A cryptoperiod (sometimes called a key lifetime or a validity period) is a specific time span during which a cryptographic key setting remains in effect. A key uses an algorithm to create ciphertext from plaintext (ordinary unencrypted text) and, for the receiver of the encrypted text, to decipher it. Once the crptoperiod ends, the key is no longer available for either encryption or decryption.
The cryptoperiod is decided by weighing factors such as the sensitivity of the encrypted data, the risk of key compromise, and the cost of rekeying (encrypting the same material with a new key). Throughout the cryptoperiod, a key can be used to verify or decrypt data. The effective use of cryptoperiods is an important part of key management.
A cryptoperiod is usually expressed as a span of calendar or clock time, but may also be expressed as a maximum volume of data to be encrypted by an algorithm for a particular key. The span of a cryptoperiod can be a number of decades where keys are needed for encrypted text that is archived.