Here's my code to get a child public key from a parent HD key. I adapted it from freedomnode:
public function address_from_master_pub($path = '0/0') {
if ($this->xpub === NULL && $this->ypub === NULL && $this->zpub === NULL) {
throw new Exception("XPUB, YPUB or ZPUB key is not present!");
}
$adapter = Bitcoin::getEcAdapter();
$slip132 = new Slip132(new KeyToScriptHelper($adapter));
$registry_classname = 'BitWasp\\Bitcoin\\Network\\Slip132\\'.$this->network_name.'Registry';
$bitcoin_prefixes = new $registry_classname();
if ($this->xpub !== NULL) {
$pubPrefix = $slip132->p2pkh($bitcoin_prefixes);
$pub = $this->xpub;
} else if ($this->ypub !== NULL) {
$pubPrefix = $slip132->p2shP2wpkh($bitcoin_prefixes);
$pub = $this->ypub;
} else if ($this->zpub !== NULL) {
$pubPrefix = $slip132->p2wpkh($bitcoin_prefixes);
$pub = $this->zpub;
}
$config = new GlobalPrefixConfig([
new NetworkConfig($this->network, [
$pubPrefix,
])
]);
$serializer = new Base58ExtendedKeySerializer(
new ExtendedKeySerializer($adapter, $config)
);
$key = $serializer->parse($this->network, $pub);
$child_key = $key->derivePath($path);
return $child_key->getAddress(new AddressCreator())->getAddress();
}
If I use it for index 0 or 1 or 2 (paths 0/0, 0/1, 0/2), it works fine in the sense that if I send bitcoin to that address, I can see the transaction on the public blockchain under the parent xpub on blockchain.com and it shows the funds. Plus, the child addresses which I generate match what shows up in Mycelium HD account receiving address.
But when I used index 243 (thus creating a path of 0/243 it didn't show up on the receiving end (under that xpub) even though it showed up on my sending end as a confirmed transaction. That path 0/243 generated a valid bitcoin address, but it didn't show up under that xpub on blockchain.com even after it was confirmed.
What's the rule involved? If i > some limit it no longer works? Or if I use an index "out of order" it doesn't work? Or something else, like Mycelium stopping recognizing child addresses past a certain index (i) and really the fundsa safa just under a higher level new HD xpub? I used the same code to generate all the child addresses for i = 0, 1, 2, and 243.
