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Technology 6 min reading


Teriano Porter

7 Mar 2024



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Technology 1 min reading

Velas Expands Cross-Chain Bridging to Avalanche

Exciting news for the Velas community! We're thrilled to announce that Velas has extended its cross-chain interoperability by enabling bridging to Avalanche, a prominent blockchain platform known for its high throughput and low fees.


Teriano Porter

4 Apr 2024


Technology, Engineering 1 min reading

Smart Contracts on Steroids

Welcome to the latest edition in our series, Exploring Velas' Innovative Technologies. Throughout this series, we delve into the cutting-edge technologies propelling Velas forward as a leading blockchain platform, reshaping the landscape...


Teriano Porter

2 Apr 2024

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Section 2 (Finale).

So far, we’ve explored the fundamental principles of consensus, delved into the Byzantine Generals Problem, and uncovered the limitations of traditional Byzantine Fault Tolerance (BFT) mechanisms. This understanding equips us to appreciate the critical role consensus plays in ensuring trustless record-keeping and data transfer in blockchain networks.

But the story doesn’t end there. Innovation thrives on overcoming challenges, and the future of blockchain consensus brims with possibilities. In this final section, we embark on a thrilling journey into the heart of a groundbreaking solution — Velas Tower BFT.

Practical Byzantine Fault Tolerance and Its Limitations

Recognizing the limitations of traditional BFT, Practical Byzantine Fault Tolerance (pBFT) emerged as an optimization. Introduced by Miguel Castro and Barbara Liskov in 1999, pBFT aims to enhance original BFT consensus mechanisms and has been implemented in several modern distributed computer systems, including blockchain platforms.

pBFT focuses on providing a practical Byzantine state machine replication that tolerates Byzantine faults through an assumption of independent node failures and manipulated messages propagated by specific, independent nodes. The algorithm works in asynchronous systems and is optimized for high performance with minimal latency.

In the pBFT model, all nodes are ordered in a sequence with one node as the primary node (leader) and the others as backup nodes. The nodes communicate extensively, with the goal of all honest nodes reaching an agreement on the system’s state through a majority. For pBFT to work, the assumption is that the number of malicious nodes in the network cannot simultaneously equal or exceed one-third of the overall nodes in a given window of vulnerability.

The consensus process involves a series of well-defined phases, ensuring that nodes collectively agree on the result of a service operation. Each round of the consensus, also known as a “view,” consists of four phases:

  • Client Request: A client sends a request to the primary (leader) node.
  • Broadcast Request: The primary node broadcasts the request to all secondary (backup) nodes.
  • Execution and Reply: Nodes execute the request and send a reply to the client.
  • Result Agreement: The client awaits replies from a majority of nodes with the same result, which becomes the agreed-upon result.

This design ensures both liveness and safety, with the algorithm providing finality for transactions without the need for confirmations. The use of views, leader changes, and majority agreement also contributes to the robustness and fault tolerance of the consensus mechanism in distributed systems.


  • Fast Finality: pBFT achieves transaction finality without the need for confirmations, making approved blocks final.
  • Scalability: Compared to traditional BFT, pBFT offers improved scalability, processing transactions efficiently.
  • Fault Tolerance: pBFT is designed to tolerate node failures, crucial in applications like blockchain consensus where nodes may go down without warning.
  • High Throughput: pBFT has high throughput capability, processing more transactions per second compared to some other consensus mechanisms.
  • Security: Its fault-tolerant design enhances the security of the system against malicious actors.


While pBFT addresses some challenges, it comes with its own set of limitations. The use of digital signatures and Method Authentication Codes (MACs) for message authentication poses efficiency concerns, especially in large consensus groups like cryptocurrency networks. Communication overhead and susceptibility to sybil attacks, where a single party manipulates a large number of identities (nodes), are also challenges that need to be addressed for efficient implementation.

Velas Tower Byzantine Fault Tolerance

To understand Tower BFT, it’s essential to have a brief on Solana’s Proof of History (PoH) mechanism, where nodes reach consensus on the order in which transactions are processed. PoH serves as a global time source before consensus and acts as a key element in Velas’ Tower BFT protocol which is implemented as a Verifiable Delay Function (VDF) that operates as a sequential hash function with specific principles as follows:

  • Sha256 loops as fast as possible, with each output serving as the next input.
  • The loop is sampled, recording the number of iterations and state, representing the passage of time.
  • Messages referencing these samples guarantee their creation after the sample, establishing a time and event order.

PoH’s verifiable data structure ensures all nodes compute the same result without peer-to-peer communication. This structure uniquely identifies the ledger fork, and validation votes are only valid if referencing a PoH hash present in the ledger.

Velas Tower Byzantine Fault Tolerance (Tower BFT) represents a strategic optimization of the Practical Byzantine Fault Tolerance (pBFT) algorithm. This enhancement was introduced to address inherent limitations and improve the protocol’s performance in large-scale asynchronous systems. Recall that, one of the primary limitations of pBFT lies in its inefficiency and lack of scalability, especially as the network size increases. Velas inherits the Tower BFT functionality from Solana, aligning with its core vision of being the blockchain for future decentralized applications (DApps). This inheritance plays a pivotal role in ensuring the security and reliability of the network and significantly reduces messaging overhead and latency making Velas a robust platform for the next generation of DApps.

Tower BFT emphasizes liveness over consistency, preferring to maximize the time when non-faulty replicas are in the same view and it is Implemented as a sequential hash function that guarantees time and event order, forming the basis for major technical optimizations in Solana. Tower BFT integrates PoH, encoding PBFT timeouts in the PoH ledger itself. This asynchronous approach ensures liveness and consistency by leveraging the network’s unique time structure.

In each consensus round (view), Tower BFT follows a phased approach, encompassing client requests, leader broadcasts, node execution, and client confirmation through a majority of replies. The utilization of PoH allows for the encoding of timeouts within fixed slots, ensuring the stability of the network while minimizing the potential for rollbacks.


In conclusion, Velas emerges as a transformative force in the blockchain realm, seamlessly harmonizing diverse solutions to achieve unparalleled scalability and positioning itself as a frontrunner in the future of decentralized applications (DApps) with state of art security measures, unprecedented transaction speeds, and an unwavering commitment to sustainability, Velas’s Tower BFT protocol marks a significant milestone in the evolution of consensus mechanisms.

Building upon the foundational challenges addressed by Eisenberg and Gale, and the subsequent advancements in Practical Byzantine Fault Tolerance (pBFT), Velas showcases an innovative approach that encapsulates the ethos of efficiency, scalability, and security. As the blockchain landscape continues to evolve, Velas stands at the forefront, exemplifying the relentless pursuit of optimal consensus in the dynamic and ever-expanding domain of decentralized systems. Through Tower BFT, Velas not only addresses the limitations of traditional consensus mechanisms but also sets a precedent for the seamless integration of groundbreaking technologies, propelling the blockchain ecosystem towards new horizons.