diff --git a/Cargo.toml b/Cargo.toml
index 21200ff..9bb8088 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -6,6 +6,7 @@ description = "EIP-7732 — Enshrined Proposer-Builder Separation (ePBS) referen
 license = "Apache-2.0"
 repository = "https://github.com/EIPs-CodeLab/EIP-7732"
 keywords   = ["ethereum", "eip-7732", "epbs", "consensus", "builder"]
+# PR #1: BLS signing roots and verification wiring
 
 [[bin]]
 name = "epbs-cli"
diff --git a/src/beacon_chain/process_payload_attestation.rs b/src/beacon_chain/process_payload_attestation.rs
index e3ef2b8..4044397 100644
--- a/src/beacon_chain/process_payload_attestation.rs
+++ b/src/beacon_chain/process_payload_attestation.rs
@@ -104,7 +104,7 @@ fn verify_aggregate_ptc_signature(
     pubkeys: &[BLSPubkey],
 ) -> Result<(), PayloadAttestationError> {
     let domain = ssz::compute_domain_simple(DOMAIN_PTC_ATTESTER);
-    let signing_root = ssz::signing_root(data, domain);
+    let signing_root = ssz::signing_root_json(data, domain);
     crypto::bls_verify_aggregate(pubkeys, &signing_root, signature)
         .map_err(|_| PayloadAttestationError::InvalidSignature)
 }
diff --git a/src/beacon_chain/process_payload_bid.rs b/src/beacon_chain/process_payload_bid.rs
index 324295a..fef6e01 100644
--- a/src/beacon_chain/process_payload_bid.rs
+++ b/src/beacon_chain/process_payload_bid.rs
@@ -117,7 +117,7 @@ fn verify_builder_signature<S: BeaconStateMut>(
         .ok_or(PayloadBidError::MissingPubkey(message.builder_index))?;
 
     let domain = ssz::compute_domain_simple(DOMAIN_BEACON_BUILDER);
-    let signing_root = ssz::signing_root(message, domain);
+    let signing_root = ssz::signing_root_json(message, domain);
     crypto::bls_verify(&pk, &signing_root, &signed_bid.signature)
         .map_err(|_| PayloadBidError::InvalidSignature)
 }
diff --git a/src/builder/bid.rs b/src/builder/bid.rs
index cd0ceff..61d37a4 100644
--- a/src/builder/bid.rs
+++ b/src/builder/bid.rs
@@ -91,7 +91,7 @@ pub fn construct_bid(
     };
 
     let domain = ssz::compute_domain_simple(DOMAIN_BEACON_BUILDER);
-    let signing_root = ssz::signing_root(&message, domain);
+    let signing_root = ssz::signing_root_json(&message, domain);
 
     let signature = sign_fn(&signing_root).map_err(BidError::SigningFailed)?;
 
diff --git a/src/builder/envelope.rs b/src/builder/envelope.rs
index c6264fd..047d521 100644
--- a/src/builder/envelope.rs
+++ b/src/builder/envelope.rs
@@ -84,7 +84,7 @@ pub fn construct_envelope(
     };
 
     let domain = ssz::compute_domain_simple(DOMAIN_BEACON_BUILDER);
-    let signing_root = ssz::signing_root(&message, domain);
+    let signing_root = ssz::signing_root_json(&message, domain);
     let signature = sign_fn(&signing_root).map_err(EnvelopeError::SigningFailed)?;
 
     Ok(SignedExecutionPayloadEnvelope { message, signature })
diff --git a/src/utils/ssz.rs b/src/utils/ssz.rs
index b557c8b..ef65306 100644
--- a/src/utils/ssz.rs
+++ b/src/utils/ssz.rs
@@ -10,12 +10,19 @@ pub fn compute_domain_simple(domain_type: [u8; 4]) -> [u8; 32] {
     domain
 }
 
-/// Compute a signing root by hashing serialized message bytes plus domain.
-/// This stays deterministic and domain-separated even before full SSZ support lands.
-pub fn signing_root<T: Serialize>(message: &T, domain: [u8; 32]) -> [u8; 32] {
-    let encoded = serde_json::to_vec(message).expect("serialize message for signing");
+/// Minimal hash_tree_root stand-in: SHA256 over JSON serialization of the message.
+/// This keeps signing deterministic and domain-separated until full SSZ is wired.
+pub fn hash_tree_root_json<T: Serialize>(value: &T) -> [u8; 32] {
+    let encoded = serde_json::to_vec(value).expect("serialize message");
     let mut hasher = Sha256::new();
     hasher.update(encoded);
+    hasher.finalize().into()
+}
+
+/// signing_root = hash_tree_root(message) mixed with domain.
+pub fn signing_root_json<T: Serialize>(message: &T, domain: [u8; 32]) -> [u8; 32] {
+    let mut hasher = Sha256::new();
+    hasher.update(hash_tree_root_json(message));
     hasher.update(domain);
     hasher.finalize().into()
 }
diff --git a/tests/unit/beacon_chain_test.rs b/tests/unit/beacon_chain_test.rs
index 8049e99..0409063 100644
--- a/tests/unit/beacon_chain_test.rs
+++ b/tests/unit/beacon_chain_test.rs
@@ -99,7 +99,7 @@ fn make_valid_bid(slot: Slot) -> SignedExecutionPayloadBid {
         blob_kzg_commitments: vec![],
     };
     let domain = ssz::compute_domain_simple(DOMAIN_BEACON_BUILDER);
-    let signing_root = ssz::signing_root(&message, domain);
+    let signing_root = ssz::signing_root_json(&message, domain);
     SignedExecutionPayloadBid {
         message,
         signature: crypto::bls_sign(&test_secret_key(), &signing_root),
@@ -214,7 +214,7 @@ fn valid_ptc_attestation_accepted() {
         blob_data_available: true,
     };
     let domain = ssz::compute_domain_simple(DOMAIN_PTC_ATTESTER);
-    let signing_root = ssz::signing_root(&data, domain);
+    let signing_root = ssz::signing_root_json(&data, domain);
     let signature = aggregate_signature(&aggregation_bits, &signing_root);
     let att = PayloadAttestation {
         aggregation_bits,