In summary, symmetric-key and public-key are the two basic types of encryption used in data cryptography. The symmetric-key encryption is based on one secret key and the public-key encryption based on a pair of keys. For a sender and recipient to communicate securely using symmetric-key encryption, a key must be agreed upon and it must be kept secret between only themselves. Anyone that has the key can read, modify, or forge information encrypted or authenticated with that key. When using public-key encryption, the encryption key is available to the world while the private key is kept secret. The public key can be used to encrypt information that only the recipient can read. This allows people who have no preexisting security arrangement with the recipient to exchange secure messages. In public-key encryption the need for the sender and receiver to share secret keys is eliminated. No private key is ever transmitted or shared.