sha2: Add tests that check stability of the serialized state

These tests use SHA-512 and serialize its state, comparing it to a well-known values.
Then, they rebuild the hasher from that state and check if the final digest is correctly calculated.

As documented in the compatibility section fro the `SerializableState` these values should be stable for semver-compatible releases.

See: RustCrypto/traits#1693
Signed-off-by: Wiktor Kwapisiewicz <wiktor@metacode.biz>

Author: wiktor-k

sha2/tests/mod.rs

@@ -41,3 +41,37 @@ fn sha512_rand() {
         ),
     );
 }
+
+#[test]
+fn sha512_serializable_state_is_stable() {
+    use sha2::digest::common::hazmat::SerializableState;
+    let mut h = Sha512::new();
+    h.update("just a random example text");
+    let state: &[u8] = &h.serialize();
+    assert_eq!(
+        state,
+        [
+            8, 201, 188, 243, 103, 230, 9, 106, 59, 167, 202, 132, 133, 174, 103, 187, 43, 248,
+            148, 254, 114, 243, 110, 60, 241, 54, 29, 95, 58, 245, 79, 165, 209, 130, 230, 173,
+            127, 82, 14, 81, 31, 108, 62, 43, 140, 104, 5, 155, 107, 189, 65, 251, 171, 217, 131,
+            31, 121, 33, 126, 19, 25, 205, 224, 91, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+            26, 106, 117, 115, 116, 32, 97, 32, 114, 97, 110, 100, 111, 109, 32, 101, 120, 97, 109,
+            112, 108, 101, 32, 116, 101, 120, 116, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+            0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+            0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+            0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0
+        ]
+    );
+    let h = Sha512::deserialize(state.try_into().expect("state to be of correct length"))
+        .expect("state to be deserialized");
+    let digest: &[u8] = &h.finalize();
+    assert_eq!(
+        digest,
+        [
+            193, 156, 193, 73, 92, 41, 172, 27, 181, 186, 218, 80, 174, 96, 210, 30, 235, 136, 156,
+            147, 88, 203, 90, 202, 9, 103, 158, 201, 133, 185, 63, 164, 60, 128, 240, 190, 211,
+            151, 102, 19, 52, 169, 152, 70, 87, 22, 183, 67, 32, 99, 129, 240, 116, 246, 210, 141,
+            238, 243, 135, 41, 115, 15, 166, 87
+        ]
+    );
+}