Cryptographic key types
A cryptographic key is a string of data that is used to lock or unlock cryptographic functions, including authentication, authorization and encryption. Cryptographic keys are grouped into cryptographic key types according to the functions they perform. Description. Consider a keyring that contains a variety of keys. These keys might be various shapes and sizes, but one thing is certain, each will generally serve a separate purpose. One key might be used to start an automobile, while another might be used to open a safety deposit box. The automobile key will not work to open the safety deposit  box and vice versa. This analogy provides some insight on how cryptographic key types work. These keys are categorized in respect to how they are used and what properties they possess. A cryptographic key is categorized according to how it will be used and what properties it has. For example, a key might have one of the following properties: Symmetric, Public or Private. Keys may also be grouped into pairs that have one private and one public key, which is referred to as an Asymmetric key pair. Asymmetric versus symmetric keys. Asymmetric keys differ from symmetric keys in that the  algorithms use separate keys for encryption and decryption while a symmetric key’s algorithm uses a single key for both processes. Because multiple keys are used with an asymmetric algorithm, the process takes longer to produce than a symmetric key algorithm would. However, the benefits lay in the fact that an asymmetric algorithm is much more secure than a symmetric key algorithm is. With a symmetric key, the key needs to be transmitted to the receiver where there is always the possibility that the key could be intercepted or tampered with. With an asymmetric key, the message and/or accompanying data  can be sent or received by using a public key; however, the receiver or sender would use his or her personal private key to access the message and/or accompanying data. Thus, asymmetric keys are suited for use for transmitting confidential messages and data and when authentication is required for assurance that the message has not been tampered with. Only the receiver, who is in possession of the private key’s corresponding to the public key(encryption only key), has the ability to decode the message. A public key can be sent back and forth between recipients, but a private key remains  fixed to one location and is not sent back and forth, which keeps it safe from being intercepted during transmission. Long term versus single use. Cryptographic keys may also have keys that designate they can be used for long-term (static, archived) use or used for a single session (ephemeral). The latter generally applies to the use of an Ephemeral Key Agreement Key. Most other key types are designed to last for long crypto-periods from about one to two years. When a shorter crypto-period is designed different key types may be used, such as Data Encryption keys, Symmetric  Authentication keys, Private Key-Transport keys, Key-Wrapping keys, Authorization keys or RNG keys. Key types. This page shows the classification of key types from the point of view of key management. In a key management system, each key should be labeled with one such type and that key should never be used for a different purpose. According to NIST SP 800-57 (Revision 4) the following types of keys exist: