How does asymmetric encryption support nonrepudiation?

By using a sender's private key, digital signatures provide non-repudiation as they enable the sender to demonstrate that they indeed sent a message. As long as the sender's private key has not been compromised, signing a message with their private key and allowing the recipient to verify the signature using their public key ensures that the sender is the one who sent the message. Longer keys do not necessarily establish the identity of the sender, hashes are irreversible, and the public key in use belongs to the sender, not the recipient.