, test_case| {
                assert_eq!(section, "");

                let digest_name = test_case.consume_string("Digest");
                let alg = match digest_name.as_ref() {
                    "SHA256" => &RSA_PSS_SHA256,
                    "SHA384" => &RSA_PSS_SHA384,
                    "SHA512" => &RSA_PSS_SHA512,
                    _ => panic!("Unsupported digest: {}", digest_name),
                };

                let msg = test_case.consume_bytes("Msg");
                let salt = test_case.consume_bytes("Salt");
                let encoded = test_case.consume_bytes("EM");
                let bit_len = test_case.consume_usize_bits("Len");
                let expected_result = test_case.consume_string("Result");

                // Only test the valid outputs
                if expected_result != "P" {
                    return Ok(());
                }

                let rng = test::rand::FixedSliceRandom { bytes: &salt };

                let mut m_out = vec![0u8; bit_len.as_usize_bytes_rounded_up()];
                let digest = digest::digest(alg.digest_alg(), &msg);
                alg.encode(&digest, &mut m_out, bit_len, &rng).unwrap();
                assert_eq!(m_out, encoded);

                Ok(())
            },
        );
    }
}