From 5e7de2cdb26216c54372f91ccb487b8410c55524 Mon Sep 17 00:00:00 2001
From: swrup <swrup@protonmail.com>
Date: Fri, 13 Feb 2026 09:34:03 +0100
Subject: [PATCH] add kdf; wip FDH-RSA

---
 dune-project   |  1 +
 mte.opam       |  1 +
 src/dune       |  1 +
 src/fdh.ml     |  9 +++++++++
 src/rsa.ml     |  0
 test/crypto.ml | 21 +++++++++++++++++++++
 6 files changed, 33 insertions(+)
 create mode 100644 src/fdh.ml
 create mode 100644 src/rsa.ml

diff --git a/dune-project b/dune-project
index 1aadd32c..d4fc79ff 100644
--- a/dune-project
+++ b/dune-project
@@ -35,6 +35,7 @@
    bin
    angstrom
    mirage-crypto
+   kdf
    digestif
    duration
    jsont
diff --git a/mte.opam b/mte.opam
index 53820528..3d706521 100644
--- a/mte.opam
+++ b/mte.opam
@@ -22,6 +22,7 @@ depends: [
   "bin"
   "angstrom"
   "mirage-crypto"
+  "kdf"
   "digestif"
   "duration"
   "jsont"
diff --git a/src/dune b/src/dune
index a9322eed..0a6fa0ea 100644
--- a/src/dune
+++ b/src/dune
@@ -17,6 +17,7 @@
   caqti-driver-pgx
   bin
   mirage-crypto
+  kdf.hkdf
   digestif
   duration
   vif
diff --git a/src/fdh.ml b/src/fdh.ml
new file mode 100644
index 00000000..5d4b2157
--- /dev/null
+++ b/src/fdh.ml
@@ -0,0 +1,9 @@
+module Kdf = struct
+  module XTR = Hkdf.Make (Digestif.SHA512)
+  module PRF = Hkdf.Make (Digestif.SHA256)
+
+  let kdf ~xts ~ikm ~ctx ~len =
+    let prk = XTR.extract ~salt:xts ikm in
+    let okm = PRF.expand ~prk ~info:ctx len in
+    okm
+end
diff --git a/src/rsa.ml b/src/rsa.ml
new file mode 100644
index 00000000..e69de29b
diff --git a/test/crypto.ml b/test/crypto.ml
index 9b7578e7..0d09e8a8 100644
--- a/test/crypto.ml
+++ b/test/crypto.ml
@@ -73,3 +73,24 @@ let () =
   in
 
   ()
+
+let () =
+  (* kdf *)
+  let salt = "94KPT83PCNS7J83KC5P78Y8" in
+  let ikm = "94KPT83MD1JJ0WV5CDS6AX10D5Q70XBM41NPAY90DNGQ8SBJD5GPR" in
+  let ctx =
+    "94KPT83141HPYVKMCNW78833D1TPWTSC41GPRWVF41NPWVVQDRG62WS04XMPWSKF4WG6JVH0EHM6A82J8S1G"
+  in
+  let out_len = 64 in
+  let out =
+    "GTMR4QT05Z9WF5HKVG0WK9RPXGHSMHJNW377G9GJXCA8B0FEKPF4D27RJMSJZYWSQNTBJ5EYVV7ZW18B48Z0JVJJ80RHB706Y96Q358"
+  in
+
+  let xts = salt |> decode in
+  let ikm = ikm |> decode in
+  let ctx = ctx |> decode in
+  let okm = Fdh.Kdf.kdf ~xts ~ikm ~ctx ~len:out_len in
+  let okm = okm |> encode in
+  assert (okm = out);
+
+  ()