Implement GetKey for KeyMap

Create a `KeyMay` type to replace the current `BTreeMap` alias and
implement `bitcoin::psbt::GetKey` for it.

Close: rust-bitcoin#709

src/descriptor/key_map.rs

@@ -0,0 +1,287 @@
+// SPDX-License-Identifier: CC0-1.0
+
+//! A map of public key to secret key.
+
+use bitcoin::psbt::{GetKey, GetKeyError, KeyRequest};
+use bitcoin::secp256k1::{Secp256k1, Signing};
+
+use super::{DescriptorPublicKey, DescriptorSecretKey, SinglePubKey};
+use crate::prelude::BTreeMap;
+
+/// Alias type for a map of public key to secret key
+///
+/// This map is returned whenever a descriptor that contains secrets is parsed using
+/// [`Descriptor::parse_descriptor`], since the descriptor will always only contain
+/// public keys. This map allows looking up the corresponding secret key given a
+/// public key from the descriptor.
+#[derive(Debug, Eq, PartialEq, Clone)]
+pub struct KeyMap {
+    /// The map.
+    pub map: BTreeMap<DescriptorPublicKey, DescriptorSecretKey>,
+}
+
+impl KeyMap {
+    /// Creates a new empty `KeyMap`.
+    pub fn new() -> Self { Self { map: BTreeMap::new() } }
+
+    /// Inserts `key` and `value` into the map.
+    ///
+    /// See [`BTreeMap::insert`] for more information.
+    pub fn insert(
+        &mut self,
+        key: DescriptorPublicKey,
+        value: DescriptorSecretKey,
+    ) -> Option<DescriptorSecretKey> {
+        self.map.insert(key, value)
+    }
+
+    /// Gets `key` if it exists.
+    ///
+    /// See [`BTreeMap::insert`] for more information.
+    pub fn get(&self, key: &DescriptorPublicKey) -> Option<&DescriptorSecretKey> {
+        self.map.get(key)
+    }
+
+    /// Returns the number of items in this map.
+    ///
+    /// See [`BTreeMap::insert`] for more information.
+    pub fn len(&self) -> usize { self.map.len() }
+}
+
+impl GetKey for KeyMap {
+    type Error = GetKeyError;
+
+    fn get_key<C: Signing>(
+        &self,
+        key_request: KeyRequest,
+        secp: &Secp256k1<C>,
+    ) -> Result<Option<bitcoin::PrivateKey>, Self::Error> {
+        Ok(self.map.iter().find_map(|(k, v)| {
+            match k {
+                DescriptorPublicKey::Single(ref pk) => match key_request {
+                    KeyRequest::Pubkey(ref request) => match pk.key {
+                        SinglePubKey::FullKey(ref pk) => {
+                            if pk == request {
+                                match v {
+                                    DescriptorSecretKey::Single(ref sk) => Some(sk.key),
+                                    _ => unreachable!("Single maps to Single"),
+                                }
+                            } else {
+                                None
+                            }
+                        }
+                        SinglePubKey::XOnly(_) => None,
+                    },
+                    _ => None,
+                },
+                // Performance: Might be faster to check the origin and then if it matches return
+                // the key directly instead of calling `get_key` on the xpriv.
+                DescriptorPublicKey::XPub(ref xpub) => {
+                    let pk = xpub.xkey.public_key;
+                    match key_request {
+                        KeyRequest::Pubkey(ref request) => {
+                            if pk == request.inner {
+                                match v {
+                                    DescriptorSecretKey::XPrv(xpriv) => {
+                                        let xkey = xpriv.xkey;
+                                        if let Ok(child) = xkey.derive_priv(secp, &xpriv.derivation_path) {
+                                            Some(bitcoin::PrivateKey::new(
+                                                child.private_key,
+                                                xkey.network,
+                                            ))
+                                        } else {
+                                            None
+                                        }
+                                    }
+                                    _ => unreachable!("XPrv maps to XPrv"),
+                                }
+                            } else {
+                                None
+                            }
+                        }
+                        KeyRequest::Bip32(..) => match v {
+                            DescriptorSecretKey::XPrv(xpriv) => {
+                                if let Ok(Some(sk)) = xpriv.xkey.get_key(key_request.clone(), secp) {
+                                    Some(sk)
+                                } else {
+                                    None
+                                }
+                            }
+                            _ => unreachable!("XPrv maps to XPrv"),
+                        },
+                        _ => unreachable!("rust-bitcoin v0.32"),
+                    }
+                }
+                DescriptorPublicKey::MultiXPub(ref xpub) => {
+                    let pk = xpub.xkey.public_key;
+                    match key_request {
+                        KeyRequest::Pubkey(ref request) => {
+                            if pk == request.inner {
+                                match v {
+                                    DescriptorSecretKey::MultiXPrv(xpriv) => {
+                                        Some(xpriv.xkey.to_priv())
+                                    }
+                                    _ => unreachable!("MultiXPrv maps to MultiXPrv"),
+                                }
+                            } else {
+                                None
+                            }
+                        }
+                        KeyRequest::Bip32(..) => match v {
+                            DescriptorSecretKey::MultiXPrv(xpriv) => {
+                                if let Ok(Some(sk)) = xpriv.xkey.get_key(key_request.clone(), secp) {
+                                    Some(sk)
+                                } else {
+                                    None
+                                }
+                            }
+                            _ => unreachable!("MultiXPrv maps to MultiXPrv"),
+                        },
+                        _ => unreachable!("rust-bitcoin v0.32"),
+                    }
+                }
+            }
+        }))
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    // use bitcoin::NetworkKind;
+    use bitcoin::bip32::{ChildNumber, IntoDerivationPath, Xpriv};
+
+    use super::*;
+    use crate::Descriptor;
+
+    #[test]
+    fn get_key_single_key() {
+        let secp = Secp256k1::new();
+
+        let descriptor_sk_s =
+            "[90b6a706/44'/0'/0'/0/0]cMk8gWmj1KpjdYnAWwsEDekodMYhbyYBhG8gMtCCxucJ98JzcNij";
+
+        let single = match descriptor_sk_s.parse::<DescriptorSecretKey>().unwrap() {
+            DescriptorSecretKey::Single(single) => single,
+            _ => panic!("unexpected DescriptorSecretKey variant"),
+        };
+
+        let want_sk = single.key;
+        let descriptor_s = format!("wpkh({})", descriptor_sk_s);
+        let (_, keymap) = Descriptor::parse_descriptor(&secp, &descriptor_s).unwrap();
+
+        let pk = want_sk.public_key(&secp);
+        let request = KeyRequest::Pubkey(pk);
+        let got_sk = keymap
+            .get_key(request, &secp)
+            .expect("get_key call errored")
+            .expect("failed to find the key");
+        assert_eq!(got_sk, want_sk)
+    }
+
+    #[test]
+    fn get_key_xpriv_single_key_xpriv() {
+        let secp = Secp256k1::new();
+
+        let s = "xprv9s21ZrQH143K3QTDL4LXw2F7HEK3wJUD2nW2nRk4stbPy6cq3jPPqjiChkVvvNKmPGJxWUtg6LnF5kejMRNNU3TGtRBeJgk33yuGBxrMPHi";
+
+        let xpriv = s.parse::<Xpriv>().unwrap();
+        let xpriv_fingerprint = xpriv.fingerprint(&secp);
+
+        // Sanity check.
+        {
+            let descriptor_sk_s = format!("[{}]{}", xpriv_fingerprint, xpriv);
+            let descriptor_sk = descriptor_sk_s.parse::<DescriptorSecretKey>().unwrap();
+            let got = match descriptor_sk {
+                DescriptorSecretKey::XPrv(x) => x.xkey,
+                _ => panic!("unexpected DescriptorSecretKey variant"),
+            };
+            assert_eq!(got, xpriv);
+        }
+
+        let want_sk = xpriv.to_priv();
+        let descriptor_s = format!("wpkh([{}]{})", xpriv_fingerprint, xpriv);
+        let (_, keymap) = Descriptor::parse_descriptor(&secp, &descriptor_s).unwrap();
+
+        let pk = want_sk.public_key(&secp);
+        let request = KeyRequest::Pubkey(pk);
+        let got_sk = keymap
+            .get_key(request, &secp)
+            .expect("get_key call errored")
+            .expect("failed to find the key");
+        assert_eq!(got_sk, want_sk)
+    }
+
+    #[test]
+    fn get_key_xpriv_child_depth_one() {
+        let secp = Secp256k1::new();
+
+        let s = "xprv9s21ZrQH143K3QTDL4LXw2F7HEK3wJUD2nW2nRk4stbPy6cq3jPPqjiChkVvvNKmPGJxWUtg6LnF5kejMRNNU3TGtRBeJgk33yuGBxrMPHi";
+        let master = s.parse::<Xpriv>().unwrap();
+        let master_fingerprint = master.fingerprint(&secp);
+
+        let child_number = ChildNumber::from_hardened_idx(44).unwrap();
+        let child = master.derive_priv(&secp, &[child_number]).unwrap();
+
+        // Sanity check.
+        {
+            let descriptor_sk_s = format!("[{}/44']{}", master_fingerprint, child);
+            let descriptor_sk = descriptor_sk_s.parse::<DescriptorSecretKey>().unwrap();
+            let got = match descriptor_sk {
+                DescriptorSecretKey::XPrv(ref x) => x.xkey,
+                _ => panic!("unexpected DescriptorSecretKey variant"),
+            };
+            assert_eq!(got, child);
+        }
+
+        let want_sk = child.to_priv();
+        let descriptor_s = format!("wpkh({}/44')", s);
+        let (_, keymap) = Descriptor::parse_descriptor(&secp, &descriptor_s).unwrap();
+
+        let pk = want_sk.public_key(&secp);
+        let request = KeyRequest::Pubkey(pk);
+        let got_sk = keymap
+            .get_key(request, &secp)
+            .expect("get_key call errored")
+            .expect("failed to find the key");
+        assert_eq!(got_sk, want_sk)
+    }
+
+    #[test]
+    fn get_key_xpriv_with_path() {
+        let secp = Secp256k1::new();
+
+        let s = "xprv9s21ZrQH143K3QTDL4LXw2F7HEK3wJUD2nW2nRk4stbPy6cq3jPPqjiChkVvvNKmPGJxWUtg6LnF5kejMRNNU3TGtRBeJgk33yuGBxrMPHi";
+        let master = s.parse::<Xpriv>().unwrap();
+        let master_fingerprint = master.fingerprint(&secp);
+
+        let first_external_child = "44'/0'/0'/0/0";
+        let derivation_path = first_external_child.into_derivation_path().unwrap();
+
+        let child = master.derive_priv(&secp, &derivation_path).unwrap();
+
+        // Sanity check.
+        {
+            let descriptor_sk_s =
+                format!("[{}/{}]{}", master_fingerprint, first_external_child, child);
+            let descriptor_sk = descriptor_sk_s.parse::<DescriptorSecretKey>().unwrap();
+            let got = match descriptor_sk {
+                DescriptorSecretKey::XPrv(ref x) => x.xkey,
+                _ => panic!("unexpected DescriptorSecretKey variant"),
+            };
+            assert_eq!(got, child);
+        }
+
+        let want_sk = child.to_priv();
+        let descriptor_s = format!("wpkh({}/44'/0'/0'/0/*)", s);
+        let (_, keymap) = Descriptor::parse_descriptor(&secp, &descriptor_s).unwrap();
+
+        let key_source = (master_fingerprint, derivation_path);
+        let request = KeyRequest::Bip32(key_source);
+        let got_sk = keymap
+            .get_key(request, &secp)
+            .expect("get_key call errored")
+            .expect("failed to find the key");
+
+        assert_eq!(got_sk, want_sk)
+    }
+}

src/descriptor/mod.rs

@@ -46,20 +46,14 @@ pub use self::tr::{TapTree, Tr};
 
 pub mod checksum;
 mod key;
+mod key_map;
 
 pub use self::key::{
     ConversionError, DefiniteDescriptorKey, DerivPaths, DescriptorKeyParseError,
     DescriptorMultiXKey, DescriptorPublicKey, DescriptorSecretKey, DescriptorXKey, InnerXKey,
     SinglePriv, SinglePub, SinglePubKey, Wildcard,
 };
-
-/// Alias type for a map of public key to secret key
-///
-/// This map is returned whenever a descriptor that contains secrets is parsed using
-/// [`Descriptor::parse_descriptor`], since the descriptor will always only contain
-/// public keys. This map allows looking up the corresponding secret key given a
-/// public key from the descriptor.
-pub type KeyMap = BTreeMap<DescriptorPublicKey, DescriptorSecretKey>;
+pub use self::key_map::KeyMap;
 
 /// Script descriptor
 #[derive(Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
@@ -728,7 +722,7 @@ impl Descriptor<DescriptorPublicKey> {
             Ok(public_key)
         }
 
-        let mut keymap_pk = KeyMapWrapper(BTreeMap::new(), secp);
+        let mut keymap_pk = KeyMapWrapper(KeyMap::new(), secp);
 
         struct KeyMapWrapper<'a, C: secp256k1::Signing>(KeyMap, &'a secp256k1::Secp256k1<C>);
 

src/plan.rs

@@ -661,7 +661,7 @@ pub trait IntoAssets {
 }
 
 impl IntoAssets for KeyMap {
-    fn into_assets(self) -> Assets { Assets::from_iter(self.into_iter().map(|(k, _)| k)) }
+    fn into_assets(self) -> Assets { Assets::from_iter(self.map.into_iter().map(|(k, _)| k)) }
 }
 
 impl IntoAssets for DescriptorPublicKey {