speeded up BIP32 public derivation by caching

btclib/bip32/bip32.py

@@ -34,6 +34,7 @@
 from __future__ import annotations
 
 import copy
+import functools
 import hmac
 from dataclasses import dataclass
 from typing import Union
@@ -277,7 +278,7 @@ def xpub_from_xprv(xprv: BIP32Key) -> str:
 
 
 @dataclass
-class _ExtendedBIP32KeyData(BIP32KeyData):
+class _BIP32KeyData(BIP32KeyData):
     # extensions used to cache intermediate results
     # in multi-level derivation: do not rely on them elsewhere
 
@@ -308,17 +309,15 @@ def __init__(
         if check_validity:
             self.assert_valid()
 
+    def __tuple(self) -> tuple[bytes, int, bytes, bytes]:
+        return (self.parent_fingerprint, self.index, self.chain_code, self.key)
 
-def __child_key_derivation(xkey: _ExtendedBIP32KeyData, index: int) -> None:
-    xkey.depth += 1
-    xkey.index = index
-    if xkey.is_private:
-        __private_key_derivation(xkey, index)
-    else:
-        __public_key_derivation(xkey, index)
+    def __hash__(self) -> int:
+        return hash(self.__tuple())
 
 
-def __private_key_derivation(xkey: _ExtendedBIP32KeyData, index: int) -> None:
+def __prv_key_derivation(xkey: _BIP32KeyData, index: int) -> None:
+    xkey.index = index
     Q_bytes = bytes_from_point(mult(xkey.prv_key_int))
     xkey.parent_fingerprint = hash160(Q_bytes)[:4]
     hmac_ = (
@@ -341,10 +340,10 @@ def __private_key_derivation(xkey: _ExtendedBIP32KeyData, index: int) -> None:
     xkey.pub_key_point = INF
 
 
-def __public_key_derivation(xkey: _ExtendedBIP32KeyData, index: int) -> None:
+@functools.lru_cache()  # results are cached to increase efficiency
+def __pub_key_derivation(xkey: _BIP32KeyData, index: int) -> None:
+    xkey.index = index
     xkey.parent_fingerprint = hash160(xkey.key)[:4]
-    if xkey.is_hardened:
-        raise BTClibValueError("invalid hardened derivation from public key")
     hmac_ = hmac.new(
         xkey.chain_code,
         xkey.key + index.to_bytes(4, byteorder="big", signed=False),
@@ -370,16 +369,14 @@ def _derive(
         err_msg = f"final depth greater than 255: {final_depth}"
         raise BTClibValueError(err_msg)
 
-    xkey = _ExtendedBIP32KeyData(
+    xkey = _BIP32KeyData(
         version=xkey.version,
-        depth=xkey.depth,
+        depth=final_depth,
         parent_fingerprint=xkey.parent_fingerprint,
         index=xkey.index,
         chain_code=xkey.chain_code,
         key=xkey.key,
     )
-    for index in indexes:
-        __child_key_derivation(xkey, index)
 
     if forced_version:
         if xkey.version in XPRV_VERSIONS_ALL:
@@ -393,6 +390,15 @@ def _derive(
             raise BTClibValueError(err_msg)
         xkey.version = fversion
 
+    if xkey.is_private:
+        for index in indexes:
+            __prv_key_derivation(xkey, index)
+    else:
+        if any(index >= 0x80000000 for index in indexes):
+            raise BTClibValueError("invalid hardened derivation from public key")
+        for index in indexes:
+            __pub_key_derivation(xkey, index)
+
     return xkey
 
 

btclib/ec/curve_group.py

@@ -481,7 +481,7 @@ def multiples(Q: JacPoint, size: int, ec: CurveGroup) -> list[JacPoint]:
 MAX_W = 5
 
 
-@functools.lru_cache()  # least recently used cache
+@functools.lru_cache()  # results are cached to increase efficiency
 def cached_multiples(Q: JacPoint, ec: CurveGroup) -> list[JacPoint]:
     T = [INFJ, Q]
     for i in range(3, 2**MAX_W, 2):
@@ -490,7 +490,7 @@ def cached_multiples(Q: JacPoint, ec: CurveGroup) -> list[JacPoint]:
     return T
 
 
-@functools.lru_cache()
+@functools.lru_cache()  # results are cached to increase efficiency
 def cached_multiples_fixwind(
     Q: JacPoint, ec: CurveGroup, w: int = 4
 ) -> list[list[JacPoint]]: