Key expression export

diff --git a/releases/Next-ChangeLog.md b/releases/Next-ChangeLog.md
index 9b0de56..4685571 100644
--- a/releases/Next-ChangeLog.md
+++ b/releases/Next-ChangeLog.md
@@ -4,7 +4,8 @@ This lists the new changes that have not yet been published in a normal release.
 
 # Shared Improvements - Both Mk4 and Q
 
-- tbd
+- New Feature: Export [BIP-380](https://github.com/bitcoin/bips/blob/master/bip-0380.mediawiki) extended key expression.
+  Navigate to `Advanced/Tools -> Export Wallet -> Key Expression`
 
 
 # Mk4 Specific Changes
diff --git a/shared/actions.py b/shared/actions.py
index a0a7f65..690c997 100644
--- a/shared/actions.py
+++ b/shared/actions.py
@@ -14,7 +14,7 @@ from ux import ux_show_story, the_ux, ux_confirm, ux_dramatic_pause, ux_aborted
 from ux import ux_enter_bip32_index, ux_input_text, import_export_prompt, OK, X, ux_render_words
 from export import export_contents, make_summary_file, make_descriptor_wallet_export
 from export import make_bitcoin_core_wallet, generate_wasabi_wallet, generate_generic_export
-from export import generate_unchained_export, generate_electrum_wallet
+from export import generate_unchained_export, generate_electrum_wallet, make_key_expression_export
 from files import CardSlot, CardMissingError, needs_microsd
 from public_constants import AF_CLASSIC, AF_P2WPKH, AF_P2WPKH_P2SH
 from glob import settings
@@ -1193,6 +1193,46 @@ async def ss_descriptor_skeleton(_0, _1, item):
         ]
         the_ux.push(MenuSystem(rv))
 
+
+async def key_expression_skeleton_step2(_1, _2, item):
+    # pick a semi-random file name, render and save it.
+    orig_path = item.arg
+    await make_key_expression_export(orig_path)
+
+async def key_expression_skeleton(_0, _1, item):
+    # Export key expression -> [xfp/d/e/r]xpub
+
+    acct_num = 0
+    ch = await ux_show_story("This saves a extended key expression."
+                             + PICK_ACCOUNT + SENSITIVE_NOT_SECRET, escape='1')
+    if ch == '1':
+        acct_num = await ux_enter_bip32_index('Account Number:', unlimited=True) or 0
+    elif ch != 'y':
+        return
+
+    todo = [
+        ("Segwit P2WPKH", "m/84h/%dh/%dh"),
+        ("Classic P2PKH", "m/44h/%dh/%dh"),
+        ("P2SH-Segwit", "m/49h/%dh/%dh"),
+        ("Multi P2WSH", "m/48h/%dh/%dh/2h"),
+        ("Multi P2SH-P2WSH", "m/48h/%dh/%dh/1h"),
+    ]
+
+    from address_explorer import KeypathMenu
+
+    async def doit(*a):
+        return KeypathMenu(ranged=False, done_fn=make_key_expression_export)
+
+    ct = chains.current_chain().b44_cointype
+
+    rv = [
+        MenuItem(label, f=key_expression_skeleton_step2, arg=orig_der % (ct, acct_num))
+        for label, orig_der in todo
+    ]
+    rv += [MenuItem("Custom Path", menu=doit)]
+
+    the_ux.push(MenuSystem(rv))
+
 async def samourai_post_mix_descriptor_export(*a):
     name = "POST-MIX"
     post_mix_acct_num = 2147483646
diff --git a/shared/address_explorer.py b/shared/address_explorer.py
index 0452a6c..c0c3ba8 100644
--- a/shared/address_explorer.py
+++ b/shared/address_explorer.py
@@ -30,8 +30,10 @@ def censor_address(addr):
     return addr[0:12] + '___' + addr[12+3:]
 
 class KeypathMenu(MenuSystem):
-    def __init__(self, path=None, nl=0):
+    def __init__(self, path=None, nl=0, ranged=True, done_fn=None):
         self.prefix = None
+        self.done_fn = done_fn
+        self.ranged = ranged
 
         if path is None:
             # Top level menu; useful shortcuts, and special case just "m"
@@ -40,10 +42,13 @@ class KeypathMenu(MenuSystem):
                 MenuItem("m/44h/⋯", f=self.deeper),
                 MenuItem("m/49h/⋯", f=self.deeper),
                 MenuItem("m/84h/⋯", f=self.deeper),
-                MenuItem("m/0/{idx}", menu=self.done),
-                MenuItem("m/{idx}", menu=self.done),
                 MenuItem("m", f=self.done),
             ]
+            if self.ranged:
+                items += [
+                    MenuItem("m/0/{idx}", menu=self.done),
+                    MenuItem("m/{idx}", menu=self.done),
+                ]
         else:
             # drill down one layer: (nl) is the current leaf
             # - hardened choice first
@@ -53,11 +58,14 @@ class KeypathMenu(MenuSystem):
                 MenuItem(p+"/⋯",  menu=self.deeper),
                 MenuItem(p+"h", menu=self.done),
                 MenuItem(p, menu=self.done),
-                MenuItem(p+"h/0/{idx}", menu=self.done),
-                MenuItem(p+"/0/{idx}", menu=self.done),      #useful shortcut?
-                MenuItem(p+"h/{idx}", menu=self.done),
-                MenuItem(p+"/{idx}", menu=self.done),
             ]
+            if self.ranged:
+                items += [
+                    MenuItem(p + "h/0/{idx}", menu=self.done),
+                    MenuItem(p + "/0/{idx}", menu=self.done),  # useful shortcut?
+                    MenuItem(p + "h/{idx}", menu=self.done),
+                    MenuItem(p + "/{idx}", menu=self.done),
+                ]
 
         # simple consistent truncation when needed
         max_wide = max(len(mi.label) for mi in items)
@@ -95,9 +103,12 @@ class KeypathMenu(MenuSystem):
             if isinstance(top, KeypathMenu):
                 the_ux.pop()
                 continue
-            assert isinstance(top, AddressListMenu)
+            # assert isinstance(top, AddressListMenu), type(top)
             break
 
+        if self.done_fn:
+            return await self.done_fn(final_path)
+
         return PickAddrFmtMenu(final_path, top)
 
     async def deeper(self, _1, _2, item):
@@ -105,7 +116,7 @@ class KeypathMenu(MenuSystem):
         assert val.endswith('/⋯')
         cpath = val[:-2]
         nl = await ux_enter_bip32_index('%s/' % cpath, unlimited=True)
-        return KeypathMenu(cpath, nl)
+        return KeypathMenu(cpath, nl, ranged=self.ranged, done_fn=self.done_fn)
 
 class PickAddrFmtMenu(MenuSystem):
     def __init__(self, path, parent):
diff --git a/shared/export.py b/shared/export.py
index b30bb3d..52e8094 100644
--- a/shared/export.py
+++ b/shared/export.py
@@ -471,7 +471,7 @@ async def make_descriptor_wallet_export(addr_type, account_num=0, mode=None, int
     dis.fullscreen('Generating...')
     chain = chains.current_chain()
 
-    xfp = settings.get('xfp')
+    xfp = settings.get('xfp', 0)
     dis.progress_bar_show(0.1)
     if mode is None:
         mode = chains.af_to_bip44_purpose(addr_type)
@@ -503,5 +503,18 @@ async def make_descriptor_wallet_export(addr_type, account_num=0, mode=None, int
     await export_contents("Descriptor", body, fname_pattern, derive + "/0/0",
                           addr_type, force_prompt=True, direct_way=direct_way)
 
+
+async def make_key_expression_export(orig_der, fname_pattern="key_expr.txt"):
+
+    xfp = xfp2str(settings.get('xfp', 0)).lower()
+
+    with stash.SensitiveValues() as sv:
+        ek = chains.current_chain().serialize_public(sv.derive_path(orig_der))
+
+    body = "[%s/%s]%s" % (xfp, orig_der.replace("m/", ""), ek)
+
+    await export_contents("Key Expression", body, fname_pattern,
+                          None, None, force_prompt=True)
+
 # EOF
 
diff --git a/shared/flow.py b/shared/flow.py
index b0f0800..45392d3 100644
--- a/shared/flow.py
+++ b/shared/flow.py
@@ -235,6 +235,7 @@ WalletExportMenu = [
     MenuItem("Descriptor", f=ss_descriptor_skeleton),
     MenuItem("Generic JSON", f=generic_skeleton),
     MenuItem("Export XPUB", menu=XpubExportMenu),
+    MenuItem("Key Expression", f=key_expression_skeleton),
     MenuItem("Dump Summary", predicate=has_secrets, f=dump_summary),
 ]
 
diff --git a/testing/conftest.py b/testing/conftest.py
index 14e4308..1bd5d76 100644
--- a/testing/conftest.py
+++ b/testing/conftest.py
@@ -2568,8 +2568,8 @@ def skip_if_useless_way(is_q1, nfc_disabled, vdisk_disabled):
     # when NFC is disabled, no point trying to do a PSBT via NFC
     # - important: run_sim_tests.py will enable NFC for complete testing
     # - similarly: the Mk4 and earlier had no QR scanner, so cannot use that as input
-    def doit(way):
-        if way == "qr" and not is_q1:
+    def doit(way, allow_mk4_qr=False):
+        if way == "qr" and (not is_q1 and not allow_mk4_qr):
             raise pytest.skip("mk4 QR not supported")
         elif way == 'nfc' and nfc_disabled():
             # runner will test these cases, but fail faster otherwise
diff --git a/testing/test_export.py b/testing/test_export.py
index 9c539d1..a9f0235 100644
--- a/testing/test_export.py
+++ b/testing/test_export.py
@@ -13,7 +13,6 @@ from bip32 import BIP32Node
 from ckcc_protocol.constants import *
 from helpers import xfp2str, slip132undo
 from conftest import simulator_fixed_xfp, simulator_fixed_tprv, simulator_fixed_words, simulator_fixed_xprv
-from ckcc_protocol.constants import AF_CLASSIC, AF_P2WPKH
 from pprint import pprint
 from charcodes import KEY_NFC, KEY_QR
 
@@ -888,4 +887,131 @@ def test_samourai_vs_generic(chain, account, settings_set, pick_menu_item, goto_
     file_desc = load_export("sd", label="Descriptor", is_json=False, addr_fmt=AF_P2WPKH)
     assert file_desc.strip() == file_desc_generic.strip()
 
+
+@pytest.mark.parametrize("chain", ["BTC", "XTN"])
+@pytest.mark.parametrize("way", ["sd", "vdisk", "nfc", "qr"])
+@pytest.mark.parametrize("addr_fmt", [AF_P2WPKH, AF_P2WPKH_P2SH, AF_CLASSIC, AF_P2WSH, AF_P2WSH_P2SH])
+@pytest.mark.parametrize("acct_num", [None, (2 ** 31) - 1])
+def test_key_expression_export(chain, addr_fmt, acct_num, goto_home, settings_set, need_keypress,
+                               pick_menu_item, way, cap_story, cap_menu, virtdisk_path, dev,
+                               load_export, press_select, skip_if_useless_way):
+
+    skip_if_useless_way(way, allow_mk4_qr=True)
+
+    settings_set('chain', chain)
+    chain_num = 1 if chain in ["XTN", "XRT"] else 0
+    goto_home()
+    pick_menu_item("Advanced/Tools")
+    pick_menu_item("Export Wallet")
+    pick_menu_item("Key Expression")
+    time.sleep(.1)
+    _, story = cap_story()
+    assert "This saves a extended key expression" in story
+    assert "Press (1) to enter a non-zero account number" in story
+    assert "sensitive--in terms of privacy" in story
+    assert "not compromise your funds directly" in story
+
+    if isinstance(acct_num, int):
+        need_keypress("1")        # chosse account number
+        for ch in str(acct_num):
+            need_keypress(ch)     # input num
+        press_select()        # confirm selection
+    else:
+        press_select()  # confirm story
+        acct_num = 0
+
+    menu = cap_menu()
+    if addr_fmt == AF_P2WPKH:
+        menu_item = "Segwit P2WPKH"
+        derive = f"m/84h/{chain_num}h/{acct_num}h"
+    elif addr_fmt == AF_P2WPKH_P2SH:
+        menu_item = "P2SH-Segwit"
+        derive = f"m/49h/{chain_num}h/{acct_num}h"
+    elif addr_fmt == AF_CLASSIC:
+        menu_item = "Classic P2PKH"
+        derive = f"m/44h/{chain_num}h/{acct_num}h"
+    elif addr_fmt == AF_P2WSH:
+        menu_item = "Multi P2WSH"
+        derive = f"m/48h/{chain_num}h/{acct_num}h/2h"
+    else:
+        assert addr_fmt == AF_P2WSH_P2SH
+        menu_item = "Multi P2SH-P2WSH"
+        derive = f"m/48h/{chain_num}h/{acct_num}h/1h"
+
+    assert menu_item in menu
+    pick_menu_item(menu_item)
+
+    contents = load_export(way, label="Key Expression", is_json=False, sig_check=False)
+    key_exp = contents.strip()
+
+    xfp = dev.master_fingerprint
+    xfp = xfp2str(xfp).lower()
+
+    seed = Mnemonic.to_seed(simulator_fixed_words)
+    node = BIP32Node.from_master_secret(
+        seed, netcode="BTC" if chain == "BTC" else "XTN"
+    ).subkey_for_path(derive)
+
+    target = f"[{xfp}/{derive.replace('m/', '')}]{node.hwif()}"
+    assert key_exp == target
+
+
+@pytest.mark.parametrize('path', [
+    # NOTE: (2**31)-1 = 0x7fff_ffff = 2147483647
+    "m/2147483647/2147483647/2147483647/2147483647/2147483647/2147483647/2147483647/2147483647",
+    "m/1/2/3/4/5",
+    "m/1h/2h/3h/4h/5h",
+    "m/45h",
+])
+def test_custom_key_expression_export(path, goto_home, pick_menu_item, cap_menu, need_keypress,
+                                      press_select, load_export, use_testnet, dev):
+    use_testnet()
+    goto_home()
+    pick_menu_item("Advanced/Tools")
+    pick_menu_item("Export Wallet")
+    pick_menu_item("Key Expression")
+    press_select() # story
+    pick_menu_item("Custom Path")
+
+    # blind entry, using only first 2 menu items
+    deeper = path.split("/")[1:]
+    for depth, part in enumerate(deeper):
+        time.sleep(.01)
+        m = cap_menu()
+        for mi in m:
+            assert "{idx}" not in mi  # ranged values not allowed here
+        if depth == 0:
+            assert m[0] == 'm/⋯'
+            pick_menu_item(m[0])
+        else:
+            assert m[0].endswith("h/⋯")
+            assert m[1].endswith("/⋯")
+            assert m[0] != m[1]
+
+            pick_menu_item(m[0 if last_part[-1] == "h" else 1])
+
+        # enter path component
+        for d in part:
+            if d == "h": break
+            need_keypress(d)
+        press_select()
+
+        last_part = part
+
+    time.sleep(.01)
+    m = cap_menu()
+    pick_menu_item(m[2 if part[-1] == "h" else 3])
+
+    contents = load_export("sd", label="Key Expression", is_json=False, sig_check=False)
+    key_exp = contents.strip()
+
+    xfp = dev.master_fingerprint
+    xfp = xfp2str(xfp).lower()
+
+    seed = Mnemonic.to_seed(simulator_fixed_words)
+    node = BIP32Node.from_master_secret(seed, netcode="XTN").subkey_for_path(path)
+
+    target = f"[{xfp}/{path.replace('m/', '')}]{node.hwif()}"
+    assert key_exp == target
+
 # EOF