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
// Bitcoin Dev Kit
// Written in 2020 by Alekos Filini <alekos.filini@gmail.com>
//
// Copyright (c) 2020-2021 Bitcoin Dev Kit Developers
//
// This file is licensed under the Apache License, Version 2.0 <LICENSE-APACHE
// or http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your option.
// You may not use this file except in accordance with one or both of these
// licenses.

//! Key formats

use std::any::TypeId;
use std::collections::HashSet;
use std::marker::PhantomData;
use std::ops::Deref;
use std::str::FromStr;

use bitcoin::secp256k1::{self, Secp256k1, Signing};

use bitcoin::util::bip32;
use bitcoin::{Network, PrivateKey, PublicKey};

use miniscript::descriptor::{Descriptor, DescriptorXKey, Wildcard};
pub use miniscript::descriptor::{
    DescriptorPublicKey, DescriptorSecretKey, DescriptorSinglePriv, DescriptorSinglePub, KeyMap,
    SortedMultiVec,
};
pub use miniscript::ScriptContext;
use miniscript::{Miniscript, Terminal};

use crate::descriptor::{CheckMiniscript, DescriptorError};
use crate::wallet::utils::SecpCtx;

#[cfg(feature = "keys-bip39")]
#[cfg_attr(docsrs, doc(cfg(feature = "keys-bip39")))]
pub mod bip39;

/// Set of valid networks for a key
pub type ValidNetworks = HashSet<Network>;

/// Create a set containing mainnet, testnet and regtest
pub fn any_network() -> ValidNetworks {
    vec![
        Network::Bitcoin,
        Network::Testnet,
        Network::Regtest,
        Network::Signet,
    ]
    .into_iter()
    .collect()
}
/// Create a set only containing mainnet
pub fn mainnet_network() -> ValidNetworks {
    vec![Network::Bitcoin].into_iter().collect()
}
/// Create a set containing testnet and regtest
pub fn test_networks() -> ValidNetworks {
    vec![Network::Testnet, Network::Regtest, Network::Signet]
        .into_iter()
        .collect()
}
/// Compute the intersection of two sets
pub fn merge_networks(a: &ValidNetworks, b: &ValidNetworks) -> ValidNetworks {
    a.intersection(b).cloned().collect()
}

/// Container for public or secret keys
#[derive(Debug)]
pub enum DescriptorKey<Ctx: ScriptContext> {
    #[doc(hidden)]
    Public(DescriptorPublicKey, ValidNetworks, PhantomData<Ctx>),
    #[doc(hidden)]
    Secret(DescriptorSecretKey, ValidNetworks, PhantomData<Ctx>),
}

impl<Ctx: ScriptContext> DescriptorKey<Ctx> {
    /// Create an instance given a public key and a set of valid networks
    pub fn from_public(public: DescriptorPublicKey, networks: ValidNetworks) -> Self {
        DescriptorKey::Public(public, networks, PhantomData)
    }

    /// Create an instance given a secret key and a set of valid networks
    pub fn from_secret(secret: DescriptorSecretKey, networks: ValidNetworks) -> Self {
        DescriptorKey::Secret(secret, networks, PhantomData)
    }

    /// Override the computed set of valid networks
    pub fn override_valid_networks(self, networks: ValidNetworks) -> Self {
        match self {
            DescriptorKey::Public(key, _, _) => DescriptorKey::Public(key, networks, PhantomData),
            DescriptorKey::Secret(key, _, _) => DescriptorKey::Secret(key, networks, PhantomData),
        }
    }

    // This method is used internally by `bdk::fragment!` and `bdk::descriptor!`. It has to be
    // public because it is effectively called by external crates, once the macros are expanded,
    // but since it is not meant to be part of the public api we hide it from the docs.
    #[doc(hidden)]
    pub fn extract(
        self,
        secp: &SecpCtx,
    ) -> Result<(DescriptorPublicKey, KeyMap, ValidNetworks), KeyError> {
        match self {
            DescriptorKey::Public(public, valid_networks, _) => {
                Ok((public, KeyMap::default(), valid_networks))
            }
            DescriptorKey::Secret(secret, valid_networks, _) => {
                let mut key_map = KeyMap::with_capacity(1);

                let public = secret
                    .as_public(secp)
                    .map_err(|e| miniscript::Error::Unexpected(e.to_string()))?;
                key_map.insert(public.clone(), secret);

                Ok((public, key_map, valid_networks))
            }
        }
    }
}

/// Enum representation of the known valid [`ScriptContext`]s
#[derive(Debug, Eq, PartialEq, Copy, Clone)]
pub enum ScriptContextEnum {
    /// Legacy scripts
    Legacy,
    /// Segwitv0 scripts
    Segwitv0,
}

impl ScriptContextEnum {
    /// Returns whether the script context is [`ScriptContextEnum::Legacy`]
    pub fn is_legacy(&self) -> bool {
        self == &ScriptContextEnum::Legacy
    }

    /// Returns whether the script context is [`ScriptContextEnum::Segwitv0`]
    pub fn is_segwit_v0(&self) -> bool {
        self == &ScriptContextEnum::Segwitv0
    }
}

/// Trait that adds extra useful methods to [`ScriptContext`]s
pub trait ExtScriptContext: ScriptContext {
    /// Returns the [`ScriptContext`] as a [`ScriptContextEnum`]
    fn as_enum() -> ScriptContextEnum;

    /// Returns whether the script context is [`Legacy`](miniscript::Legacy)
    fn is_legacy() -> bool {
        Self::as_enum().is_legacy()
    }

    /// Returns whether the script context is [`Segwitv0`](miniscript::Segwitv0)
    fn is_segwit_v0() -> bool {
        Self::as_enum().is_segwit_v0()
    }
}

impl<Ctx: ScriptContext + 'static> ExtScriptContext for Ctx {
    fn as_enum() -> ScriptContextEnum {
        match TypeId::of::<Ctx>() {
            t if t == TypeId::of::<miniscript::Legacy>() => ScriptContextEnum::Legacy,
            t if t == TypeId::of::<miniscript::Segwitv0>() => ScriptContextEnum::Segwitv0,
            _ => unimplemented!("Unknown ScriptContext type"),
        }
    }
}

/// Trait for objects that can be turned into a public or secret [`DescriptorKey`]
///
/// The generic type `Ctx` is used to define the context in which the key is valid: some key
/// formats, like the mnemonics used by Electrum wallets, encode internally whether the wallet is
/// legacy or segwit. Thus, trying to turn a valid legacy mnemonic into a `DescriptorKey`
/// that would become part of a segwit descriptor should fail.
///
/// For key types that do care about this, the [`ExtScriptContext`] trait provides some useful
/// methods that can be used to check at runtime which `Ctx` is being used.
///
/// For key types that can do this check statically (because they can only work within a
/// single `Ctx`), the "specialized" trait can be implemented to make the compiler handle the type
/// checking.
///
/// Keys also have control over the networks they support: constructing the return object with
/// [`DescriptorKey::from_public`] or [`DescriptorKey::from_secret`] allows to specify a set of
/// [`ValidNetworks`].
///
/// ## Examples
///
/// Key type valid in any context:
///
/// ```
/// use bdk::bitcoin::PublicKey;
///
/// use bdk::keys::{DescriptorKey, IntoDescriptorKey, KeyError, ScriptContext};
///
/// pub struct MyKeyType {
///     pubkey: PublicKey,
/// }
///
/// impl<Ctx: ScriptContext> IntoDescriptorKey<Ctx> for MyKeyType {
///     fn into_descriptor_key(self) -> Result<DescriptorKey<Ctx>, KeyError> {
///         self.pubkey.into_descriptor_key()
///     }
/// }
/// ```
///
/// Key type that is only valid on mainnet:
///
/// ```
/// use bdk::bitcoin::PublicKey;
///
/// use bdk::keys::{
///     mainnet_network, DescriptorKey, DescriptorPublicKey, DescriptorSinglePub,
///     IntoDescriptorKey, KeyError, ScriptContext,
/// };
///
/// pub struct MyKeyType {
///     pubkey: PublicKey,
/// }
///
/// impl<Ctx: ScriptContext> IntoDescriptorKey<Ctx> for MyKeyType {
///     fn into_descriptor_key(self) -> Result<DescriptorKey<Ctx>, KeyError> {
///         Ok(DescriptorKey::from_public(
///             DescriptorPublicKey::SinglePub(DescriptorSinglePub {
///                 origin: None,
///                 key: self.pubkey,
///             }),
///             mainnet_network(),
///         ))
///     }
/// }
/// ```
///
/// Key type that internally encodes in which context it's valid. The context is checked at runtime:
///
/// ```
/// use bdk::bitcoin::PublicKey;
///
/// use bdk::keys::{DescriptorKey, ExtScriptContext, IntoDescriptorKey, KeyError, ScriptContext};
///
/// pub struct MyKeyType {
///     is_legacy: bool,
///     pubkey: PublicKey,
/// }
///
/// impl<Ctx: ScriptContext + 'static> IntoDescriptorKey<Ctx> for MyKeyType {
///     fn into_descriptor_key(self) -> Result<DescriptorKey<Ctx>, KeyError> {
///         if Ctx::is_legacy() == self.is_legacy {
///             self.pubkey.into_descriptor_key()
///         } else {
///             Err(KeyError::InvalidScriptContext)
///         }
///     }
/// }
/// ```
///
/// Key type that can only work within [`miniscript::Segwitv0`] context. Only the specialized version
/// of the trait is implemented.
///
/// This example deliberately fails to compile, to demonstrate how the compiler can catch when keys
/// are misused. In this case, the "segwit-only" key is used to build a `pkh()` descriptor, which
/// makes the compiler (correctly) fail.
///
/// ```compile_fail
/// use bdk::bitcoin::PublicKey;
/// use std::str::FromStr;
///
/// use bdk::keys::{DescriptorKey, IntoDescriptorKey, KeyError};
///
/// pub struct MySegwitOnlyKeyType {
///     pubkey: PublicKey,
/// }
///
/// impl IntoDescriptorKey<bdk::miniscript::Segwitv0> for MySegwitOnlyKeyType {
///     fn into_descriptor_key(self) -> Result<DescriptorKey<bdk::miniscript::Segwitv0>, KeyError> {
///         self.pubkey.into_descriptor_key()
///     }
/// }
///
/// let key = MySegwitOnlyKeyType {
///     pubkey: PublicKey::from_str("...")?,
/// };
/// let (descriptor, _, _) = bdk::descriptor!(pkh(key))?;
/// //                                       ^^^^^ changing this to `wpkh` would make it compile
///
/// # Ok::<_, Box<dyn std::error::Error>>(())
/// ```
pub trait IntoDescriptorKey<Ctx: ScriptContext>: Sized {
    /// Turn the key into a [`DescriptorKey`] within the requested [`ScriptContext`]
    fn into_descriptor_key(self) -> Result<DescriptorKey<Ctx>, KeyError>;
}

/// Enum for extended keys that can be either `xprv` or `xpub`
///
/// An instance of [`ExtendedKey`] can be constructed from an [`ExtendedPrivKey`](bip32::ExtendedPrivKey)
/// or an [`ExtendedPubKey`](bip32::ExtendedPubKey) by using the `From` trait.
///
/// Defaults to the [`Legacy`](miniscript::Legacy) context.
pub enum ExtendedKey<Ctx: ScriptContext = miniscript::Legacy> {
    /// A private extended key, aka an `xprv`
    Private((bip32::ExtendedPrivKey, PhantomData<Ctx>)),
    /// A public extended key, aka an `xpub`
    Public((bip32::ExtendedPubKey, PhantomData<Ctx>)),
}

impl<Ctx: ScriptContext> ExtendedKey<Ctx> {
    /// Return whether or not the key contains the private data
    pub fn has_secret(&self) -> bool {
        match self {
            ExtendedKey::Private(_) => true,
            ExtendedKey::Public(_) => false,
        }
    }

    /// Transform the [`ExtendedKey`] into an [`ExtendedPrivKey`](bip32::ExtendedPrivKey) for the
    /// given [`Network`], if the key contains the private data
    pub fn into_xprv(self, network: Network) -> Option<bip32::ExtendedPrivKey> {
        match self {
            ExtendedKey::Private((mut xprv, _)) => {
                xprv.network = network;
                Some(xprv)
            }
            ExtendedKey::Public(_) => None,
        }
    }

    /// Transform the [`ExtendedKey`] into an [`ExtendedPubKey`](bip32::ExtendedPubKey) for the
    /// given [`Network`]
    pub fn into_xpub<C: Signing>(
        self,
        network: bitcoin::Network,
        secp: &Secp256k1<C>,
    ) -> bip32::ExtendedPubKey {
        let mut xpub = match self {
            ExtendedKey::Private((xprv, _)) => bip32::ExtendedPubKey::from_private(secp, &xprv),
            ExtendedKey::Public((xpub, _)) => xpub,
        };

        xpub.network = network;
        xpub
    }
}

impl<Ctx: ScriptContext> From<bip32::ExtendedPubKey> for ExtendedKey<Ctx> {
    fn from(xpub: bip32::ExtendedPubKey) -> Self {
        ExtendedKey::Public((xpub, PhantomData))
    }
}

impl<Ctx: ScriptContext> From<bip32::ExtendedPrivKey> for ExtendedKey<Ctx> {
    fn from(xprv: bip32::ExtendedPrivKey) -> Self {
        ExtendedKey::Private((xprv, PhantomData))
    }
}

/// Trait for keys that can be derived.
///
/// When extra metadata are provided, a [`DerivableKey`] can be transofrmed into a
/// [`DescriptorKey`]: the trait [`IntoDescriptorKey`] is automatically implemented
/// for `(DerivableKey, DerivationPath)` and
/// `(DerivableKey, KeySource, DerivationPath)` tuples.
///
/// For key types that don't encode any indication about the path to use (like bip39), it's
/// generally recommended to implemented this trait instead of [`IntoDescriptorKey`]. The same
/// rules regarding script context and valid networks apply.
///
/// ## Examples
///
/// Key types that can be directly converted into an [`ExtendedPrivKey`] or
/// an [`ExtendedPubKey`] can implement only the required `into_extended_key()` method.
///
/// ```
/// use bdk::bitcoin;
/// use bdk::bitcoin::util::bip32;
/// use bdk::keys::{DerivableKey, ExtendedKey, KeyError, ScriptContext};
///
/// struct MyCustomKeyType {
///     key_data: bitcoin::PrivateKey,
///     chain_code: Vec<u8>,
///     network: bitcoin::Network,
/// }
///
/// impl<Ctx: ScriptContext> DerivableKey<Ctx> for MyCustomKeyType {
///     fn into_extended_key(self) -> Result<ExtendedKey<Ctx>, KeyError> {
///         let xprv = bip32::ExtendedPrivKey {
///             network: self.network,
///             depth: 0,
///             parent_fingerprint: bip32::Fingerprint::default(),
///             private_key: self.key_data,
///             chain_code: bip32::ChainCode::from(self.chain_code.as_ref()),
///             child_number: bip32::ChildNumber::Normal { index: 0 },
///         };
///
///         xprv.into_extended_key()
///     }
/// }
/// ```
///
/// Types that don't internally encode the [`Network`](bitcoin::Network) in which they are valid need some extra
/// steps to override the set of valid networks, otherwise only the network specified in the
/// [`ExtendedPrivKey`] or [`ExtendedPubKey`] will be considered valid.
///
/// ```
/// use bdk::bitcoin;
/// use bdk::bitcoin::util::bip32;
/// use bdk::keys::{
///     any_network, DerivableKey, DescriptorKey, ExtendedKey, KeyError, ScriptContext,
/// };
///
/// struct MyCustomKeyType {
///     key_data: bitcoin::PrivateKey,
///     chain_code: Vec<u8>,
/// }
///
/// impl<Ctx: ScriptContext> DerivableKey<Ctx> for MyCustomKeyType {
///     fn into_extended_key(self) -> Result<ExtendedKey<Ctx>, KeyError> {
///         let xprv = bip32::ExtendedPrivKey {
///             network: bitcoin::Network::Bitcoin, // pick an arbitrary network here
///             depth: 0,
///             parent_fingerprint: bip32::Fingerprint::default(),
///             private_key: self.key_data,
///             chain_code: bip32::ChainCode::from(self.chain_code.as_ref()),
///             child_number: bip32::ChildNumber::Normal { index: 0 },
///         };
///
///         xprv.into_extended_key()
///     }
///
///     fn into_descriptor_key(
///         self,
///         source: Option<bip32::KeySource>,
///         derivation_path: bip32::DerivationPath,
///     ) -> Result<DescriptorKey<Ctx>, KeyError> {
///         let descriptor_key = self
///             .into_extended_key()?
///             .into_descriptor_key(source, derivation_path)?;
///
///         // Override the set of valid networks here
///         Ok(descriptor_key.override_valid_networks(any_network()))
///     }
/// }
/// ```
///
/// [`DerivationPath`]: (bip32::DerivationPath)
/// [`ExtendedPrivKey`]: (bip32::ExtendedPrivKey)
/// [`ExtendedPubKey`]: (bip32::ExtendedPubKey)
pub trait DerivableKey<Ctx: ScriptContext = miniscript::Legacy>: Sized {
    /// Consume `self` and turn it into an [`ExtendedKey`]
    ///
    /// This can be used to get direct access to `xprv`s and `xpub`s for types that implement this trait,
    /// like [`Mnemonic`](bip39::Mnemonic) when the `keys-bip39` feature is enabled.
    #[cfg_attr(
        feature = "keys-bip39",
        doc = r##"
```rust
use bdk::bitcoin::Network;
use bdk::keys::{DerivableKey, ExtendedKey};
use bdk::keys::bip39::{Mnemonic, Language};

# fn main() -> Result<(), Box<dyn std::error::Error>> {
let xkey: ExtendedKey =
    Mnemonic::from_phrase(
        "jelly crash boy whisper mouse ecology tuna soccer memory million news short",
        Language::English
    )?
    .into_extended_key()?;
let xprv = xkey.into_xprv(Network::Bitcoin).unwrap();
# Ok(()) }
```
"##
    )]
    fn into_extended_key(self) -> Result<ExtendedKey<Ctx>, KeyError>;

    /// Consume `self` and turn it into a [`DescriptorKey`] by adding the extra metadata, such as
    /// key origin and derivation path
    fn into_descriptor_key(
        self,
        origin: Option<bip32::KeySource>,
        derivation_path: bip32::DerivationPath,
    ) -> Result<DescriptorKey<Ctx>, KeyError> {
        match self.into_extended_key()? {
            ExtendedKey::Private((xprv, _)) => DescriptorSecretKey::XPrv(DescriptorXKey {
                origin,
                xkey: xprv,
                derivation_path,
                wildcard: Wildcard::Unhardened,
            })
            .into_descriptor_key(),
            ExtendedKey::Public((xpub, _)) => DescriptorPublicKey::XPub(DescriptorXKey {
                origin,
                xkey: xpub,
                derivation_path,
                wildcard: Wildcard::Unhardened,
            })
            .into_descriptor_key(),
        }
    }
}

/// Identity conversion
impl<Ctx: ScriptContext> DerivableKey<Ctx> for ExtendedKey<Ctx> {
    fn into_extended_key(self) -> Result<ExtendedKey<Ctx>, KeyError> {
        Ok(self)
    }
}

impl<Ctx: ScriptContext> DerivableKey<Ctx> for bip32::ExtendedPubKey {
    fn into_extended_key(self) -> Result<ExtendedKey<Ctx>, KeyError> {
        Ok(self.into())
    }
}

impl<Ctx: ScriptContext> DerivableKey<Ctx> for bip32::ExtendedPrivKey {
    fn into_extended_key(self) -> Result<ExtendedKey<Ctx>, KeyError> {
        Ok(self.into())
    }
}

/// Output of a [`GeneratableKey`] key generation
pub struct GeneratedKey<K, Ctx: ScriptContext> {
    key: K,
    valid_networks: ValidNetworks,
    phantom: PhantomData<Ctx>,
}

impl<K, Ctx: ScriptContext> GeneratedKey<K, Ctx> {
    fn new(key: K, valid_networks: ValidNetworks) -> Self {
        GeneratedKey {
            key,
            valid_networks,
            phantom: PhantomData,
        }
    }

    /// Consumes `self` and returns the key
    pub fn into_key(self) -> K {
        self.key
    }
}

impl<K, Ctx: ScriptContext> Deref for GeneratedKey<K, Ctx> {
    type Target = K;

    fn deref(&self) -> &Self::Target {
        &self.key
    }
}

// Make generated "derivable" keys themselves "derivable". Also make sure they are assigned the
// right `valid_networks`.
impl<Ctx, K> DerivableKey<Ctx> for GeneratedKey<K, Ctx>
where
    Ctx: ScriptContext,
    K: DerivableKey<Ctx>,
{
    fn into_extended_key(self) -> Result<ExtendedKey<Ctx>, KeyError> {
        self.key.into_extended_key()
    }

    fn into_descriptor_key(
        self,
        origin: Option<bip32::KeySource>,
        derivation_path: bip32::DerivationPath,
    ) -> Result<DescriptorKey<Ctx>, KeyError> {
        let descriptor_key = self.key.into_descriptor_key(origin, derivation_path)?;
        Ok(descriptor_key.override_valid_networks(self.valid_networks))
    }
}

// Make generated keys directly usable in descriptors, and make sure they get assigned the right
// `valid_networks`.
impl<Ctx, K> IntoDescriptorKey<Ctx> for GeneratedKey<K, Ctx>
where
    Ctx: ScriptContext,
    K: IntoDescriptorKey<Ctx>,
{
    fn into_descriptor_key(self) -> Result<DescriptorKey<Ctx>, KeyError> {
        let desc_key = self.key.into_descriptor_key()?;
        Ok(desc_key.override_valid_networks(self.valid_networks))
    }
}

/// Trait for keys that can be generated
///
/// The same rules about [`ScriptContext`] and [`ValidNetworks`] from [`IntoDescriptorKey`] apply.
///
/// This trait is particularly useful when combined with [`DerivableKey`]: if `Self`
/// implements it, the returned [`GeneratedKey`] will also implement it. The same is true for
/// [`IntoDescriptorKey`]: the generated keys can be directly used in descriptors if `Self` is also
/// [`IntoDescriptorKey`].
pub trait GeneratableKey<Ctx: ScriptContext>: Sized {
    /// Type specifying the amount of entropy required e.g. `[u8;32]`
    type Entropy: AsMut<[u8]> + Default;

    /// Extra options required by the `generate_with_entropy`
    type Options;
    /// Returned error in case of failure
    type Error: std::fmt::Debug;

    /// Generate a key given the extra options and the entropy
    fn generate_with_entropy(
        options: Self::Options,
        entropy: Self::Entropy,
    ) -> Result<GeneratedKey<Self, Ctx>, Self::Error>;

    /// Generate a key given the options with a random entropy
    fn generate(options: Self::Options) -> Result<GeneratedKey<Self, Ctx>, Self::Error> {
        use rand::{thread_rng, Rng};

        let mut entropy = Self::Entropy::default();
        thread_rng().fill(entropy.as_mut());
        Self::generate_with_entropy(options, entropy)
    }
}

/// Trait that allows generating a key with the default options
///
/// This trait is automatically implemented if the [`GeneratableKey::Options`] implements [`Default`].
pub trait GeneratableDefaultOptions<Ctx>: GeneratableKey<Ctx>
where
    Ctx: ScriptContext,
    <Self as GeneratableKey<Ctx>>::Options: Default,
{
    /// Generate a key with the default options and a given entropy
    fn generate_with_entropy_default(
        entropy: Self::Entropy,
    ) -> Result<GeneratedKey<Self, Ctx>, Self::Error> {
        Self::generate_with_entropy(Default::default(), entropy)
    }

    /// Generate a key with the default options and a random entropy
    fn generate_default() -> Result<GeneratedKey<Self, Ctx>, Self::Error> {
        Self::generate(Default::default())
    }
}

/// Automatic implementation of [`GeneratableDefaultOptions`] for [`GeneratableKey`]s where
/// `Options` implements `Default`
impl<Ctx, K> GeneratableDefaultOptions<Ctx> for K
where
    Ctx: ScriptContext,
    K: GeneratableKey<Ctx>,
    <K as GeneratableKey<Ctx>>::Options: Default,
{
}

impl<Ctx: ScriptContext> GeneratableKey<Ctx> for bip32::ExtendedPrivKey {
    type Entropy = [u8; 32];

    type Options = ();
    type Error = bip32::Error;

    fn generate_with_entropy(
        _: Self::Options,
        entropy: Self::Entropy,
    ) -> Result<GeneratedKey<Self, Ctx>, Self::Error> {
        // pick a arbitrary network here, but say that we support all of them
        let xprv = bip32::ExtendedPrivKey::new_master(Network::Bitcoin, entropy.as_ref())?;
        Ok(GeneratedKey::new(xprv, any_network()))
    }
}

/// Options for generating a [`PrivateKey`]
///
/// Defaults to creating compressed keys, which save on-chain bytes and fees
#[derive(Debug, Copy, Clone)]
pub struct PrivateKeyGenerateOptions {
    /// Whether the generated key should be "compressed" or not
    pub compressed: bool,
}

impl Default for PrivateKeyGenerateOptions {
    fn default() -> Self {
        PrivateKeyGenerateOptions { compressed: true }
    }
}

impl<Ctx: ScriptContext> GeneratableKey<Ctx> for PrivateKey {
    type Entropy = [u8; secp256k1::constants::SECRET_KEY_SIZE];

    type Options = PrivateKeyGenerateOptions;
    type Error = bip32::Error;

    fn generate_with_entropy(
        options: Self::Options,
        entropy: Self::Entropy,
    ) -> Result<GeneratedKey<Self, Ctx>, Self::Error> {
        // pick a arbitrary network here, but say that we support all of them
        let key = secp256k1::SecretKey::from_slice(&entropy)?;
        let private_key = PrivateKey {
            compressed: options.compressed,
            network: Network::Bitcoin,
            key,
        };

        Ok(GeneratedKey::new(private_key, any_network()))
    }
}

impl<Ctx: ScriptContext, T: DerivableKey<Ctx>> IntoDescriptorKey<Ctx>
    for (T, bip32::DerivationPath)
{
    fn into_descriptor_key(self) -> Result<DescriptorKey<Ctx>, KeyError> {
        self.0.into_descriptor_key(None, self.1)
    }
}

impl<Ctx: ScriptContext, T: DerivableKey<Ctx>> IntoDescriptorKey<Ctx>
    for (T, bip32::KeySource, bip32::DerivationPath)
{
    fn into_descriptor_key(self) -> Result<DescriptorKey<Ctx>, KeyError> {
        self.0.into_descriptor_key(Some(self.1), self.2)
    }
}

fn expand_multi_keys<Pk: IntoDescriptorKey<Ctx>, Ctx: ScriptContext>(
    pks: Vec<Pk>,
    secp: &SecpCtx,
) -> Result<(Vec<DescriptorPublicKey>, KeyMap, ValidNetworks), KeyError> {
    let (pks, key_maps_networks): (Vec<_>, Vec<_>) = pks
        .into_iter()
        .map(|key| key.into_descriptor_key()?.extract(secp))
        .collect::<Result<Vec<_>, _>>()?
        .into_iter()
        .map(|(a, b, c)| (a, (b, c)))
        .unzip();

    let (key_map, valid_networks) = key_maps_networks.into_iter().fold(
        (KeyMap::default(), any_network()),
        |(mut keys_acc, net_acc), (key, net)| {
            keys_acc.extend(key.into_iter());
            let net_acc = merge_networks(&net_acc, &net);

            (keys_acc, net_acc)
        },
    );

    Ok((pks, key_map, valid_networks))
}

// Used internally by `bdk::fragment!` to build `pk_k()` fragments
#[doc(hidden)]
pub fn make_pk<Pk: IntoDescriptorKey<Ctx>, Ctx: ScriptContext>(
    descriptor_key: Pk,
    secp: &SecpCtx,
) -> Result<(Miniscript<DescriptorPublicKey, Ctx>, KeyMap, ValidNetworks), DescriptorError> {
    let (key, key_map, valid_networks) = descriptor_key.into_descriptor_key()?.extract(secp)?;
    let minisc = Miniscript::from_ast(Terminal::PkK(key))?;

    minisc.check_minsicript()?;

    Ok((minisc, key_map, valid_networks))
}

// Used internally by `bdk::fragment!` to build `pk_h()` fragments
#[doc(hidden)]
pub fn make_pkh<Pk: IntoDescriptorKey<Ctx>, Ctx: ScriptContext>(
    descriptor_key: Pk,
    secp: &SecpCtx,
) -> Result<(Miniscript<DescriptorPublicKey, Ctx>, KeyMap, ValidNetworks), DescriptorError> {
    let (key, key_map, valid_networks) = descriptor_key.into_descriptor_key()?.extract(secp)?;
    let minisc = Miniscript::from_ast(Terminal::PkH(key))?;

    minisc.check_minsicript()?;

    Ok((minisc, key_map, valid_networks))
}

// Used internally by `bdk::fragment!` to build `multi()` fragments
#[doc(hidden)]
pub fn make_multi<Pk: IntoDescriptorKey<Ctx>, Ctx: ScriptContext>(
    thresh: usize,
    pks: Vec<Pk>,
    secp: &SecpCtx,
) -> Result<(Miniscript<DescriptorPublicKey, Ctx>, KeyMap, ValidNetworks), DescriptorError> {
    let (pks, key_map, valid_networks) = expand_multi_keys(pks, secp)?;
    let minisc = Miniscript::from_ast(Terminal::Multi(thresh, pks))?;

    minisc.check_minsicript()?;

    Ok((minisc, key_map, valid_networks))
}

// Used internally by `bdk::descriptor!` to build `sortedmulti()` fragments
#[doc(hidden)]
pub fn make_sortedmulti<Pk, Ctx, F>(
    thresh: usize,
    pks: Vec<Pk>,
    build_desc: F,
    secp: &SecpCtx,
) -> Result<(Descriptor<DescriptorPublicKey>, KeyMap, ValidNetworks), DescriptorError>
where
    Pk: IntoDescriptorKey<Ctx>,
    Ctx: ScriptContext,
    F: Fn(
        usize,
        Vec<DescriptorPublicKey>,
    ) -> Result<(Descriptor<DescriptorPublicKey>, PhantomData<Ctx>), DescriptorError>,
{
    let (pks, key_map, valid_networks) = expand_multi_keys(pks, secp)?;
    let descriptor = build_desc(thresh, pks)?.0;

    Ok((descriptor, key_map, valid_networks))
}

/// The "identity" conversion is used internally by some `bdk::fragment`s
impl<Ctx: ScriptContext> IntoDescriptorKey<Ctx> for DescriptorKey<Ctx> {
    fn into_descriptor_key(self) -> Result<DescriptorKey<Ctx>, KeyError> {
        Ok(self)
    }
}

impl<Ctx: ScriptContext> IntoDescriptorKey<Ctx> for DescriptorPublicKey {
    fn into_descriptor_key(self) -> Result<DescriptorKey<Ctx>, KeyError> {
        let networks = match self {
            DescriptorPublicKey::SinglePub(_) => any_network(),
            DescriptorPublicKey::XPub(DescriptorXKey { xkey, .. })
                if xkey.network == Network::Bitcoin =>
            {
                mainnet_network()
            }
            _ => test_networks(),
        };

        Ok(DescriptorKey::from_public(self, networks))
    }
}

impl<Ctx: ScriptContext> IntoDescriptorKey<Ctx> for PublicKey {
    fn into_descriptor_key(self) -> Result<DescriptorKey<Ctx>, KeyError> {
        DescriptorPublicKey::SinglePub(DescriptorSinglePub {
            key: self,
            origin: None,
        })
        .into_descriptor_key()
    }
}

impl<Ctx: ScriptContext> IntoDescriptorKey<Ctx> for DescriptorSecretKey {
    fn into_descriptor_key(self) -> Result<DescriptorKey<Ctx>, KeyError> {
        let networks = match &self {
            DescriptorSecretKey::SinglePriv(sk) if sk.key.network == Network::Bitcoin => {
                mainnet_network()
            }
            DescriptorSecretKey::XPrv(DescriptorXKey { xkey, .. })
                if xkey.network == Network::Bitcoin =>
            {
                mainnet_network()
            }
            _ => test_networks(),
        };

        Ok(DescriptorKey::from_secret(self, networks))
    }
}

impl<Ctx: ScriptContext> IntoDescriptorKey<Ctx> for &'_ str {
    fn into_descriptor_key(self) -> Result<DescriptorKey<Ctx>, KeyError> {
        DescriptorSecretKey::from_str(self)
            .map_err(|e| KeyError::Message(e.to_string()))?
            .into_descriptor_key()
    }
}

impl<Ctx: ScriptContext> IntoDescriptorKey<Ctx> for PrivateKey {
    fn into_descriptor_key(self) -> Result<DescriptorKey<Ctx>, KeyError> {
        DescriptorSecretKey::SinglePriv(DescriptorSinglePriv {
            key: self,
            origin: None,
        })
        .into_descriptor_key()
    }
}

/// Errors thrown while working with [`keys`](crate::keys)
#[derive(Debug)]
pub enum KeyError {
    /// The key cannot exist in the given script context
    InvalidScriptContext,
    /// The key is not valid for the given network
    InvalidNetwork,
    /// The key has an invalid checksum
    InvalidChecksum,

    /// Custom error message
    Message(String),

    /// BIP32 error
    Bip32(bitcoin::util::bip32::Error),
    /// Miniscript error
    Miniscript(miniscript::Error),
}

impl_error!(miniscript::Error, Miniscript, KeyError);
impl_error!(bitcoin::util::bip32::Error, Bip32, KeyError);

impl std::fmt::Display for KeyError {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        write!(f, "{:?}", self)
    }
}

impl std::error::Error for KeyError {}

#[cfg(test)]
pub mod test {
    use bitcoin::util::bip32;

    use super::*;

    pub const TEST_ENTROPY: [u8; 32] = [0xAA; 32];

    #[test]
    fn test_keys_generate_xprv() {
        let generated_xprv: GeneratedKey<_, miniscript::Segwitv0> =
            bip32::ExtendedPrivKey::generate_with_entropy_default(TEST_ENTROPY).unwrap();

        assert_eq!(generated_xprv.valid_networks, any_network());
        assert_eq!(generated_xprv.to_string(), "xprv9s21ZrQH143K4Xr1cJyqTvuL2FWR8eicgY9boWqMBv8MDVUZ65AXHnzBrK1nyomu6wdcabRgmGTaAKawvhAno1V5FowGpTLVx3jxzE5uk3Q");
    }

    #[test]
    fn test_keys_generate_wif() {
        let generated_wif: GeneratedKey<_, miniscript::Segwitv0> =
            bitcoin::PrivateKey::generate_with_entropy_default(TEST_ENTROPY).unwrap();

        assert_eq!(generated_wif.valid_networks, any_network());
        assert_eq!(
            generated_wif.to_string(),
            "L2wTu6hQrnDMiFNWA5na6jB12ErGQqtXwqpSL7aWquJaZG8Ai3ch"
        );
    }
}