Digital certificates: What is the difference between encrypting and signing

Question

I am relatively new to PKI, certificates and all related stuff.

As far as I understand in public-key cryptography one encrypt with a public key and decrypt with a pr

Answer 1

Message Encryption makes the whole message unreadable to anyone but the owner of the corresponding private key.

When you sign a message, then it creates something like a checksum of the message content in combination with data from the key, which can be verified against a public key. This does not make a message unreadable to anyone, but can verify that the message really originated from the sender and was not altered since.

Of course this requires you to trust the public key, but that is another story.

To your first question: AFAIK it is theoretically possible to create a public key collision, but highly unlikely.