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Public key systems feature a key pair made up of a public and a private key. Each person who participates in the system has two keys uniquely assigned to them. In practice the public key will be published in some location whereas the private key will remain solely in the assigned user's possession and will never be used by anyone else. This system offsers advantages, such as nonrepudiation and key distribution benefits, that symmetric cryptography does not.
Both keys can be used to encrypt, but when either key is used only the other key can reverse it. For example, if you were to encrypt a message with my public key I an the only one who could decrypt it since I have the private key that can open it. The reverse is true as well.
The only requirement is that public keys must be associated with their users in a trusted manner. With PKI, anyone can send a confidential message by using public information, though the message can be decrypted only with the private key in the possession of the intended recipient. Furthermore, public key cryptography meets the needs for privacy and authentication.
Both keys can be used to encrypt, but when either key is used only the other key can reverse it. For example, if you were to encrypt a message with my public key I an the only one who could decrypt it since I have the private key that can open it. The reverse is true as well.
The only requirement is that public keys must be associated with their users in a trusted manner. With PKI, anyone can send a confidential message by using public information, though the message can be decrypted only with the private key in the possession of the intended recipient. Furthermore, public key cryptography meets the needs for privacy and authentication.