futur.blue
objective categorical abstract machine language personal data server
Use digestif for SHA256 hmac
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kleidos/rfc6979.ml
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kleidos/rfc6979.ml
···
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(* bits2int for qbits=256 (leftmost 256 bits is whole 32 bytes here) *)
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let bits2int_256 (bs : bytes) : Z.t =
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(* If bs > 32 bytes (not the case here), we'd truncate *)
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(* if bs > 32 bytes (not the case here), we'd truncate *)
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let len = Bytes.length bs in
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let take = if len <= 32 then len else 32 in
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let acc = ref Z.zero in
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let z2 = Z.(z1 mod q) in
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z_to_bytes32 z2
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(* hmac sha256 using only hash function *)
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let hmac_sha256 ~(hash : bytes -> bytes) ~(key : bytes) (data : bytes) : bytes =
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let block_size = 64 in
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let key0 = if Bytes.length key > block_size then hash key else key in
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let key_block =
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if Bytes.length key0 = block_size then key0
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else
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let b = Bytes.make block_size '\x00' in
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Bytes.blit key0 0 b 0 (Bytes.length key0) ;
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b
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in
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let ipad = 0x36 and opad = 0x5c in
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let inner_pad = Bytes.create block_size
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and outer_pad = Bytes.create block_size in
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for i = 0 to block_size - 1 do
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let kc = Char.code (Bytes.get key_block i) in
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Bytes.set inner_pad i (Char.chr (kc lxor ipad)) ;
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Bytes.set outer_pad i (Char.chr (kc lxor opad))
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done ;
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let concat a b =
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let out = Bytes.create (Bytes.length a + Bytes.length b) in
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Bytes.blit a 0 out 0 (Bytes.length a) ;
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Bytes.blit b 0 out (Bytes.length a) (Bytes.length b) ;
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out
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in
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let inner = hash (concat inner_pad data) in
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hash (concat outer_pad inner)
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(* returns 32-byte k for given order q *)
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let rfc6979_k_256_bytes ~(q : Z.t) ~(privkey : bytes) ~(msg : bytes) : bytes =
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if Bytes.length privkey <> 32 then invalid_arg "privkey must be 32 bytes" ;
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let x = bytes32_to_z privkey in
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if x <= Z.zero || x >= q then invalid_arg "privkey scalar out of range" ;
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let module H = Hacl_star.Hacl.SHA2_256 in
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let hash = H.hash in
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let hmac = hmac_sha256 ~hash in
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let hash = Hacl_star.Hacl.SHA2_256.hash in
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let h1 = hash msg in
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(* 32-byte SHA-256 digest *)
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let x_octets = privkey in
···
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0 parts ;
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out
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in
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let hmac k v =
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Digestif.SHA256.(hmac_bytes ~key:(Bytes.to_string k) v |> to_raw_string)
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|> Bytes.of_string
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in
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(* step: K = HMAC_K(V || 0x00 || x || h1); V = HMAC_K(V) *)
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let k = hmac ~key:k (concat [v; Bytes.of_string "\x00"; x_octets; h1_red]) in
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let v = hmac ~key:k v in
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let k = hmac k (concat [v; Bytes.of_string "\x00"; x_octets; h1_red]) in
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let v = hmac k v in
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(* step: K = HMAC_K(V || 0x01 || x || h1); V = HMAC_K(V) *)
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let k = hmac ~key:k (concat [v; Bytes.of_string "\x01"; x_octets; h1_red]) in
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let v = hmac ~key:k v in
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let k = hmac k (concat [v; Bytes.of_string "\x01"; x_octets; h1_red]) in
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let v = hmac k v in
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(* loop *)
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let rec loop k v =
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(* a. V = HMAC_K(V) *)
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let v = hmac ~key:k v in
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let v = hmac k v in
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let t = v in
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let k_candidate = bits2int_256 t in
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if Z.(k_candidate >= one && k_candidate < q) then t
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else
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(* K = HMAC_K(V || 0x00); V = HMAC_K(V) *)
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let k = hmac ~key:k (concat [v; Bytes.of_string "\x00"]) in
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let v = hmac ~key:k v in
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let k = hmac k (concat [v; Bytes.of_string "\x00"]) in
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let v = hmac k v in
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loop k v
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in
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loop k v