hashes: Strongly type the hash160::HashEngine

Currently we are using a type alias for the `hash160::HashEngine`.

Type alias' allow for potential mixing of types, a `hash160::HashEngine`
struct can better serve our users with not much additional complexity or
maintenance burden.

As we did for the `sha256d::HashEngine`, add a new wrapper type
`hash160::HashEngine` that replaces the current type alias.

bitcoin/src/address/mod.rs

@@ -34,7 +34,7 @@ use core::str::FromStr;
 
 use bech32::primitives::gf32::Fe32;
 use bech32::primitives::hrp::Hrp;
-use hashes::{sha256, HashEngine};
+use hashes::{hash160, HashEngine};
 use secp256k1::{Secp256k1, Verification, XOnlyPublicKey};
 
 use crate::consensus::Params;
@@ -878,11 +878,11 @@ impl FromStr for Address<NetworkUnchecked> {
 }
 
 /// Convert a byte array of a pubkey hash into a segwit redeem hash
-fn segwit_redeem_hash(pubkey_hash: PubkeyHash) -> crate::hashes::hash160::Hash {
-    let mut sha_engine = sha256::Hash::engine();
+fn segwit_redeem_hash(pubkey_hash: PubkeyHash) -> hash160::Hash {
+    let mut sha_engine = hash160::Hash::engine();
     sha_engine.input(&[0, 20]);
     sha_engine.input(pubkey_hash.as_ref());
-    crate::hashes::hash160::Hash::from_engine(sha_engine)
+    hash160::Hash::from_engine(sha_engine)
 }
 
 #[cfg(test)]

hashes/src/hash160.rs

@@ -18,10 +18,30 @@ crate::internal_macros::hash_type! {
     "Output of the Bitcoin HASH160 hash function. (RIPEMD160(SHA256))"
 }
 
-type HashEngine = sha256::HashEngine;
+/// Engine to compute HASH160 hash function.
+#[derive(Clone)]
+pub struct HashEngine(sha256::HashEngine);
+
+impl HashEngine {
+    /// Creates a new HASH160 hash engine.
+    pub const fn new() -> Self { Self(sha256::HashEngine::new()) }
+}
+
+impl Default for HashEngine {
+    fn default() -> Self { Self::new() }
+}
+
+impl crate::HashEngine for HashEngine {
+    type MidState = sha256::Midstate;
+    fn midstate(&self) -> Self::MidState { self.0.midstate() }
+
+    const BLOCK_SIZE: usize = 64; // Same as sha256::HashEngine::BLOCK_SIZE;
+    fn input(&mut self, data: &[u8]) { self.0.input(data) }
+    fn n_bytes_hashed(&self) -> usize { self.0.n_bytes_hashed() }
+}
 
 fn from_engine(e: HashEngine) -> Hash {
-    let sha2 = sha256::Hash::from_engine(e);
+    let sha2 = sha256::Hash::from_engine(e.0);
     let rmd = ripemd160::Hash::hash(&sha2[..]);
 
     let mut ret = [0; 20];

hashes/src/impls.rs

@@ -6,7 +6,16 @@
 
 use bitcoin_io::impl_write;
 
-use crate::{hmac, ripemd160, sha1, sha256, sha256d, sha512, siphash24, HashEngine};
+use crate::{hash160, hmac, ripemd160, sha1, sha256, sha256d, sha512, siphash24, HashEngine};
+
+impl_write!(
+    hash160::HashEngine,
+    |us: &mut hash160::HashEngine, buf| {
+        us.input(buf);
+        Ok(buf.len())
+    },
+    |_us| { Ok(()) }
+);
 
 impl_write!(
     sha1::HashEngine,