Fix some TODOs for PORTABLE and Streams

Author: peterdettman

crypto/src/crypto/digests/NullDigest.cs

@@ -1,6 +1,8 @@
 using System;
 using System.IO;
 
+using Org.BouncyCastle.Utilities.IO;
+
 namespace Org.BouncyCastle.Crypto.Digests
 {
 	public class NullDigest : IDigest
@@ -20,7 +22,7 @@ public int GetByteLength()
 
 		public int GetDigestSize()
 		{
-			return (int) bOut.Length;
+			return (int)bOut.Length;
 		}
 
 		public void Update(byte b)
@@ -33,15 +35,19 @@ public void BlockUpdate(byte[] inBytes, int inOff, int len)
 			bOut.Write(inBytes, inOff, len);
 		}
 
-		public int DoFinal(byte[] outBytes, int outOff)
+        public int DoFinal(byte[] outBytes, int outOff)
 		{
-			byte[] res = bOut.ToArray();
-			res.CopyTo(outBytes, outOff);
-			Reset();
-			return res.Length;
-		}
-
-		public void Reset()
+            try
+            {
+                return Streams.WriteBufTo(bOut, outBytes, outOff);
+            }
+            finally
+            {
+                Reset();
+            }
+        }
+
+        public void Reset()
 		{
 			bOut.SetLength(0);
 		}

crypto/src/crypto/signers/Ed25519Signer.cs

@@ -5,6 +5,7 @@
 using Org.BouncyCastle.Crypto.Parameters;
 using Org.BouncyCastle.Math.EC.Rfc8032;
 using Org.BouncyCastle.Utilities;
+using Org.BouncyCastle.Utilities.IO;
 
 namespace Org.BouncyCastle.Crypto.Signers
 {
@@ -114,12 +115,12 @@ internal bool VerifySignature(Ed25519PublicKeyParameters publicKey, byte[] signa
             [MethodImpl(MethodImplOptions.Synchronized)]
             internal void Reset()
             {
+                long count = Position;
 #if PORTABLE
                 this.Position = 0L;
-
-                // TODO Clear using Write method
+                Streams.WriteZeroes(this, count);
 #else
-                Array.Clear(GetBuffer(), 0, (int)Position);
+                Array.Clear(GetBuffer(), 0, (int)count);
 #endif
                 this.Position = 0L;
             }

crypto/src/crypto/signers/Ed25519ctxSigner.cs

@@ -5,6 +5,7 @@
 using Org.BouncyCastle.Crypto.Parameters;
 using Org.BouncyCastle.Math.EC.Rfc8032;
 using Org.BouncyCastle.Utilities;
+using Org.BouncyCastle.Utilities.IO;
 
 namespace Org.BouncyCastle.Crypto.Signers
 {
@@ -116,12 +117,12 @@ internal bool VerifySignature(Ed25519PublicKeyParameters publicKey, byte[] ctx,
             [MethodImpl(MethodImplOptions.Synchronized)]
             internal void Reset()
             {
+                long count = Position;
 #if PORTABLE
                 this.Position = 0L;
-
-                // TODO Clear using Write method
+                Streams.WriteZeroes(this, count);
 #else
-                Array.Clear(GetBuffer(), 0, (int)Position);
+                Array.Clear(GetBuffer(), 0, (int)count);
 #endif
                 this.Position = 0L;
             }

crypto/src/crypto/signers/Ed448Signer.cs

@@ -5,6 +5,7 @@
 using Org.BouncyCastle.Crypto.Parameters;
 using Org.BouncyCastle.Math.EC.Rfc8032;
 using Org.BouncyCastle.Utilities;
+using Org.BouncyCastle.Utilities.IO;
 
 namespace Org.BouncyCastle.Crypto.Signers
 {
@@ -116,12 +117,12 @@ internal bool VerifySignature(Ed448PublicKeyParameters publicKey, byte[] ctx, by
             [MethodImpl(MethodImplOptions.Synchronized)]
             internal void Reset()
             {
+                long count = Position;
 #if PORTABLE
                 this.Position = 0L;
-
-                // TODO Clear using Write method
+                Streams.WriteZeroes(this, count);
 #else
-                Array.Clear(GetBuffer(), 0, (int)Position);
+                Array.Clear(GetBuffer(), 0, (int)count);
 #endif
                 this.Position = 0L;
             }

crypto/src/util/io/Streams.cs

@@ -96,5 +96,30 @@ public static void WriteBufTo(MemoryStream buf, Stream output)
         {
             buf.WriteTo(output);
         }
+
+        /// <exception cref="IOException"></exception>
+        public static int WriteBufTo(MemoryStream buf, byte[] output, int offset)
+        {
+#if PORTABLE
+            byte[] bytes = buf.ToArray();
+            bytes.CopyTo(output, offset);
+            return bytes.Length;
+#else
+            int size = (int)buf.Length;
+            buf.WriteTo(new MemoryStream(output, offset, size, true));
+            return size;
+#endif
+        }
+
+        public static void WriteZeroes(Stream outStr, long count)
+        {
+            byte[] zeroes = new byte[BufferSize];
+            while (count > BufferSize)
+            {
+                outStr.Write(zeroes, 0, BufferSize);
+                count -= BufferSize;
+            }
+            outStr.Write(zeroes, 0, (int)count);
+        }
     }
 }