bitcoin: remove all use of engine/from_engine on opaque hash types

In the next commits we are going to stop exposing the ability to hash
arbitrary data into wrapped hash types like Txid etc. In preparation for
this, stop using these methods internally.

This makes our internal code a little bit uglier and less DRY. An
alternative approach would be to implement the from_engine and engine
methods, but privately (and maybe having a macro to provide this). But I
think this approach is more straightforward.

The one exception is for the Taproot hashes, which are tagged hashes and
currently do not have their own engine type. I will address these in a
later PR because this one is already too big.

bitcoin/src/bip158.rs

@@ -118,7 +118,7 @@ impl FilterHash {
         let mut header_data = [0u8; 64];
         header_data[0..32].copy_from_slice(&self[..]);
         header_data[32..64].copy_from_slice(&previous_filter_header[..]);
-        FilterHeader::hash(&header_data)
+        FilterHeader(sha256d::Hash::hash(&header_data))
     }
 }
 
@@ -146,8 +146,7 @@ impl BlockFilter {
     ///
     /// [BIP 157]: <https://github.com/bitcoin/bips/blob/master/bip-0157.mediawiki#Filter_Headers>
     pub fn filter_header(&self, previous_filter_header: FilterHeader) -> FilterHeader {
-        let filter_hash = FilterHash::hash(self.content.as_slice());
-        filter_hash.filter_header(previous_filter_header)
+        FilterHash(sha256d::Hash::hash(&self.content)).filter_header(previous_filter_header)
     }
 
     /// Returns true if any query matches against this [`BlockFilter`].

bitcoin/src/bip32.rs

@@ -11,7 +11,6 @@ use core::{fmt, slice};
 
 use hashes::{hash160, hash_newtype, sha512, GeneralHash, HashEngine, Hmac, HmacEngine};
 use internals::{impl_array_newtype, write_err};
-use io::Write;
 use secp256k1::{Secp256k1, XOnlyPublicKey};
 
 use crate::crypto::key::{CompressedPublicKey, Keypair, PrivateKey};
@@ -820,9 +819,7 @@ impl Xpub {
 
     /// Returns the HASH160 of the chaincode
     pub fn identifier(&self) -> XKeyIdentifier {
-        let mut engine = XKeyIdentifier::engine();
-        engine.write_all(&self.public_key.serialize()).expect("engines don't error");
-        XKeyIdentifier::from_engine(engine)
+        XKeyIdentifier(hash160::Hash::hash(&self.public_key.serialize()))
     }
 
     /// Returns the first four bytes of the identifier

bitcoin/src/blockdata/block.rs

@@ -73,9 +73,9 @@ impl Header {
 
     /// Returns the block hash.
     pub fn block_hash(&self) -> BlockHash {
-        let mut engine = BlockHash::engine();
+        let mut engine = sha256d::Hash::engine();
         self.consensus_encode(&mut engine).expect("engines don't error");
-        BlockHash::from_engine(engine)
+        BlockHash(sha256d::Hash::from_engine(engine))
     }
 
     /// Computes the target (range [0, T] inclusive) that a blockhash must land in to be valid.
@@ -295,10 +295,10 @@ impl Block {
         witness_root: WitnessMerkleNode,
         witness_reserved_value: &[u8],
     ) -> WitnessCommitment {
-        let mut encoder = WitnessCommitment::engine();
+        let mut encoder = sha256d::Hash::engine();
         witness_root.consensus_encode(&mut encoder).expect("engines don't error");
         encoder.input(witness_reserved_value);
-        WitnessCommitment::from_engine(encoder)
+        WitnessCommitment(sha256d::Hash::from_engine(encoder))
     }
 
     /// Computes the merkle root of transactions hashed for witness.

bitcoin/src/blockdata/script/mod.rs

@@ -109,7 +109,7 @@ impl ScriptHash {
             return Err(RedeemScriptSizeError { size: redeem_script.len() });
         }
 
-        Ok(ScriptHash::hash(redeem_script.as_bytes()))
+        Ok(ScriptHash(hash160::Hash::hash(redeem_script.as_bytes())))
     }
 
     /// Creates a `ScriptHash` from any script irrespective of script size.
@@ -118,7 +118,9 @@ impl ScriptHash {
     /// then the output will be unspendable (see [BIP-16]).
     ///
     /// [BIP-16]: <https://github.com/bitcoin/bips/blob/master/bip-0016.mediawiki#user-content-520byte_limitation_on_serialized_script_size>
-    pub fn from_script_unchecked(script: &Script) -> Self { ScriptHash::hash(script.as_bytes()) }
+    pub fn from_script_unchecked(script: &Script) -> Self {
+        ScriptHash(hash160::Hash::hash(script.as_bytes()))
+    }
 }
 
 impl WScriptHash {
@@ -135,7 +137,7 @@ impl WScriptHash {
             return Err(WitnessScriptSizeError { size: witness_script.len() });
         }
 
-        Ok(WScriptHash::hash(witness_script.as_bytes()))
+        Ok(WScriptHash(sha256::Hash::hash(witness_script.as_bytes())))
     }
 
     /// Creates a `WScriptHash` from any script irrespective of script size.
@@ -144,7 +146,9 @@ impl WScriptHash {
     /// output then the output will be unspendable (see [BIP-141]).
     ///
     /// ref: [BIP-141](https://github.com/bitcoin/bips/blob/master/bip-0141.mediawiki)
-    pub fn from_script_unchecked(script: &Script) -> Self { WScriptHash::hash(script.as_bytes()) }
+    pub fn from_script_unchecked(script: &Script) -> Self {
+        WScriptHash(sha256::Hash::hash(script.as_bytes()))
+    }
 }
 
 impl TryFrom<ScriptBuf> for ScriptHash {

bitcoin/src/blockdata/transaction.rs

@@ -754,12 +754,12 @@ impl Transaction {
     /// this will be equal to [`Transaction::compute_wtxid()`].
     #[doc(alias = "txid")]
     pub fn compute_txid(&self) -> Txid {
-        let mut enc = Txid::engine();
+        let mut enc = sha256d::Hash::engine();
         self.version.consensus_encode(&mut enc).expect("engines don't error");
         self.input.consensus_encode(&mut enc).expect("engines don't error");
         self.output.consensus_encode(&mut enc).expect("engines don't error");
         self.lock_time.consensus_encode(&mut enc).expect("engines don't error");
-        Txid::from_engine(enc)
+        Txid(sha256d::Hash::from_engine(enc))
     }
 
     /// Computes the segwit version of the transaction id.
@@ -778,9 +778,9 @@ impl Transaction {
     /// this will be equal to [`Transaction::txid()`].
     #[doc(alias = "wtxid")]
     pub fn compute_wtxid(&self) -> Wtxid {
-        let mut enc = Wtxid::engine();
+        let mut enc = sha256d::Hash::engine();
         self.consensus_encode(&mut enc).expect("engines don't error");
-        Wtxid::from_engine(enc)
+        Wtxid(sha256d::Hash::from_engine(enc))
     }
 
     /// Returns the weight of this transaction, as defined by BIP-141.

bitcoin/src/crypto/key.rs

@@ -58,7 +58,9 @@ impl PublicKey {
     }
 
     /// Returns bitcoin 160-bit hash of the public key.
-    pub fn pubkey_hash(&self) -> PubkeyHash { self.with_serialized(PubkeyHash::hash) }
+    pub fn pubkey_hash(&self) -> PubkeyHash {
+        PubkeyHash(self.with_serialized(hash160::Hash::hash))
+    }
 
     /// Returns bitcoin 160-bit hash of the public key for witness program
     pub fn wpubkey_hash(&self) -> Result<WPubkeyHash, UncompressedPublicKeyError> {
@@ -275,7 +277,7 @@ pub struct CompressedPublicKey(pub secp256k1::PublicKey);
 
 impl CompressedPublicKey {
     /// Returns bitcoin 160-bit hash of the public key.
-    pub fn pubkey_hash(&self) -> PubkeyHash { PubkeyHash::hash(&self.to_bytes()) }
+    pub fn pubkey_hash(&self) -> PubkeyHash { PubkeyHash(hash160::Hash::hash(&self.to_bytes())) }
 
     /// Returns bitcoin 160-bit hash of the public key for witness program.
     pub fn wpubkey_hash(&self) -> WPubkeyHash {

bitcoin/src/crypto/sighash.rs

@@ -55,6 +55,21 @@ hash_newtype! {
 impl_message_from_hash!(LegacySighash);
 impl_message_from_hash!(SegwitV0Sighash);
 
+// Implement private engine/from_engine methods for use within this module;
+// but outside of it, it should not be possible to construct these hash
+// types from arbitrary data (except by casting via to/from_byte_array).
+//
+// These will be uncommented in the next commit; in this one they cause
+// "duplicate definition" errors against the `hash_newtype!` macro.
+impl LegacySighash {
+    //fn engine() -> sha256::HashEngine { sha256d::Hash::engine() }
+    //fn from_engine(e: sha256::HashEngine) -> Self { Self(sha256d::Hash::from_engine(e)) }
+}
+impl SegwitV0Sighash {
+    //fn engine() -> sha256::HashEngine { sha256d::Hash::engine() }
+    //fn from_engine(e: sha256::HashEngine) -> Self { Self(sha256d::Hash::from_engine(e)) }
+}
+
 sha256t_hash_newtype! {
     pub struct TapSighashTag = hash_str("TapSighash");
 

bitcoin/src/psbt/mod.rs

@@ -2251,7 +2251,7 @@ mod tests {
     fn sign_psbt() {
         use crate::bip32::{DerivationPath, Fingerprint};
         use crate::witness_version::WitnessVersion;
-        use crate::{WPubkeyHash, WitnessProgram};
+        use crate::WitnessProgram;
 
         let unsigned_tx = Transaction {
             version: transaction::Version::TWO,
@@ -2271,7 +2271,7 @@ mod tests {
         // First input we can spend. See comment above on key_map for why we use defaults here.
         let txout_wpkh = TxOut {
             value: Amount::from_sat(10),
-            script_pubkey: ScriptBuf::new_p2wpkh(WPubkeyHash::hash(&pk.to_bytes())),
+            script_pubkey: ScriptBuf::new_p2wpkh(pk.wpubkey_hash().unwrap()),
         };
         psbt.inputs[0].witness_utxo = Some(txout_wpkh);