From 9092b7147fcb545cdbed9503002f381f13448165 Mon Sep 17 00:00:00 2001
From: scgbckbone <scgbckbone@proton.me>
Date: Tue, 16 Sep 2025 15:34:22 +0200
Subject: [PATCH] remove O(n) .index loop from next_char; replace wallycore in
 bip39.py cor cpython with stdlib hashlib

---
 ngu/bip39.py                | 41 ++++++++++++++++---------------------
 ngu/ngu_tests/test_bip39.py |  3 +++
 2 files changed, 21 insertions(+), 23 deletions(-)

diff --git a/ngu/bip39.py b/ngu/bip39.py
index 09c4796..89e0233 100644
--- a/ngu/bip39.py
+++ b/ngu/bip39.py
@@ -294,7 +294,7 @@
 
 
 def get_word_index(word):
-    "input string word; return int index in wordlist, or ValueError"
+    # input string word; return int index in wordlist, or ValueError
     # - also accepts just first four distinctive characters of the word
 
     try:
@@ -316,7 +316,7 @@ def get_word_index(word):
 
 
 def b2a_words(msg):
-    "map binary to words, including a few bits of checksum, per BIP39 spec"
+    # map binary to words, including a few bits of checksum, per BIP39 spec
     l = len(msg)
     assert 16 <= l <= 32
     assert l % 4 == 0
@@ -345,7 +345,7 @@ def b2a_words(msg):
 
 
 def _split_lookup(phrase):
-    "decode & lookup only"
+    # decode & lookup only
 
     if isinstance(phrase, str):
         phrase = phrase.split()
@@ -360,7 +360,7 @@ def _split_lookup(phrase):
     return num, rv
 
 def a2b_words(phrase):
-    "decode, raise on bad checksum"
+    # decode, raise on bad checksum
 
     num, rv = _split_lookup(phrase)
 
@@ -382,7 +382,7 @@ def a2b_words(phrase):
     return bits
 
 def a2b_words_guess(phrase):
-    "generate a list of possible final words"
+    # generate a list of possible final words
     num, rv = _split_lookup(phrase)
 
     if num not in { 11, 14, 17, 20, 23 }:
@@ -409,30 +409,25 @@ def next_char(prefix):
     assert pl >= 1
 
     try:
-        wn = wordlist_en.index(prefix)
-        if pl >= 4:
-            return (True, '', wordlist_en[wn])
-        exact = True
-    except ValueError:
-        exact = False
-        # skip down until first 1-2 char(s) match
-        try:
-            wn = _lookup[prefix[0:2]]
-        except KeyError:
-            # 2-prefix not in list
-            return (False, '', None)
+        wn = _lookup[prefix[0:2]]
+    except KeyError:
+        # prefix not in the _lookup list
+        return False, '', None
 
     first = None
     count = 0
-
+    exact = False
     chars = []
     for wn in range(wn, 0x800):
         word = wordlist_en[wn]
-        if word[0:pl] > prefix: break
-        if word[0:pl] == prefix:
+        wc = word[0:pl]
+        if wc > prefix: break  # lexicographical ordering
+        if wc == prefix:
+            if word == prefix:
+                exact = True
             if pl >= 4:
                 # they gave 4+ letter prefix of correct word; they're done
-                return (True, '', word)
+                return True, '', word
 
             if not count:
                 first = word
@@ -452,6 +447,6 @@ def master_secret(words, pw=b''):
         import ngu
         return ngu.hash.pbkdf2_sha512(words, salt, 2048)
     except ImportError:
-        import wallycore
-        return wallycore.pbkdf2_hmac_sha512(words, salt, 0, 2048)
+        import hashlib
+        return hashlib.pbkdf2_hmac("sha512", words, salt, 2048, dklen=64)
 
diff --git a/ngu/ngu_tests/test_bip39.py b/ngu/ngu_tests/test_bip39.py
index 25a117c..9f77d32 100644
--- a/ngu/ngu_tests/test_bip39.py
+++ b/ngu/ngu_tests/test_bip39.py
@@ -64,10 +64,13 @@ def test_prefix():
     assert bip39.next_char('dkfjh') == (False, '', None)
     assert bip39.next_char('a') == (False, 'bcdefghilmnprstuvwx', None)
     assert bip39.next_char('q') == (False, 'u', None)
+    assert bip39.next_char('x') == (False, '', None)  # only char not in the _lookup
     assert bip39.next_char('qu') == (False, 'aeio', None)
     assert bip39.next_char('present') == (True, '', 'present')
     assert bip39.next_char('zoo') == (True, '', 'zoo')
     assert bip39.next_char('zo') == (False, 'no', None)
+    assert bip39.next_char('fat') == (True, 'ahi', None)
+    assert bip39.next_char('win') == (True, 'degknt', None)
 
     wl = bip39.wordlist_en
     for w in wl: