Introduction
During an execution of some of the public-key-based key establishment schemes specified in NIST Special Publications 800-56A [1] and 800-56B [2], a key derivation method is used to obtain secret cryptographic keying material. This Recommendation specifies an alternative key derivation method to be used in a key establishment scheme specified in 800-56A and 800-56B.
2. Scope and Purpose
This Recommendation specifies a two-step key derivation procedure, as one of the approved key derivation methods, that employs an extraction-then-expansion technique for deriving keying material from a shared secret generated during a key establishment scheme specified in [1] or [2]. Several application-specific key derivation functions that use approved variants of this extraction-then-expansion procedure are described in NIST Special Publication 800-135 [5].
The key derivation procedure specified in this Recommendation consists of two steps: 1) randomness extraction (to obtain a single key derivation key) and 2) key expansion (to derive keying material with a desired length from the key derivation key). Since NIST Special Publication 800-108 [4] specifies several families of key derivation functions that are approved for deriving additional keying material from a given cryptographic key derivation key, those functions are employed in the second (key expansion) step of the procedure.
