diff --git a/lib/cairo.ex b/lib/cairo.ex
index 0354748..3bd1a53 100644
--- a/lib/cairo.ex
+++ b/lib/cairo.ex
@@ -38,7 +38,7 @@ defmodule Cairo do
     to: Cairo.CairoProver,
     as: :cairo_get_compliance_output
 
-  @spec sign(list(list(byte())), list(list(byte()))) :: list(byte())
+  @spec sign(list(byte()), list(list(byte()))) :: list(byte())
   defdelegate sign(private_key_segments, messages),
     to: Cairo.CairoProver,
     as: :cairo_binding_sig_sign
diff --git a/native/cairo_prover/src/lib.rs b/native/cairo_prover/src/lib.rs
index b983340..ae95bc9 100644
--- a/native/cairo_prover/src/lib.rs
+++ b/native/cairo_prover/src/lib.rs
@@ -152,11 +152,11 @@ fn cairo_get_compliance_output(public_input: Vec<u8>) -> NifResult<Vec<Vec<u8>>>
 // The private_key_segments are random values used in delta commitments.
 // The messages are nullifiers and resource commitments in the transaction.
 #[rustler::nif]
-fn cairo_binding_sig_sign(private_key_segments: Vec<Vec<u8>>, messages: Vec<Vec<u8>>) -> Vec<u8> {
+fn cairo_binding_sig_sign(private_key_segments: Vec<u8>, messages: Vec<Vec<u8>>) -> Vec<u8> {
     // Compute private key
     let private_key = {
         let result = private_key_segments
-            .iter()
+            .chunks(32)
             .fold(BigInt::zero(), |acc, key_segment| {
                 let key = BigInt::from_bytes_be(num_bigint::Sign::Plus, &key_segment);
                 acc.add(key)
diff --git a/test/cairo_binding_signature.exs b/test/cairo_binding_signature.exs
index 512889e..bdff799 100644
--- a/test/cairo_binding_signature.exs
+++ b/test/cairo_binding_signature.exs
@@ -4,12 +4,17 @@ defmodule BindingSignatureTest do
   doctest Cairo.CairoProver
 
   test "cairo_binding_signature_test" do
-    priv_keys = [Cairo.random_felt(), Cairo.random_felt()]
-    pub_keys = priv_keys |> Enum.map(fn x -> Cairo.get_public_key(x) end)
+    priv_key_1 = Cairo.random_felt()
+    priv_key_2 = Cairo.random_felt()
+
+    pub_keys =
+      [priv_key_1, priv_key_2]
+      |> Enum.map(fn x -> Cairo.get_public_key(x) end)
+
     msg = [Cairo.random_felt(), Cairo.random_felt()]
 
     # Sign and verify
-    signature = Cairo.sign(priv_keys, msg)
+    signature = (priv_key_1 ++ priv_key_2) |> Cairo.sign(msg)
     assert true = Cairo.sig_verify(pub_keys, msg, signature)
   end
 end