A cryptography that uses a "public key" and "private key" pair is referred to as a public-key cryptography.
Public key cryptography is used for the encryption of data communications via the Internet (such as SSL and TSL) and for electronic signatures (digital signatures).
The sender encrypts the document information using the recipient's "public key" and the recipient uses his/her own "private key" to restore the encrypted electronic document back to the original document (this is referred to as "decryption").
In the case of electronic signatures (digital signatures), the signer signs using his/her own "private key" and the verifier of the signature verifies it using the signer's "public key."
→ See common key cryptography