diff --git a/src/tea3/constants.py b/src/tea3/constants.py
index bf4d9e3..1d797d6 100644
--- a/src/tea3/constants.py
+++ b/src/tea3/constants.py
@@ -24,3 +24,27 @@ TEA3_LUT_A = [
 TEA3_LUT_B = [
     0x9D58, 0xA46D, 0x176C, 0x79C4, 0xC62B, 0xB2C9, 0x4D93, 0x2E93
 ]
+
+# ETSI TS 104 053-1 Figure 17
+T_F1 = [
+    [1, 1, 0, 0, 1, 0, 0, 1, 0, 1, 1, 1, 0, 1, 0, 0],  # S1
+    [1, 1, 0, 0, 1, 0, 0, 1, 1, 0, 1, 1, 0, 1, 0, 0],  # S2
+    [1, 0, 0, 1, 0, 0, 1, 1, 0, 1, 0, 0, 1, 1, 0, 1],  # S3
+    [1, 1, 0, 1, 0, 1, 0, 0, 1, 1, 0, 0, 0, 0, 1, 1],  # S4
+    [0, 0, 1, 0, 0, 0, 1, 1, 1, 0, 0, 1, 1, 1, 1, 0],  # S5
+    [0, 0, 1, 1, 0, 1, 1, 0, 1, 1, 1, 0, 1, 0, 0, 0],  # S6
+    [1, 0, 1, 1, 0, 1, 1, 0, 0, 0, 1, 0, 0, 1, 0, 1],  # S7
+    [0, 0, 0, 1, 1, 0, 1, 0, 1, 0, 1, 1, 1, 0, 0, 1],  # S8
+]
+
+# ETSI TS 104 053-1 Figure 18
+T_F2 = [
+    [1, 1, 0, 0, 0, 1, 1, 0, 0, 0, 1, 0, 1, 1, 1, 0],  # S1
+    [0, 0, 1, 0, 1, 0, 1, 1, 1, 0, 0, 1, 1, 0, 0, 0],  # S2
+    [0, 0, 1, 1, 0, 1, 1, 0, 1, 1, 0, 1, 0, 0, 0, 0],  # S3
+    [0, 1, 1, 1, 0, 0, 1, 1, 0, 0, 1, 0, 1, 0, 0, 0],  # S4
+    [0, 0, 1, 1, 0, 0, 0, 1, 1, 0, 0, 1, 1, 1, 0, 0],  # S5
+    [0, 0, 1, 1, 0, 0, 1, 0, 1, 1, 0, 1, 0, 0, 0, 1],  # S6
+    [1, 0, 0, 0, 0, 1, 1, 0, 1, 1, 1, 0, 0, 1, 0, 1],  # S7
+    [1, 1, 1, 0, 0, 1, 0, 1, 0, 1, 0, 0, 1, 0, 0, 1],  # S8
+]
diff --git a/src/tea3/tea3model.py b/src/tea3/tea3model.py
new file mode 100644
index 0000000..95d86f8
--- /dev/null
+++ b/src/tea3/tea3model.py
@@ -0,0 +1,17 @@
+from sage.all import *
+
+F = GF(2)
+
+names = (
+    [f"x{i}{j}" for i in range(5) for j in range(8)] +
+    [f"r{i}{j}" for i in range(5) for j in range(8)] +
+    [f"R{i}{j}" for i in range(8) for j in range(8)]
+)
+
+S = PolynomialRing(F, names)
+v = S.gens()
+
+x_bits = [list(v[i*8:(i+1)*8]) for i in range(5)]
+r_bits = [list(v[40 + i*8 : 40 + (i+1)*8]) for i in range(5)]
+R_bits = [list(v[80 + i*8 : 80 + (i+1)*8]) for i in range(8)]
+