commit f4f875ecde854c889ea39d29217e81a3f428589d
Author: Sam Hadow <sam.hadow@proton.me>
Date:   Thu Apr 16 16:29:49 2026 +0200

    initial commit

diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..504e2bf
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,6 @@
+*.kate-swp
+.venv/
+__pycache__/
+.pytest_cache/
+*.egg-info/
+
diff --git a/pyproject.toml b/pyproject.toml
new file mode 100644
index 0000000..23b1449
--- /dev/null
+++ b/pyproject.toml
@@ -0,0 +1,10 @@
+[project]
+name = "tea3"
+version = "0.1.0"
+description = "TEA3 implementation"
+authors = [{name = "Sam HADOW"}]
+requires-python = ">=3.11"
+
+[tool.pytest.ini_options]
+testpaths = ["tests"]
+
diff --git a/src/tea3/__init__.py b/src/tea3/__init__.py
new file mode 100644
index 0000000..ceb8a82
--- /dev/null
+++ b/src/tea3/__init__.py
@@ -0,0 +1,11 @@
+from .tea3 import (
+    Tea3,
+    tea3_reorder_state_byte,
+    tea3_state_word_to_newbyte,
+)
+
+__all__ = [
+    "Tea3",
+    "tea3_reorder_state_byte",
+    "tea3_state_word_to_newbyte",
+]
diff --git a/src/tea3/constants.py b/src/tea3/constants.py
new file mode 100644
index 0000000..bf4d9e3
--- /dev/null
+++ b/src/tea3/constants.py
@@ -0,0 +1,26 @@
+TEA3_SBOX = [
+    0x7D, 0xBF, 0x7B, 0x92, 0xAE, 0x7C, 0xF2, 0x10, 0x5A, 0x0F, 0x61, 0x7A, 0x98, 0x76, 0x07, 0x64,
+    0xEE, 0x89, 0xF7, 0xBA, 0xC2, 0x02, 0x0D, 0xE8, 0x56, 0x2E, 0xCA, 0x58, 0xC0, 0xFA, 0x2A, 0x01,
+    0x57, 0x6E, 0x3F, 0x4B, 0x9C, 0xDA, 0xA6, 0x5B, 0x41, 0x26, 0x50, 0x24, 0x3E, 0xF8, 0x0A, 0x86,
+    0xB6, 0x5C, 0x34, 0xE9, 0x06, 0x88, 0x1F, 0x39, 0x33, 0xDF, 0xD9, 0x78, 0xD8, 0xA8, 0x51, 0xB2,
+    0x09, 0xCD, 0xA1, 0xDD, 0x8E, 0x62, 0x69, 0x4D, 0x23, 0x2B, 0xA9, 0xE1, 0x53, 0x94, 0x90, 0x1E,
+    0xB4, 0x3B, 0xF9, 0x4E, 0x36, 0xFE, 0xB5, 0xD1, 0xA2, 0x8D, 0x66, 0xCE, 0xB7, 0xC4, 0x60, 0xED,
+    0x96, 0x4F, 0x31, 0x79, 0x35, 0xEB, 0x8F, 0xBB, 0x54, 0x14, 0xCB, 0xDE, 0x6B, 0x2D, 0x19, 0x82,
+    0x80, 0xAC, 0x17, 0x05, 0xFF, 0xA4, 0xCF, 0xC6, 0x6F, 0x65, 0xE6, 0x74, 0xC8, 0x93, 0xF4, 0x7E,
+    0xF3, 0x43, 0x9F, 0x71, 0xAB, 0x9A, 0x0B, 0x87, 0x55, 0x70, 0x0C, 0xAD, 0xCC, 0xA5, 0x44, 0xE7,
+    0x46, 0x45, 0x03, 0x30, 0x1A, 0xEA, 0x67, 0x99, 0xDB, 0x4A, 0x42, 0xD7, 0xAA, 0xE4, 0xC2, 0xD5,
+    0xF0, 0x77, 0x20, 0xC3, 0x3C, 0x16, 0xB9, 0xE2, 0xEF, 0x6C, 0x3D, 0x1B, 0x22, 0x84, 0x2F, 0x81,
+    0x1D, 0xB1, 0x3A, 0xE5, 0x73, 0x40, 0xD0, 0x18, 0xC7, 0x6A, 0x9E, 0x91, 0x48, 0x27, 0x95, 0x72,
+    0x68, 0x0E, 0x00, 0xFC, 0xC5, 0x5F, 0xF1, 0xF5, 0x38, 0x11, 0x7F, 0xE3, 0x5E, 0x13, 0xAF, 0x37,
+    0xE0, 0x8A, 0x49, 0x1C, 0x21, 0x47, 0xD4, 0xDC, 0xB0, 0xEC, 0x83, 0x28, 0xB8, 0xF6, 0xA7, 0xC9,
+    0x63, 0x59, 0xBD, 0x32, 0x85, 0x08, 0xBE, 0xD3, 0xFD, 0x4C, 0x2C, 0xFB, 0xA0, 0xC1, 0x9D, 0xB3,
+    0x52, 0x8C, 0x5D, 0x29, 0x6D, 0x04, 0xBC, 0x25, 0x15, 0x8B, 0x12, 0x9B, 0xD6, 0x75, 0xA3, 0x97,
+]
+
+TEA3_LUT_A = [
+    0x92A7, 0xA761, 0x974C, 0x6B8C, 0x29CE, 0x176C, 0x39D4, 0x7463
+]
+
+TEA3_LUT_B = [
+    0x9D58, 0xA46D, 0x176C, 0x79C4, 0xC62B, 0xB2C9, 0x4D93, 0x2E93
+]
diff --git a/src/tea3/tea3.py b/src/tea3/tea3.py
new file mode 100644
index 0000000..6dd5e79
--- /dev/null
+++ b/src/tea3/tea3.py
@@ -0,0 +1,106 @@
+from __future__ import annotations
+
+from dataclasses import dataclass
+from typing import Sequence
+
+from .constants import TEA3_LUT_A, TEA3_LUT_B, TEA3_SBOX
+
+MASK32 = 0xFFFFFFFF
+MASK64 = 0xFFFFFFFFFFFFFFFF
+
+
+def _ror8(x: int, n: int = 1) -> int:
+    x &= 0xFF
+    return ((x >> n) | ((x << (8 - n)) & 0xFF)) & 0xFF
+
+
+def tea3_reorder_state_byte(b_st_byte: int) -> int:
+    b_st_byte &= 0xFF
+    b_out = 0
+    b_out |= (b_st_byte << 6) & 0x40
+    b_out |= (b_st_byte << 1) & 0x20
+    b_out |= (b_st_byte << 2) & 0x98
+    b_out |= (b_st_byte >> 4) & 0x04
+    b_out |= (b_st_byte >> 3) & 0x01
+    b_out |= (b_st_byte >> 6) & 0x02
+    return b_out & 0xFF
+
+
+def tea3_state_word_to_newbyte(w_st: int, aw_lut: Sequence[int]) -> int:
+    w_st &= 0xFFFF
+    b_st0 = w_st & 0xFF
+    b_st1 = (w_st >> 8) & 0xFF
+    b_out = 0
+
+    for i in range(8):
+        b_dist = ((b_st0 >> 5) & 0x03) | ((b_st1 >> 3) & 0x0C)
+        if aw_lut[i] & (1 << b_dist):
+            b_out |= 1 << i
+        b_st0 = _ror8(b_st0, 1)
+        b_st1 = _ror8(b_st1, 1)
+
+    return b_out & 0xFF
+
+
+@dataclass
+class Tea3:
+    key_register: list[int]
+    iv: int
+    next_skip_rounds: int
+
+    def __init__(self, frame_number: int, key_register: Sequence[int]):
+        if len(key_register) != 10:
+            raise ValueError("TEA3 key register must be 10 bytes")
+        self.key_register = [b & 0xFF for b in key_register]
+        self.iv = self.compute_iv(frame_number)
+        self.next_skip_rounds = 51
+
+    @staticmethod
+    def compute_iv(frame_number: int) -> int:
+        frame_number &= MASK32
+        dw_xorred = (frame_number ^ 0xC43A7D51) & MASK32
+        dw_xorred = ((dw_xorred << 8) | (dw_xorred >> 24)) & MASK32
+        qw_iv = ((frame_number << 32) | dw_xorred) & MASK64
+        qw_iv = ((qw_iv >> 8) | ((qw_iv & 0xFF) << 56)) & MASK64
+        return qw_iv
+
+    def reset(self, frame_number: int, key_register: Sequence[int]) -> None:
+        if len(key_register) != 10:
+            raise ValueError("TEA3 key register must be 10 bytes")
+        self.key_register = [b & 0xFF for b in key_register]
+        self.iv = self.compute_iv(frame_number)
+        self.next_skip_rounds = 51
+
+    def step(self) -> None:
+        # Step 1: key schedule byte
+        b_sbox_out = TEA3_SBOX[self.key_register[7] ^ self.key_register[2]] ^ self.key_register[0]
+
+        self.key_register = self.key_register[1:] + [b_sbox_out & 0xFF]
+
+        # Step 2: state-derived bytes
+        b_deriv_byte12 = tea3_state_word_to_newbyte((self.iv >> 8) & 0xFFFF, TEA3_LUT_A)
+        b_deriv_byte56 = tea3_state_word_to_newbyte((self.iv >> 40) & 0xFFFF, TEA3_LUT_B)
+        b_reord_byte4 = tea3_reorder_state_byte((self.iv >> 32) & 0xFF)
+
+        # Step 3: combine
+        b_new_byte = (((self.iv >> 56) & 0xFF) ^ b_reord_byte4 ^ b_deriv_byte12 ^ b_sbox_out) & 0xFF
+        b_mix_byte = b_deriv_byte56 & 0xFF
+
+        # Step 4: update 64-bit state
+        self.iv = (((self.iv << 8) & MASK64) ^ ((b_mix_byte & 0xFF) << 40)) | b_new_byte
+        self.iv &= MASK64
+
+    def next_byte(self) -> int:
+        for _ in range(self.next_skip_rounds):
+            self.step()
+        self.next_skip_rounds = 19
+        return (self.iv >> 56) & 0xFF
+
+    def keystream(self, length: int) -> list[int]:
+        return [self.next_byte() for _ in range(length)]
+
+    def key_register_view(self) -> tuple[int, ...]:
+        return tuple(self.key_register)
+
+    def iv_view(self) -> int:
+        return self.iv
diff --git a/tests/test_tea3.py b/tests/test_tea3.py
new file mode 100644
index 0000000..def8f7c
--- /dev/null
+++ b/tests/test_tea3.py
@@ -0,0 +1,33 @@
+import pytest
+
+from tea3 import Tea3
+
+
+@pytest.mark.parametrize(
+    "frame, expected_iv",
+    [
+        (0x11111111, 0xD5111111112B6C40),
+    ],
+)
+def test_compute_iv(frame, expected_iv):
+    assert Tea3.compute_iv(frame) == expected_iv
+
+
+@pytest.mark.parametrize(
+    "key, frame, expected",
+    [
+        (
+            [0x00] * 10,
+            0x11111111,
+            [0x06, 0xA6, 0x58, 0x8C, 0x5D, 0x9A, 0x99, 0x6D, 0xD2, 0x5E],
+        ),
+        (
+            [0xA7, 0x98, 0x39, 0xE4, 0xBA, 0x88, 0xEE, 0x54, 0xA0, 0x29],
+            0x01234567,
+            [0x02, 0x49, 0x1E, 0xF5, 0x57, 0xC5, 0x1C, 0x17, 0x73, 0x0C],
+        ),
+    ],
+)
+def test_known_vectors(key, frame, expected):
+    cipher = Tea3(frame, key)
+    assert cipher.keystream(len(expected)) == expected