Added logic to calculate SMB 3.x encryption / decryption keys

SMBLibrary/Helpers/SP800_1008.cs

@@ -0,0 +1,53 @@
+/// Adapted from https://referencesource.microsoft.com/#system.web/Security/Cryptography/SP800_108.cs
+using System;
+using System.Security.Cryptography;
+using Utilities;
+
+namespace SMBLibrary
+{
+    /// <summary>
+    /// Implements the NIST SP800-108 key derivation routine in counter mode with an HMAC PRF.
+    /// See: http://csrc.nist.gov/publications/nistpubs/800-108/sp800-108.pdf
+    /// </summary>
+    internal class SP800_1008
+    {
+        public static byte[] DeriveKey(HMAC hmac, byte[] label, byte[] context, int keyLengthInBits)
+        {
+            int labelLength = (label != null) ? label.Length : 0;
+            int contextLength = (context != null) ? context.Length : 0;
+            byte[] buffer = new byte[4 /* [i]_2 */ + labelLength /* label */ + 1 /* 0x00 */ + contextLength /* context */ + 4 /* [L]_2 */];
+
+            if (labelLength != 0)
+            {
+                Buffer.BlockCopy(label, 0, buffer, 4, labelLength); // the 4 accounts for the [i]_2 length
+            }
+            if (contextLength != 0)
+            {
+                Buffer.BlockCopy(context, 0, buffer, 5 + labelLength, contextLength); // the '5 +' accounts for the [i]_2 length, the label, and the 0x00 byte
+            }
+
+            BigEndianWriter.WriteUInt32(buffer, 5 + labelLength + contextLength, (uint)keyLengthInBits); // the '5 +' accounts for the [i]_2 length, the label, the 0x00 byte, and the context
+
+            // Initialization
+            int numBytesWritten = 0;
+            int numBytesRemaining = keyLengthInBits / 8;
+            byte[] output = new byte[numBytesRemaining];
+
+            // Calculate each K_i value and copy the leftmost bits to the output buffer as appropriate.
+            for (uint i = 1; numBytesRemaining > 0; i++)
+            {
+                BigEndianWriter.WriteUInt32(buffer, 0, i); // set the first 32 bits of the buffer to be the current iteration value
+                byte[] K_i = hmac.ComputeHash(buffer);
+
+                // copy the leftmost bits of K_i into the output buffer
+                int numBytesToCopy = Math.Min(numBytesRemaining, K_i.Length);
+                Buffer.BlockCopy(K_i, 0, output, numBytesWritten, numBytesToCopy);
+                numBytesWritten += numBytesToCopy;
+                numBytesRemaining -= numBytesToCopy;
+            }
+
+            // finished
+            return output;
+        }
+    }
+}

SMBLibrary/SMB2/SMB2Cryptography.cs

@@ -0,0 +1,52 @@
+/* Copyright (C) 2020 Tal Aloni <tal.aloni.il@gmail.com>. All rights reserved.
+ * 
+ * You can redistribute this program and/or modify it under the terms of
+ * the GNU Lesser Public License as published by the Free Software Foundation,
+ * either version 3 of the License, or (at your option) any later version.
+ */
+using System;
+using System.Security.Cryptography;
+using Utilities;
+
+namespace SMBLibrary.SMB2
+{
+    internal class SMB2Cryptography
+    {
+        public static byte[] GenerateEncryptionKey(byte[] sessionKey, SMB2Dialect dialect, byte[] preauthIntegrityHashValue)
+        {
+            if (dialect == SMB2Dialect.SMB311 && preauthIntegrityHashValue == null)
+            {
+                throw new ArgumentNullException("preauthIntegrityHashValue");
+            }
+
+            string labelString = (dialect == SMB2Dialect.SMB311) ? "SMBC2SCipherKey" : "SMB2AESCCM";
+            byte[] label = GetNullTerminatedAnsiString(labelString);
+            byte[] context = (dialect == SMB2Dialect.SMB311) ? preauthIntegrityHashValue : GetNullTerminatedAnsiString("ServerIn ");
+
+            HMACSHA256 hmac = new HMACSHA256(sessionKey);
+            return SP800_1008.DeriveKey(hmac, label, context, 128);
+        }
+
+        public static byte[] GenerateDecryptionKey(byte[] sessionKey, SMB2Dialect dialect, byte[] preauthIntegrityHashValue)
+        {
+            if (dialect == SMB2Dialect.SMB311 && preauthIntegrityHashValue == null)
+            {
+                throw new ArgumentNullException("preauthIntegrityHashValue");
+            }
+
+            string labelString = (dialect == SMB2Dialect.SMB311) ? "SMBS2CCipherKey" : "SMB2AESCCM";
+            byte[] label = GetNullTerminatedAnsiString(labelString);
+            byte[] context = (dialect == SMB2Dialect.SMB311) ? preauthIntegrityHashValue : GetNullTerminatedAnsiString("ServerOut");
+
+            HMACSHA256 hmac = new HMACSHA256(sessionKey);
+            return SP800_1008.DeriveKey(hmac, label, context, 128);
+        }
+
+        private static byte[] GetNullTerminatedAnsiString(string value)
+        {
+            byte[] result = new byte[value.Length + 1];
+            ByteWriter.WriteNullTerminatedAnsiString(result, 0, value);
+            return result;
+        }
+    }
+}

SMBLibrary/SMBLibrary.VS2005.csproj

@@ -74,6 +74,8 @@
     <Compile Include="Enums\Win32Error.cs" />
     <Compile Include="Exceptions\UnsupportedInformationLevelException.cs" />
     <Compile Include="Helpers\FileTimeHelper.cs" />
+    <Compile Include="Helpers\SP800_1008.cs" />
+    <Compile Include="SMB2\SMB2Cryptography.cs" />
     <Compile Include="NetBios\NameServicePackets\Enums\ResourceRecordClass.cs" />
     <Compile Include="NetBios\NameServicePackets\Enums\NameRecordType.cs" />
     <Compile Include="NetBios\NameServicePackets\Enums\NameServiceOperation.cs" />