👩‍🏫Introduction

Blocks must spread quickly to all network miners in order for the Bitcoin system to be secure. The need that each block to carry a proof-of-work slows down block generation itself. Block propagation must be quicker than the normal time it takes the network as a whole to construct the next block for the Bitcoin protocol to be secure. The protocol for Bitcoin restricts block creation to taking place only once every 10 minutes in order to guarantee this property. Additionally, the block size is constrained to allow for quick transmission.

In this paper we present PHANTOM METCHAIN, a protocol that generalizes Nakamoto's longest-chain protocol. In Bitcoin, blocks reference a single predecessor in the chain, hence forming a tree, in contrast, PHANTOM blocks reference multiple predecessors, thus forming a Directed Acyclic Graph, a blockDAG. Each block can thus include several hash references to predecessors. PHANTOM then provides a total ordering over all blocks and transactions and outputs a consistent set of accepted transactions. Unlike the Bitcoin protocol, where blocks that are not on the main chain are discarded, PHANTOM incorporates all blocks in the blockDAG into the ledger, but all keeping in count the attack 51%, PHANTOM METCHAIN has an added split hash rate algorithm.

In rough terms, PHANTOM METCHAIN consists of a four-step procedure. This method, which is the core of the protocol, is used to exclude blocks made by misbehaving nodes and recognizes a set of well-connected blocks using the blockDAG's structure (later referred to as blue blocks) Blocks that are either withheld by their creator for a while for reference only older blocks from the DAG will almost certainly not be included in the set of blue blocks.

Our method encourages blocks inside the chosen cluster and penalizes those outside of it in order to convert the DAG's naturally occurring partial order into a full topological one (i.e., an order that respects the topology). Transactions within a block are arranged according to the order in which they appear in the block as a result of the order over blocks. We go over each transaction in this order iteratively and approve any that are compatible (in terms of the underlying consistency idea) with the previous transactions.

• Hashrate split algorithm which splits the hashrate to 3 block types.

• Mini MetBlock (Interval of 10 Seconds) 6 blocks per minute.

• Mega Metblock (Interval of 2 Minutes)

• MET Metblock (Interval of 10 Minutes)

Mini Metblocks generated are reconfirmed after every 2 minutes to form a Mega Metblock which helps METCHAIN to attain more security over other Proof-Of-Work chains and helps to avoid 51% attacks. As the mining hash rate will be automatically split as per the block time to avoid any false blockchain from being created. Same is followed by MET Metblock.

The PHANTOM protocol assumes a malicious mining coalition is not the majority, i.e. an attacker has <50% mining power. This puts the asymptotic maximum-security threshold of the system at 1/2, similar to that of GHOST and SPECTRE. The PHANTOM protocol differs from SPECTRE in that it enforces strict ordering over blocks and thus transactions in the system. PHANTOM is usable for smart contract systems in this light but only at the cost of forcing a proper ordering over blocks. The tradeoff can be quantified in the time that it takes nodes in the PHANTOM protocol to reach consensus, which although scalable is not as fast as a protocol like SPECTRE which can run without these guarantees.

The mining protocol utilized by PHANTOM follows a similar Proof of Work system as Bitcoin, where the computational puzzles are finding hashes under a target difficulty. At each step in an individual node’s mining process, it examines its view of the blockDAG network and does the following:

• Finds the set of all blocks with 0 in-degree, denoted B. Computes hashes until it finds a hash h<D.

• Creates a block b with hash h, includes B in the header (directed edges to those blocks), and broadcasts b."

Purely topological methods are used by PHANTOM to reach consensus. In contrast to SPECTRE's voting system, the PHANTOM protocol selects a "correct blockchain" within the blockDAG as it assembles the total number of legitimate blocks. Recursively locating this chain forces the overall ordering of the transactions contained within it. Using a greedy approximation algorithm to solve an optimization problem that will be described below, PHANTOM adds these blocks.

Finding the maximum m-cluster subDAG, as shown in Figure 1, is the first step in the process of identifying the finest, honest blocks. The official issue is described below. Due to the fact that it includes several trade-offs and the fact that the real network delay is unknown, the task of choosing the best parameter m also poses an intriguing problem. To begin with, the parameter has a direct relationship with the anticipated propagation delay of the complete network. The fact that this delay is bounded but not explicitly known is due to the partially synchronous model that we work under.