Fix build break: inadvertently removed PBKDF2.cs and related functionality

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

@@ -31,11 +31,11 @@ namespace Microsoft.AspNet.Security.DataProtection
 
             return algHandle;
         }
-        private static BCryptAlgorithmHandle CreateHMACSHA256AlgorithmHandle()
+
+        internal static BCryptAlgorithmHandle CreateGenericHMACHandleFromPrimitiveProvider(string algorithmName)
         {
-            // create the HMACSHA-256 instance
             BCryptAlgorithmHandle algHandle;
-            int status = UnsafeNativeMethods.BCryptOpenAlgorithmProvider(out algHandle, Constants.BCRYPT_SHA256_ALGORITHM, Constants.MS_PRIMITIVE_PROVIDER, dwFlags: BCryptAlgorithmFlags.BCRYPT_ALG_HANDLE_HMAC_FLAG);
+            int status = UnsafeNativeMethods.BCryptOpenAlgorithmProvider(out algHandle, algorithmName, Constants.MS_PRIMITIVE_PROVIDER, dwFlags: BCryptAlgorithmFlags.BCRYPT_ALG_HANDLE_HMAC_FLAG);
             if (status != 0 || algHandle == null || algHandle.IsInvalid)
             {
                 throw new CryptographicException(status);
@@ -44,17 +44,16 @@ namespace Microsoft.AspNet.Security.DataProtection
             return algHandle;
         }
 
+        private static BCryptAlgorithmHandle CreateHMACSHA256AlgorithmHandle()
+        {
+            // create the HMACSHA-256 instance
+            return CreateGenericHMACHandleFromPrimitiveProvider(Constants.BCRYPT_SHA256_ALGORITHM);
+        }
+
         private static BCryptAlgorithmHandle CreateHMACSHA512AlgorithmHandle()
         {
             // create the HMACSHA-512 instance
-            BCryptAlgorithmHandle algHandle;
+            return CreateGenericHMACHandleFromPrimitiveProvider(Constants.BCRYPT_SHA512_ALGORITHM);
-            int status = UnsafeNativeMethods.BCryptOpenAlgorithmProvider(out algHandle, Constants.BCRYPT_SHA512_ALGORITHM, Constants.MS_PRIMITIVE_PROVIDER, dwFlags: BCryptAlgorithmFlags.BCRYPT_ALG_HANDLE_HMAC_FLAG);
-            if (status != 0 || algHandle == null || algHandle.IsInvalid)
-            {
-                throw new CryptographicException(status);
-            }
-
-            return algHandle;
         }
     }
 }

src/Microsoft.AspNet.Security.DataProtection/PBKDF2.cs

@@ -0,0 +1,65 @@
+using System;
+using System.Security.Cryptography;
+
+namespace Microsoft.AspNet.Security.DataProtection
+{
+    /// <summary>
+    /// Helper class to derive keys from low-entropy passwords using the PBKDF2 algorithm.
+    /// </summary>
+    public static class PBKDF2
+    {
+        /// <summary>
+        /// Derives a key from a low-entropy password.
+        /// </summary>
+        /// <param name="algorithmName">The name of the PRF to use for key derivation.</param>
+        /// <param name="password">The low-entropy password from which to generate a key.</param>
+        /// <param name="salt">The salt used to randomize the key derivation.</param>
+        /// <param name="iterationCount">The number of iterations to perform.</param>
+        /// <param name="numBytesToDerive">The desired byte length of the derived key.</param>
+        /// <returns>A key derived from the provided password.</returns>
+        /// <remarks>For compatibility with the Rfc2898DeriveBytes class, specify "SHA1" for the <em>algorithmName</em> parameter.</remarks>
+        public unsafe static byte[] DeriveKey(string algorithmName, byte[] password, byte[] salt, ulong iterationCount, uint numBytesToDerive)
+        {
+            if (String.IsNullOrEmpty(algorithmName))
+            {
+                throw new ArgumentException(Res.Common_NullOrEmpty, "algorithmName");
+            }
+            if (password == null || password.Length == 0)
+            {
+                throw new ArgumentException(Res.Common_NullOrEmpty, "password");
+            }
+            if (salt == null || salt.Length == 0)
+            {
+                throw new ArgumentException(Res.Common_NullOrEmpty, "salt");
+            }
+            if (iterationCount <= 0)
+            {
+                throw new ArgumentOutOfRangeException("iterationCount");
+            }
+
+            byte[] derivedKey = new byte[numBytesToDerive];
+            int status;
+
+            using (BCryptAlgorithmHandle algHandle = Algorithms.CreateGenericHMACHandleFromPrimitiveProvider(algorithmName))
+            {
+                fixed (byte* pPassword = password)
+                fixed (byte* pSalt = salt)
+                fixed (byte* pDerivedKey = derivedKey)
+                {
+                    status = UnsafeNativeMethods.BCryptDeriveKeyPBKDF2(
+                        algHandle, pPassword, (uint)password.Length, pSalt, (uint)salt.Length, iterationCount,
+                        pDerivedKey, numBytesToDerive, dwFlags: 0);
+                }
+            }
+
+            if (status == 0 /* STATUS_SUCCESS */)
+            {
+                return derivedKey;
+            }
+            else
+            {
+                throw new CryptographicException(status);
+            }
+        }
+    }
+}

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

@@ -46,6 +46,19 @@ namespace Microsoft.AspNet.Security.DataProtection
             [Out] out uint pcbResult,
             [In] BCryptEncryptFlags dwFlags);
 
+        [DllImport(BCRYPT_LIB, CallingConvention = CallingConvention.Winapi)]
+        // http://msdn.microsoft.com/en-us/library/windows/desktop/dd433795(v=vs.85).aspx
+        internal static extern int BCryptDeriveKeyPBKDF2(
+            [In] BCryptAlgorithmHandle hPrf,
+            [In] byte* pbPassword,
+            [In] uint cbPassword,
+            [In] byte* pbSalt,
+            [In] uint cbSalt,
+            [In] ulong cIterations,
+            [In] byte* pbDerivedKey,
+            [In] uint cbDerivedKey,
+            [In] uint dwFlags);
+
         [DllImport(BCRYPT_LIB, CallingConvention = CallingConvention.Winapi)]
         // http://msdn.microsoft.com/en-us/library/windows/desktop/aa375399(v=vs.85).aspx
         internal static extern int BCryptDestroyHash(