Add 256-bit seed support

codex32_terminal/.gitignore

@@ -0,0 +1,27 @@
+# Python artifacts
+__pycache__/
+*.py[cod]
+*.so
+*.egg-info/
+dist/
+build/
+
+# Virtual environments
+venv/
+.venv/
+env/
+
+# IDE
+.idea/
+.vscode/
+*.swp
+*.swo
+
+# Testing
+.pytest_cache/
+.coverage
+htmlcov/
+
+# OS
+.DS_Store
+Thumbs.db

codex32_terminal/README.md

@@ -1,6 +1,13 @@
 # Codex32 Terminal MVP
 
-This folder contains a terminal-based MVP for validating Codex32 shares, recovering a secret `S` share from `k-of-n` shares, and converting the master seed into a 12-word BIP39 mnemonic (display-only).
+This folder contains a terminal-based MVP for validating Codex32 shares, recovering a secret `S` share from `k-of-n` shares, and converting the master seed into a BIP39 mnemonic (display-only).
+
+## Supported Seed Sizes
+
+| Seed Size | Codex32 Length | BIP39 Output |
+|-----------|----------------|--------------|
+| 128-bit   | 48 characters  | 12 words     |
+| 256-bit   | 74 characters  | 24 words     |
 
 ## Current status (Jan 31, 2026)
 
@@ -11,43 +18,102 @@ This folder contains a terminal-based MVP for validating Codex32 shares, recover
 - Checksum + header validation
 - `k-of-n` share recovery via interpolation
 - Display recovered `S` share, seed hex, and BIP39 mnemonic
+- **128-bit and 256-bit seed support** (auto-detected)
 
 ⚠️ Not an ECW yet (no error correction). The codex32 Python library does **not** provide substitution/erasure correction, so this tool does not attempt it. Error-correction should be implemented separately before advertising ECW behavior.
 
-## Setup (Windows PowerShell)
+## Setup
+
+### macOS / Linux
+
+```bash
+cd codex32_terminal
+python3 -m venv venv
+source venv/bin/activate
+pip install codex32 embit
+```
+
+### Windows PowerShell
 
 From the repo root:
 
 ```powershell
 python -m venv .\codex32_terminal\venv
 .\codex32_terminal\venv\Scripts\Activate.ps1 ; pip install codex32 embit
-pip freeze > .\codex32_terminal\requirements.txt
 ```
 
-> Note: Use a semicolon between `Activate.ps1` and subsequent commands in PowerShell.
-
 ## Run
 
 ### Box-by-box entry (default)
 
+**macOS / Linux:**
+```bash
+source venv/bin/activate
+python src/main.py
+```
+
+**Windows PowerShell:**
 ```powershell
-.\codex32_terminal\venv\Scripts\Activate.ps1 ; python .\codex32_terminal\src\main.py
+.\venv\Scripts\Activate.ps1 ; python src\main.py
 ```
 
 Features:
 
-- Prefix `MS1` is pre-filled.
-- Enter one character per box.
-- Backspace: press Enter on empty input or type `<` to go back.
-- Ctrl+C cancels entry.
+- Prompts for seed size (128-bit or 256-bit) at start
+- Prefix `MS1` is pre-filled
+- Enter one character per box
+- Backspace: press Enter on empty input or type `<` to go back
+- Ctrl+C cancels entry
 
 ### Full-share paste mode
 
+**macOS / Linux:**
+```bash
+source venv/bin/activate
+python src/main.py --full
+```
+
+**Windows PowerShell:**
 ```powershell
-.\codex32_terminal\venv\Scripts\Activate.ps1 ; python .\codex32_terminal\src\main.py --full
+.\venv\Scripts\Activate.ps1 ; python src\main.py --full
 ```
 
-Paste full shares in sequence. For `k-of-n` shares, the tool will ask for additional shares until the threshold is met.
+Paste full shares in sequence. Seed size is auto-detected from string length (48 or 74 chars). For `k-of-n` shares, the tool will ask for additional shares until the threshold is met.
+
+## Run Tests
+
+**macOS / Linux:**
+```bash
+source venv/bin/activate
+python tests/test_vectors.py
+python tests/test_256bit.py
+```
+
+**Windows PowerShell:**
+```powershell
+.\venv\Scripts\Activate.ps1
+python tests\test_vectors.py
+python tests\test_256bit.py
+```
+
+### Expected test output
+
+```
+vector2: seed OK -> spice afford liquid stool forest agent choose draw clinic cram obvious enough
+vector3: seed OK -> zoo ivory industry jar praise service talk skirt during october lounge absurd
+test_valid_lengths_constant: PASS
+test_256bit_parse: PASS
+test_256bit_validate_s_share: PASS
+test_256bit_seed_extraction: PASS
+test_256bit_to_mnemonic: PASS (24 words)
+  Mnemonic: zoo ivory industry jar praise service talk skirt during october lounge acid year humble cream inspire office dry sunset pride drip much dune arm
+test_128bit_still_works: PASS (12 words)
+test_auto_detect_length: PASS
+test_invalid_length_rejected: PASS
+test_seed_bytes_to_mnemonic_both_sizes: PASS
+
+All 256-bit tests passed!
+```
 
 ## Test vectors
 
@@ -64,7 +130,7 @@ Expected output:
 - Seed hex: `d1808e096b35b209ca12132b264662a5`
 - BIP39 mnemonic: `spice afford liquid stool forest agent choose draw clinic cram obvious enough`
 
-### Vector 3 (k=3, cash)
+### Vector 3 (k=3, cash, 128-bit)
 
 - Share a: `ms13casha320zyxwvutsrqpnmlkjhgfedca2a8d0zehn8a0t`
 - Share c: `ms13cashcacdefghjklmnpqrstuvwxyz023949xq35my48dr`
@@ -74,7 +140,16 @@ Expected output:
 
 - Recovered S-share: `ms13cashsllhdmn9m42vcsamx24zrxgs3qqjzqud4m0d6nln`
 - Seed hex: `ffeeddccbbaa99887766554433221100`
-- BIP39 mnemonic: `zoo ivory industry jar praise service talk skirt during october lounge absurd`
+- BIP39 mnemonic (12 words): `zoo ivory industry jar praise service talk skirt during october lounge absurd`
+
+### Vector 4 (256-bit seed)
+
+- S-share: `ms10leetsllhdmn9m42vcsamx24zrxgs3qrl7ahwvhw4fnzrhve25gvezzyqqtum9pgv99ycma`
+
+Expected output:
+
+- Seed hex: `ffeeddccbbaa99887766554433221100ffeeddccbbaa99887766554433221100`
+- BIP39 mnemonic (24 words): `zoo ivory industry jar praise service talk skirt during october lounge acid year humble cream inspire office dry sunset pride drip much dune arm`
 
 ## Codebase overview
 
@@ -94,13 +169,17 @@ Expected output:
   - Progress display, preview/confirm, prompts
 
 - `tests/test_vectors.py`
-  - Manual harness for BIP-93 vectors 2/3
+  - Manual harness for BIP-93 vectors 2/3 (128-bit)
+
+- `tests/test_256bit.py`
+  - Tests for 256-bit seed support (BIP-93 vector 4)
+  - Verifies both 128-bit and 256-bit paths work correctly
 
 ### Implementation rationale
 
 - **Validation** uses `codex32.Codex32String`, which enforces checksum + header correctness.
 - **Recovery** uses `Codex32String.interpolate_at` to reconstruct the `S` share from `k` valid shares.
-- **BIP39 mnemonic** is a display encoding of the 16-byte master seed (no PBKDF2). This mirrors BIP-93 guidance.
+- **BIP39 mnemonic** is a display encoding of the master seed (no PBKDF2). 128-bit seeds produce 12 words, 256-bit seeds produce 24 words. This mirrors BIP-93 guidance.
 
 ## Next steps (SeedSigner port)
 

codex32_terminal/src/controller.py

@@ -14,7 +14,10 @@
 )
 
 
-TOTAL_LEN = 48
+# Supported seed sizes - must match VALID_LENGTHS in model.py
+# 128-bit (48 chars) or 256-bit (74 chars)
+LEN_128BIT = 48
+LEN_256BIT = 74
 BASE_PREFIX = "MS1"
 FIRST_BOX = len(BASE_PREFIX) + 1
 CANCELLED = object()
@@ -34,18 +37,18 @@ def _is_backspace(value: str) -> bool:
     return value == "" or value == "<"
 
 
-def collect_codex32_boxes(prefix: str, start_box: int) -> str:
+def collect_codex32_boxes(prefix: str, start_box: int, total_len: int) -> str:
     current = prefix
-    view.display_progress(current, TOTAL_LEN)
+    view.display_progress(current, total_len)
     box_number = start_box
-    while box_number <= TOTAL_LEN:
+    while box_number <= total_len:
         raw = view.get_box_input(box_number)
         ch = _normalize_box_char(raw)
         if _is_backspace(ch):
             if len(current) > len(prefix):
                 current = current[:-1]
                 box_number -= 1
-                view.display_progress(current, TOTAL_LEN)
+                view.display_progress(current, total_len)
             else:
                 view.display_error("Already at the first editable box.")
             continue
@@ -56,7 +59,7 @@ def collect_codex32_boxes(prefix: str, start_box: int) -> str:
             view.display_error("Invalid bech32 character. Use bech32 charset.")
             continue
         current += ch
-        view.display_progress(current, TOTAL_LEN)
+        view.display_progress(current, total_len)
         box_number += 1
     return current
 
@@ -66,10 +69,10 @@ def _display_and_confirm(codex_str: str) -> bool:
     return view.confirm("Submit this codex32 string?")
 
 
-def _collect_share_box(prefix: str, start_box: int, index: int, total: int) -> str | object | None:
+def _collect_share_box(prefix: str, start_box: int, index: int, total: int, total_len: int) -> str | object | None:
     view.display_share_prompt(index, total)
     try:
-        codex_str = collect_codex32_boxes(prefix, start_box)
+        codex_str = collect_codex32_boxes(prefix, start_box, total_len)
     except KeyboardInterrupt:
         view.display_cancelled()
         return CANCELLED
@@ -99,11 +102,19 @@ def _collect_share_full(prefix: str | None, index: int, total: int) -> str | obj
 
 def run(entry_mode: str = "box") -> int:
     view.display_welcome(entry_mode)
+
+    # For box mode, ask user about seed size
+    total_len = LEN_128BIT  # default
+    if entry_mode == "box":
+        seed_size = view.get_seed_size_choice()
+        if seed_size == "256":
+            total_len = LEN_256BIT
+
     while True:
         if entry_mode == "full":
             result = _collect_share_full(BASE_PREFIX, 1, 1)
         else:
-            result = _collect_share_box(BASE_PREFIX, FIRST_BOX, 1, 1)
+            result = _collect_share_box(BASE_PREFIX, FIRST_BOX, 1, 1, total_len)
         if result is CANCELLED:
             return 1
         if result is None:
@@ -142,12 +153,15 @@ def run(entry_mode: str = "box") -> int:
         if first_share.s.isupper():
             prefix = prefix.upper()
 
+        # For subsequent shares, use the same total_len as detected from first share
+        share_total_len = len(first_share.s)
+
         while len(shares) < threshold:
             share_index = len(shares) + 1
             if entry_mode == "full":
                 result = _collect_share_full(prefix, share_index, threshold)
             else:
-                result = _collect_share_box(prefix, len(prefix) + 1, share_index, threshold)
+                result = _collect_share_box(prefix, len(prefix) + 1, share_index, threshold, share_total_len)
             if result is CANCELLED:
                 return 1
             if result is None: