42 lines
1.2 KiB
OCaml
42 lines
1.2 KiB
OCaml
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module type S = sig
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val extract : ?salt:string -> string -> string
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val expand : prk:string -> ?info:string -> int -> string
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end
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module Make (H : Digestif.S) : S = struct
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let extract ?salt ikm =
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let key = match salt with
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| None -> String.make H.digest_size '\x00'
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| Some x -> x
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in
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H.(to_raw_string (hmac_string ~key ikm))
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let expand ~prk ?info len =
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let info = match info with
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| None -> ""
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| Some x -> x
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in
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let t n last =
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let nc = String.make 1 (Char.unsafe_chr n) in
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H.(to_raw_string (hmac_string ~key:prk (String.concat "" [last ; info ; nc])))
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in
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let n = succ (len / H.digest_size) in
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let rec compute acc count = match count, acc with
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| c, xs when c > n -> String.concat "" (List.rev xs)
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| c, x::_ -> compute (t c x :: acc) (succ c)
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| _, [] -> invalid_arg "can not happen"
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in
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let buf = compute [""] 1 in
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String.sub buf 0 len
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end
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let extract ~hash ?salt ikm =
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let module H = (val (Digestif.module_of_hash' hash)) in
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let module HKDF = Make (H) in
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HKDF.extract ?salt ikm
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let expand ~hash ~prk ?info len =
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let module H = (val (Digestif.module_of_hash' hash)) in
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let module HKDF = Make (H) in
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HKDF.expand ~prk ?info len
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