diff --git a/src/crypto.ml b/src/crypto.ml
index 92d1dadb..4a9a378d 100644
--- a/src/crypto.ml
+++ b/src/crypto.ml
@@ -282,3 +282,22 @@ 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
diff --git a/src/fdh.ml b/src/fdh.ml
index 31f4c893..f9fbd3ca 100644
--- a/src/fdh.ml
+++ b/src/fdh.ml
@@ -8,11 +8,11 @@ module Kdf = struct
     okm
 end
 
-(* WIP
 let kdf_mod_n ~n ~xts ~ikm ~ctx =
   let nbits = Z.numbits n in
+  let len = ((nbits - 1) / 8) + 1 in
+  assert (8 * len = nbits);
   let rec go ctr =
-    let len = ((nbits - 1) / 8) + 1 in
     let ctr_be =
       let b = Bytes.create 2 in
       Bytes.set_uint16_be b 0 ctr;
@@ -20,36 +20,16 @@ let kdf_mod_n ~n ~xts ~ikm ~ctx =
     in
     let ctx = String.cat ctx ctr_be in
     let okm = Kdf.kdf ~xts ~ikm ~ctx ~len in
-    let r = Z.of_bits okm in
-    (* we do that because n is odd?
-       TODO
-       gcry_mpi_clear_highbit .. *)
+    assert (String.length okm = len);
+    let r = Mirage_crypto_pk.Z_extra.of_octets_be okm in
     if Z.gt r n then go (succ ctr) else r
   in
   go 0
 
-let rsa_full_domain_hash pub msg =
-  let xts = RsaPublicKey.to_octets pub in
-  let ctx = "RSA-FDA FTpsW!" in
-  let r = kdf_mod_n ~n:pub.n ~xts ~ikm:msg ~ctx in
-  r
-
+(*
 let rsa_sign_fdh priv msg =
   let pub = Mirage_crypto_pk.Rsa.pub_of_priv priv in
   let v = rsa_full_domain_hash pub msg in
   let v = Z.to_bits v in
   Mirage_crypto_pk.Rsa.PKCS1.sig_encode ~crt_hardening:true ~key:priv v
-
-let rsa_blinding_key_derive (pub : RsaPublicKey.t) bks =
-  let xts = "Blinding KDF extractor HMAC key" in
-  let ctx = "Blinding KDF" in
-  let r = 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
-  Z.to_bits data_r_e
   *)
diff --git a/test/crypto.ml b/test/crypto.ml
index 0d09e8a8..be0f85aa 100644
--- a/test/crypto.ml
+++ b/test/crypto.ml
@@ -94,3 +94,46 @@ let () =
   assert (okm = out);
 
   ()
+
+let () =
+  let message_hash =
+    "XKQMJ4CNTXBFE1V2WR6JS063J7PZQE4XMB5JH3RS5X0THQ1JQSQ69Y7KDBC9TYRJEZH48MEPY2SF4QHQ4VHXC0YQX5935MQEGP0AX6R"
+  in
+  let rsa_private_key =
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
+  in
+  let rsa_public_key =
+    "040000YRN1NVJ68RS6RJF52PGRCQG19ZKWQPSTJX2G7ZDCKSZFE2VW3HHA81YF5C639JHJF5TX8YTEE2FW2WQCG1PTKNBSPPJEJGA032CN3E8QZ27VWY0K6JFT8ZSYWRH2SKDMXW56A4QKY46JJBWJ6T0ZRVBW6S1HTHXVE2RW8MXRW5T801077MDY13N5F8Z1JZVKBJ06TK3S0YPEDBXK0VEHRHEQJ5X5XYKR4KQTFAZNBMKXY8836VCHBXTK4YNX6AJ1CK29SMJH3Z3QRM16A2TNQGFR0HSMV446BF7FMT2E379ZAT5ST4G3BM2NWZYW545S2SW5MG5S6M88XZZ7SKFD48YVXNZ205GGSEYJPVBMR76WG4ZG30WBCPC1N54XE12RMAG81D8C09WG22PKGGDHYXX68N04002"
+  in
+  let blinding_key_secret =
+    "3SWF49XZPHQMENTSBZQR7Z0B8ZSZ2JRARE79Q4VXZMQ7W6QABXMG"
+  in
+  let blinded_message =
+    "3KHKZJZ30ABB4E56MA2V0EQWGCWH0QQG9P2ZHYHR186C5HZXJMM4N9WXAQTKS94QSV9Y17GGNXN5MB1PZZFG7Q0FY88QPKKRG4MYCPSMTZK5W59R0MJVNJ4P4AQM96TDG5W7RV8GSNR1QQZ1GNHW3CX6D6ZRTMXB2NKB5SSYTDJS79F5ZFBRZ4HVED9JBBPWSR79KVV5QQ4APBGHBCKGMF9NJJS53A1BVYHDEVYAGFYF2SNEP827ZP50FKJ5GKGV8NQ15ESEZ69AT7GJG0T3TZVENY2YN9CVR98W3BKEZ53J7VTANARG8SJS8AMJQ7S23P5HRJ7XE9KTNRNXKH49MXV9JHHYE5535N7AGWEKR47SBCGNF44Z7XJ9RV5BQV12ZRJKN4HBZQHDNCMH3QKX9Z6G64"
+  in
+  let open Crypto in
+  let msg = message_hash |> decode in
+  let pub =
+    rsa_public_key |> decode |> RsaPublicKey.of_octets |> Result.get_ok
+  in
+  let bks = blinding_key_secret |> decode in
+  let s = rsa_blind pub ~bks ~msg |> encode in
+  assert (s = blinded_message);
+
+  (* wip parse gcrypt sexp *)
+  let priv = rsa_private_key |> decode in
+  let l = String.split_on_char '\n' priv in
+  let l = List.filter (fun s -> String.starts_with ~prefix:"   (1:" s) l in
+  let l = match l with _ :: _ :: l -> l | _ -> assert false in
+  let l =
+    List.map
+      (fun s ->
+        let s = String.trim s in
+        let k = String.get s 3 in
+        let v = String.sub s 4 (String.length s - 4 - 1) in
+        (k, v))
+      l
+  in
+  List.iter (fun (k, v) -> Fmt.pr "%c : %S@." k v) l;
+
+  ()