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(** {{:https://tools.ietf.org/html/rfc5869}RFC 5869} specifies a HMAC-based
Extract-and-Expand Key Derivation Function (HKDF), which is abstracted over
a specific hash function. *)
module type S = sig
(** [extract salt ikm] is [prk], the pseudorandom key of hash length octets.
The [salt] is an optional non-secret random value, [ikm] the input key
material. *)
val extract : ?salt:string -> string -> string
(** [extract prk info length] is [okm], the output keying material. Given the
pseudorandom key of hash length (usually output of [!extract] step), and an
optional context and application specific information [info], the [okm] is
generated. *)
val expand : prk:string -> ?info:string -> int -> string
end
(** Given a Hash function, get the HKDF *)
module Make (H : Digestif.S) : S
(** convenience [extract hash salt ikm] where the [hash] has to be provided explicitly *)
val extract : hash:Digestif.hash' -> ?salt:string -> string -> string
(** convenience [expand hash prk info len] where the [hash] has to be provided explicitly *)
val expand : hash:Digestif.hash' -> prk:string -> ?info:string -> int -> string
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