Minor cleanup for AES from review feedback.

* Added BitsPerByte, and replaced all of the magic 8s with it
* Removed some "this."s which were not necessary for compilation
* Switched to Array.Empty<byte>() vs new byte[0]
* Tweaked the wording of a comment to hopefully be better understood on the first pass.

Author: bartonjs

src/System.Security.Cryptography.Encryption.Aes/src/Internal/Cryptography/AesCngCryptoTransform.cs

@@ -77,7 +77,7 @@ protected override void Reset()
         protected abstract byte[] UncheckedTransformFinalBlock(SafeKeyHandle hKey, byte[] currentIv, byte[] inputBuffer, int inputOffset, int inputCount);
 
         private SafeKeyHandle _hKey;
-        private byte[] _iv;         // This IV never changes.
+        private byte[] _iv;         // _iv holds a copy of the original IV for Reset(), until it is cleared by Dispose().
         private byte[] _currentIv;  // CNG mutates this with the updated IV for the next stage on each Encrypt/Decrypt call.
 
         private static readonly SafeAlgorithmHandle s_hAlg = Cng.BCryptOpenAlgorithmProvider(Cng.BCRYPT_AES_ALGORITHM, null, Cng.OpenAlgorithmProviderFlags.NONE);

src/System.Security.Cryptography.Encryption.Aes/src/Internal/Cryptography/AesImplementation.cs

@@ -2,7 +2,6 @@
 // Licensed under the MIT license. See LICENSE file in the project root for full license information.
 
 using System;
-using System.Diagnostics;
 using System.Security.Cryptography;
 
 namespace Internal.Cryptography
@@ -21,16 +20,16 @@ public sealed override ICryptoTransform CreateEncryptor(byte[] rgbKey, byte[] rg
 
         public sealed override void GenerateIV()
         {
-            byte[] iv = new byte[this.BlockSize / 8];
+            byte[] iv = new byte[BlockSize / BitsPerByte];
             s_rng.GetBytes(iv);
-            this.IV = iv;
+            IV = iv;
         }
 
         public sealed override void GenerateKey()
         {
-            byte[] key = new byte[this.KeySize / 8];
+            byte[] key = new byte[KeySize / BitsPerByte];
             s_rng.GetBytes(key);
-            this.Key = key;
+            Key = key;
         }
 
         protected sealed override void Dispose(bool disposing)
@@ -42,18 +41,19 @@ private ICryptoTransform CreateTransform(byte[] rgbKey, byte[] rgbIV, bool encry
         {
             if (rgbKey == null)
                 throw new ArgumentNullException("key");
-            int keySize = rgbKey.Length * 8;
+            int keySize = rgbKey.Length * BitsPerByte;
             if (!keySize.IsLegalSize(this.LegalKeySizes))
                 throw new ArgumentException(SR.Format(SR.Cryptography_InvalidKeySize, "key"));
-            if (rgbIV != null && rgbIV.Length * 8 != this.BlockSize)
+            if (rgbIV != null && rgbIV.Length * BitsPerByte != BlockSize)
                 throw new ArgumentException(SR.Format(SR.Cryptography_InvalidIVSize, "iv"));
 
             if (encrypting)
-                return CreateEncryptor(Mode, Padding, rgbKey, rgbIV, BlockSize / 8);
+                return CreateEncryptor(Mode, Padding, rgbKey, rgbIV, BlockSize / BitsPerByte);
             else
-                return CreateDecryptor(Mode, Padding, rgbKey, rgbIV, BlockSize / 8);
+                return CreateDecryptor(Mode, Padding, rgbKey, rgbIV, BlockSize / BitsPerByte);
         }
 
+        private const int BitsPerByte = 8;
         private static readonly RandomNumberGenerator s_rng = RandomNumberGenerator.Create();
     }
 }

src/System.Security.Cryptography.Encryption.Aes/src/Internal/Cryptography/AesOpenSslCryptoTransform.cs

@@ -231,7 +231,7 @@ private byte[] DecryptFinalBlock(byte[] inputBuffer, int inputOffset, int inputC
 
             if (rawDecrypt.Length == 0)
             {
-                return new byte[0];
+                return Array.Empty<byte>();
             }
 
             return DepadBlock(rawDecrypt, 0, rawDecrypt.Length);
@@ -262,7 +262,7 @@ private unsafe byte[] ProcessFinalBlock(byte[] paddedBlock, int offset, int leng
 
             if (outputBytes == 0)
             {
-                return new byte[0];
+                return Array.Empty<byte>();
             }
 
             byte[] userData = new byte[outputBytes];