How do I generate master key from the root seed

Question

I created a mnemonics and it is hashed using pbdkf2 function to get a root seed. So this root seed should be hashed again with HMAC-SHA512 to get the master key (Master private key and chain code). So for a HMAC-SAH512 we need a key and data, so in this case what should be the key? Data should be the root seed and what should I give as key in hmac function.

I gave "Bitcoin Seed" as key and generated a hash, but it is not matching the output showed on Ian Coleman's bip39 website.

Answer 1

The BIP32 Root Key described on iancoleman tool is called master node, serialized in base58.

The HMAC function needs a key (the string "Bitcoin seed" encoded in bytes), a data (the seed) and the hash function (sha512).

In python, it looks like:

master_node = hmac.new(b'Bitcoin seed', bytes.fromhex(mseed), digestmod="sha512").digest()

Serializing...

• version = '0488ade4'
• depth = '00'
• fingerprint = '00000000'
• index = '00000000'
• private = first 32 bytes of master node
• chaincode = last 32 bytes of master node

Sum, checksum, encode everything and you'll get there.

Follow the steps of chapter 5 -> https://learnmeabitcoin.com/technical/extended-keys