&gt; it is possible that one or several intermediaries sign a key and this key can become trusted<p>Yes, but as far as I understand this only occurs if you give them a trust rating (e.g., I marginally trust). If a key K is signed by multiple other keys which you know are valid but where you have no reason to trust the holders (and don&#x27;t claim to trust them), then (as far as I understand) GnuPG will never infer that K is valid (and rightfully so).