wip FDH-RSA

src/crypto.ml

@@ -259,15 +259,10 @@ end
 module RsaSignature : sig
   type t
 
-  val sign : key:Mirage_crypto_pk.Rsa.priv -> string -> t
   val jsont : t Jsont.t
 end = struct
   type t = string
 
-  (* TODO rsa sign *)
-  let sign ~key s =
-    Mirage_crypto_pk.Rsa.decrypt ~crt_hardening:true ~mask:`Yes ~key s
-
   let jsont =
     let of_b32 s = B32.decode s in
     let to_b32 t = B32.encode t in
@@ -282,3 +277,22 @@ type rsa_priv = RsaPrivateKey.t
 type rsa_pub = RsaPublicKey.t
 type rsa_sig = RsaSignature.t
 type denomination_hash = Hash.DenominationHash.t
+
+let rsa_full_domain_hash pub msg =
+  let xts = RsaPublicKey.to_octets pub in
+  let ctx = "RSA-FDA FTpsW!" in
+  let r = Fdh.kdf_mod_n ~n:pub.n ~xts ~ikm:msg ~ctx in
+  r
+
+let rsa_blinding_key_derive (pub : RsaPublicKey.t) bks =
+  let xts = "Blinding KDF extractor HMAC key" in
+  let ctx = "Blinding KDF" in
+  let r = Fdh.kdf_mod_n ~n:pub.n ~xts ~ikm:bks ~ctx in
+  r
+
+let rsa_blind pub ~bks ~msg =
+  let data = rsa_full_domain_hash pub msg in
+  let bkey = rsa_blinding_key_derive pub bks in
+  let r_e = Z.powm bkey pub.e pub.n in
+  let data_r_e = Z.rem (Z.mul data r_e) pub.n in
+  Mirage_crypto_pk.Z_extra.to_octets_be data_r_e