Asymmetric encryption
Asymmetric encryption uses a public key to encrypt and a mathematically related private key to decrypt.
Definition
Asymmetric encryption uses a key pair. The public key may be distributed and encrypts data for its owner; the private key is kept secret and decrypts it. Knowing the public key should not make deriving the private key computationally feasible.
Public keys and hybrid encryption
Public-key operations are slower and handle limited message sizes, so systems usually encrypt a random symmetric session key and use symmetric authenticated encryption for the actual data. Certificates or another trusted mechanism bind a public key to the intended owner.
Encryption is not signing
Digital signatures also use public and private keys, but serve authenticity rather than confidentiality. Calling a signature “encryption with the private key” is misleading. Secure schemes define separate algorithms, padding, and key uses, and private keys must never be exposed.
Yes, but only the holder of the matching private key should be able to decrypt. The sender must first verify that the public key belongs to the intended recipient.
It is slower and often accepts only short inputs. Hybrid encryption combines public-key key establishment with fast symmetric data encryption.
Normally no. Without a backup or recovery design, ciphertext for that key may become permanently inaccessible.