From 3bef7915dd0083514c94100d790e82a992fe6b1a Mon Sep 17 00:00:00 2001
From: Uncled1023 <admin@teknik.io>
Date: Mon, 10 Apr 2017 17:15:18 -0700
Subject: [PATCH] Adding some handling of block offsets for in place
 encryption/decryption

---
 Utilities/Utilities/Crypto.cs         | 12 ++++++------
 Utilities/Utilities/ResponseHelper.cs |  2 +-
 Utilities/Utilities/StreamHelper.cs   | 15 ++++++++++++++-
 3 files changed, 21 insertions(+), 8 deletions(-)

diff --git a/Utilities/Utilities/Crypto.cs b/Utilities/Utilities/Crypto.cs
index 32e5cfc..8820c95 100644
--- a/Utilities/Utilities/Crypto.cs
+++ b/Utilities/Utilities/Crypto.cs
@@ -209,7 +209,7 @@ namespace Teknik.Utilities
             // Process the stream and save the bytes to the output
             do
             {
-                int processedBytes = ProcessCipherBlock(cipher, input, chunkSize, output, cipherOffset, out bytesRead);
+                int processedBytes = ProcessCipherBlock(cipher, input, 0, chunkSize, output, cipherOffset, out bytesRead);
                 cipherOffset += processedBytes;
             }
             while (bytesRead > 0);
@@ -234,7 +234,7 @@ namespace Teknik.Utilities
                 int bytesRead = 0;
                 do
                 {
-                    processedBytes = ProcessCipherBlock(cipher, input, chunkSize, buffer, 0, out bytesRead);
+                    processedBytes = ProcessCipherBlock(cipher, input, 0, chunkSize, buffer, 0, out bytesRead);
                     if (processedBytes > 0)
                     {
                         // We have bytes, lets write them to the file
@@ -268,17 +268,17 @@ namespace Teknik.Utilities
             return cipher;
         }
 
-        public static int ProcessCipherBlock(IBufferedCipher cipher, Stream input, int chunkSize, byte[] output, int outputOffset, out int bytesRead)
+        public static int ProcessCipherBlock(IBufferedCipher cipher, Stream input, int inputOffset, int chunkSize, byte[] output, int outputOffset, out int bytesRead)
         {
             // Initialize buffer
-            byte[] buffer = new byte[chunkSize];
+            byte[] buffer = new byte[chunkSize + inputOffset];
 
             // Read the next block of data
-            bytesRead = input.Read(buffer, 0, chunkSize);
+            bytesRead = input.Read(buffer, 0, chunkSize + inputOffset);
             if (bytesRead > 0)
             {
                 // process the cipher for the read block and add it to the output
-                return cipher.ProcessBytes(buffer, 0, bytesRead, output, outputOffset);
+                return cipher.ProcessBytes(buffer, inputOffset, bytesRead - inputOffset, output, outputOffset);
             }
 
             return 0;
diff --git a/Utilities/Utilities/ResponseHelper.cs b/Utilities/Utilities/ResponseHelper.cs
index f9a8016..dcf2ec8 100644
--- a/Utilities/Utilities/ResponseHelper.cs
+++ b/Utilities/Utilities/ResponseHelper.cs
@@ -100,7 +100,7 @@ namespace Teknik.Utilities
                     {
                         bytesToRead = bytesRemaining;
                     }
-                    processedBytes = AES.ProcessCipherBlock(cipher, stream, bytesToRead, buffer, 0, out bytesRead);
+                    processedBytes = AES.ProcessCipherBlock(cipher, stream, 0, bytesToRead, buffer, 0, out bytesRead);
                     if (processedBytes > 0)
                     {
                         response.OutputStream.Write(buffer, 0, processedBytes);
diff --git a/Utilities/Utilities/StreamHelper.cs b/Utilities/Utilities/StreamHelper.cs
index e5559f1..bfb69ca 100644
--- a/Utilities/Utilities/StreamHelper.cs
+++ b/Utilities/Utilities/StreamHelper.cs
@@ -24,9 +24,22 @@ namespace Teknik.Utilities
             if (_Inner != null && CanRead)
             {
                 int bytesRead = 0;
+                long startPosition = _Inner.Position;
+                int blockSize = _Cipher.GetBlockSize();
+                long blockOffset = (startPosition % blockSize);
+
+                // Determine if we are at the start of a block, or not
+                if (blockOffset != 0)
+                {
+                    // We are not a multiple of the block size, so let's backup to get the current block
+                    _Inner.Seek(startPosition - blockOffset, SeekOrigin.Begin);
+                }
 
                 // Process the cipher
-                int processed = AES.ProcessCipherBlock(_Cipher, _Inner, count, buffer, offset, out bytesRead);
+                int processed = AES.ProcessCipherBlock(_Cipher, _Inner, 0, count + (int)blockOffset, buffer, offset, out bytesRead);
+
+                // Adjust bytes read by the block offset
+                bytesRead -= (int)blockOffset;
 
                 if (processed < bytesRead)
                 {