static Bytes initPublicKeyBytes(final Map<String, Bytes> data) {
    var keyBytes = data.get("secp256k1");
    if (keyBytes == null) {
      throw new IllegalArgumentException("Missing secp256k1 entry in ENR");
    }
    // convert 33 bytes compressed public key to uncompressed using Bouncy Castle
    var curve = SignatureAlgorithmFactory.getInstance().getCurve();
    var ecPoint = curve.getCurve().decodePoint(keyBytes.toArrayUnsafe());
    // uncompressed public key is 65 bytes, first byte is 0x04.
    var encodedPubKey = ecPoint.getEncoded(false);
    return Bytes.of(Arrays.copyOfRange(encodedPubKey, 1, encodedPubKey.length));
  }
Returns the public key of the ENR

@return the public key of the ENR
ethereum/p2p/src/main/java/org/hyperledger/besu/ethereum/p2p/discovery/dns/EthereumNodeRecord.java