[Cfrg] RE: KDF algorithm and properties

["Allen Pulsifer" <pulsifer3 at comcast.net>]

> It is an improvement on the PRF used in SSH 
> because the secret is protected by HMAC, which is more secure 
> than an unpadded hash.

Just to follow up on that last sentence, if you are going to keep the secret
around and use it later to derive more keys, then you want to protect its
secrecy.  For this reason, the secret should be used as the key in an HMAC
rather than placing it into an unpadded hash, since the HMAC has been proven
to protect the secrecy of its key.

Allen


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