What is the difference between KDF based on NIST SP800-108 vs. the older one in ANSI X9.63? When should one be selected over the other? Thanks.

  • 1
    $\begingroup$ ANSI X9.63 uses SHA-1, whereas SP800-108 uses PRF based KDF. $\endgroup$
    – kelalaka
    Commented Nov 26, 2018 at 19:12

1 Answer 1


The ANSI X9.63 uses SHA-1 for Key Derivation Function:

Ingredients: The key derivation function employs the hash function SHA-1 specified in Section 5.6.2

NIST SP800-108 uses PRFs:

This Section defines several families of key derivation functions that use PRFs.

First look at their dates;

  • 1998 : ANSI X9.63
  • 2009 : NIST SP800-108

And, SHA-1 is no longer recomended. So you should prefer NIST SP800-108

There are two other reasons for not to use SHA-1:

Note: Depending on your case, there is also password-based key derivations; as PBKDF2


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