From 249e5cb1e18fc25a215f160568b02510dbfbd809 Mon Sep 17 00:00:00 2001
From: Sam Hadow <sam.hadow@proton.me>
Date: Tue, 9 Jun 2026 10:16:12 +0200
Subject: [PATCH] exhaustive 2 bits XOR search

---
 src/tea3/cli.py          | 20 ++++++++++++++++++--
 src/tea3/variable_xor.py | 38 ++++++++++++++++++++++++++++++++++++++
 2 files changed, 56 insertions(+), 2 deletions(-)

diff --git a/src/tea3/cli.py b/src/tea3/cli.py
index cfdca7f..dd4d9e1 100644
--- a/src/tea3/cli.py
+++ b/src/tea3/cli.py
@@ -3,7 +3,7 @@ from tea3.cliutils import prompt_int, prompt_choice, prompt_list
 from tea3.tea3model import Tea3Model
 from tea3.variable_search import run_exhaustive
 from tea3.sbox import run_sbox
-from tea3.variable_xor import run_variable_xor
+from tea3.variable_xor import run_variable_xor, run_exhaustive_two_bit_xor
 from tea3.f31f32 import run_f31f32
 
 
@@ -70,6 +70,19 @@ def run_variable_xor_cli():
     print("\n" + "=" * 50)
     print("Done.")
 
+def run_exhaustive_two_bit_xor_cli():
+    print("\nR registers are indexed 0–7; bits within each register are 0–7.")
+    print("This mode checks all 2-bit XOR pairs and prints the best one(s) at each step.")
+
+    steps = prompt_int("How many steps? (1–100): ", 1, 100)
+    target_reg = prompt_int("Target register (0–7): ", 0, 7)
+
+    print("-" * 50)
+    run_exhaustive_two_bit_xor(steps, target_reg)
+
+    print("\n" + "=" * 50)
+    print("Done.")
+
 
 
 def main():
@@ -83,8 +96,9 @@ def main():
     print("  3) S box analysis")
     print("  4) variable XOR")
     print("  5) F31, F32 analysis")
+    print("  6) Exhaustive 2-bit XOR search")
 
-    mode = prompt_choice("Your choice (1, 2, 3, 4 or 5): ", {1, 2, 3, 4, 5})
+    mode = prompt_choice("Your choice (1, 2, 3, 4, 5 or 6): ", {1, 2, 3, 4, 5, 6})
 
     if mode == 1:
         run_classic_cli()
@@ -96,6 +110,8 @@ def main():
         run_variable_xor_cli()
     elif mode == 5:
         run_f31f32()
+    elif mode == 6:
+        run_exhaustive_two_bit_xor_cli()
 
 
 main()
diff --git a/src/tea3/variable_xor.py b/src/tea3/variable_xor.py
index d8538ce..febdbf0 100644
--- a/src/tea3/variable_xor.py
+++ b/src/tea3/variable_xor.py
@@ -1,6 +1,11 @@
+from itertools import combinations
+
 from tea3.tea3model import Tea3Model
 from tea3.pretty_print import pretty_print
 
+def monomial_count(poly):
+    return len(poly.monomials())
+
 def run_variable_xor(steps, target_reg, bits_to_xor):
     model = Tea3Model()
 
@@ -23,3 +28,36 @@ def run_variable_xor(steps, target_reg, bits_to_xor):
         print(f"XOR of R_bits[{target_reg}][{bits_to_xor}] =")
         print(pretty_print(xor_poly))
         print()
+
+
+def run_exhaustive_two_bit_xor(steps, target_reg, bit_indices=range(8)):
+    model = Tea3Model()
+
+    bit_pairs = list(combinations(bit_indices, 2))
+
+    print(f"Target register: R{target_reg}")
+    print(f"Searching all 2-bit XORs among bits: {list(bit_indices)}")
+    print("-" * 50)
+
+    for i in range(steps):
+        model.step()
+
+        best_count = None
+        best_pairs = []
+        best_poly = None
+
+        for b1, b2 in bit_pairs:
+            xor_poly = model.R_bits[target_reg][b1] + model.R_bits[target_reg][b2]
+            count = monomial_count(xor_poly)
+
+            if best_count is None or count < best_count:
+                best_count = count
+                best_pairs = [(b1, b2)]
+                best_poly = xor_poly
+            elif count == best_count:
+                best_pairs.append((b1, b2))
+
+        print(f"\n[Step {i + 1}]")
+        print(f"Best XOR(s) with {best_count} total monomials:")
+        for b1, b2 in best_pairs:
+            print(f"  bits XORed: ({b1}, {b2})")