From cceba591b21ef1588fff3a7ea4a050c90906a2d8 Mon Sep 17 00:00:00 2001
From: Ed Tubbs <ectubbs@gmail.com>
Date: Wed, 5 Feb 2025 14:13:10 -0600
Subject: [PATCH] wallet: update derivation path to m/0'/3'/n'

tests: added DeriveNewChildKey test
---
 src/wallet/test/wallet_tests.cpp | 45 ++++++++++++++++++++++++++++++++
 src/wallet/wallet.cpp            | 11 ++++----
 2 files changed, 51 insertions(+), 5 deletions(-)

diff --git a/src/wallet/test/wallet_tests.cpp b/src/wallet/test/wallet_tests.cpp
index 39e44c026..debab5365 100644
--- a/src/wallet/test/wallet_tests.cpp
+++ b/src/wallet/test/wallet_tests.cpp
@@ -547,4 +547,49 @@ BOOST_AUTO_TEST_CASE(GetMinimumFee_dust_test)
     CWallet::discardThreshold = COIN / 100;
 }
 
+BOOST_FIXTURE_TEST_CASE(derive_new_child_key_test, WalletTestingSetup)
+{
+    CWallet* wallet = pwalletMain;
+    LOCK(wallet->cs_wallet);
+
+    // Use a fixed seed and known child public key
+    std::string testSeedHex = "000102030405060708090a0b0c0d0e0f101112131415161718191a1b1c1d1e1f";
+    std::string expectedPubKeyHex = "0305a077194300e27d320a9504f808a16f05b38dabead31f10104c075d88f81a38";
+    std::vector<unsigned char> seed = ParseHex(testSeedHex);
+
+    // Initialize the master key with the fixed seed and get the public key
+    CKey masterKey;
+    masterKey.Set(seed.begin(), seed.end(), true);
+    CPubKey masterPubKey = masterKey.GetPubKey();
+    BOOST_CHECK(masterKey.VerifyPubKey(masterPubKey));
+
+    // Set up master metadata: path "m" and master key ID equal to the public key hash
+    int64_t nCreationTime = GetTime();
+    CKeyMetadata masterMetadata(nCreationTime);
+    masterMetadata.hdKeypath = "m";
+    masterMetadata.hdMasterKeyID = masterPubKey.GetID();
+
+    // Store the master key and metadata in the wallet
+    wallet->mapKeyMetadata[masterPubKey.GetID()] = masterMetadata;
+    BOOST_CHECK(wallet->AddKeyPubKey(masterKey, masterPubKey));
+    BOOST_CHECK(wallet->SetHDMasterKey(masterPubKey));
+
+    // Derive a new child key using at derivation path (m/0'/3'/0')
+    CKeyMetadata childMetadata(GetTime());
+    CKey childKey;
+    wallet->DeriveNewChildKey(childMetadata, childKey);
+
+    // Verify the child key is valid
+    CPubKey childPubKey = childKey.GetPubKey();
+    BOOST_CHECK(childKey.IsValid());
+    BOOST_CHECK(childPubKey.IsFullyValid());
+
+    // Verify that the metadata reflects the path "m/0'/3'/0'"
+    BOOST_CHECK_EQUAL(childMetadata.hdKeypath, "m/0'/3'/0'");
+
+    // Verify the child public key matches the expected value
+    std::string derivedPubKeyHex = HexStr(childPubKey.begin(), childPubKey.end());
+    BOOST_CHECK_EQUAL(derivedPubKeyHex, expectedPubKeyHex);
+}
+
 BOOST_AUTO_TEST_SUITE_END()
diff --git a/src/wallet/wallet.cpp b/src/wallet/wallet.cpp
index 524e44fa4..55ccb1ba8 100644
--- a/src/wallet/wallet.cpp
+++ b/src/wallet/wallet.cpp
@@ -48,6 +48,7 @@ bool fWalletRbf = DEFAULT_WALLET_RBF;
 
 const char * DEFAULT_WALLET_DAT = "wallet.dat";
 const uint32_t BIP32_HARDENED_KEY_LIMIT = 0x80000000;
+const uint32_t BIP44_COIN_TYPE = 3;
 
 /**
  * Fees smaller than this (in satoshi) are considered zero fee (for transaction creation)
@@ -130,12 +131,12 @@ CPubKey CWallet::GenerateNewKey()
 
 void CWallet::DeriveNewChildKey(CKeyMetadata& metadata, CKey& secret)
 {
-    // for now we use a fixed keypath scheme of m/0'/0'/k
+    // for now we use a fixed keypath scheme of m/0'/3'/k
     CKey key;                      //master key seed (256bit)
     CExtKey masterKey;             //hd master key
     CExtKey accountKey;            //key at m/0'
-    CExtKey externalChainChildKey; //key at m/0'/0'
-    CExtKey childKey;              //key at m/0'/0'/<n>'
+    CExtKey externalChainChildKey; //key at m/0'/3'
+    CExtKey childKey;              //key at m/0'/3'/<n>'
 
     // try to get the master key
     if (!GetKey(hdChain.masterKeyID, key))
@@ -147,8 +148,8 @@ void CWallet::DeriveNewChildKey(CKeyMetadata& metadata, CKey& secret)
     // use hardened derivation (child keys >= 0x80000000 are hardened after bip32)
     masterKey.Derive(accountKey, BIP32_HARDENED_KEY_LIMIT);
 
-    // derive m/0'/0'
-    accountKey.Derive(externalChainChildKey, BIP32_HARDENED_KEY_LIMIT);
+    // derive m/0'/3'
+    accountKey.Derive(externalChainChildKey, BIP44_COIN_TYPE | BIP32_HARDENED_KEY_LIMIT);
 
     // derive child key at next index, skip keys already known to the wallet
     do {