Could you please explain what do you mean with "more than 1 digital signature can be used to calc the priv key"?
If I sign some messages/addresses with the same wallet (private key) and share the signed message e.g. on the forum (because of proving ownership or for anything else), was it possible in the past to decrypt the private key somehow?
If a wallet provides new public key for every transaction (sendig) does it solve this kind of problem?
This is what I meant with "k-collisions" in my previous post.
To sign a transaction or message, besides the message M and private key Pr, you also need a 256 bit parameter K, usually chosen at random.
If you sign two different messages M with the same key Pr and the same parameter K, a hacker can recover your private key.
Some bitcoin wallets were designed by incompetent amateurs who used a poor randomness source for K, and hackers quickly stole the coins.
If you have a reputable wallet, you don't have to worry about it.