Code cleanup

Rename IAuthenticatedEncryptor2 -> IOptimizedAuthenticatedEncryptor
Rename ProtectedMemoryBlob -> Secret
Add some missing doc comments explaining

src/Microsoft.AspNet.Security.DataProtection/AuthenticatedEncryption/AuthenticatedEncryptorExtensions.cs

@@ -12,7 +12,7 @@ namespace Microsoft.AspNet.Security.DataProtection.AuthenticatedEncryption
         public static byte[] Encrypt(this IAuthenticatedEncryptor encryptor, ArraySegment<byte> plaintext, ArraySegment<byte> additionalAuthenticatedData, uint preBufferSize, uint postBufferSize)
         {
             // Can we call the optimized version?
-            IAuthenticatedEncryptor2 optimizedEncryptor = encryptor as IAuthenticatedEncryptor2;
+            IOptimizedAuthenticatedEncryptor optimizedEncryptor = encryptor as IOptimizedAuthenticatedEncryptor;
             if (optimizedEncryptor != null)
             {
                 return optimizedEncryptor.Encrypt(plaintext, additionalAuthenticatedData, preBufferSize, postBufferSize);

src/Microsoft.AspNet.Security.DataProtection/AuthenticatedEncryption/CngCbcAuthenticatedEncryptorConfigurationFactory.cs

@@ -23,7 +23,7 @@ namespace Microsoft.AspNet.Security.DataProtection.AuthenticatedEncryption
         {
             // generate a 512-bit secret randomly
             const int KDK_SIZE_IN_BYTES = 512 / 8;
-            var secret = ProtectedMemoryBlob.Random(KDK_SIZE_IN_BYTES);
+            var secret = Secret.Random(KDK_SIZE_IN_BYTES);
             return new CngCbcAuthenticatedEncryptorConfiguration(_options, secret);
         }
     }

src/Microsoft.AspNet.Security.DataProtection/AuthenticatedEncryption/CngCbcAuthenticatedEncryptorConfigurationOptions.cs

@@ -96,7 +96,7 @@ namespace Microsoft.AspNet.Security.DataProtection.AuthenticatedEncryption
 
             // and we're good to go!
             return new CbcAuthenticatedEncryptor(
-                keyDerivationKey: new ProtectedMemoryBlob(secret),
+                keyDerivationKey: new Secret(secret),
                 symmetricAlgorithmHandle: encryptionAlgorithmHandle,
                 symmetricAlgorithmKeySizeInBytes: encryptionAlgorithmKeySizeInBits / 8,
                 hmacAlgorithmHandle: hashAlgorithmHandle);

src/Microsoft.AspNet.Security.DataProtection/AuthenticatedEncryption/CngCbcAuthenticatedEncryptorConfigurationXmlReader.cs

@@ -58,8 +58,8 @@ namespace Microsoft.AspNet.Security.DataProtection.AuthenticatedEncryption
             byte[] decryptedSecretBytes = Convert.FromBase64String((string)decryptedSecretElement);
             try
             {
-                var protectedMemoryBlob = new ProtectedMemoryBlob(decryptedSecretBytes);
-                return new CngCbcAuthenticatedEncryptorConfiguration(options, protectedMemoryBlob);
+                var secret = new Secret(decryptedSecretBytes);
+                return new CngCbcAuthenticatedEncryptorConfiguration(options, secret);
             }
             finally
             {

src/Microsoft.AspNet.Security.DataProtection/AuthenticatedEncryption/CngGcmAuthenticatedEncryptorConfigurationFactory.cs

@@ -23,7 +23,7 @@ namespace Microsoft.AspNet.Security.DataProtection.AuthenticatedEncryption
         {
             // generate a 512-bit secret randomly
             const int KDK_SIZE_IN_BYTES = 512 / 8;
-            var secret = ProtectedMemoryBlob.Random(KDK_SIZE_IN_BYTES);
+            var secret = Secret.Random(KDK_SIZE_IN_BYTES);
             return new CngGcmAuthenticatedEncryptorConfiguration(_options, secret);
         }
     }

src/Microsoft.AspNet.Security.DataProtection/AuthenticatedEncryption/CngGcmAuthenticatedEncryptorConfigurationOptions.cs

@@ -67,7 +67,7 @@ namespace Microsoft.AspNet.Security.DataProtection.AuthenticatedEncryption
 
             // and we're good to go!
             return new GcmAuthenticatedEncryptor(
-                keyDerivationKey: new ProtectedMemoryBlob(secret),
+                keyDerivationKey: new Secret(secret),
                 symmetricAlgorithmHandle: encryptionAlgorithmHandle,
                 symmetricAlgorithmKeySizeInBytes: encryptionAlgorithmKeySizeInBits / 8);
         }

src/Microsoft.AspNet.Security.DataProtection/AuthenticatedEncryption/CngGcmAuthenticatedEncryptorConfigurationXmlReader.cs

@@ -52,8 +52,8 @@ namespace Microsoft.AspNet.Security.DataProtection.AuthenticatedEncryption
             byte[] decryptedSecretBytes = Convert.FromBase64String((string)decryptedSecretElement);
             try
             {
-                var protectedMemoryBlob = new ProtectedMemoryBlob(decryptedSecretBytes);
-                return new CngGcmAuthenticatedEncryptorConfiguration(options, protectedMemoryBlob);
+                var secret = new Secret(decryptedSecretBytes);
+                return new CngGcmAuthenticatedEncryptorConfiguration(options, secret);
             }
             finally
             {

src/Microsoft.AspNet.Security.DataProtection/AuthenticatedEncryption/IAuthenticatedEncryptor2.cs

@@ -1,12 +0,0 @@
-// Copyright (c) Microsoft Open Technologies, Inc. All rights reserved.
-// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
-
-using System;
-
-namespace Microsoft.AspNet.Security.DataProtection.AuthenticatedEncryption
-{
-    internal interface IAuthenticatedEncryptor2 : IAuthenticatedEncryptor
-    {
-        byte[] Encrypt(ArraySegment<byte> plaintext, ArraySegment<byte> additionalAuthenticatedData, uint preBufferSize, uint postBufferSize);
-    }
-}

src/Microsoft.AspNet.Security.DataProtection/AuthenticatedEncryption/IOptimizedAuthenticatedEncryptor.cs

@@ -0,0 +1,35 @@
+// Copyright (c) Microsoft Open Technologies, Inc. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using System;
+
+namespace Microsoft.AspNet.Security.DataProtection.AuthenticatedEncryption
+{
+    /// <summary>
+    /// An optimized encryptor that can avoid buffer allocations in common code paths.
+    /// </summary>
+    internal interface IOptimizedAuthenticatedEncryptor : IAuthenticatedEncryptor
+    {
+        /// <summary>
+        /// Encrypts and tamper-proofs a piece of data.
+        /// </summary>
+        /// <param name="plaintext">The plaintext to encrypt. This input may be zero bytes in length.</param>
+        /// <param name="additionalAuthenticatedData">A piece of data which will not be included in
+        /// the returned ciphertext but which will still be covered by the authentication tag.
+        /// This input may be zero bytes in length. The same AAD must be specified in the corresponding
+        /// call to Decrypt.</param>
+        /// <param name="preBufferSize">The number of bytes to include before the ciphertext in the return value.</param>
+        /// <param name="postBufferSize">The number of bytes to include after the ciphertext in the return value.</param>
+        /// <returns>
+        /// A buffer containing the ciphertext and authentication tag.
+        /// If a non-zero pre-buffer or post-buffer size is specified, the returned buffer will contain appropriate padding
+        /// on either side of the ciphertext and authentication tag. For instance, if a pre-buffer size of 4 and a post-buffer
+        /// size of 7 are specified, and if the ciphertext and tag are a combined 48 bytes, then the returned buffer will
+        /// be a total 59 bytes in length. The first four bytes will be undefined, the next 48 bytes will contain the
+        /// ciphertext and tag, and the last seven bytes will be undefined. The intent is that the caller can overwrite the
+        /// pre-buffer or post-buffer with a header or footer without needing to allocate an additional buffer object.
+        /// </returns>
+        /// <remarks>All cryptography-related exceptions should be homogenized to CryptographicException.</remarks>
+        byte[] Encrypt(ArraySegment<byte> plaintext, ArraySegment<byte> additionalAuthenticatedData, uint preBufferSize, uint postBufferSize);
+    }
+}

src/Microsoft.AspNet.Security.DataProtection/AuthenticatedEncryption/ManagedAuthenticatedEncryptorConfigurationFactory.cs

@@ -21,10 +21,10 @@ namespace Microsoft.AspNet.Security.DataProtection.AuthenticatedEncryption
             // generate a 512-bit secret randomly
             const int KDK_SIZE_IN_BYTES = 512 / 8;
             byte[] kdk = ManagedGenRandomImpl.Instance.GenRandom(KDK_SIZE_IN_BYTES);
-            ProtectedMemoryBlob secret;
+            Secret secret;
             try
             {
-                secret = new ProtectedMemoryBlob(kdk);
+                secret = new Secret(kdk);
             }
             finally
             {

src/Microsoft.AspNet.Security.DataProtection/AuthenticatedEncryption/ManagedAuthenticatedEncryptorConfigurationOptions.cs

@@ -70,7 +70,7 @@ namespace Microsoft.AspNet.Security.DataProtection.AuthenticatedEncryption
 
             // We're good to go!
             return new ManagedAuthenticatedEncryptor(
-                keyDerivationKey: new ProtectedMemoryBlob(secret),
+                keyDerivationKey: new Secret(secret),
                 symmetricAlgorithmFactory: encryptorFactory,
                 symmetricAlgorithmKeySizeInBytes: keySizeInBytes,
                 validationAlgorithmFactory: validatorFactory);

src/Microsoft.AspNet.Security.DataProtection/AuthenticatedEncryption/ManagedAuthenticatedEncryptorConfigurationXmlReader.cs

@@ -56,8 +56,8 @@ namespace Microsoft.AspNet.Security.DataProtection.AuthenticatedEncryption
             byte[] decryptedSecretBytes = Convert.FromBase64String((string)decryptedSecretElement);
             try
             {
-                var protectedMemoryBlob = new ProtectedMemoryBlob(decryptedSecretBytes);
-                return new ManagedAuthenticatedEncryptorConfiguration(options, protectedMemoryBlob);
+                var secret = new Secret(decryptedSecretBytes);
+                return new ManagedAuthenticatedEncryptorConfiguration(options, secret);
             }
             finally
             {

src/Microsoft.AspNet.Security.DataProtection/BitHelpers.cs

@@ -21,6 +21,20 @@ namespace Microsoft.AspNet.Security.DataProtection
             bytePtr[3] = (byte)(value);
         }
 
+        /// <summary>
+        /// Writes an unsigned 32-bit value to a memory address, big-endian.
+        /// </summary>
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public static void WriteTo(ref byte* ptr, uint value)
+        {
+            byte* pTemp = ptr;
+            pTemp[0] = (byte)(value >> 24);
+            pTemp[1] = (byte)(value >> 16);
+            pTemp[2] = (byte)(value >> 8);
+            pTemp[3] = (byte)(value);
+            ptr = &pTemp[4];
+        }
+
         /// <summary>
         /// Writes a signed 32-bit value to a memory address, big-endian.
         /// </summary>

src/Microsoft.AspNet.Security.DataProtection/Cng/CbcAuthenticatedEncryptor.cs

@@ -2,7 +2,6 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using System;
-using System.Security.Cryptography;
 using Microsoft.AspNet.Security.DataProtection.SafeHandles;
 using Microsoft.AspNet.Security.DataProtection.SP800_108;
 
@@ -41,7 +40,7 @@ namespace Microsoft.AspNet.Security.DataProtection.Cng
         private readonly uint _symmetricAlgorithmBlockSizeInBytes;
         private readonly uint _symmetricAlgorithmSubkeyLengthInBytes;
 
-        public CbcAuthenticatedEncryptor(ProtectedMemoryBlob keyDerivationKey, BCryptAlgorithmHandle symmetricAlgorithmHandle, uint symmetricAlgorithmKeySizeInBytes, BCryptAlgorithmHandle hmacAlgorithmHandle, IBCryptGenRandom genRandom = null)
+        public CbcAuthenticatedEncryptor(Secret keyDerivationKey, BCryptAlgorithmHandle symmetricAlgorithmHandle, uint symmetricAlgorithmKeySizeInBytes, BCryptAlgorithmHandle hmacAlgorithmHandle, IBCryptGenRandom genRandom = null)
         {
             CryptoUtil.Assert(KEY_MODIFIER_SIZE_IN_BYTES <= symmetricAlgorithmKeySizeInBytes && symmetricAlgorithmKeySizeInBytes <= Constants.MAX_STACKALLOC_BYTES,
                 "KEY_MODIFIER_SIZE_IN_BYTES <= symmetricAlgorithmKeySizeInBytes && symmetricAlgorithmKeySizeInBytes <= Constants.MAX_STACKALLOC_BYTES");
@@ -88,16 +87,12 @@ namespace Microsoft.AspNet.Security.DataProtection.Cng
                 *(ptr++) = 0; // 0x00 = CBC encryption + HMAC authentication
 
                 // Next is information about the symmetric algorithm (key size followed by block size)
-                BitHelpers.WriteTo(ptr, _symmetricAlgorithmSubkeyLengthInBytes);
-                ptr += sizeof(uint);
-                BitHelpers.WriteTo(ptr, _symmetricAlgorithmBlockSizeInBytes);
-                ptr += sizeof(uint);
+                BitHelpers.WriteTo(ref ptr, _symmetricAlgorithmSubkeyLengthInBytes);
+                BitHelpers.WriteTo(ref ptr, _symmetricAlgorithmBlockSizeInBytes);
 
                 // Next is information about the HMAC algorithm (key size followed by digest size)
-                BitHelpers.WriteTo(ptr, _hmacAlgorithmSubkeyLengthInBytes);
-                ptr += sizeof(uint);
-                BitHelpers.WriteTo(ptr, _hmacAlgorithmDigestLengthInBytes);
-                ptr += sizeof(uint);
+                BitHelpers.WriteTo(ref ptr, _hmacAlgorithmSubkeyLengthInBytes);
+                BitHelpers.WriteTo(ref ptr, _hmacAlgorithmDigestLengthInBytes);
 
                 // See the design document for an explanation of the following code.
                 byte[] tempKeys = new byte[_symmetricAlgorithmSubkeyLengthInBytes + _hmacAlgorithmSubkeyLengthInBytes];
@@ -348,7 +343,7 @@ namespace Microsoft.AspNet.Security.DataProtection.Cng
 
                 using (var symmetricKeyHandle = _symmetricAlgorithmHandle.GenerateSymmetricKey(pbSymmetricEncryptionSubkey, _symmetricAlgorithmSubkeyLengthInBytes))
                 {
-                    // We can't assume PKCS#7 padding (maybe the underlying provided is using CTS),
+                    // We can't assume PKCS#7 padding (maybe the underlying provider is really using CTS),
                     // so we need to query the padded output size before we can allocate the return value array.
                     uint cbOutputCiphertext = GetCbcEncryptedOutputSizeWithPadding(symmetricKeyHandle, pbPlaintext, cbPlaintext);
 

src/Microsoft.AspNet.Security.DataProtection/Cng/CngAuthenticatedEncryptorBase.cs

@@ -2,12 +2,14 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using System;
-using System.Security.Cryptography;
 using Microsoft.AspNet.Security.DataProtection.AuthenticatedEncryption;
 
 namespace Microsoft.AspNet.Security.DataProtection.Cng
 {
-    internal unsafe abstract class CngAuthenticatedEncryptorBase : IAuthenticatedEncryptor, IDisposable
+    /// <summary>
+    /// Base class used for all CNG-related authentication encryption operations.
+    /// </summary>
+    internal unsafe abstract class CngAuthenticatedEncryptorBase : IOptimizedAuthenticatedEncryptor, IDisposable
     {
         public byte[] Decrypt(ArraySegment<byte> ciphertext, ArraySegment<byte> additionalAuthenticatedData)
         {
@@ -30,7 +32,7 @@ namespace Microsoft.AspNet.Security.DataProtection.Cng
                             pbAdditionalAuthenticatedData: (pbAdditionalAuthenticatedDataArray != null) ? &pbAdditionalAuthenticatedDataArray[additionalAuthenticatedData.Offset] : &dummy,
                             cbAdditionalAuthenticatedData: (uint)additionalAuthenticatedData.Count);
                     }
-                    catch (Exception ex) when (!(ex is CryptographicException))
+                    catch (Exception ex) when (ex.RequiresHomogenization())
                     {
                         // Homogenize to CryptographicException.
                         throw Error.CryptCommon_GenericError(ex);
@@ -71,7 +73,7 @@ namespace Microsoft.AspNet.Security.DataProtection.Cng
                             cbPreBuffer: preBufferSize,
                             cbPostBuffer: postBufferSize);
                     }
-                    catch (Exception ex) when (!(ex is CryptographicException))
+                    catch (Exception ex) when (ex.RequiresHomogenization())
                     {
                         // Homogenize to CryptographicException.
                         throw Error.CryptCommon_GenericError(ex);

src/Microsoft.AspNet.Security.DataProtection/Cng/DpapiSecretSerializerHelper.cs

@@ -172,7 +172,7 @@ namespace Microsoft.AspNet.Security.DataProtection.Cng
             }
         }
 
-        public static ProtectedMemoryBlob UnprotectWithDpapi(byte[] protectedSecret)
+        public static Secret UnprotectWithDpapi(byte[] protectedSecret)
         {
             Debug.Assert(protectedSecret != null);
 
@@ -185,7 +185,7 @@ namespace Microsoft.AspNet.Security.DataProtection.Cng
             }
         }
 
-        internal static ProtectedMemoryBlob UnprotectWithDpapiImpl(byte* pbProtectedData, uint cbProtectedData, byte* pbOptionalEntropy, uint cbOptionalEntropy)
+        internal static Secret UnprotectWithDpapiImpl(byte* pbProtectedData, uint cbProtectedData, byte* pbOptionalEntropy, uint cbOptionalEntropy)
         {
             byte dummy; // provides a valid memory address if the secret or entropy has zero length
 
@@ -220,7 +220,7 @@ namespace Microsoft.AspNet.Security.DataProtection.Cng
                     throw new CryptographicException(errorCode);
                 }
 
-                return new ProtectedMemoryBlob(dataOut.pbData, checked((int)dataOut.cbData));
+                return new Secret(dataOut.pbData, checked((int)dataOut.cbData));
             }
             finally
             {
@@ -234,7 +234,7 @@ namespace Microsoft.AspNet.Security.DataProtection.Cng
             }
         }
 
-        public static ProtectedMemoryBlob UnprotectWithDpapiNG(byte[] protectedData)
+        public static Secret UnprotectWithDpapiNG(byte[] protectedData)
         {
             Debug.Assert(protectedData != null);
 
@@ -247,7 +247,7 @@ namespace Microsoft.AspNet.Security.DataProtection.Cng
             }
         }
 
-        private static ProtectedMemoryBlob UnprotectWithDpapiNGImpl(byte* pbData, uint cbData)
+        private static Secret UnprotectWithDpapiNGImpl(byte* pbData, uint cbData)
         {
             Debug.Assert(pbData != null);
 
@@ -280,7 +280,7 @@ namespace Microsoft.AspNet.Security.DataProtection.Cng
                 try
                 {
                     unencryptedPayloadHandle.DangerousAddRef(ref handleAcquired);
-                    return new ProtectedMemoryBlob((byte*)unencryptedPayloadHandle.DangerousGetHandle(), checked((int)cbUnencryptedPayload));
+                    return new Secret((byte*)unencryptedPayloadHandle.DangerousGetHandle(), checked((int)cbUnencryptedPayload));
                 }
                 finally
                 {

src/Microsoft.AspNet.Security.DataProtection/Cng/GcmAuthenticatedEncryptor.cs

@@ -35,7 +35,7 @@ namespace Microsoft.AspNet.Security.DataProtection.Cng
         private readonly BCryptAlgorithmHandle _symmetricAlgorithmHandle;
         private readonly uint _symmetricAlgorithmSubkeyLengthInBytes;
 
-        public GcmAuthenticatedEncryptor(ProtectedMemoryBlob keyDerivationKey, BCryptAlgorithmHandle symmetricAlgorithmHandle, uint symmetricAlgorithmKeySizeInBytes, IBCryptGenRandom genRandom = null)
+        public GcmAuthenticatedEncryptor(Secret keyDerivationKey, BCryptAlgorithmHandle symmetricAlgorithmHandle, uint symmetricAlgorithmKeySizeInBytes, IBCryptGenRandom genRandom = null)
         {
             CryptoUtil.Assert(KEY_MODIFIER_SIZE_IN_BYTES <= symmetricAlgorithmKeySizeInBytes && symmetricAlgorithmKeySizeInBytes <= Constants.MAX_STACKALLOC_BYTES,
                 "KEY_MODIFIER_SIZE_IN_BYTES <= symmetricAlgorithmKeySizeInBytes && symmetricAlgorithmKeySizeInBytes <= Constants.MAX_STACKALLOC_BYTES");
@@ -67,14 +67,10 @@ namespace Microsoft.AspNet.Security.DataProtection.Cng
                 *(ptr++) = 1; // 0x01 = GCM encryption + authentication
 
                 // Next is information about the symmetric algorithm (key size, nonce size, block size, tag size)
-                BitHelpers.WriteTo(ptr, _symmetricAlgorithmSubkeyLengthInBytes);
-                ptr += sizeof(uint);
-                BitHelpers.WriteTo(ptr, NONCE_SIZE_IN_BYTES);
-                ptr += sizeof(uint);
-                BitHelpers.WriteTo(ptr, TAG_SIZE_IN_BYTES); // block size
-                ptr += sizeof(uint);
-                BitHelpers.WriteTo(ptr, TAG_SIZE_IN_BYTES);
-                ptr += sizeof(uint);
+                BitHelpers.WriteTo(ref ptr, _symmetricAlgorithmSubkeyLengthInBytes);
+                BitHelpers.WriteTo(ref ptr, NONCE_SIZE_IN_BYTES);
+                BitHelpers.WriteTo(ref ptr, TAG_SIZE_IN_BYTES); // block size = tag size
+                BitHelpers.WriteTo(ref ptr, TAG_SIZE_IN_BYTES);
 
                 // See the design document for an explanation of the following code.
                 byte[] tempKeys = new byte[_symmetricAlgorithmSubkeyLengthInBytes];

src/Microsoft.AspNet.Security.DataProtection/CryptoUtil.cs

@@ -48,6 +48,8 @@ namespace Microsoft.AspNet.Security.DataProtection
             throw new CryptographicException("Assertion failed: " + message);
         }
 
+        // Allows callers to write "var x = Method() ?? Fail<T>(message);" as a convenience to guard
+        // against a method returning null unexpectedly.
         [MethodImpl(MethodImplOptions.NoInlining)]
         public static T Fail<T>(string message) where T : class
         {

src/Microsoft.AspNet.Security.DataProtection/DataProtectionExtensions.cs

@@ -36,7 +36,7 @@ namespace Microsoft.AspNet.Security.DataProtection
                 byte[] protectedDataAsBytes = protector.Protect(unprotectedDataAsBytes);
                 return WebEncoders.Base64UrlEncode(protectedDataAsBytes);
             }
-            catch (Exception ex) when (!(ex is CryptographicException))
+            catch (Exception ex) when (ex.RequiresHomogenization())
             {
                 // Homogenize exceptions to CryptographicException
                 throw Error.CryptCommon_GenericError(ex);
@@ -60,7 +60,7 @@ namespace Microsoft.AspNet.Security.DataProtection
                 byte[] unprotectedDataAsBytes = protector.Unprotect(protectedDataAsBytes);
                 return CryptoUtil.SecureUtf8Encoding.GetString(unprotectedDataAsBytes);
             }
-            catch (Exception ex) when (!(ex is CryptographicException))
+            catch (Exception ex) when (ex.RequiresHomogenization())
             {
                 // Homogenize exceptions to CryptographicException
                 throw Error.CryptCommon_GenericError(ex);

src/Microsoft.AspNet.Security.DataProtection/Dpapi/DpapiDataProtector.cs

@@ -43,7 +43,7 @@ namespace Microsoft.AspNet.Security.DataProtection.Dpapi
                 return _shim.Protect(unprotectedData, _combinedPurposes, _scope)
                     ?? CryptoUtil.Fail<byte[]>("Null return value.");
             }
-            catch (Exception ex) when (!(ex is CryptographicException))
+            catch (Exception ex) when (ex.RequiresHomogenization())
             {
                 // Homogenize to CryptographicException
                 throw Error.CryptCommon_GenericError(ex);
@@ -57,7 +57,7 @@ namespace Microsoft.AspNet.Security.DataProtection.Dpapi
                 return _shim.Unprotect(protectedData, _combinedPurposes, _scope)
                     ?? CryptoUtil.Fail<byte[]>("Null return value.");
             }
-            catch (Exception ex) when (!(ex is CryptographicException))
+            catch (Exception ex) when (ex.RequiresHomogenization())
             {
                 // Homogenize to CryptographicException
                 throw Error.CryptCommon_GenericError(ex);

src/Microsoft.AspNet.Security.DataProtection/Dpapi/ProtectedDataImpl.cs

@@ -32,7 +32,7 @@ namespace Microsoft.AspNet.Security.DataProtection.Dpapi
         public byte[] Unprotect(byte[] encryptedData, byte[] optionalEntropy, DataProtectionScope scope)
         {
 #if ASPNETCORE50
-            ProtectedMemoryBlob blob;
+            Secret blob;
             fixed (byte* pbEncryptedData = encryptedData)
             {
                 fixed (byte* pbOptionalEntropy = optionalEntropy)

src/Microsoft.AspNet.Security.DataProtection/EphemeralDataProtectionProvider.cs

@@ -50,7 +50,7 @@ namespace Microsoft.AspNet.Security.DataProtection
             // Currently hardcoded to a 512-bit KDK.
             private const int NUM_BYTES_IN_KDK = 512 / 8;
 
-            public IAuthenticatedEncryptor DefaultAuthenticatedEncryptor { get; } = new T().CreateAuthenticatedEncryptor(ProtectedMemoryBlob.Random(NUM_BYTES_IN_KDK));
+            public IAuthenticatedEncryptor DefaultAuthenticatedEncryptor { get; } = new T().CreateAuthenticatedEncryptor(Secret.Random(NUM_BYTES_IN_KDK));
 
             public Guid DefaultKeyId { get; } = default(Guid);
 

src/Microsoft.AspNet.Security.DataProtection/ExceptionExtensions.cs

@@ -0,0 +1,20 @@
+// Copyright (c) Microsoft Open Technologies, Inc. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using System;
+using System.Security.Cryptography;
+
+namespace Microsoft.AspNet.Security.DataProtection
+{
+    internal static class ExceptionExtensions
+    {
+        /// <summary>
+        /// Determines whether an exception must be homogenized by being wrapped inside a
+        /// CryptographicException before being rethrown.
+        /// </summary>
+        public static bool RequiresHomogenization(this Exception ex)
+        {
+            return !(ex is CryptographicException);
+        }
+    }
+}

src/Microsoft.AspNet.Security.DataProtection/ISecret.cs

@@ -11,7 +11,7 @@ namespace Microsoft.AspNet.Security.DataProtection
     public interface ISecret : IDisposable
     {
         /// <summary>
-        /// The length (in bytes) of the value.
+        /// The length (in bytes) of the secret value.
         /// </summary>
         int Length { get; }
 

src/Microsoft.AspNet.Security.DataProtection/KeyManagement/KeyRingBasedDataProtector.cs

@@ -131,7 +131,7 @@ namespace Microsoft.AspNet.Security.DataProtection.KeyManagement
                     postBufferSize: 0);
                 CryptoUtil.Assert(retVal != null && retVal.Length >= sizeof(uint) + sizeof(Guid), "retVal != null && retVal.Length >= sizeof(uint) + sizeof(Guid)");
             }
-            catch (Exception ex) when (!(ex is CryptographicException))
+            catch (Exception ex) when (ex.RequiresHomogenization())
             {
                 // homogenize all errors to CryptographicException
                 throw Error.Common_EncryptionFailed(ex);
@@ -247,7 +247,7 @@ namespace Microsoft.AspNet.Security.DataProtection.KeyManagement
                 CryptoUtil.Assert(retVal != null, "retVal != null");
                 return retVal;
             }
-            catch (Exception ex) when (!(ex is CryptographicException))
+            catch (Exception ex) when (ex.RequiresHomogenization())
             {
                 // homogenize all failures to CryptographicException
                 throw Error.DecryptionFailed(ex);

src/Microsoft.AspNet.Security.DataProtection/KeyManagement/XmlKeyManager.cs

@@ -111,7 +111,7 @@ namespace Microsoft.AspNet.Security.DataProtection.KeyManagement
                     var thisKey = ParseKeyElement(element);
                     if (idToKeyMap.ContainsKey(thisKey.KeyId))
                     {
-                        CryptoUtil.Fail("TODO: Duplicate key.");
+                        throw CryptoUtil.Fail("TODO: Duplicate key.");
                     }
                     idToKeyMap.Add(thisKey.KeyId, thisKey);
                 }
@@ -140,7 +140,7 @@ namespace Microsoft.AspNet.Security.DataProtection.KeyManagement
                 }
                 else
                 {
-                    CryptoUtil.Fail("TODO: Unknown element.");
+                    throw CryptoUtil.Fail("TODO: Unknown element.");
                 }
             }
 

src/Microsoft.AspNet.Security.DataProtection/Managed/ManagedAuthenticatedEncryptor.cs

@@ -36,7 +36,7 @@ namespace Microsoft.AspNet.Security.DataProtection.Managed
 
         private readonly byte[] _contextHeader;
         private readonly IManagedGenRandom _genRandom;
-        private readonly ProtectedMemoryBlob _keyDerivationKey;
+        private readonly Secret _keyDerivationKey;
         private readonly Func<SymmetricAlgorithm> _symmetricAlgorithmFactory;
         private readonly int _symmetricAlgorithmBlockSizeInBytes;
         private readonly int _symmetricAlgorithmSubkeyLengthInBytes;
@@ -44,7 +44,7 @@ namespace Microsoft.AspNet.Security.DataProtection.Managed
         private readonly int _validationAlgorithmSubkeyLengthInBytes;
         private readonly Func<KeyedHashAlgorithm> _validationAlgorithmFactory;
 
-        public ManagedAuthenticatedEncryptor(ProtectedMemoryBlob keyDerivationKey, Func<SymmetricAlgorithm> symmetricAlgorithmFactory, int symmetricAlgorithmKeySizeInBytes, Func<KeyedHashAlgorithm> validationAlgorithmFactory, IManagedGenRandom genRandom = null)
+        public ManagedAuthenticatedEncryptor(Secret keyDerivationKey, Func<SymmetricAlgorithm> symmetricAlgorithmFactory, int symmetricAlgorithmKeySizeInBytes, Func<KeyedHashAlgorithm> validationAlgorithmFactory, IManagedGenRandom genRandom = null)
         {
             CryptoUtil.Assert(KEY_MODIFIER_SIZE_IN_BYTES <= symmetricAlgorithmKeySizeInBytes && symmetricAlgorithmKeySizeInBytes <= Constants.MAX_STACKALLOC_BYTES,
                 "KEY_MODIFIER_SIZE_IN_BYTES <= symmetricAlgorithmKeySizeInBytes && symmetricAlgorithmKeySizeInBytes <= Constants.MAX_STACKALLOC_BYTES");
@@ -278,7 +278,7 @@ namespace Microsoft.AspNet.Security.DataProtection.Managed
                     }
                 }
             }
-            catch (Exception ex) when (!(ex is CryptographicException))
+            catch (Exception ex) when (ex.RequiresHomogenization())
             {
                 // Homogenize all exceptions to CryptographicException.
                 throw Error.CryptCommon_GenericError(ex);
@@ -382,7 +382,7 @@ namespace Microsoft.AspNet.Security.DataProtection.Managed
                     }
                 }
             }
-            catch (Exception ex) when (!(ex is CryptographicException))
+            catch (Exception ex) when (ex.RequiresHomogenization())
             {
                 // Homogenize all exceptions to CryptographicException.
                 throw Error.CryptCommon_GenericError(ex);

src/Microsoft.AspNet.Security.DataProtection/SP800_108/SP800_108_CTR_HMACSHA512Util.cs

@@ -36,7 +36,7 @@ namespace Microsoft.AspNet.Security.DataProtection.SP800_108
         }
 
         // Creates a provider from the given secret.
-        public static ISP800_108_CTR_HMACSHA512Provider CreateProvider(ProtectedMemoryBlob kdk)
+        public static ISP800_108_CTR_HMACSHA512Provider CreateProvider(Secret kdk)
         {
             uint secretLengthInBytes = checked((uint)kdk.Length);
             if (secretLengthInBytes == 0)

src/Microsoft.AspNet.Security.DataProtection/Secret.cs

@@ -8,7 +8,10 @@ using Microsoft.AspNet.Security.DataProtection.SafeHandles;
 
 namespace Microsoft.AspNet.Security.DataProtection
 {
-    public unsafe sealed class ProtectedMemoryBlob : IDisposable, ISecret
+    /// <summary>
+    /// Represents a secret value stored in memory.
+    /// </summary>
+    public unsafe sealed class Secret : IDisposable, ISecret
     {
         // from wincrypt.h
         private const uint CRYPTPROTECTMEMORY_BLOCK_SIZE = 16;
@@ -16,42 +19,57 @@ namespace Microsoft.AspNet.Security.DataProtection
         private readonly SecureLocalAllocHandle _localAllocHandle;
         private readonly uint _plaintextLength;
 
-        public ProtectedMemoryBlob(ArraySegment<byte> plaintext)
+        /// <summary>
+        /// Creates a new Secret from the provided input value, where the input value
+        /// is specified as an array segment.
+        /// </summary>
+        public Secret(ArraySegment<byte> value)
         {
-            plaintext.Validate();
+            value.Validate();
 
-            _localAllocHandle = Protect(plaintext);
-            _plaintextLength = (uint)plaintext.Count;
+            _localAllocHandle = Protect(value);
+            _plaintextLength = (uint)value.Count;
         }
 
-        public ProtectedMemoryBlob(byte[] plaintext)
-            : this(new ArraySegment<byte>(plaintext))
+        /// <summary>
+        /// Creates a new Secret from the provided input value, where the input value
+        /// is specified as an array.
+        /// </summary>
+        public Secret(byte[] value)
+            : this(new ArraySegment<byte>(value))
         {
         }
 
-        public ProtectedMemoryBlob(byte* plaintext, int plaintextLength)
+        /// <summary>
+        /// Creates a new Secret from the provided input value, where the input value
+        /// is specified as a pointer to unmanaged memory.
+        /// </summary>
+        public Secret(byte* secret, int secretLength)
         {
-            if (plaintext == null)
+            if (secret == null)
             {
-                throw new ArgumentNullException("plaintext");
+                throw new ArgumentNullException("secret");
             }
-            if (plaintextLength < 0)
+            if (secretLength < 0)
             {
-                throw new ArgumentOutOfRangeException("plaintextLength");
+                throw new ArgumentOutOfRangeException("secretLength");
             }
 
-            _localAllocHandle = Protect(plaintext, (uint)plaintextLength);
-            _plaintextLength = (uint)plaintextLength;
+            _localAllocHandle = Protect(secret, (uint)secretLength);
+            _plaintextLength = (uint)secretLength;
         }
 
-        public ProtectedMemoryBlob(ISecret secret)
+        /// <summary>
+        /// Creates a new Secret from another secret object.
+        /// </summary>
+        public Secret(ISecret secret)
         {
             if (secret == null)
             {
                 throw new ArgumentNullException("secret");
             }
 
-            ProtectedMemoryBlob other = secret as ProtectedMemoryBlob;
+            Secret other = secret as Secret;
             if (other != null)
             {
                 // Fast-track: simple deep copy scenario.
@@ -79,6 +97,9 @@ namespace Microsoft.AspNet.Security.DataProtection
             }
         }
 
+        /// <summary>
+        /// The length (in bytes) of the secret value.
+        /// </summary>
         public int Length
         {
             get
@@ -87,6 +108,9 @@ namespace Microsoft.AspNet.Security.DataProtection
             }
         }
 
+        /// <summary>
+        /// Wipes the secret from memory.
+        /// </summary>
         public void Dispose()
         {
             _localAllocHandle.Dispose();
@@ -134,21 +158,25 @@ namespace Microsoft.AspNet.Security.DataProtection
             return encryptedMemoryHandle;
         }
 
-        public static ProtectedMemoryBlob Random(int numBytes)
+        /// <summary>
+        /// Returns a Secret comprised entirely of random bytes retrieved from
+        /// a cryptographically secure RNG.
+        /// </summary>
+        public static Secret Random(int numBytes)
         {
             CryptoUtil.Assert(numBytes >= 0, "numBytes >= 0");
 
             if (numBytes == 0)
             {
                 byte dummy;
-                return new ProtectedMemoryBlob(&dummy, 0);
+                return new Secret(&dummy, 0);
             }
             else
             {
                 // Don't use CNG if we're not on Windows.
                 if (!OSVersionUtil.IsBCryptOnWin7OrLaterAvailable())
                 {
-                    return new ProtectedMemoryBlob(ManagedGenRandomImpl.Instance.GenRandom(numBytes));
+                    return new Secret(ManagedGenRandomImpl.Instance.GenRandom(numBytes));
                 }
 
                 byte[] bytes = new byte[numBytes];
@@ -157,7 +185,7 @@ namespace Microsoft.AspNet.Security.DataProtection
                     try
                     {
                         BCryptUtil.GenRandom(pbBytes, (uint)numBytes);
-                        return new ProtectedMemoryBlob(pbBytes, numBytes);
+                        return new Secret(pbBytes, numBytes);
                     }
                     finally
                     {
@@ -196,6 +224,12 @@ namespace Microsoft.AspNet.Security.DataProtection
             }
         }
 
+        /// <summary>
+        /// Writes the secret value to the specified buffer.
+        /// </summary>
+        /// <remarks>
+        /// The buffer size must exactly match the length of the secret value.
+        /// </remarks>
         public void WriteSecretIntoBuffer(ArraySegment<byte> buffer)
         {
             // Parameter checking
@@ -215,6 +249,12 @@ namespace Microsoft.AspNet.Security.DataProtection
             }
         }
 
+        /// <summary>
+        /// Writes the secret value to the specified buffer.
+        /// </summary>
+        /// <remarks>
+        /// The 'bufferLength' parameter must exactly match the length of the secret value.
+        /// </remarks>
         public void WriteSecretIntoBuffer(byte* buffer, int bufferLength)
         {
             if (buffer == null)

src/Microsoft.AspNet.Security.DataProtection/TimeLimitedDataProtector.cs

@@ -86,7 +86,7 @@ namespace Microsoft.AspNet.Security.DataProtection
                 expiration = new DateTimeOffset((long)utcTicksExpiration, TimeSpan.Zero);
                 return retVal;
             }
-            catch (Exception ex) when (!(ex is CryptographicException))
+            catch (Exception ex) when (ex.RequiresHomogenization())
             {
                 // Homogenize all failures to CryptographicException
                 throw Error.CryptCommon_GenericError(ex);

src/Microsoft.AspNet.Security.DataProtection/XmlEncryption/DpapiNGXmlEncryptor.cs

@@ -46,20 +46,19 @@ namespace Microsoft.AspNet.Security.DataProtection.XmlEncryption
         public XElement Encrypt([NotNull] XElement plaintextElement)
         {
             // First, convert the XML element to a byte[] so that it can be encrypted.
-            ProtectedMemoryBlob secret;
+            Secret secret;
             using (var memoryStream = new MemoryStream())
             {
                 plaintextElement.Save(memoryStream);
-
 #if !ASPNETCORE50
                 // If we're on full desktop CLR, utilize the underlying buffer directly as an optimization.
                 byte[] underlyingBuffer = memoryStream.GetBuffer();
-                secret = new ProtectedMemoryBlob(new ArraySegment<byte>(underlyingBuffer, 0, checked((int)memoryStream.Length)));
+                secret = new Secret(new ArraySegment<byte>(underlyingBuffer, 0, checked((int)memoryStream.Length)));
                 Array.Clear(underlyingBuffer, 0, underlyingBuffer.Length);
 #else
                 // Otherwise, need to make a copy of the buffer.
                 byte[] clonedBuffer = memoryStream.ToArray();
-                secret = new ProtectedMemoryBlob(clonedBuffer);
+                secret = new Secret(clonedBuffer);
                 Array.Clear(clonedBuffer, 0, clonedBuffer.Length);
 #endif
             }

src/Microsoft.AspNet.Security.DataProtection/XmlEncryption/DpapiXmlEncryptor.cs

@@ -31,7 +31,7 @@ namespace Microsoft.AspNet.Security.DataProtection.XmlEncryption
         public XElement Encrypt([NotNull] XElement plaintextElement)
         {
             // First, convert the XML element to a byte[] so that it can be encrypted.
-            ProtectedMemoryBlob secret;
+            Secret secret;
             using (var memoryStream = new MemoryStream())
             {
                 plaintextElement.Save(memoryStream);
@@ -39,12 +39,12 @@ namespace Microsoft.AspNet.Security.DataProtection.XmlEncryption
 #if !ASPNETCORE50
                 // If we're on full desktop CLR, utilize the underlying buffer directly as an optimization.
                 byte[] underlyingBuffer = memoryStream.GetBuffer();
-                secret = new ProtectedMemoryBlob(new ArraySegment<byte>(underlyingBuffer, 0, checked((int)memoryStream.Length)));
+                secret = new Secret(new ArraySegment<byte>(underlyingBuffer, 0, checked((int)memoryStream.Length)));
                 Array.Clear(underlyingBuffer, 0, underlyingBuffer.Length);
 #else
                 // Otherwise, need to make a copy of the buffer.
                 byte[] clonedBuffer = memoryStream.ToArray();
-                secret = new ProtectedMemoryBlob(clonedBuffer);
+                secret = new Secret(clonedBuffer);
                 Array.Clear(clonedBuffer, 0, clonedBuffer.Length);
 #endif
             }

test/Microsoft.AspNet.Security.DataProtection.Test/Cng/CbcAuthenticatedEncryptorTests.cs

@@ -18,7 +18,7 @@ namespace Microsoft.AspNet.Security.DataProtection.Test.Cng
         public void Encrypt_Decrypt_RoundTrips()
         {
             // Arrange
-            ProtectedMemoryBlob kdk = new ProtectedMemoryBlob(new byte[512 / 8]);
+            Secret kdk = new Secret(new byte[512 / 8]);
             CbcAuthenticatedEncryptor encryptor = new CbcAuthenticatedEncryptor(kdk,
                 symmetricAlgorithmHandle: CachedAlgorithmHandles.AES_CBC,
                 symmetricAlgorithmKeySizeInBytes: 256 / 8,
@@ -39,7 +39,7 @@ namespace Microsoft.AspNet.Security.DataProtection.Test.Cng
         public void Encrypt_Decrypt_Tampering_Fails()
         {
             // Arrange
-            ProtectedMemoryBlob kdk = new ProtectedMemoryBlob(new byte[512 / 8]);
+            Secret kdk = new Secret(new byte[512 / 8]);
             CbcAuthenticatedEncryptor encryptor = new CbcAuthenticatedEncryptor(kdk,
                 symmetricAlgorithmHandle: CachedAlgorithmHandles.AES_CBC,
                 symmetricAlgorithmKeySizeInBytes: 256 / 8,
@@ -86,7 +86,7 @@ namespace Microsoft.AspNet.Security.DataProtection.Test.Cng
         public void Encrypt_KnownKey()
         {
             // Arrange
-            ProtectedMemoryBlob kdk = new ProtectedMemoryBlob(Encoding.UTF8.GetBytes("master key"));
+            Secret kdk = new Secret(Encoding.UTF8.GetBytes("master key"));
             CbcAuthenticatedEncryptor encryptor = new CbcAuthenticatedEncryptor(kdk,
                 symmetricAlgorithmHandle: CachedAlgorithmHandles.AES_CBC,
                 symmetricAlgorithmKeySizeInBytes: 256 / 8,

test/Microsoft.AspNet.Security.DataProtection.Test/Cng/GcmAuthenticatedEncryptorTests.cs

@@ -18,7 +18,7 @@ namespace Microsoft.AspNet.Security.DataProtection.Test.Cng
         public void Encrypt_Decrypt_RoundTrips()
         {
             // Arrange
-            ProtectedMemoryBlob kdk = new ProtectedMemoryBlob(new byte[512 / 8]);
+            Secret kdk = new Secret(new byte[512 / 8]);
             GcmAuthenticatedEncryptor encryptor = new GcmAuthenticatedEncryptor(kdk, CachedAlgorithmHandles.AES_GCM, symmetricAlgorithmKeySizeInBytes: 256 / 8);
             ArraySegment<byte> plaintext = new ArraySegment<byte>(Encoding.UTF8.GetBytes("plaintext"));
             ArraySegment<byte> aad = new ArraySegment<byte>(Encoding.UTF8.GetBytes("aad"));
@@ -36,7 +36,7 @@ namespace Microsoft.AspNet.Security.DataProtection.Test.Cng
         public void Encrypt_Decrypt_Tampering_Fails()
         {
             // Arrange
-            ProtectedMemoryBlob kdk = new ProtectedMemoryBlob(new byte[512 / 8]);
+            Secret kdk = new Secret(new byte[512 / 8]);
             GcmAuthenticatedEncryptor encryptor = new GcmAuthenticatedEncryptor(kdk, CachedAlgorithmHandles.AES_GCM, symmetricAlgorithmKeySizeInBytes: 256 / 8);
             ArraySegment<byte> plaintext = new ArraySegment<byte>(Encoding.UTF8.GetBytes("plaintext"));
             ArraySegment<byte> aad = new ArraySegment<byte>(Encoding.UTF8.GetBytes("aad"));
@@ -80,7 +80,7 @@ namespace Microsoft.AspNet.Security.DataProtection.Test.Cng
         public void Encrypt_KnownKey()
         {
             // Arrange
-            ProtectedMemoryBlob kdk = new ProtectedMemoryBlob(Encoding.UTF8.GetBytes("master key"));
+            Secret kdk = new Secret(Encoding.UTF8.GetBytes("master key"));
             GcmAuthenticatedEncryptor encryptor = new GcmAuthenticatedEncryptor(kdk, CachedAlgorithmHandles.AES_GCM, symmetricAlgorithmKeySizeInBytes: 128 / 8, genRandom: new SequentialGenRandom());
             ArraySegment<byte> plaintext = new ArraySegment<byte>(new byte[] { 0, 1, 2, 3, 4, 5, 6, 7 }, 2, 3);
             ArraySegment<byte> aad = new ArraySegment<byte>(new byte[] { 7, 6, 5, 4, 3, 2, 1, 0 }, 1, 4);

test/Microsoft.AspNet.Security.DataProtection.Test/Managed/ManagedAuthenticatedEncryptorTests.cs

@@ -16,7 +16,7 @@ namespace Microsoft.AspNet.Security.DataProtection.Test.Managed
         public void Encrypt_Decrypt_RoundTrips()
         {
             // Arrange
-            ProtectedMemoryBlob kdk = new ProtectedMemoryBlob(new byte[512 / 8]);
+            Secret kdk = new Secret(new byte[512 / 8]);
             ManagedAuthenticatedEncryptor encryptor = new ManagedAuthenticatedEncryptor(kdk,
                 symmetricAlgorithmFactory: Aes.Create,
                 symmetricAlgorithmKeySizeInBytes: 256 / 8,
@@ -36,7 +36,7 @@ namespace Microsoft.AspNet.Security.DataProtection.Test.Managed
         public void Encrypt_Decrypt_Tampering_Fails()
         {
             // Arrange
-            ProtectedMemoryBlob kdk = new ProtectedMemoryBlob(new byte[512 / 8]);
+            Secret kdk = new Secret(new byte[512 / 8]);
             ManagedAuthenticatedEncryptor encryptor = new ManagedAuthenticatedEncryptor(kdk,
                 symmetricAlgorithmFactory: Aes.Create,
                 symmetricAlgorithmKeySizeInBytes: 256 / 8,
@@ -82,7 +82,7 @@ namespace Microsoft.AspNet.Security.DataProtection.Test.Managed
         public void Encrypt_KnownKey()
         {
             // Arrange
-            ProtectedMemoryBlob kdk = new ProtectedMemoryBlob(Encoding.UTF8.GetBytes("master key"));
+            Secret kdk = new Secret(Encoding.UTF8.GetBytes("master key"));
             ManagedAuthenticatedEncryptor encryptor = new ManagedAuthenticatedEncryptor(kdk,
                 symmetricAlgorithmFactory: Aes.Create,
                 symmetricAlgorithmKeySizeInBytes: 256 / 8,