Part 1: General - Computer Security Resource Center - National ...

March, 2007
they have been encrypted for transport, the cryptoperiod of the public key transport key
may be shorter than that of the associated private key.
b. Cryptoperiod: Based on cryptoperiod assumptions for associated private keys, a
maximum recommended cryptoperiod might be about 1 - 2 years.
12. Symmetric key agreement key:
a. Type Considerations: A symmetric key agreement key may be used multiple times.
Generally, the cryptoperiod equals the originator usage period which equals the recipient
usage period. The cryptoperiod of these keys depend on 1) environmental security
factors, 2) the nature (e.g., types and formats) and volume of keys they are used to
establish, and 3) the details of the key agreement algorithms and protocols employed.
Note that symmetric key agreement keys may be used to establish symmetric keys (e.g.,
symmetric data encryption keys) or other keying material (e.g., IVs).
b. Cryptoperiod: Given an assumption that the cryptography that employs symmetric key
agreement keys 1) employs an algorithm and key scheme compliant with NIST standards,
2) the cryptographic device meets [FIPS140-2] requirements, and 3) the risk levels are
established in conformance to [FIPS199], an appropriate cryptoperiod for the key would
be 1-2 years.
13. Private static key agreement key:
a. Type Considerations: A private static key agreement key may be used multiple times.
As in the case of symmetric key agreement keys, the cryptoperiod of these keys depend
on 1) environmental security factors, 2) the nature (e.g., types and formats) and volume
of keys they are used to establish, and 3) the details of the key agreement algorithms and
protocols employed. Note that private static key agreement keys may be used to establish
symmetric keys (e.g., key wrapping keys) or other secret keying material.
b. Cryptoperiod: Given an assumption that the cryptography that employs private static
key agreement keys 1) employs an algorithm and key scheme compliant with NIST
standards, 2) the cryptographic device meets [FIPS140-2] requirements, and 3) the risk
levels are established in conformance to [FIPS199], an appropriate cryptoperiod for the
key would be 1-2 years. In certain applications (e.g., email), whereby received messages
are stored and decrypted at a later time, the cryptoperiod of the private static key
agreement key may exceed the cryptoperiod of the public static key agreement key.
14. Public static key agreement key:
a. Type Considerations: The cryptoperiod for a public static key agreement key is the
same as the cryptoperiod of the associated private static key agreement key. See the
discussion for the private static key agreement key. However, the length of the public
static key agreement key cryptoperiod is of far less concern, from a security point of
view, than is that of the associated private key.
b. Cryptoperiod: The cryptoperiod of the public static key agreement key may be 1-2
years.
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