Add legacy derivation to nsec_to_bitcoin_address.py ?

[TheButterZone]

From nostr-protocol/nips#2332 (comment)

I'm not confident I could submit a PR adding this without breaking your original... but do you think ChatGPT or another could do it correctly if I just provide the URLs to this & the .py & say some magic words?

Hopefully get it on https://openetr.org/bitcoin/check-balance as its own box beneath Taproot Wallet Details, formatted much the same way?

Full Reference Implementation (Python)

import hashlib
import base58

from Crypto.Hash import RIPEMD160
from bech32 import bech32_encode, convertbits


# -----------------------------
# HASH160 (Bitcoin standard)
# -----------------------------

def hash160(data: bytes) -> bytes:
    sha = hashlib.sha256(data).digest()
    ripemd = RIPEMD160.new()
    ripemd.update(sha)
    return ripemd.digest()


# -----------------------------
# x-only -> compressed pubkey
# -----------------------------

def xonly_to_compressed_pubkey(xonly_pubkey: bytes) -> bytes:
    """
    Deterministic compatibility rule:

    Prefix x-only secp256k1 pubkey with 0x02 (even-y assumption)
    to produce a valid compressed ECDSA public key.

    This is a convention ONLY and not a reconstruction of the
    original elliptic curve point.
    """

    if len(xonly_pubkey) != 32:
        raise ValueError("Invalid x-only pubkey length")

    return b"\x02" + xonly_pubkey


# -----------------------------
# P2PKH (legacy)
# -----------------------------

def pubkey_to_p2pkh(pubkey: bytes) -> str:
    h160 = hash160(pubkey)

    payload = b"\x00" + h160  # mainnet version byte

    checksum = hashlib.sha256(
        hashlib.sha256(payload).digest()
    ).digest()[:4]

    return base58.b58encode(payload + checksum).decode()


# -----------------------------
# P2WPKH (SegWit v0)
# -----------------------------

def pubkey_to_p2wpkh(pubkey: bytes) -> str:
    h160 = hash160(pubkey)

    data = [0] + convertbits(h160, 8, 5)

    return bech32_encode("bc", data)


# -----------------------------
# Compatibility API
# -----------------------------

def nostr_xonly_to_legacy_bitcoin_addresses(xonly_pubkey: bytes) -> dict:
    """
    Optional compatibility layer.

    Not part of Taproot or core Nostr semantics.

    Provides deterministic legacy Bitcoin address derivation
    from x-only secp256k1 pubkeys.
    """

    compressed_pubkey = xonly_to_compressed_pubkey(xonly_pubkey)

    return {
        "compressed_pubkey_hex": compressed_pubkey.hex(),
        "p2pkh": pubkey_to_p2pkh(compressed_pubkey),
        "p2wpkh": pubkey_to_p2wpkh(compressed_pubkey),
    }

And... probably out of scope for your website if you wouldn't want to be touching nsecs+passphrases and/or nobody would want to risk putting them in your site, but there's also hardening them via salting.