BlockCap: Blockchain-Based Capability Authorization for IoT

BlockCap is a capability-based authorization system designed to enforce fine-grained, auditable access control in resource-constrained IoT infrastructures. The system addresses the limitations of centralized identity- and role-based access control in IoT by combining capability tokens with blockchain-backed governance and traceability.

Rather than assuming that IoT endpoints can participate in consensus or store global policy state, BlockCap introduces a role-separated trust model in which authorization decisions are locally enforced while globally governed through smart contracts. The design explicitly targets heterogeneous deployments spanning cloud, fog, edge gateways, and constrained sensors/actuators.

System Model and Trust Assumptions

BlockCap system model showing validators, non-validator gateways, and constrained endpoints. Blockchain participation is restricted to capable nodes, while enforcement occurs at the service boundary.

BlockCap defines a network of nodes \(N = \{n_1, \dots, n_k\}\), each assigned a role:

Validators (cloud/fog): maintain blockchain state, execute consensus, and approve policy-critical operations.
Non-validator gateways (edge/fog): enforce access decisions and query on-chain capability state.
Endpoints (sensors/actuators): expose services but remain blockchain-agnostic.

Authorization is expressed as directed capability grants between nodes and services, enabling least-privilege, flow-specific access control.

Capability-Based Authorization Model

Directed graph representation of BlockCap’s trust model. Capabilities are defined as subject → object → operation tuples and enforced at API boundaries.

BlockCap encodes authorization as capability tokens that specify:

Subject node identity
Target node and service
Permitted operations (READ, WRITE, EXECUTE, TRANSMIT)
Issuance time, validity window, and revocation state

Capabilities are:

Issued and revoked on-chain via smart contracts
Checked off-chain by gateways before request forwarding
Auditable through immutable blockchain logs

This design enables decentralized enforcement without pushing cryptographic or blockchain overhead onto constrained devices.

Governance and Consensus

BlockCap is implemented on Hyperledger Besu using a Proof-of-Authority (PoA) network with QBFT for validator consensus. Governance-sensitive actions—such as node registration, validator admission, and capability issuance—are coordinated through smart contracts and validator voting.

This approach ensures:

Low-latency block finality
Resistance to single-point-of-failure
Deterministic authorization state across validators

Security Analysis

The system is analyzed using the STRIDE threat model, covering:

Spoofing of node identities
Tampering with authorization state
Repudiation of access decisions
Information disclosure
Denial-of-service
Elevation of privilege

BlockCap mitigates these threats through cryptographic identities, immutable logging, validator-governed policy changes, and strict capability validation at enforcement points.

Experimental Evaluation

BlockCap is evaluated on a heterogeneous testbed comprising:

Cloud and fog nodes (validator-capable)
Edge gateways (non-validator enforcers)
Resource-constrained IoT endpoints

Measured metrics include:

Capability issuance and validation latency
CPU and memory overhead on gateways
RPC performance under concurrent requests
Blockchain synchronization and throughput

Results demonstrate that BlockCap introduces minimal runtime overhead while providing strong security guarantees and full authorization traceability.

Key Contributions

Blockchain-backed capability authorization tailored for IoT constraints
Decoupled enforcement and governance via role separation
Fine-grained, bidirectional access control
Formal STRIDE-based security analysis
Practical deployment and evaluation on real hardware