Key Storage and Destruction

Key Storage and Destruction

All keys need to be protected against modification, and secret and private keys need to be protected against unauthorized disclosure.

Methods for protecting stored keys include trusted, tamper proof hardware security modules, passphrase protected smart cards, key wrapping the session keys using long-term storage KEKs, splitting cipher keys and storing in physically separate storage locations, and protecting keys using strong passwords and passphrases, key expiry, and the like.

Keys may be protected by the integrity of the storage mechanism itself. For example, the mechanism can be designed so that once the key is installed, it cannot be observed from outside the encryption mechanism itself. Indeed, some key storage devices are designed to selfdestruct when subjected to forces that might disclose the key. Alternatively, the key can be stored in an encrypted form so that knowledge of the stored form does not disclose information about the behavior of the device under the key.

To guard against a long-term cryptanalytic attack, every key must have an expiration date after which it is no longer valid.

The key length must be long enough to make the chances extremely small of cryptanalysis before key expiration. The validity period for a key pair may also depend on the circumstances in which the key needs to be used.

Keys must be disposed of and destroyed in such a way as to resist disclosure. At the end of a key life cycle, it must be properly destroyed as to avoid the reconstruction of that key, and the purpose must be to make it impossibleto regenerate or reconstruct the key.