Imported Upstream version 4.8.0.309

Former-commit-id: 5f9c6ae75f295e057a7d2971f3a6df4656fa8850

mcs/class/referencesource/System.Data/System/Data/SqlClient/SqlClientSymmetricKey.cs

@@ -15,10 +15,9 @@ namespace System.Data.SqlClient
     /// Base class containing raw key bytes for symmetric key algorithms. Some encryption algorithms can use the key directly while others derive sub keys from this.
     /// If an algorithm needs to derive more keys, have a derived class from this and use it in the corresponding encryption algorithm.
     /// </summary>
-    internal class SqlClientSymmetricKey
-    {
+    internal class SqlClientSymmetricKey {
         /// <summary>
-        /// DPAPI protected key
+        /// The underlying key material
         /// </summary>
         protected readonly byte[] _rootKey;
 
@@ -26,8 +25,7 @@ namespace System.Data.SqlClient
         /// Constructor that initializes the root key.
         /// </summary>
         /// <param name="rootKey">root key</param>
-        internal SqlClientSymmetricKey(byte[] rootKey)
-        {
+        internal SqlClientSymmetricKey(byte[] rootKey) {
             // Key validation
             if (rootKey == null || rootKey.Length == 0) {
                 throw SQL.NullColumnEncryptionKeySysErr();
@@ -36,14 +34,24 @@ namespace System.Data.SqlClient
             _rootKey = rootKey;
         }
 
+        /// <summary>
+        /// Destructor that cleans up the key material.
+        /// This is a best effort approach since there are no guarantees around GC.
+        /// </summary>
+        ~SqlClientSymmetricKey() {
+            if (_rootKey != null) {
+                for (int i = 0; i < _rootKey.Length; i++) {
+                    _rootKey[i] = 0;
+                }
+            }
+        }
+
         /// <summary>
         /// Returns a copy of the plain text key
         /// This is needed for actual encryption/decryption.
         /// </summary>
-        internal virtual byte[] RootKey
-        {
-            get 
-            {
+        internal virtual byte[] RootKey {
+            get {
                 return _rootKey; 
             }
         }
@@ -52,8 +60,7 @@ namespace System.Data.SqlClient
         /// Computes SHA256 value of the plain text key bytes
         /// </summary>
         /// <returns>A string containing SHA256 hash of the root key</returns>
-        internal virtual string GetKeyHash()
-        {
+        internal virtual string GetKeyHash() {
             return SqlSecurityUtility.GetSHA256Hash(RootKey);
         }
 
@@ -63,10 +70,7 @@ namespace System.Data.SqlClient
         /// <returns>
         /// Returns the length of the root key
         /// </returns>
-        internal virtual int Length()
-        {
-            // Note: DPAPI preserves the original byte length
-            // so for now, this is as same as returning the length of the raw key.
+        internal virtual int Length() {
             return _rootKey.Length;
         }
     }