From e40da4e8bc5ec5b6605de2fc6f123f78fa62a232 Mon Sep 17 00:00:00 2001
From: Sam Hadow <sam.hadow@proton.me>
Date: Mon, 22 Jun 2026 14:42:58 +0200
Subject: [PATCH] BP matrix family

---
 src/tea3/cli.py             |  9 ++++++---
 src/tea3/variable_search.py | 30 ++++++++++++++++++++++++++++++
 2 files changed, 36 insertions(+), 3 deletions(-)

diff --git a/src/tea3/cli.py b/src/tea3/cli.py
index 52e53ac..d5eb9f2 100644
--- a/src/tea3/cli.py
+++ b/src/tea3/cli.py
@@ -1,7 +1,7 @@
 from tea3.pretty_print import pretty_print
 from tea3.cliutils import prompt_int, prompt_choice, prompt_list
 from tea3.tea3model import Tea3Model
-from tea3.variable_search import run_exhaustive, run_exhaustive_staircase, run_exhaustive_staircase2
+from tea3.variable_search import run_exhaustive, run_exhaustive_staircase, run_exhaustive_staircase2, run_exhaustive_bp
 from tea3.sbox import run_sbox
 from tea3.variable_xor import run_variable_xor, run_exhaustive_xor
 from tea3.f31f32 import run_f31f32
@@ -41,8 +41,9 @@ def run_exhaustive_cli():
     print("  1) First-row matrix")
     print("  2) Staircase matrix")
     print("  3) Staircase 2 matrix")
+    print("  4) BP matrix")
 
-    family = prompt_choice("Your choice (1, 2 or 3): ", {1, 2, 3})
+    family = prompt_choice("Your choice (1, 2, 3 or 4): ", {1, 2, 3, 4})
 
     print("\nR registers are indexed 0–7; bits within each register are 0–7.")
     print("Enter -1 to print all bits in the chosen register.")
@@ -57,8 +58,10 @@ def run_exhaustive_cli():
         run_exhaustive(steps, target_reg, target_bit)
     elif family == 2:
         run_exhaustive_staircase(steps, target_reg, target_bit)
-    else:
+    elif family == 3:
         run_exhaustive_staircase2(steps, target_reg, target_bit)
+    else:
+        run_exhaustive_bp(steps, target_reg, target_bit)
 
     print("\n" + "=" * 50)
     print("Done.")
diff --git a/src/tea3/variable_search.py b/src/tea3/variable_search.py
index 83b1c71..fef5973 100644
--- a/src/tea3/variable_search.py
+++ b/src/tea3/variable_search.py
@@ -96,6 +96,30 @@ def make_staircase2_matrix(coeffs):
     M[7, 6] = GF(2)(coeffs[7])
     return M
 
+def make_bp_matrix(coeffs):
+    """
+    | 1   0   0   a1  0   0   0   0 |
+    | 0   1   0   0   0   0   0   a2|
+    | 0   0   1   0   0   0   a3  0 |
+    | 0   a4  0   1   0   0   0   0 |
+    | 0   0   a5  0   1   0   0   0 |
+    | 0   0   0   0   a6  1   0   0 |
+    | a7  0   0   0   0   0   1   0 |
+    | 0   0   0   0   0   a8  0   1 |
+    """
+    M = identity_matrix(GF(2), 8)
+
+    M[0, 3] = GF(2)(coeffs[0])
+    M[1, 7] = GF(2)(coeffs[1])
+    M[2, 6] = GF(2)(coeffs[2])
+    M[3, 1] = GF(2)(coeffs[3])
+    M[4, 2] = GF(2)(coeffs[4])
+    M[5, 4] = GF(2)(coeffs[5])
+    M[6, 0] = GF(2)(coeffs[6])
+    M[7, 5] = GF(2)(coeffs[7])
+
+    return M
+
 # wrappers
 
 def run_exhaustive_generic(
@@ -169,3 +193,9 @@ def run_exhaustive_staircase2(steps: int, target_reg: int = 0, target_bit: int =
         steps, make_staircase2_matrix, n_params=8,
         target_reg=target_reg, target_bit=target_bit,
     )
+
+def run_exhaustive_bp(steps: int, target_reg: int = 0, target_bit: int = -1):
+    return run_exhaustive_generic(
+        steps, make_bp_matrix, n_params=8,
+        target_reg=target_reg, target_bit=target_bit,
+    )