BTC Adresse Public Key ab wann öffentlich?

Auch bei der BitBox02 werden keine Public Keys übermittelt. Es werden ausschliesslich die verwendeten Bitcoin-Adressen mittels Electrum-Server abgefragt (der von Shift Crypto, oder auch Dein eigener) bis 20 Adressen ungenutzt sind (das „Gap limit“).

Als Randnotiz: über Quantencomputer-Sicherheit muss man sich nicht wirklich Sorgen machen. Es geht sogar soweit, dass mit dem nächsten Bitcoin Protokoll-Update (Taproot) alle Public Keys direkt auf der Blockchain sichtbar sein werden:

Why is the public key directly included in the output? While typical earlier constructions store a hash of a script or a public key in the output, this is rather wasteful when a public key is always involved. To guarantee batch verifiability, the public key must be known to every verifier, and thus only revealing its hash as an output would imply adding an additional 32 bytes to the witness. Furthermore, to maintain 128-bit collision security for outputs, a 256-bit hash would be required anyway, which is comparable in size (and thus in cost for senders) to revealing the public key directly. While the usage of public key hashes is often said to protect against ECDLP breaks or quantum computers, this protection is very weak at best: transactions are not protected while being confirmed, and a very large portion of the currency’s supply is not under such protection regardless. Actual resistance to such systems can be introduced by relying on different cryptographic assumptions, but this proposal focuses on improvements that do not change the security model.

Auszug aus BIP0341: Taproot: SegWit version 1 spending rules

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