Key derivation functions | Cryptography

HKDF

HKDF is a simple key derivation function (KDF) based on HMAC message authentication code. It was initially proposed by its authors as a building block in various protocols and applications, as well as to discourage the proliferation of multiple KDF mechanisms. The main approach HKDF follows is the "extract-then-expand" paradigm, where the KDF logically consists of two modules: the first stage takes the input keying material and "extracts" from it a fixed-length pseudorandom key, and then the second stage "expands" this key into several additional pseudorandom keys (the output of the KDF). It can be used, for example, to convert shared secrets exchanged via Diffie–Hellman into key material suitable for use in encryption, integrity checking or authentication. It is formally described in RFC 5869. One of its authors also described the algorithm in a companion paper in 2010. NIST SP800-56Cr2 specifies a parameterizable extract-then-expand scheme, noting that RFC5869 HKDF is a version of it and citing its paper for the rationale for the recommendations' extract-and-expand mechanisms. There are implementations of HKDF for C#, Go, Java, JavaScript, Perl, PHP, Python, Ruby, and other programming languages. (Wikipedia).

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Related pages

Deterministic encryption | Key derivation function | HMAC | Pseudorandom number generator | Message authentication code | Salt (cryptography) | Entropy (information theory)