Properly dispose of managed digest instances.

Author: JVanloofsvelt

NBitcoin/BIP39/Mnemonic.cs

@@ -175,11 +175,17 @@ public byte[] DeriveSeed(string passphrase = null)
 #if NO_NATIVE_HMACSHA512
 #if NONATIVEHASH
 			var mac = new NBitcoin.BouncyCastle.Crypto.Macs.HMac(new NBitcoin.BouncyCastle.Crypto.Digests.Sha512Digest());
-#else
-			var mac = new NBitcoin.BouncyCastle.Crypto.Macs.HMac(new Crypto.digests.ManagedSha512Digest());
-#endif
 			mac.Init(new NBitcoin.BouncyCastle.Crypto.Parameters.KeyParameter(bytes));
 			return Pbkdf2.ComputeDerivedKey(mac, salt, 2048, 64);
+#else
+			using (var sha512 = new Crypto.NativeDigests.ManagedSha512Digest())
+			{
+				var mac = new NBitcoin.BouncyCastle.Crypto.Macs.HMac(sha512);
+				mac.Init(new NBitcoin.BouncyCastle.Crypto.Parameters.KeyParameter(bytes));
+				return Pbkdf2.ComputeDerivedKey(mac, salt, 2048, 64);
+			}
+#endif
+
 #elif NO_NATIVE_RFC2898_HMACSHA512
 			return NBitcoin.Crypto.Pbkdf2.ComputeDerivedKey(new System.Security.Cryptography.HMACSHA512(bytes), salt, 2048, 64);
 #else

NBitcoin/Crypto/Hashes.cs

@@ -835,12 +835,15 @@ public static byte[] HMACSHA256(byte[] key, byte[] data)
 #elif NO_NATIVE_HMACSHA512 // There is a native hash, but no native HMAC.
 		public static byte[] HMACSHA512(byte[] key, byte[] data)
 		{
-			var mac = new NBitcoin.BouncyCastle.Crypto.Macs.HMac(new ManagedSha512Digest());
-			mac.Init(new KeyParameter(key));
-			mac.BlockUpdate(data, 0, data.Length);
-			byte[] result = new byte[mac.GetMacSize()];
-			mac.DoFinal(result, 0);
-			return result;
+			using (var sha512 = new ManagedSha512Digest())
+			{
+				var mac = new NBitcoin.BouncyCastle.Crypto.Macs.HMac(sha512);
+				mac.Init(new KeyParameter(key));
+				mac.BlockUpdate(data, 0, data.Length);
+				byte[] result = new byte[mac.GetMacSize()];
+				mac.DoFinal(result, 0);
+				return result;
+			}
 		}
 
 #if HAS_SPAN
@@ -859,12 +862,15 @@ public static bool HMACSHA512(byte[] key, ReadOnlySpan<byte> data, Span<byte> ou
 
 		public static byte[] HMACSHA256(byte[] key, byte[] data)
 		{
-			var mac = new NBitcoin.BouncyCastle.Crypto.Macs.HMac(new ManagedSha256Digest());
-			mac.Init(new KeyParameter(key));
-			mac.BlockUpdate(data, 0, data.Length);
-			byte[] result = new byte[mac.GetMacSize()];
-			mac.DoFinal(result, 0);
-			return result;
+			using (var sha256 = new ManagedSha256Digest())
+			{
+				var mac = new NBitcoin.BouncyCastle.Crypto.Macs.HMac(sha256);
+				mac.Init(new KeyParameter(key));
+				mac.BlockUpdate(data, 0, data.Length);
+				byte[] result = new byte[mac.GetMacSize()];
+				mac.DoFinal(result, 0);
+				return result;
+			}
 		}
 #else // There is no native hash and no native HMAC
 		public static byte[] HMACSHA512(byte[] key, byte[] data)