# About Public Key Cryptography

Public key cryptographic algorithms create a pair of keys per individual. One is a private key, and the other is a public key.
A private key is known only to its owner and kept by the owner on his/her own responsibility. A public key is publicly known.
When used for security, the sender obtains the receiver's certificate, and encryption using the public key is performed on the sender side. The party who received the encrypted data can decrypt it with his/her own private key. Thus, only the authentic person can open it.
When used for a signature, a hash value of the document is calculated, then the result is processed using the sender's private key, and it is added to the document. The other party who received the signature-bearing document takes the public key out of the sender's certificate, and decrypts the signature data that was added to the document. If the hash value of the document itself agrees with the value obtained by decryption, verification of the signature is performed.