From 101a1e0fd64eaf003981c1e6c0d67793d36d59ee Mon Sep 17 00:00:00 2001
From: Leonetienne <leon@etiennes.de>
Date: Thu, 26 May 2022 02:44:22 +0200
Subject: [PATCH] Add additional jumbling-up in feistel rounds

---
 GCryptLib/include/GCrypt/Feistel.h |  2 +-
 GCryptLib/src/Feistel.cpp          | 48 ++++++++++++++++++++++--------
 2 files changed, 37 insertions(+), 13 deletions(-)

diff --git a/GCryptLib/include/GCrypt/Feistel.h b/GCryptLib/include/GCrypt/Feistel.h
index 60f3d10..5d30334 100644
--- a/GCryptLib/include/GCrypt/Feistel.h
+++ b/GCryptLib/include/GCrypt/Feistel.h
@@ -32,7 +32,7 @@ namespace Leonetienne::GCrypt {
   private:
     //! Will run the feistel rounds, with either regular key
     //! order or reversed key order
-    Block Run(const Block& data, bool reverseKeys);
+    Block Run(const Block& data, bool modeEncrypt);
 
     //! Arbitrary cipher function
     static Halfblock F(Halfblock m, const Key& key);
diff --git a/GCryptLib/src/Feistel.cpp b/GCryptLib/src/Feistel.cpp
index 7fb731e..1c54a7f 100644
--- a/GCryptLib/src/Feistel.cpp
+++ b/GCryptLib/src/Feistel.cpp
@@ -30,7 +30,7 @@ namespace Leonetienne::GCrypt {
     return Run(data, true);
   }
 
-  Block Feistel::Run(const Block& data, bool reverseKeys) {
+  Block Feistel::Run(const Block& data, bool modeEncrypt) {
     const auto splitData = FeistelSplit(data);
     Halfblock l = splitData.first;
     Halfblock r = splitData.second;
@@ -38,19 +38,43 @@ namespace Leonetienne::GCrypt {
     Halfblock tmp;
 
     for (std::size_t i = 0; i < N_ROUNDS; i++) {
-      // Calculate key index
-      std::size_t keyIndex;
-      if (reverseKeys) {
-        keyIndex = N_ROUNDS - i - 1;
-      }
-      else {
-        keyIndex = i;
+
+      // Encryption
+      if (modeEncrypt) {
+        const std::size_t keyIndex = i;
+
+        // Do a feistel round
+        tmp = r;
+        r = l ^ F(r, roundKeys[keyIndex]);
+        l = tmp;
+
+        // Jumble it up a bit more
+        l.ShiftRowsUpInplace();
+        l.ShiftCellsRightInplace();
+        l.ShiftBitsLeftInplace();
+        l.ShiftColumnsLeftInplace();
+        // Seal all these operations with a key
+        l += ReductionFunction(roundKeys[keyIndex]);
+      }
+
+      // Decryption
+      else {
+        // Decryption needs keys in reverse order
+        const std::size_t keyIndex = N_ROUNDS - i - 1;
+
+        // Unjumble the jumble
+        r -= ReductionFunction(roundKeys[keyIndex]);
+        r.ShiftColumnsRightInplace();
+        r.ShiftBitsRightInplace();
+        r.ShiftCellsLeftInplace();
+        r.ShiftRowsDownInplace();
+
+        // Do a feistel round
+        tmp = r;
+        r = l ^ F(r, roundKeys[keyIndex]);
+        l = tmp;
       }
 
-      // Do a feistel round
-      tmp = r;
-      r = l ^ F(r, roundKeys[keyIndex]);
-      l = tmp;
     }
 
     // Block has finished de*ciphering.