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
 602
 603
 604
 605
 606
 607
 608
 609
 610
 611
 612
 613
 614
 615
 616
 617
 618
 619
 620
 621
 622
 623
 624
 625
 626
 627
 628
 629
 630
 631
 632
 633
 634
 635
 636
 637
 638
 639
 640
 641
 642
 643
 644
 645
 646
 647
 648
 649
 650
 651
 652
 653
 654
 655
 656
 657
 658
 659
 660
 661
 662
 663
 664
 665
 666
 667
 668
 669
 670
 671
 672
 673
 674
 675
 676
 677
 678
 679
 680
 681
 682
 683
 684
 685
 686
 687
 688
 689
 690
 691
 692
 693
 694
 695
 696
 697
 698
 699
 700
 701
 702
 703
 704
 705
 706
 707
 708
 709
 710
 711
 712
 713
 714
 715
 716
 717
 718
 719
 720
 721
 722
 723
 724
 725
 726
 727
 728
 729
 730
 731
 732
 733
 734
 735
 736
 737
 738
 739
 740
 741
 742
 743
 744
 745
 746
 747
 748
 749
 750
 751
 752
 753
 754
 755
 756
 757
 758
 759
 760
 761
 762
 763
 764
 765
 766
 767
 768
 769
 770
 771
 772
 773
 774
 775
 776
 777
 778
 779
 780
 781
 782
 783
 784
 785
 786
 787
 788
 789
 790
 791
 792
 793
 794
 795
 796
 797
 798
 799
 800
 801
 802
 803
 804
 805
 806
 807
 808
 809
 810
 811
 812
 813
 814
 815
 816
 817
 818
 819
 820
 821
 822
 823
 824
 825
 826
 827
 828
 829
 830
 831
 832
 833
 834
 835
 836
 837
 838
 839
 840
 841
 842
 843
 844
 845
 846
 847
 848
 849
 850
 851
 852
 853
 854
 855
 856
 857
 858
 859
 860
 861
 862
 863
 864
 865
 866
 867
 868
 869
 870
 871
 872
 873
 874
 875
 876
 877
 878
 879
 880
 881
 882
 883
 884
 885
 886
 887
 888
 889
 890
 891
 892
 893
 894
 895
 896
 897
 898
 899
 900
 901
 902
 903
 904
 905
 906
 907
 908
 909
 910
 911
 912
 913
 914
 915
 916
 917
 918
 919
 920
 921
 922
 923
 924
 925
 926
 927
 928
 929
 930
 931
 932
 933
 934
 935
 936
 937
 938
 939
 940
 941
 942
 943
 944
 945
 946
 947
 948
 949
 950
 951
 952
 953
 954
 955
 956
 957
 958
 959
 960
 961
 962
 963
 964
 965
 966
 967
 968
 969
 970
 971
 972
 973
 974
 975
 976
 977
 978
 979
 980
 981
 982
 983
 984
 985
 986
 987
 988
 989
 990
 991
 992
 993
 994
 995
 996
 997
 998
 999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
// Rust BIP47 Implementation
// Written in 2021 by
//  Straylight <https://github.com/straylight-orbit>
//
// To the extent possible under law, the author(s) have dedicated all
// copyright and related and neighboring rights to this software to
// the public domain worldwide. This software is distributed without
// any warranty.
//
// You should have received a copy of the CC0 Public Domain Dedication
// along with this software.
// If not, see <http://creativecommons.org/publicdomain/zero/1.0/>.

//! # Rust BIP47 Library
//!
//! This library implements the BIP47 standard and provides functionality
//! for generating static payment codes that two parties can use to create
//! a private payment address space between them.
//!
//! Original specification: [BIP-0047](https://github.com/bitcoin/bips/blob/master/bip-0047.mediawiki).
//!
//! ## Usage
//! ```
//! # extern crate bitcoin;
//! # extern crate bip47;
//! # use {bip47::PrivateCode, bip47::PublicCode, bitcoin::Network};
//! # let alice_seed = [0_u8];
//! // Alice constructs her own payment code using a BIP32 seed
//! let alice_private = PrivateCode::from_seed(&alice_seed, 0, Network::Bitcoin).unwrap();
//!
//! // Alice parses Bob's payment code
//! let bob_public = PublicCode::from_wif("PM8TJS2JxQ5ztXUpBBRnpTbcUXbUHy2T1abfrb3KkAAtMEGNbey4oumH7Hc578WgQJhPjBxteQ5GHHToTYHE3A1w6p7tU6KSoFmWBVbFGjKPisZDbP97").unwrap();
//!
//! // Alice calculates Bob's receive address at index 0, known only to them
//! let bob_address_0 = bob_public.address(&alice_private, 0, false).unwrap();
//!
//! // Alice can now pay Bob privately
//! assert_eq!("12edoJAofkjCsWrtmVjuQgMUKJ6Z7Ntpzx", bob_address_0.to_string());
//!
//! ```

use std::str::FromStr;

pub extern crate bitcoin;

use bitcoin::hashes::{sha256, Hash};
use bitcoin::secp256k1::Secp256k1;
use bitcoin::util::address::{self, Address};
use bitcoin::util::bip32::{ChainCode, ChildNumber, DerivationPath, ExtendedPubKey};
use bitcoin::util::psbt::serialize::Serialize;
use bitcoin::util::{base58, bip32};
use bitcoin::{secp256k1, OutPoint, PrivateKey, PublicKey, Script, Transaction};

const PAYMENT_CODE_BIN_LENGTH: usize = 80;
const LETTER_P: u8 = 0x47;

/// Represents the version number of a BIP47 payment code.
#[derive(Debug, Clone)]
pub enum Version {
    V1,
    V2,
}

impl Version {
    /// Returns the byte representation of a version.
    pub fn as_byte(&self) -> u8 {
        match self {
            Version::V1 => 0x01,
            Version::V2 => 0x02,
        }
    }

    /// Constructs a `Version` enum from a byte
    pub fn from_byte(value: u8) -> Result<Self, Error> {
        match value {
            0x01 => Ok(Version::V1),
            0x02 => Ok(Version::V2),
            _ => Err(Error::UnsupportedVersion),
        }
    }
}

/// Represents the private side of a payment code, as seen from the perspective of the sender.
/// This is what the sender will use in conjunction with a receiver's public payment code in order
/// to be able to send funds.
pub struct PrivateCode {
    identity_key: bip32::ExtendedPrivKey,
    curve: Secp256k1<secp256k1::All>,
    network: bitcoin::Network,
}

impl PrivateCode {
    /// Constructs a new payment code from the private side using a BIP32 seed.
    pub fn from_seed(
        seed: &[u8],
        account: u32,
        network: bitcoin::Network,
    ) -> Result<Self, bip32::Error> {
        let curve = Secp256k1::new();
        let path = DerivationPath::from_str(&format!("m/47'/0'/{}'", account))?;
        let root_key = bip32::ExtendedPrivKey::new_master(network, seed)?;
        let identity_key = root_key.derive_priv(&curve, &path)?;

        Ok(Self {
            identity_key,
            curve,
            network,
        })
    }

    /// Constructs a new **ephemeral** payment code at the given index from the private side using a BIP32 seed.
    pub fn from_seed_ephemeral(
        seed: &[u8],
        account: u32,
        network: bitcoin::Network,
        ephemeral_index: u32,
    ) -> Result<Self, bip32::Error> {
        let curve = Secp256k1::new();
        let path =
            DerivationPath::from_str(&format!("m/47'/0'/{}'/{}'", account, ephemeral_index))?;
        let root_key = bip32::ExtendedPrivKey::new_master(network, seed)?;
        let identity_key = root_key.derive_priv(&curve, &path)?;

        Ok(Self {
            identity_key,
            curve,
            network,
        })
    }

    /// Generates a version 1 public payment code matching this private payment code, optionally with bitmessage.
    pub fn v1_public_code(&self, bitmessage: Option<BitMessagePreference>) -> PublicCode {
        let xpub = ExtendedPubKey::from_private(&self.curve, &self.identity_key);

        PublicCode {
            version: Version::V1,
            bitmessage,
            xpub,
            curve: self.curve.clone(),
            network: self.network,
        }
    }

    /// Generates a version 2 public payment code matching this private payment code.
    pub fn v2_public_code(&self) -> PublicCode {
        let xpub = ExtendedPubKey::from_private(&self.curve, &self.identity_key);

        PublicCode {
            version: Version::V1,
            bitmessage: None,
            xpub,
            curve: self.curve.clone(),
            network: self.network,
        }
    }

    /// Derives a child private key at the given index. If the result is invalid, the index should be incremented.
    fn child(&self, i: u32) -> Result<PrivateKey, bip32::Error> {
        let child_number = ChildNumber::from_normal_idx(i)?;
        let key = self.identity_key.ckd_priv(&self.curve, child_number)?;

        Ok(key.private_key)
    }

    /// Derives a receive address at the given index. If the index is invalid, it should be incremented.
    pub fn address(
        &self,
        sender_code: &PublicCode,
        i: u32,
        segwit: bool,
    ) -> Result<Address, Error> {
        let sk = self.child(i)?;
        let pk = sender_code.child(0)?;
        let sp = secret_point(&sk, pk)?;
        let ss = shared_secret(sp)?;

        let mut sk_prime = sk.key;
        sk_prime.add_assign(&ss)?;
        let sk_prime = PrivateKey::new(sk_prime, self.network);
        let pk_prime = PublicKey::from_private_key(&self.curve, &sk_prime);

        if segwit {
            Address::p2wpkh(&pk_prime, self.network).map_err(Error::Address)
        } else {
            Ok(Address::p2pkh(&pk_prime, self.network))
        }
    }
}

/// Represents the public side of a payment code. This is what the party that wishes to receive
/// funds shares with sending parties.
#[derive(Debug)]
pub struct PublicCode {
    version: Version,
    bitmessage: Option<BitMessagePreference>,
    xpub: ExtendedPubKey,
    curve: Secp256k1<secp256k1::All>,
    pub network: bitcoin::Network,
}

impl PublicCode {
    /// The version of this BIP47 payment code.
    pub fn version(&self) -> &Version {
        &self.version
    }

    /// Parses a WIF-formatted payment code.
    pub fn from_wif(payment_code: &str) -> Result<Self, Error> {
        PublicCode::try_from_str(payment_code)
    }

    /// Returns the notification mode to be used with this payment code.
    pub fn notification_mode(&self) -> NotificationMode {
        match &self.version {
            Version::V1 => match self.bitmessage.as_ref() {
                Some(bitmessage) => NotificationMode::Bitmessage(Bitmessage {
                    code: self,
                    preferences: bitmessage,
                }),
                None => NotificationMode::BasicTransaction(BasicTransaction(self)),
            },
            Version::V2 => NotificationMode::BloomMultisig(BloomMultisig(self)),
        }
    }

    /// Derives the child public key at the given index. If the result is invalid, the index should be incremented.
    fn child(&self, i: u32) -> Result<PublicKey, bip32::Error> {
        let child_number = ChildNumber::from_normal_idx(i)?;
        let key = self.xpub.ckd_pub(&self.curve, child_number)?;

        Ok(key.public_key)
    }

    /// Derives a send address at the given index. If the index is invalid, it should be incremented.
    pub fn address(&self, code: &PrivateCode, i: u32, segwit: bool) -> Result<Address, Error> {
        let sk = code.child(0)?;
        let pk = self.child(i)?;
        let sp = secret_point(&sk, pk)?;
        let ss = shared_secret(sp)?;

        let ss = secp256k1::SecretKey::from_slice(&ss)?;
        let sg = secp256k1::PublicKey::from_secret_key(&self.curve, &ss);
        let pk_prime = PublicKey::new(sg.combine(&pk.key)?);

        if segwit {
            Address::p2wpkh(&pk_prime, self.network).map_err(Error::Address)
        } else {
            Ok(Address::p2pkh(&pk_prime, self.network))
        }
    }

    /// Interprets the payment code as an 80 byte long array.
    fn as_bytes(&self) -> [u8; PAYMENT_CODE_BIN_LENGTH] {
        let mut payment_code = [0_u8; PAYMENT_CODE_BIN_LENGTH];

        payment_code[0] = self.version.as_byte();
        payment_code[1] = if self.bitmessage.is_some() {
            0x80
        } else {
            0x00
        };
        payment_code[2..35].copy_from_slice(&self.xpub.public_key.serialize());
        payment_code[35..67].copy_from_slice(self.xpub.chain_code.as_bytes());

        if let Some(bitmessage) = &self.bitmessage {
            payment_code[67] = bitmessage.version;
            payment_code[68] = bitmessage.stream_number;
        }

        payment_code
    }

    /// Attempts to extract a public payment code from a notification transaction. If the designated pubkey
    /// and input are unknown and set to `None`, automatic extraction will be attempted. They can also be
    /// supplied if they are known (for example if acquired through a side channel).
    pub fn from_notification(
        receiver_code: &PrivateCode,
        designated: Option<(PublicKey, OutPoint)>,
        tx: &Transaction,
    ) -> Result<Self, Error> {
        let (designated_pk, designated_utxo) =
            designated
                .or_else(|| find_designated(tx))
                .ok_or(Error::Notification(
                    "Designated pubkey and output not found",
                ))?;

        let notification_sk = receiver_code.child(0)?;

        let blinding_factor = blinding_factor(&notification_sk, &designated_pk, &designated_utxo)?;

        let op_return = tx
            .output
            .iter()
            .find(|out| out.script_pubkey.is_op_return())
            .ok_or(Error::Notification("OP_RETURN not found"))?;

        use bitcoin::blockdata::script::Instruction::PushBytes;

        // skip the OP_RETURN opcode, move on to the actual bytes
        if let Some(Ok(PushBytes(data))) = op_return.script_pubkey.instructions().nth(1) {
            if data.len() == PAYMENT_CODE_BIN_LENGTH {
                let mut code_bytes: [u8; PAYMENT_CODE_BIN_LENGTH] = [0; PAYMENT_CODE_BIN_LENGTH];
                code_bytes.copy_from_slice(data);

                blind_payment_code(&mut code_bytes, &blinding_factor);

                PublicCode::try_from_bytes(&code_bytes[..])
            } else {
                Err(Error::Notification("OP_RETURN incorrect length"))
            }
        } else {
            Err(Error::Notification("OP_RETURN not found"))
        }
    }
}

impl std::fmt::Display for PublicCode {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        let bytes = self.as_bytes();
        let mut extended: Vec<u8> = Vec::with_capacity(1 + PAYMENT_CODE_BIN_LENGTH);

        extended.push(LETTER_P);
        extended.extend_from_slice(&bytes);

        base58::check_encode_slice_to_fmt(f, &extended)
    }
}

impl PublicCode {
    fn try_from_bytes(payment_code: &[u8]) -> Result<Self, Error> {
        if payment_code.len() != PAYMENT_CODE_BIN_LENGTH {
            return Err(Error::Format("Incorrect binary length"));
        }

        let version = Version::from_byte(payment_code[0])?;
        let bitmessage = payment_code[1] == 0x80;
        let public_key = PublicKey::from_slice(&payment_code[2..35])?;
        let chain_code = ChainCode::from(&payment_code[35..67]);
        let bitmessage = if bitmessage {
            Some(BitMessagePreference {
                version: payment_code[67],
                stream_number: payment_code[68],
            })
        } else {
            None
        };

        // when parsing a WIF-formatted paymenty code, we assume mainnet
        let network = bitcoin::Network::Bitcoin;

        let xpub = ExtendedPubKey {
            network,
            chain_code,
            child_number: ChildNumber::Normal { index: 0 },
            depth: 3,
            parent_fingerprint: bip32::Fingerprint::default(),
            public_key,
        };

        Ok(Self {
            version,
            bitmessage,
            xpub,
            curve: Secp256k1::new(),
            network,
        })
    }

    fn try_from_str(value: &str) -> Result<Self, Error> {
        let payment_code = base58::from_check(value).map_err(Error::Base58)?;

        if payment_code.first() != Some(&LETTER_P) {
            return Err(Error::Format("Incorrect format version"));
        }

        PublicCode::try_from_bytes(&payment_code[1..])
    }
}

/// The notification mode to be used with a payment code.
pub enum NotificationMode<'a> {
    BasicTransaction(BasicTransaction<'a>),
    Bitmessage(Bitmessage<'a>),
    BloomMultisig(BloomMultisig<'a>),
}

/// Represents the on-chain notification mode and provides functionality for constructing
/// an on-chain notification message.
pub struct BasicTransaction<'a>(&'a PublicCode);

impl<'a> BasicTransaction<'a> {
    /// Derives the notification address belonging to this payment code.
    pub fn notification_address(&self, segwit: bool) -> Result<Address, Error> {
        let child = self
            .0
            .xpub
            .ckd_pub(&self.0.curve, ChildNumber::from_normal_idx(0)?);
        let key = child?.public_key;

        if segwit {
            Address::p2wpkh(&key, self.0.network).map_err(Error::Address)
        } else {
            Ok(Address::p2pkh(&key, self.0.network))
        }
    }

    /// Generates output scripts (scriptpubkeys) for a v1 notification transaction. Both outputs must
    /// be included and the notification input and key must not be easily associated with the sender.
    pub fn make_notification_scripts(
        &self,
        sender_code: &PublicCode,
        notification_sk: &PrivateKey,
        notification_utxo: &bitcoin::OutPoint,
    ) -> Result<(Script, Script), Error> {
        make_v1_notification_scripts(sender_code, self.0, notification_sk, notification_utxo)
    }
}

/// Represents the Bitmessage notification mode and provides functionality for constructing
/// a Bitmessage notification message.
pub struct Bitmessage<'a> {
    code: &'a PublicCode,
    preferences: &'a BitMessagePreference,
}

impl<'a> Bitmessage<'a> {
    /// Makes the required parameters needed to send a bitmessage to a recipient.
    pub fn make_send_params(&self, n: u32) -> Result<BitMessageSendParams, Error> {
        let signing_key = self
            .code
            .xpub
            .ckd_pub(&self.code.curve, ChildNumber::from_normal_idx(0)?)?
            .ckd_pub(&self.code.curve, ChildNumber::from_normal_idx(0)?)?
            .public_key;

        let encryption_key = self
            .code
            .xpub
            .ckd_pub(&self.code.curve, ChildNumber::from_normal_idx(0)?)?
            .ckd_pub(&self.code.curve, ChildNumber::from_normal_idx(n)?)?
            .public_key;

        Ok(BitMessageSendParams {
            encryption_key,
            signing_key,
            stream_number: self.preferences.stream_number,
            version: self.preferences.version,
        })
    }
}

/// Represents the "bloom-multisig" (also known as v2) notification mode and provides functionality for
/// constructing an on-chain notification message.
pub struct BloomMultisig<'a>(&'a PublicCode);

impl<'a> BloomMultisig<'a> {
    /// Generates a bloom filter identifier to watch for. This is what the receiving party
    /// should add to their bloom filter in order to notice bloom filter type notifications.
    pub fn identifier(&self) -> Vec<u8> {
        let hashed_payment_code = sha256::Hash::hash(&self.0.as_bytes());
        let mut identifier = Vec::with_capacity(33);
        identifier.push(0x02_u8);
        identifier.extend_from_slice(&hashed_payment_code);
        identifier
    }

    /// Generates output scripts for a v2 notification transaction. The change key belongs to the **sender's wallet**.
    pub fn notification_params(
        &self,
        sender_code: &PublicCode,
        notification_sk: &PrivateKey,
        notification_utxo: &bitcoin::OutPoint,
        change_pk: &PublicKey,
    ) -> Result<(Script, Script), Error> {
        use bitcoin::blockdata::opcodes::all as opcode;
        use bitcoin::blockdata::script::Builder;

        let op_return_script = {
            let notification_pk = self.0.child(0)?;
            let blinding_factor =
                blinding_factor(notification_sk, &notification_pk, notification_utxo)?;

            let mut sender_code = sender_code.as_bytes();
            blind_payment_code(&mut sender_code, &blinding_factor);

            Script::new_op_return(&sender_code)
        };

        // lexicographic ordering
        let serialized_pk = change_pk.serialize();
        let identifier = self.identifier();
        let (first_push, second_push) = match &serialized_pk.cmp(&identifier) {
            std::cmp::Ordering::Less => (serialized_pk, identifier),
            _ => (identifier, serialized_pk),
        };

        let multisig_script = Builder::new()
            .push_opcode(opcode::OP_PUSHNUM_1)
            .push_slice(&first_push)
            .push_slice(&second_push)
            .push_opcode(opcode::OP_PUSHNUM_2)
            .push_opcode(opcode::OP_CHECKMULTISIG)
            .into_script();

        Ok((multisig_script, op_return_script))
    }
}

/// A set of Bitmessage preferences indicated by the receiving party.
#[derive(Debug)]
pub struct BitMessagePreference {
    pub version: u8,
    pub stream_number: u8,
}

/// Contains all the parameters needed to send a bitmessage to a recipient.
#[derive(Debug)]
pub struct BitMessageSendParams {
    pub signing_key: PublicKey,
    pub encryption_key: PublicKey,
    pub version: u8,
    pub stream_number: u8,
}

/// Calculates a secret point given a private key and a public key.
fn secret_point(sk: &PrivateKey, mut pk: PublicKey) -> Result<[u8; 32], secp256k1::Error> {
    let _ = pk.key.mul_assign(&Secp256k1::new(), &sk.to_bytes())?;
    let mut point = [0_u8; 32];
    point.copy_from_slice(&pk.key.serialize()[1..]);
    Ok(point)
}

/// Calculates a shared secret given a secret point.
fn shared_secret(secret_point: [u8; 32]) -> Result<[u8; 32], secp256k1::Error> {
    let hash = sha256::Hash::hash(&secret_point);
    secp256k1::SecretKey::from_slice(&hash)?;
    Ok(hash.into_inner())
}

/// Calculates a blinding factor. The operation is symmetrical, therefore the key combination can be:
/// 1. notification private key, designated public key
/// 2. designated private key, notification public key
fn blinding_factor(
    sk: &PrivateKey,
    pk: &PublicKey,
    utxo: &bitcoin::OutPoint,
) -> Result<[u8; 64], secp256k1::Error> {
    let mut pk = pk.key;
    pk.mul_assign(&Secp256k1::new(), &sk.to_bytes())?;

    let mut encoded_utxo = Vec::with_capacity(36);
    encoded_utxo.extend_from_slice(&utxo.txid);
    encoded_utxo.extend_from_slice(&u32_to_le_bytes(utxo.vout));

    use bitcoin::hashes::{self, sha512, HashEngine, Hmac};
    let mut hmac = hashes::hmac::HmacEngine::<sha512::Hash>::new(&encoded_utxo);
    hmac.input(&pk.serialize()[1..]);
    let hash = Hmac::<sha512::Hash>::from_engine(hmac);

    Ok(hash.into_inner())
}

/// Blinds a payment code using a byte mask.
fn blind_payment_code(bytes: &mut [u8; PAYMENT_CODE_BIN_LENGTH], mask: &[u8; 64]) {
    bytes
        .iter_mut()
        .skip(3)
        .zip(mask.iter())
        .for_each(|(a, b)| {
            *a ^= b;
        });
}

/// Generates outputs for a notification transaction. Both outputs must be included and the notification
/// input and key must not be easily associated with the sender.
fn make_v1_notification_scripts(
    sender_code: &PublicCode,
    recipient_code: &PublicCode,
    notification_sk: &PrivateKey,
    notification_utxo: &bitcoin::OutPoint,
) -> Result<(Script, Script), Error> {
    let notification_pk = recipient_code.child(0)?;
    let blinding_factor = blinding_factor(notification_sk, &notification_pk, notification_utxo)?;

    let mut sender_code = sender_code.as_bytes();
    blind_payment_code(&mut sender_code, &blinding_factor);

    Ok((
        bitcoin::Script::new_p2pkh(&notification_pk.pubkey_hash()),
        bitcoin::Script::new_op_return(&sender_code),
    ))
}

/// Attempts to extract the designated input and its associated pubkey from a transaction.
/// A designated input is the first input whose scriptsig or witness exposes a pubkey
/// (designated pubkey).
fn find_designated(tx: &Transaction) -> Option<(PublicKey, OutPoint)> {
    use bitcoin::blockdata::script::Instruction::PushBytes;

    fn from_scriptsig(tx: &Transaction) -> Option<(PublicKey, OutPoint)> {
        tx.input
            .iter()
            .filter_map(|tx_in| {
                let first_pk = tx_in
                    .script_sig
                    .instructions()
                    .filter_map(|op| match op {
                        Ok(PushBytes(bytes)) => PublicKey::from_slice(bytes).ok(),
                        _ => None,
                    })
                    .next();

                first_pk.map(|pk| (pk, tx_in.previous_output))
            })
            .next()
    }

    fn from_witness(tx: &Transaction) -> Option<(PublicKey, OutPoint)> {
        tx.input
            .iter()
            .filter_map(|tx_in| {
                let first_pk = tx_in
                    .witness
                    .iter()
                    .filter_map(|witness| PublicKey::from_slice(witness).ok())
                    .next();

                first_pk.map(|pk| (pk, tx_in.previous_output))
            })
            .next()
    }

    from_scriptsig(tx).or_else(|| from_witness(tx))
}

/// Represents an error as pertaining to BIP47 operations.
#[derive(Debug, PartialEq, Eq, PartialOrd, Ord, Hash, Clone)]
pub enum Error {
    Format(&'static str),
    Base58(base58::Error),
    Bip32(bip32::Error),
    Ecdsa(secp256k1::Error),
    UnsupportedVersion,
    Notification(&'static str),
    Address(address::Error),
}

impl From<bip32::Error> for Error {
    fn from(error: bip32::Error) -> Self {
        Error::Bip32(error)
    }
}

impl From<secp256k1::Error> for Error {
    fn from(error: secp256k1::Error) -> Self {
        Error::Ecdsa(error)
    }
}

impl From<bitcoin::util::key::Error> for Error {
    fn from(error: bitcoin::util::key::Error) -> Self {
        match error {
            bitcoin::util::key::Error::Base58(error) => Error::Base58(error),
            bitcoin::util::key::Error::Secp256k1(error) => Error::Ecdsa(error),
        }
    }
}

impl From<address::Error> for Error {
    fn from(error: address::Error) -> Self {
        Error::Address(error)
    }
}

fn u32_to_le_bytes(x: u32) -> [u8; 4] {
    let b1: u8 = (x & 0xff) as u8;
    let b2: u8 = ((x >> 8) & 0xff) as u8;
    let b3: u8 = ((x >> 16) & 0xff) as u8;
    let b4: u8 = ((x >> 24) & 0xff) as u8;
    [b1, b2, b3, b4]
}

#[cfg(test)]
#[allow(non_snake_case)]
#[allow(non_upper_case_globals)]
mod tests {
    use std::fmt::Write;
    use std::str::FromStr;

    extern crate bitcoin;

    use bitcoin::hashes::{self, hex::HexIterator};
    use bitcoin::secp256k1::Secp256k1;
    use bitcoin::util::psbt::serialize::Deserialize;
    use bitcoin::{Address, Network, PrivateKey, PublicKey};

    use super::{
        blind_payment_code, blinding_factor, find_designated, make_v1_notification_scripts,
        secret_point, NotificationMode, PrivateCode, PublicCode,
    };

    const ALICE_BIP32_SEED: &str = "64dca76abc9c6f0cf3d212d248c380c4622c8f93b2c425ec6a5567fd5db57e10d3e6f94a2f6af4ac2edb8998072aad92098db73558c323777abf5bd1082d970a";
    const ALICE_PAYMENT_CODE: &str = "PM8TJTLJbPRGxSbc8EJi42Wrr6QbNSaSSVJ5Y3E4pbCYiTHUskHg13935Ubb7q8tx9GVbh2UuRnBc3WSyJHhUrw8KhprKnn9eDznYGieTzFcwQRya4GA";
    const ALICE_NOTIFICATION_ADDRESS: &str = "1JDdmqFLhpzcUwPeinhJbUPw4Co3aWLyzW";
    const ALICE_a0: &str = "8d6a8ecd8ee5e0042ad0cb56e3a971c760b5145c3917a8e7beaf0ed92d7a520c";
    const ALICE_A0: &str = "0353883a146a23f988e0f381a9507cbdb3e3130cd81b3ce26daf2af088724ce683";

    const BOB_BIP32_SEED: &str = "87eaaac5a539ab028df44d9110defbef3797ddb805ca309f61a69ff96dbaa7ab5b24038cf029edec5235d933110f0aea8aeecf939ed14fc20730bba71e4b1110";
    const BOB_PAYMENT_CODE: &str = "PM8TJS2JxQ5ztXUpBBRnpTbcUXbUHy2T1abfrb3KkAAtMEGNbey4oumH7Hc578WgQJhPjBxteQ5GHHToTYHE3A1w6p7tU6KSoFmWBVbFGjKPisZDbP97";
    const BOB_NOTIFICATION_ADDRESS: &str = "1ChvUUvht2hUQufHBXF8NgLhW8SwE2ecGV";

    const BOB_b0: &str = "04448fd1be0c9c13a5ca0b530e464b619dc091b299b98c5cab9978b32b4a1b8b";
    const BOB_B0: &str = "024ce8e3b04ea205ff49f529950616c3db615b1e37753858cc60c1ce64d17e2ad8";
    const BOB_b1: &str = "6bfa917e4c44349bfdf46346d389bf73a18cec6bc544ce9f337e14721f06107b";
    const BOB_B1: &str = "03e092e58581cf950ff9c8fc64395471733e13f97dedac0044ebd7d60ccc1eea4d";
    const BOB_b2: &str = "46d32fbee043d8ee176fe85a18da92557ee00b189b533fce2340e4745c4b7b8c";
    const BOB_B2: &str = "029b5f290ef2f98a0462ec691f5cc3ae939325f7577fcaf06cfc3b8fc249402156";

    // Secret points are essentially public EC points but the first byte (used for compression)
    // has been ommitted here because that is the way the test vectors were originally written.
    const SECRET_POINT_0: &str = "f5bb84706ee366052471e6139e6a9a969d586e5fe6471a9b96c3d8caefe86fef";
    const SECRET_POINT_1: &str = "adfb9b18ee1c4460852806a8780802096d67a8c1766222598dc801076beb0b4d";
    const SECRET_POINT_2: &str = "79e860c3eb885723bb5a1d54e5cecb7df5dc33b1d56802906762622fa3c18ee5";

    const BOB_ADDR_0: &str = "141fi7TY3h936vRUKh1qfUZr8rSBuYbVBK";
    const BOB_ADDR_1: &str = "12u3Uued2fuko2nY4SoSFGCoGLCBUGPkk6";
    const BOB_ADDR_2: &str = "1FsBVhT5dQutGwaPePTYMe5qvYqqjxyftc";

    const ALICE_DESIGNATED_PRIVATE_KEY: &str =
        "Kx983SRhAZpAhj7Aac1wUXMJ6XZeyJKqCxJJ49dxEbYCT4a1ozRD";
    // The endianess here is reversed with respect to the test vector value for easier parsing.
    // (was "86f411ab1c8e70ae8a0795ab7a6757aea6e4d5ae1826fc7b8f00c597d500609c01000000")
    const ALICE_NOTIFICATION_UTXO: &str =
        "9c6000d597c5008f7bfc2618aed5e4a6ae57677aab95078aae708e1cab11f486:1";
    const NOTIFICATION_BLINDING_FACTOR: &str = "be6e7a4256cac6f4d4ed4639b8c39c4cb8bece40010908e70d17ea9d77b4dc57f1da36f2d6641ccb37cf2b9f3146686462e0fa3161ae74f88c0afd4e307adbd5";
    const ALICE_BLINDED_CODE: &str = "010002063e4eb95e62791b06c50e1a3a942e1ecaaa9afbbeb324d16ae6821e091611fa96c0cf048f607fe51a0327f5e2528979311c78cb2de0d682c61e1180fc3d543b00000000000000000000000000";

    const NOTIFICATION_SCRIPT: &str = "76a9148066a8e7ee82e5c5b9b7dc1765038340dc5420a988ac";
    const OP_RETURN_SCRIPT: &str = "6a4c50010002063e4eb95e62791b06c50e1a3a942e1ecaaa9afbbeb324d16ae6821e091611fa96c0cf048f607fe51a0327f5e2528979311c78cb2de0d682c61e1180fc3d543b00000000000000000000000000";

    const NOTIFICATION_TX: &str = "\
    010000000186f411ab1c8e70ae8a0795ab7a6757aea6e4d5ae1826fc7b8f00c597d500609c010000006b48304502210\
    0ac8c6dbc482c79e86c18928a8b364923c774bfdbd852059f6b3778f2319b59a7022029d7cc5724e2f41ab1fcfc0ba5\
    a0d4f57ca76f72f19530ba97c860c70a6bf0a801210272d83d8a1fa323feab1c085157a0791b46eba34afb8bfbfaeb3\
    a3fcc3f2c9ad8ffffffff0210270000000000001976a9148066a8e7ee82e5c5b9b7dc1765038340dc5420a988ac1027\
    000000000000536a4c50010002063e4eb95e62791b06c50e1a3a942e1ecaaa9afbbeb324d16ae6821e091611fa96c0c\
    f048f607fe51a0327f5e2528979311c78cb2de0d682c61e1180fc3d543b0000000000000000000000000000000000";

    fn from_hex(hex: &str) -> Vec<u8> {
        HexIterator::new(hex)
            .unwrap()
            .filter_map(|a| a.ok())
            .collect()
    }

    fn to_hex(bytes: &[u8]) -> Option<String> {
        let mut s = String::with_capacity(2 * bytes.len());
        for byte in bytes {
            write!(s, "{:02x}", byte).ok()?;
        }
        Some(s)
    }

    #[test]
    fn test_payment_code_from_seed() {
        let seed: Vec<u8> = hashes::hex::FromHex::from_hex(ALICE_BIP32_SEED).unwrap();
        let private = PrivateCode::from_seed(&seed, 0, Network::Bitcoin).unwrap();
        let public = private.v1_public_code(None);

        assert_eq!(public.to_string(), ALICE_PAYMENT_CODE);
    }

    #[test]
    fn test_payment_code_from_text() {
        let payment_code = PublicCode::from_wif(ALICE_PAYMENT_CODE).unwrap();

        assert_eq!(payment_code.to_string(), ALICE_PAYMENT_CODE);
    }

    #[test]
    fn test_notification_address() {
        // Alice
        let alice_payment_code = PublicCode::from_wif(ALICE_PAYMENT_CODE).unwrap();
        if let NotificationMode::BasicTransaction(onchain) = alice_payment_code.notification_mode()
        {
            assert_eq!(
                onchain.notification_address(false).unwrap(),
                Address::from_str(ALICE_NOTIFICATION_ADDRESS).unwrap()
            );
        } else {
            panic!("should not be using bitmessage here");
        }

        // Bob
        let bob_payment_code = PublicCode::from_wif(BOB_PAYMENT_CODE).unwrap();

        if let NotificationMode::BasicTransaction(onchain) = bob_payment_code.notification_mode() {
            assert_eq!(
                onchain.notification_address(false).unwrap(),
                Address::from_str(BOB_NOTIFICATION_ADDRESS).unwrap()
            );
        } else {
            panic!("should not be using bitmessage here");
        }
    }

    #[test]
    #[allow(non_snake_case)]
    fn test_ecdh_params() {
        // Alice
        let alice_seed: Vec<u8> = hashes::hex::FromHex::from_hex(ALICE_BIP32_SEED).unwrap();
        let alice_private = PrivateCode::from_seed(&alice_seed, 0, Network::Bitcoin).unwrap();

        let alice_a0 = alice_private.child(0).unwrap();
        let alice_A0 = PublicKey::from_private_key(&Secp256k1::new(), &alice_a0);
        assert_eq!(ALICE_a0, alice_a0.key.to_string());
        assert_eq!(ALICE_A0, alice_A0.key.to_string());

        // Bob
        let bob_seed: Vec<u8> = hashes::hex::FromHex::from_hex(BOB_BIP32_SEED).unwrap();
        let bob_private = PrivateCode::from_seed(&bob_seed, 0, Network::Bitcoin).unwrap();

        let bob_b0 = bob_private.child(0).unwrap();
        let bob_b1 = bob_private.child(1).unwrap();
        let bob_b2 = bob_private.child(2).unwrap();
        let bob_B0 = PublicKey::from_private_key(&Secp256k1::new(), &bob_b0);
        let bob_B1 = PublicKey::from_private_key(&Secp256k1::new(), &bob_b1);
        let bob_B2 = PublicKey::from_private_key(&Secp256k1::new(), &bob_b2);
        assert_eq!(BOB_b0, bob_b0.key.to_string());
        assert_eq!(BOB_b1, bob_b1.key.to_string());
        assert_eq!(BOB_b2, bob_b2.key.to_string());
        assert_eq!(BOB_B0, bob_B0.key.to_string());
        assert_eq!(BOB_B1, bob_B1.key.to_string());
        assert_eq!(BOB_B2, bob_B2.key.to_string());
    }

    #[test]
    #[allow(non_snake_case)]
    fn test_ecdh_params_from_public() {
        let alice_public = PublicCode::from_wif(ALICE_PAYMENT_CODE).unwrap();

        let alice_A0 = alice_public.child(0).unwrap();
        assert_eq!(ALICE_A0, alice_A0.key.to_string());
    }

    #[test]
    fn test_secret_point_alice_side() {
        let sk = PrivateKey::from_slice(&from_hex(&ALICE_a0), bitcoin::Network::Bitcoin).unwrap();
        let pk0 = PublicKey::from_slice(&from_hex(&BOB_B0)).unwrap();
        let pk1 = PublicKey::from_slice(&from_hex(&BOB_B1)).unwrap();
        let pk2 = PublicKey::from_slice(&from_hex(&BOB_B2)).unwrap();

        let sp0 = secret_point(&sk, pk0).unwrap();
        let sp1 = secret_point(&sk, pk1).unwrap();
        let sp2 = secret_point(&sk, pk2).unwrap();

        assert_eq!(SECRET_POINT_0, to_hex(&sp0).unwrap());
        assert_eq!(SECRET_POINT_1, to_hex(&sp1).unwrap());
        assert_eq!(SECRET_POINT_2, to_hex(&sp2).unwrap());
    }

    #[test]
    fn test_secret_point_bob_side() {
        let pk = PublicKey::from_slice(&from_hex(&ALICE_A0)).unwrap();
        let sk0 = PrivateKey::from_slice(&from_hex(&BOB_b0), bitcoin::Network::Bitcoin).unwrap();
        let sk1 = PrivateKey::from_slice(&from_hex(&BOB_b1), bitcoin::Network::Bitcoin).unwrap();
        let sk2 = PrivateKey::from_slice(&from_hex(&BOB_b2), bitcoin::Network::Bitcoin).unwrap();

        let sp0 = secret_point(&sk0, pk).unwrap();
        let sp1 = secret_point(&sk1, pk).unwrap();
        let sp2 = secret_point(&sk2, pk).unwrap();

        assert_eq!(SECRET_POINT_0, to_hex(&sp0).unwrap());
        assert_eq!(SECRET_POINT_1, to_hex(&sp1).unwrap());
        assert_eq!(SECRET_POINT_2, to_hex(&sp2).unwrap());
    }

    #[test]
    fn test_payment_address_alice_side() {
        let alice_seed: Vec<u8> =
            bitcoin::hashes::hex::FromHex::from_hex(ALICE_BIP32_SEED).unwrap();
        let alice_private = PrivateCode::from_seed(&alice_seed, 0, Network::Bitcoin).unwrap();

        let bob_public = PublicCode::from_wif(BOB_PAYMENT_CODE).unwrap();

        let addr_0 = bob_public.address(&alice_private, 0, false).unwrap();
        let addr_1 = bob_public.address(&alice_private, 1, false).unwrap();
        let addr_2 = bob_public.address(&alice_private, 2, false).unwrap();

        assert_eq!(BOB_ADDR_0, addr_0.to_string());
        assert_eq!(BOB_ADDR_1, addr_1.to_string());
        assert_eq!(BOB_ADDR_2, addr_2.to_string());
    }

    #[test]
    fn test_payment_address_bob_side() {
        let alice_public = PublicCode::from_wif(ALICE_PAYMENT_CODE).unwrap();

        let bob_seed: Vec<u8> = bitcoin::hashes::hex::FromHex::from_hex(BOB_BIP32_SEED).unwrap();
        let bob_private = PrivateCode::from_seed(&bob_seed, 0, Network::Bitcoin).unwrap();

        let addr_0 = bob_private.address(&alice_public, 0, false).unwrap();
        let addr_1 = bob_private.address(&alice_public, 1, false).unwrap();
        let addr_2 = bob_private.address(&alice_public, 2, false).unwrap();

        assert_eq!(BOB_ADDR_0, addr_0.to_string());
        assert_eq!(BOB_ADDR_1, addr_1.to_string());
        assert_eq!(BOB_ADDR_2, addr_2.to_string());
    }

    #[test]
    fn test_blinding() {
        let bob_public = PublicCode::from_wif(BOB_PAYMENT_CODE).unwrap();

        let alice_designated_sk = PrivateKey::from_wif(&ALICE_DESIGNATED_PRIVATE_KEY).unwrap();
        let pk = bob_public.child(0).unwrap();
        let utxo = bitcoin::OutPoint::from_str(ALICE_NOTIFICATION_UTXO).unwrap();

        let blinding_factor = blinding_factor(&alice_designated_sk, &pk, &utxo).unwrap();
        assert_eq!(
            NOTIFICATION_BLINDING_FACTOR,
            to_hex(&blinding_factor).unwrap()
        );

        let alice_public = PublicCode::from_wif(ALICE_PAYMENT_CODE).unwrap();
        let mut alice_bytes = alice_public.as_bytes();

        // Blind
        blind_payment_code(&mut alice_bytes, &blinding_factor);
        assert_eq!(to_hex(&alice_bytes).unwrap(), ALICE_BLINDED_CODE);

        // Unblind
        blind_payment_code(&mut alice_bytes, &blinding_factor);
        assert_eq!(
            PublicCode::try_from_bytes(&alice_bytes)
                .unwrap()
                .to_string(),
            ALICE_PAYMENT_CODE
        );
    }

    #[test]
    fn test_make_v1_notification_scripts() {
        let alice_public = PublicCode::from_wif(ALICE_PAYMENT_CODE).unwrap();
        let bob_public = PublicCode::from_wif(BOB_PAYMENT_CODE).unwrap();

        let alice_notification_private_key =
            PrivateKey::from_wif(ALICE_DESIGNATED_PRIVATE_KEY).unwrap();
        let alice_notification_utxo = bitcoin::OutPoint::from_str(ALICE_NOTIFICATION_UTXO).unwrap();

        let (notification_script, op_return_script) = make_v1_notification_scripts(
            &alice_public,
            &bob_public,
            &alice_notification_private_key,
            &alice_notification_utxo,
        )
        .unwrap();

        assert_eq!(
            to_hex(notification_script.as_bytes()).unwrap(),
            NOTIFICATION_SCRIPT
        );

        assert_eq!(
            to_hex(op_return_script.as_bytes()).unwrap(),
            OP_RETURN_SCRIPT
        );
    }

    #[test]
    fn test_find_designated_in_notification() {
        // p2pkh
        let tx = bitcoin::Transaction::deserialize(&from_hex(NOTIFICATION_TX)).unwrap();

        let expected_designated_input =
            bitcoin::OutPoint::from_str(ALICE_NOTIFICATION_UTXO).unwrap();
        let expected_designated_pk = PrivateKey::from_wif(ALICE_DESIGNATED_PRIVATE_KEY)
            .map(|sk| sk.public_key(&Secp256k1::new()))
            .unwrap();

        let (actual_pk, actual_input) = find_designated(&tx).unwrap();

        assert_eq!(expected_designated_input, actual_input);
        assert_eq!(expected_designated_pk, actual_pk);

        // p2wpkh (these are not in the original test vectors)
        let expected_segwit_input = bitcoin::OutPoint::from_str(
            "1fda2a46b57af5ddb087294ed7f98c218311474336fb92638881db71ec6039f6:91",
        )
        .unwrap();
        let expected_segwit_address =
            Address::from_str("bc1qpflfdc2fu9e4udp788h0pdrehjf202h75m86s0");

        let segwit_tx = bitcoin::Transaction::deserialize(&from_hex("01000000000101f63960ec71db81886392fb3643471183218cf9d74e2987b0ddf57ab5462ada1f5b000000000000000001aa7c0100000000001600145866fcd59dcdabf34dee30abd4c9924ec387830402483045022100f31b80da6c620a2f9d12b65b2010d962390f57560169dde54368b4b5cf122b11022001915d1693cac8bea16e28d941ed7a34eec3bb231a475f5d1616cf5af3f13329012102df62d69f610e2bf7463480a8dd52b96aefeeb3111d66e5e579a0971bc41ce77200000000")).unwrap();

        let (actual_segwit_pk, actual_segwit_input) = find_designated(&segwit_tx).unwrap();

        assert_eq!(expected_segwit_input, actual_segwit_input);
        assert_eq!(
            expected_segwit_address,
            Address::p2wpkh(&actual_segwit_pk, Network::Bitcoin)
        );
    }

    #[test]
    fn test_extract_payment_code_from_tx() {
        let tx = bitcoin::Transaction::deserialize(&from_hex(NOTIFICATION_TX)).unwrap();

        let bob_seed: Vec<u8> = bitcoin::hashes::hex::FromHex::from_hex(BOB_BIP32_SEED).unwrap();
        let bob_private = PrivateCode::from_seed(&bob_seed, 0, Network::Bitcoin).unwrap();

        let alice_public = PublicCode::from_notification(&bob_private, None, &tx).unwrap();
        assert_eq!(
            PublicCode::from_wif(ALICE_PAYMENT_CODE)
                .unwrap()
                .to_string(),
            alice_public.to_string()
        );
    }
}