Add Keccak hasher (#6101)

* fix keccak hasher

* Update hasher.rs

Co-authored-by: Gavin Wood <i@gavwood.com>

substrate/primitives/runtime/src/traits.rs

@@ -376,6 +376,33 @@ impl Hash for BlakeTwo256 {
 	}
 }
 
+/// Keccak-256 Hash implementation.
+#[derive(PartialEq, Eq, Clone, RuntimeDebug)]
+#[cfg_attr(feature = "std", derive(Serialize, Deserialize))]
+pub struct Keccak256;
+
+impl Hasher for Keccak256 {
+	type Out = sp_core::H256;
+	type StdHasher = hash256_std_hasher::Hash256StdHasher;
+	const LENGTH: usize = 32;
+
+	fn hash(s: &[u8]) -> Self::Out {
+		sp_io::hashing::keccak_256(s).into()
+	}
+}
+
+impl Hash for Keccak256 {
+	type Output = sp_core::H256;
+
+	fn trie_root(input: Vec<(Vec<u8>, Vec<u8>)>) -> Self::Output {
+		sp_io::trie::keccak_256_root(input)
+	}
+
+	fn ordered_trie_root(input: Vec<Vec<u8>>) -> Self::Output {
+		sp_io::trie::keccak_256_ordered_root(input)
+	}
+}
+
 /// Something that can be checked for equality and printed out to a debug channel if bad.
 pub trait CheckEqual {
 	/// Perform the equality check.