From fa8eeccfef4b2af9d74b53aee68496326a1d9151 Mon Sep 17 00:00:00 2001
From: swrup <swrup@protonmail.com>
Date: Tue, 24 Feb 2026 20:11:52 +0100
Subject: [PATCH] ~

---
 src/fdh_rsa.ml      | 38 ++++++++++++++------------------------
 test/test_crypto.ml |  6 +++---
 2 files changed, 17 insertions(+), 27 deletions(-)

diff --git a/src/fdh_rsa.ml b/src/fdh_rsa.ml
index ec5eb08e..692ecd30 100644
--- a/src/fdh_rsa.ml
+++ b/src/fdh_rsa.ml
@@ -64,29 +64,12 @@ let rsa_blind pub ~bks ~msg =
   let data_r_e = Z.rem (Z.mul data r_e) pub.n in
   Z_extra.to_octets_be data_r_e
 
-(* -- WIP crypto -- *)
-
 (* decrypt <=> sign *)
-let rsa_sign_z priv r =
-  let data = Z_extra.to_octets_be r in
-  Mirage_crypto_pk.Rsa.decrypt ~crt_hardening:true ~key:priv data
-
-(* TODO crypto
-   look into mirage-crypto for this
-   use Eqaf for constant time string compare *)
-let rsa_verify_z pub r sig_ =
-  let data = Z_extra.to_octets_be r in
-  let sig_' = Mirage_crypto_pk.Rsa.encrypt ~key:pub data in
-  match String.equal sig_ sig_' with
-  | false -> Fmt.error "RSA signature verification failed"
-  | true -> Ok ()
-
-let rsa_sign_fdh priv msg =
-  let pub = RsaPrivateKey.pub_of_priv priv in
-  let r = rsa_full_domain_hash pub msg in
-  rsa_sign_z priv r
+let rsa_sign_blinded priv ~bmsg =
+  Mirage_crypto_pk.Rsa.decrypt ~crt_hardening:true ~key:priv bmsg
 
 let rsa_unblind pub ~bks ~sig_ =
+  let data = Z_extra.of_octets_be sig_ in
   let bkey = rsa_blinding_key_derive pub bks in
   let r_inv =
     try Z.invert bkey pub.n
@@ -94,9 +77,16 @@ let rsa_unblind pub ~bks ~sig_ =
       (* => gcd(r,n) <> 1, should be already checked for *)
       assert false
   in
-  let ubsig = Z.rem (Z.mul sig_ r_inv) pub.n in
-  ubsig
+  let data = Z.rem (Z.mul data r_inv) pub.n in
+  Z_extra.to_octets_be data
 
+(* TODO crypto
+   look into mirage-crypto for this
+   at least use Eqaf for constant time string compare *)
 let rsa_verify pub ~msg ~sig_ =
-  let r = rsa_full_domain_hash pub msg in
-  rsa_verify_z pub r sig_
+  let msg_fdh = rsa_full_domain_hash pub msg in
+  let s1 = Z_extra.to_octets_be msg_fdh in
+  let s2 = Mirage_crypto_pk.Rsa.encrypt ~key:pub sig_ in
+  match String.equal s1 s2 with
+  | false -> Fmt.error "RSA signature verification failed"
+  | true -> Ok ()
diff --git a/test/test_crypto.ml b/test/test_crypto.ml
index ec16fa9c..d146a633 100644
--- a/test/test_crypto.ml
+++ b/test/test_crypto.ml
@@ -99,12 +99,12 @@ let () =
     "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 = Fdh_rsa.rsa_blind pub ~bks ~msg |> encode in
-  assert (s = blinded_message);
+  let msg = decode message_hash in
+  let bmsg = Fdh_rsa.rsa_blind pub ~bks ~msg in
+  assert (encode bmsg = blinded_message);
 
   ()