external entropy required for CCC key and temporary seeds

### releases/Next-ChangeLog.md
@@ -22,6 +22,8 @@ This lists the new changes that have not yet been published in a normal release.
       continue mashing beyond 65 presses to contribute additional timing entropy.
 - Enhancement: Dice-only seed generation now warns that no hardware randomness is
   included and the final hash shown on-screen must be kept secret.
+- Change: Generated Temporary Seeds and generated CCC key C now require extra
+  user supplied entropy.
 - Bugfix: Detect RNG_SR_SEIS and RNG_SR_SECS, retry safely, and fail closed on persistent faults.
 - Bugfix: Prevent access to Seed Vault entries through Seed XOR restore in Delta Mode. Thanks to
   Rety for reporting this.

### shared/ccc.py
@@ -14,7 +14,7 @@
 from chains import NLOCK_IS_TIME
 from utils import swab32, xfp2str, truncate_address, deserialize_secret, show_single_address
 from glob import settings, dis
-from ux import ux_confirm, ux_show_story, the_ux, OK, ux_dramatic_pause, ux_enter_number, ux_aborted
+from ux import ux_confirm, ux_show_story, the_ux, OK, ux_enter_number, ux_aborted
 from menu import MenuSystem, MenuItem, start_chooser
 from seed import seed_words_to_encoded_secret
 from stash import SecretStash
@@ -856,7 +856,8 @@ async def toggle_2fa(self, *a):
 
 async def gen_or_import():
     # returns 12 words, or None to abort
-    from seed import WordNestMenu, generate_seed, approve_word_list, SeedVaultChooserMenu
+    from seed import WordNestMenu, generate_seed_with_user_entropy, approve_word_list
+    from seed import SeedVaultChooserMenu, PURPOSE_CCC
 
     msg = "Press %s to generate a new 12-word seed phrase to be used "\
           "as the Coldcard Co-Signing Secret (key C).\n\nOr press (1) to import existing "\
@@ -895,8 +896,10 @@ async def done_key_C_import(words):
 
     elif ch == 'y':
         # normal path: pick 12 words, quiz them
-        await ux_dramatic_pause('Generating...', 3)
-        seed = generate_seed()
+        seed = await generate_seed_with_user_entropy(PURPOSE_CCC)
+        if seed is None:
+            return None
+
         words = await approve_word_list(seed, 12)
     else:
         return None

### shared/seed.py
@@ -50,6 +50,9 @@
 METHOD_MASH = b'M'
 METHOD_DICE = b'D'
 METHOD_COIN = b'C'
+PURPOSE_MASTER = b'M'
+PURPOSE_EPHEMERAL = b'T'
+PURPOSE_CCC = b'C'
 
 BAD_DICE_MSG = ('Distribution of dice rolls is not random. '
                 'Some numbers occurred more than 30% of the time.')
@@ -797,9 +800,8 @@ async def collect_mash_entropy():
 
     return md.digest()
 
-async def make_new_wallet(nwords):
-    # Generate the primary seed first, then require one human entropy source.
-    await ux_dramatic_pause('Generating...', 3)
+async def generate_seed_with_user_entropy(purpose):
+    # Require one human entropy source and mix it with device-generated entropy.
     base_seed = None
     extra_entropy = None
     mix = None
@@ -811,6 +813,7 @@ async def make_new_wallet(nwords):
     ])
     try:
         base_seed = generate_seed()
+        await ux_dramatic_pause('Generating...', 3)
 
         while extra_entropy is None:
             the_ux.push(choices)
@@ -841,14 +844,20 @@ async def make_new_wallet(nwords):
             else:
                 extra_entropy = await collect_symbol_entropy(spec)
 
-        mix = DOMAIN_SEED + method + base_seed + extra_entropy
-        seed = ngu.hash.sha256d(mix)
+        mix = DOMAIN_SEED + purpose + method + base_seed + extra_entropy
+        return ngu.hash.sha256d(mix)
 
     finally:
         blank_object(base_seed)
         blank_object(extra_entropy)
         blank_object(mix)
 
+
+async def make_new_wallet(nwords):
+    seed = await generate_seed_with_user_entropy(PURPOSE_MASTER)
+    if seed is None:
+        return
+
     words = await approve_word_list(seed, nwords)
     if words:
         await commit_new_words(words)
@@ -866,12 +875,14 @@ async def import_done_cb(words):
         return WordNestMenu(nwords, done_cb=import_done_cb)
 
 async def ephemeral_seed_generate(nwords):
-    await ux_dramatic_pause('Generating...', 3)
-    seed = generate_seed()
+    seed = await generate_seed_with_user_entropy(PURPOSE_EPHEMERAL)
+    if seed is None:
+        return
+
     words = await approve_word_list(seed, nwords, ephemeral=True)
     if words:
         dis.fullscreen("Applying...")
-        await set_ephemeral_seed_words(words, origin="TRNG Words")
+        await set_ephemeral_seed_words(words, origin="Generated Words")
 
 async def set_seed_extended_key(extended_key):
     encoded, chain = xprv_to_encoded_secret(extended_key)

### testing/test_ccc.py
@@ -189,7 +189,7 @@ def doit():
 def setup_ccc(goto_ccc_menu, pick_menu_item, cap_story, press_select, pass_word_quiz, is_q1,
               seed_story_to_words, cap_menu, OK, word_menu_entry, press_cancel, press_delete,
               enter_number, scan_a_qr, cap_screen, settings_get, need_keypress, microsd_path,
-              master_settings_get):
+              master_settings_get, enter_mash_entropy):
 
     def doit(c_words=None, mag=None, vel=None, whitelist=None, w2fa=None, first_time=True):
         if first_time:
@@ -211,6 +211,7 @@ def doit(c_words=None, mag=None, vel=None, whitelist=None, w2fa=None, first_time
             if c_words is None:
                 nwords = 12  # always 12 words if generated by us
                 press_select()
+                enter_mash_entropy()
                 time.sleep(.1)
                 title, story = cap_story()
                 assert f'Record these {nwords} secret words!' in (title if is_q1 else story)

### testing/test_ephemeral.py
@@ -367,7 +367,8 @@ def doit(mnemonic=None, xpub=None, expected_xfp=None, seed_vault=False,
 @pytest.fixture
 def generate_ephemeral_words(goto_eph_seed_menu, pick_menu_item, press_select,
                              need_keypress, cap_story, settings_set, seed_story_to_words,
-                             ephemeral_seed_disabled_ui, confirm_tmp_seed, is_q1):
+                             ephemeral_seed_disabled_ui, confirm_tmp_seed, is_q1,
+                             enter_mash_entropy):
     def doit(num_words, dice=False, from_main=False, seed_vault=None, testnet=True):
         if testnet:
             netcode = "XTN"
@@ -383,6 +384,7 @@ def doit(num_words, dice=False, from_main=False, seed_vault=None, testnet=True):
         pick_menu_item("Generate Words")
         if not dice:
             pick_menu_item(f"{num_words} Words")
+            enter_mash_entropy()
             time.sleep(0.1)
         else:
             pick_menu_item(f"{num_words} Word Dice Roll")
@@ -1575,7 +1577,7 @@ def test_import_master_as_tmp(reset_seed_words, goto_eph_seed_menu, cap_story,
                               need_keypress, word_menu_entry, settings_set,
                               confirm_tmp_seed, cap_menu, microsd_path,
                               restore_main_seed, get_identity_story, press_select,
-                              press_cancel, settings_remove):
+                              press_cancel, settings_remove, enter_mash_entropy):
     
     
     reset_seed_words()
@@ -1608,6 +1610,7 @@ def test_import_master_as_tmp(reset_seed_words, goto_eph_seed_menu, cap_story,
     # random temporary seed
     pick_menu_item("Generate Words")
     pick_menu_item(f"12 Words")
+    enter_mash_entropy()
     need_keypress("6")  # skip quiz
     press_select()  # yes - I'm sure
     confirm_tmp_seed(seedvault=False)
@@ -1658,7 +1661,8 @@ def test_import_master_as_tmp(reset_seed_words, goto_eph_seed_menu, cap_story,
     assert xfp_str == parsed_ident["xfp"]
 
 def test_home_menu_xfp(goto_home, pick_menu_item, press_select, cap_story, cap_menu,
-                       settings_get, goto_eph_seed_menu, need_keypress):
+                       settings_get, goto_eph_seed_menu, need_keypress,
+                       enter_mash_entropy):
     goto_home()
     pick_menu_item("Settings")
     pick_menu_item("Buried Settings")
@@ -1676,6 +1680,7 @@ def test_home_menu_xfp(goto_home, pick_menu_item, press_select, cap_story, cap_m
     goto_eph_seed_menu()
     pick_menu_item("Generate Words")
     pick_menu_item(f"12 Words")
+    enter_mash_entropy()
     time.sleep(0.1)
     need_keypress("6")  # skip quiz
     press_select()