Add sha2-256 hash function (#4218)

* Add sha2-256 hash function

Widely used hash function, supported by bitcoin and ethereum

* Add runtime io support

* add test

* add test

* Update hashing.rs

* Update hashing.rs

substrate/primitives/core/src/hashing.rs

@@ -17,6 +17,7 @@
 //! Hashing functions.
 
 use blake2_rfc;
+use sha2::{Digest, Sha256};
 use tiny_keccak::{Hasher, Keccak};
 use twox_hash;
 
@@ -123,7 +124,7 @@ pub fn twox_256(data: &[u8]) -> [u8; 32] {
 	r
 }
 
-/// Do a keccak 256 hash and return result.
+/// Do a keccak 256-bit hash and return result.
 pub fn keccak_256(data: &[u8]) -> [u8; 32] {
 	let mut keccak = Keccak::v256();
 	keccak.update(data);
@@ -131,3 +132,12 @@ pub fn keccak_256(data: &[u8]) -> [u8; 32] {
 	keccak.finalize(&mut output);
 	output
 }
+
+/// Do a sha2 256-bit hash and return result.
+pub fn sha2_256(data: &[u8]) -> [u8; 32] {
+	let mut hasher = Sha256::new();
+	hasher.input(data);
+	let mut output = [0u8; 32];
+	output.copy_from_slice(&hasher.result());
+	output
+}