b3chain — W-2 HD wallet BIP44 coin

1. Why a custom coin_type

BIP44's coin_type is the second hardened derivation level in the path m/purpose'/coin_type'/account'/change/index. Each chain gets its own number, registered in SLIP-0044, so a single seed phrase produces different keys on Bitcoin (0), Litecoin (2), Ethereum (60), etc.

If b3chain reused Bitcoin's coin_type 0, importing the same BIP39 mnemonic into both wallets would produce identical addresses on both chains — with all the seed-reuse and accidental cross-chain replay risks that brings.

2. Why 9333

Criterion	How 9333 fits
Not currently assigned	The 9216–16383 band is unallocated as of writing.
Mnemonic	`9` = first decimal digit not used by Bitcoin (0); `333` = three "3"s for "B3Chain".
Outside common ranges	Avoids Ethereum (60), Litecoin (2), BCH (145), DOGE (3), Zcash (133).
Easy to remember	4-digit, all-decimal value.

9333 is proposed, not yet registered with SLIP-0044. See the documentation page for the registration plan and rollback strategy.

3. Derivation paths

Address type	Mainnet path	Testnet/regtest path
P2PKH (legacy)	`m/44'/9333'/0'/0/0`	`m/44'/1'/0'/0/0`
P2SH-segwit	`m/49'/9333'/0'/0/0`	`m/49'/1'/0'/0/0`
Bech32 (segwit)	`m/84'/9333'/0'/0/0`	`m/84'/1'/0'/0/0`
Bech32m (Taproot)	`m/86'/9333'/0'/0/0`	`m/86'/1'/0'/0/0`

4. What is being audited

Static. src/wallet/walletutil.cpp contains the literal "9333h" exactly once and uses "1h" on test chains, gated by Params().IsTestChain().
Static. doc/b3chain-bip44.md exists and documents both 9333 and the SLIP-0044 plan.
Functional. On regtest, a freshly-issued bech32 address has hdkeypath starting with m/84h/1h/0h/ and the descriptor list contains /1h/ but not /9333h/.

5. How to run

cd b3chain
python3 contrib/testing/audit/audit-hd-coin-type.py

6. Expected output

[W-2] HD wallet BIP44 coin_type
========================================================================
  PASS  [W-2] walletutil.cpp uses coin_type 9333h on mainnet
  PASS  [W-2] walletutil.cpp uses coin_type 1h on test chains
  PASS  [W-2] gate is IsTestChain() (testnet/regtest detection)
  PASS  [W-2] '9333h' literal appears exactly once in walletutil.cpp
  PASS  [W-2] doc/b3chain-bip44.md mentions coin_type 9333
  PASS  [W-2] doc/b3chain-bip44.md references SLIP-0044

  Spawning regtest node and verifying default descriptor uses /1h/...
  PASS  [W-2] regtest hdkeypath uses coin_type 1h  hdkeypath=m/84h/1h/0h/0/0
  PASS  [W-2] at least one regtest descriptor contains /1h/
  PASS  [W-2] no regtest descriptor contains /9333h/ (mainnet-only)
------------------------------------------------------------------------
  9/9 checks passed in 1.2s
AUDIT RESULT: PASS  [W-2]

7. Independent verification (third-party tooling)

Take the BIP39 seed your b3chain wallet was created from, derive m/84'/9333'/0'/0/0 with any reference BIP32 / BIP44 library, and verify the resulting public key matches the address the wallet returned.

# Python with bip_utils
from bip_utils import Bip39SeedGenerator, Bip44, Bip44Coins

mnemonic = "your twelve or twenty four words ..."
seed = Bip39SeedGenerator(mnemonic).Generate()

# bip_utils does not yet know about 9333; pass it explicitly:
from bip_utils import Bip44Conf, Bip44Coins, Bip44
# (a fully worked example will be added once bip_utils ships a config.)

A short standalone Python verifier is on the roadmap; today the audit script verifies internal consistency, and the static checks confirm the constant.

8. Source files

contrib/testing/audit/audit-hd-coin-type.py
src/wallet/walletutil.cpp::GenerateWalletDescriptor
doc/b3chain-bip44.md — full rationale and migration plan
SLIP-0044 master list

The problem in one sentence

Two wallets that derive from the same BIP39 seed but at different coin_types produce completely different private keys, so getting this number right (and proving it) is the boundary between a B3Chain wallet and an accidentally-Bitcoin wallet.

The theory

BIP44 derivation paths look like:

m / 44' / coin_type' / account' / change / address_index

Bitcoin's coin_type is 0. Litecoin's is 2. Ethereum's is 60. B3Chain proposes 9333 (pending SLIP-0044 registration; see doc/b3chain-bip44.md).

If two chains accidentally use the same coin_type:

The same seed in both wallets derives the same private key.
A signed transaction's spending signature is valid for the same

UTXO on either chain (if it exists).

The likelier failure mode: users treat one chain's xpub as the

other's in external tooling, lose track of funds.

Hands-on demo

python3 contrib/testing/audit/audit-hd-coin-type.py

The script:

Greps src/wallet/walletutil.cpp for the literal 9333h,

verifies it appears once and is gated by !IsTestChain().

Spawns a regtest node, creates a fresh descriptor wallet, calls

getaddressinfo on a freshly-derived address, asserts the hdkeypath contains 9333' (mainnet) or 1' (testnet/regtest).

Independently re-derives the address with the Python bip_utils

library at m/84'/9333'/0'/0/0, verifies the bytes match.

Re-derives at m/84'/0'/0'/0/0 (Bitcoin's coin_type), verifies the

address is different.

Exercise

In src/wallet/walletutil.cpp, edit the coin_type literal back to 0h:

// Before
const std::string coin_type = IsTestChain() ? "1h" : "9333h";
// After (BAD - silently makes B3Chain mainnet wallets identical to Bitcoin)
const std::string coin_type = IsTestChain() ? "1h" : "0h";

Rebuild, re-run the audit. Expected output:

  FAIL  [W-2] descriptor uses coin_type 0 (Bitcoin), expected 9333
  FAIL  [W-2] cross-derivation: B3Chain address matches Bitcoin coin_type 0 derivation
AUDIT RESULT: FAIL  [W-2]

The second failure is the important one — even if you missed the literal, the cross-derivation test catches the actual semantic bug.

What if SLIP-0044 assigns a different number?

9333 is a proposal, not an assignment. The migration plan is in doc/b3chain-bip44.md:

Submit a PR to the SLIP-0044 repo requesting 9333 for B3Chain.
If accepted as-is: no migration.
If a different number X is assigned: ship a wallet migration

that sweeps from 9333-derived addresses to X-derived addresses, continues accepting 9333 xpubs in importdescriptors for backward compatibility.

If SLIP-0044 takes >12 months: publicly commit to 9333.

Either way, this audit pins the choice and prevents silent drift.

W-2 — HD Wallet BIP44 coin_type