Merge pull request #10933 from SomberNight/202609_crandom_prep

prep crandom.py: trivial refactor to centralise our RNG code

Author: ecdsa

electrum/commands.py

@@ -79,6 +79,7 @@
 from . import crypto
 from . import constants
 from . import descriptor
+from . import crandom
 
 if TYPE_CHECKING:
     from .network import Network
@@ -2329,7 +2330,7 @@ async def get_blinded_path_via(self, node_id: str, dummy_hops: int = 0, wallet:
         assert peer, 'node_id not a peer'
 
         path = [pubkey, wallet.lnworker.node_keypair.pubkey]
-        session_key = os.urandom(32)
+        session_key = crandom.get_rand_bytes(32)
         blinded_path = create_blinded_path(session_key, path=path, final_recipient_data={}, dummy_hops=dummy_hops)
 
         with io.BytesIO() as blinded_path_fd:

electrum/crandom.py

@@ -0,0 +1,21 @@
+# Copyright (C) 2026 The Electrum developers
+# Distributed under the MIT software license, see the accompanying
+# file LICENCE or http://www.opensource.org/licenses/mit-license.php
+#
+# Cryptographically secure RNG.
+
+import os
+import secrets
+
+
+def get_rand_bytes(nbytes: int) -> bytes:
+    """Returns uniformly distributed bytes, of length nbytes."""
+    assert nbytes >= 0, nbytes
+    return os.urandom(nbytes)
+
+
+def get_rand_below(upper_bound: int) -> int:
+    """Return a uniformly distributed int in the range [0, upper_bound)."""
+    assert upper_bound > 0, upper_bound
+    return secrets.randbelow(upper_bound)
+

electrum/crypto.py

@@ -36,6 +36,7 @@
 from .util import assert_bytes, InvalidPassword, to_bytes, to_string, WalletFileException, versiontuple
 from .i18n import _
 from .logging import get_logger
+from . import crandom
 
 _logger = get_logger(__name__)
 
@@ -179,7 +180,7 @@ def aes_decrypt_with_iv(key: bytes, iv: bytes, data: bytes) -> bytes:
 
 def EncodeAES_bytes(secret: bytes, msg: bytes) -> bytes:
     assert_bytes(msg)
-    iv = bytes(os.urandom(16))
+    iv = crandom.get_rand_bytes(16)
     ct = aes_encrypt_with_iv(secret, iv, msg)
     return iv + ct
 

electrum/daemon.py

@@ -40,11 +40,12 @@
 from aiohttp import web, client_exceptions
 from aiorpcx import ignore_after
 
+from . import crandom
 from . import util
 from .network import Network
 from .util import (
     json_decode, to_bytes, to_string, profiler, standardize_path, constant_time_compare, InvalidPassword,
-    log_exceptions, randrange, OldTaskGroup, UserFacingException, JsonRPCError, os_chmod
+    log_exceptions, OldTaskGroup, UserFacingException, JsonRPCError, os_chmod
 )
 from .wallet import Wallet, Abstract_Wallet
 from .storage import WalletStorage
@@ -186,7 +187,7 @@ def get_rpc_credentials(config: SimpleConfig) -> Tuple[str, str]:
         rpc_user = 'user'
         bits = 128
         nbytes = bits // 8 + (bits % 8 > 0)
-        pw_int = randrange(pow(2, bits))
+        pw_int = crandom.get_rand_below(pow(2, bits))
         pw_b64 = b64encode(
             pw_int.to_bytes(nbytes, 'big'), b'-_')
         rpc_password = to_string(pw_b64, 'ascii')

electrum/gui/qml/qebiometrics.py

@@ -1,10 +1,10 @@
 import os
-import secrets
 from enum import Enum
 from typing import Optional, TYPE_CHECKING
 
 from PyQt6.QtCore import QObject, pyqtSignal, pyqtSlot, pyqtProperty, QMetaObject, Qt
 
+from electrum import crandom
 from electrum.i18n import _
 from electrum.logging import get_logger
 from electrum.base_crash_reporter import send_exception_to_crash_reporter
@@ -81,7 +81,7 @@ def enable(self, unified_wallet_password: str):
         The encryption key for the wrap_key is stored in the AndroidKeyStore.
         This way the wallet password doesn't have to leave the process.
         """
-        wrap_key, iv = secrets.token_bytes(32), secrets.token_bytes(16)
+        wrap_key, iv = crandom.get_rand_bytes(32), crandom.get_rand_bytes(16)
         wrapped_wallet_password = aes_encrypt_with_iv(
             key=wrap_key,
             iv=iv,

electrum/lnutil.py

@@ -25,6 +25,7 @@
     Transaction, PartialTransaction, PartialTxInput, TxOutpoint, PartialTxOutput, opcodes, OPPushDataPubkey
 )
 from . import bitcoin, crypto, transaction, descriptor, segwit_addr
+from . import crandom
 from .bitcoin import redeem_script_to_address, address_to_script, construct_witness, \
     construct_script, NLOCKTIME_BLOCKHEIGHT_MAX
 from .i18n import _
@@ -2007,8 +2008,7 @@ def generate_keypair(node: BIP32Node, key_family: LnKeyFamily) -> Keypair:
 
 
 def generate_random_keypair() -> Keypair:
-    import secrets
-    k = secrets.token_bytes(32)
+    k = crandom.get_rand_bytes(32)
     cK = ecc.ECPrivkey(k).get_public_key_bytes()
     return Keypair(cK, k)
 

electrum/lnworker.py

@@ -35,6 +35,7 @@
 
 from . import constants, util, lnutil
 from . import bitcoin
+from . import crandom
 from .util import (
     profiler, OldTaskGroup, ESocksProxy, NetworkRetryManager, JsonRPCClient, NotEnoughFunds, EventListener,
     event_listener, bfh, InvoiceError, resolve_dns_srv, is_ip_address, log_exceptions, ignore_exceptions,
@@ -664,7 +665,7 @@ class LNGossip(Logger):
 
     def __init__(self, config: 'SimpleConfig'):
         self.config = config
-        seed = os.urandom(32)
+        seed = crandom.get_rand_bytes(32)
         node = BIP32Node.from_rootseed(seed, xtype='standard')
         xprv = node.to_xprv()
         node_keypair = generate_keypair(BIP32Node.from_xkey(xprv), LnKeyFamily.NODE_KEY)
@@ -1695,7 +1696,7 @@ async def _open_channel_coroutine(
             public=public,
             zeroconf=zeroconf,
             opening_fee=opening_fee,
-            temp_channel_id=os.urandom(32))
+            temp_channel_id=crandom.get_rand_bytes(32))
         chan, funding_tx = await util.wait_for2(coro, LN_P2P_NETWORK_TIMEOUT)
         util.trigger_callback('channels_updated', self.wallet)
         self.wallet.adb.add_transaction(funding_tx)  # save tx as local into the wallet
@@ -1752,7 +1753,7 @@ def make_local_config_for_new_channel(
         channel_seed: bytes | None = None,
     ) -> LocalConfig:
         if channel_seed is None:
-            channel_seed = os.urandom(32)
+            channel_seed = crandom.get_rand_bytes(32)
         initial_msat = funding_sat * 1000 - push_msat if initiator == LOCAL else push_msat
 
         # sending empty bytes as the upfront_shutdown_script will give us the
@@ -2508,7 +2509,7 @@ async def create_routes_for_payment(
                             budget=budget._replace(fee_msat=budget.fee_msat // len(per_trampoline_channel_amounts)),
                         )
                         # node_features is only used to determine is_tlv
-                        per_trampoline_secret = os.urandom(32)
+                        per_trampoline_secret = crandom.get_rand_bytes(32)
                         per_trampoline_fees = per_trampoline_amount_with_fees - per_trampoline_amount
                         self.logger.info(f'created route with trampoline fee level={paysession.trampoline_fee_level}')
                         self.logger.info(f'trampoline hops: {[hop.end_node.hex() for hop in trampoline_route]}')
@@ -2776,7 +2777,7 @@ def create_payment_info(
     ) -> bytes:
         if amount_msat == 0:
             raise ValueError("amount_msat must not be 0. Use None instead.")
-        payment_preimage = os.urandom(32)
+        payment_preimage = crandom.get_rand_bytes(32)
         payment_hash = sha256(payment_preimage)
         min_final_cltv_delta = min_final_cltv_delta or MIN_FINAL_CLTV_DELTA_ACCEPTED
         invoice_features = self._prepare_invoice_features(self.features.for_bolt11_invoice(), amount_msat=amount_msat)
@@ -4175,7 +4176,7 @@ async def _maybe_forward_trampoline(
         payload = any_trampoline_onion.hop_data.payload
         payment_data = payload.get('payment_data')
         try:
-            payment_secret = payment_data['payment_secret'] if payment_data else os.urandom(32)
+            payment_secret = payment_data['payment_secret'] if payment_data else crandom.get_rand_bytes(32)
             outgoing_node_id = payload["outgoing_node_id"]["outgoing_node_id"]
             amt_to_forward = payload["amt_to_forward"]["amt_to_forward"]
             out_cltv_abs = payload["outgoing_cltv_value"]["outgoing_cltv_value"]
@@ -4332,7 +4333,7 @@ def create_onion_for_route(
         for i in range(len(route)):
             self.logger.info(f"  {i}: edge={route[i].short_channel_id} hop_data={hops_data[i]!r}")
         assert final_cltv_abs <= cltv_abs, (final_cltv_abs, cltv_abs)
-        session_key = os.urandom(32) # session_key
+        session_key = crandom.get_rand_bytes(32)  # session_key
         # if we are forwarding a trampoline payment, add trampoline onion
         if trampoline_onion:
             self.logger.info(f'adding trampoline onion to final payload')

electrum/mnemonic.py

@@ -30,7 +30,8 @@
 from typing import Sequence, Dict, Iterator, Optional
 from types import MappingProxyType
 
-from .util import resource_path, bfh, randrange
+from . import crandom
+from .util import resource_path, bfh
 from .crypto import hmac_oneshot
 from . import version
 from .logging import Logger
@@ -212,7 +213,7 @@ def make_seed(self, *, seed_type: str | None = None, num_bits: int | None = None
         # generate random
         entropy = 1
         while entropy < pow(2, num_bits - bpw):  # try again if seed would not contain enough words
-            entropy = randrange(pow(2, num_bits))
+            entropy = crandom.get_rand_below(pow(2, num_bits))
         # brute-force seed that has correct "version number"
         nonce = 0
         while True:

electrum/onion_message.py

@@ -45,6 +45,7 @@
 from electrum.lnutil import (LnFeatures, MIN_FINAL_CLTV_DELTA_ACCEPTED, MAXIMUM_REMOTE_TO_SELF_DELAY_ACCEPTED,
                              MIN_FINAL_CLTV_DELTA_BUFFER_INVOICE)
 from electrum.util import OldTaskGroup, log_exceptions, random_shuffled_copy
+from electrum import crandom
 
 
 def now() -> float:
@@ -268,7 +269,7 @@ def send_onion_message_to(
         session_key: bytes | None = None
 ) -> None:
     if session_key is None:
-        session_key = os.urandom(32)
+        session_key = crandom.get_rand_bytes(32)
 
     if len(node_id_or_blinded_path) > 33:  # assume blinded path
         with io.BytesIO(node_id_or_blinded_path) as blinded_path_fd:
@@ -447,7 +448,7 @@ def get_blinded_paths_to_me(
                     continue
                 payinfos.append(payinfo)
             blinded_path = create_blinded_path(
-                session_key=os.urandom(32),
+                session_key=crandom.get_rand_bytes(32),
                 path=[chan.node_id, mynodeid],
                 final_recipient_data=final_recipient_data,
                 hop_extras=hop_extras,
@@ -466,7 +467,7 @@ def get_blinded_paths_to_me(
                 raise NoOnionMessagePeers('no ONION_MESSAGE capable peers')
             rpeers = random_shuffled_copy(my_onionmsg_peers)
             for peer in rpeers[:max_paths]:
-                blinded_path = create_blinded_path(os.urandom(32), [peer.pubkey, mynodeid], final_recipient_data)
+                blinded_path = create_blinded_path(crandom.get_rand_bytes(32), [peer.pubkey, mynodeid], final_recipient_data)
                 result.append(blinded_path)
 
     assert result
@@ -683,7 +684,7 @@ def submit_send(
 
            :return: returns awaitable task"""
         if not key:
-            key = os.urandom(8)
+            key = crandom.get_rand_bytes(8)
         assert type(key) is bytes and len(key) >= 8
 
         self.logger.debug(f'submit_send {key=} {payload=} {node_id_or_blinded_paths=}')

electrum/plugin.py

@@ -50,6 +50,7 @@
                    make_dir, make_aiohttp_session)
 from . import bip32
 from . import plugins
+from . import crandom
 from .simple_config import SimpleConfig
 from .logging import get_logger, Logger
 from .crypto import sha256
@@ -440,7 +441,7 @@ def _delete_plugin_key_from_windows_registry(self) -> None:
             pass
 
     def create_new_key(self, password:str) -> str:
-        salt = os.urandom(32)
+        salt = crandom.get_rand_bytes(32)
         privkey = self.derive_privkey(password, salt)
         pubkey = privkey.get_public_key_bytes()
         key = bytes([PLUGIN_PASSWORD_VERSION]) + salt + pubkey