Signature Aggregation and Verification

This section explains how to aggregate signed balance responses from multiple nodes and verify that a quorum of replicas attested to the same value using BLS signature aggregation.

All examples here are located in:

📁 examples/verification

Overview

  • Each replica signs a balance query using its private BLS key

  • These signatures are returned via /balance APIs

  • A client (e.g. an exchange) can query multiple nodes

  • If enough nodes return the same value and valid signatures, they are aggregated

  • The aggregated signature acts as a cryptographic proof of correctness

Nodes and Configuration

Nodes are listed in a shared config file:

📄 nodes.json

Each node entry includes:

  • A url for the /balance endpoint

  • A pubkey string representing its BLS public key

Example:

{
  "node1": {
    "url": "http://localhost:5001/balance",
    "pubkey": "aabbcc..."
  },
  "node2": {
    "...": "..."
  }
}

Aggregating Signatures

📄 signature_aggregator.py

This script:

  • Sends balance queries to all nodes

  • Verifies each response’s signature

  • Filters out any invalid or inconsistent responses

  • Aggregates the valid BLS signatures (using PopSchemeMPL.aggregate)

  • Ensures that at least 2/3 of nodes agreed on the same value

Run the script:

python examples/verification/signature_aggregator.py

The result includes:

  • The original signed message

  • The aggregated BLS signature

  • List of nodes that failed to respond or disagreed

Verifying Aggregated Signatures

📄 verify_aggregated_signature.py

This implementation uses the EigenLayer-style BLS verification model, where the verifier starts with a precomputed aggregate public key representing all expected nodes.

When a subset of nodes fail to sign (or return invalid responses), their public keys are effectively subtracted from the aggregated key — not by using subtraction directly (which blspy doesn’t support), but by adding the negation of each missing key:

node_pubkey = G1Element.from_bytes(bytes.fromhex(pubkey)).negate()
aggregated_pubkey += node_pubkey  # Equivalent to subtraction

This adjusted public key reflects only the nodes that signed.

The final verification step looks like:

PopSchemeMPL.verify(adjusted_pubkey, message, aggregated_signature)

This verifies that a quorum of nodes cryptographically agreed on the result.

Benefits of This Approach

  • ✅ Efficient: avoids re-aggregating signer keys on each query

  • ✅ Optimized for the honest majority case (typical in production)

  • ✅ Allows caching the full key and incrementally adjusting

  • ✅ Matches EigenLayer’s BLS verification strategy