“Your proposal seems unlikely to scale to the necessary magnitude,” noted Satashi Nakamoto, James A. Donald.
A decade later, that criticism remains relevant. Even those most passionate about Bitcoin acknowledge its inefficacy for routine, modest purchases. However, the Lightning Network, a significant project aimed at enhancing Bitcoin’s scalability, might alter this perception.
Lightning Labs CEO Elizabeth Stark spoke at the Blockstack Summit in July 2017 about the nascent state of the Lightning Network.
The network, while operational, is still in its early stages of development. Real Bitcoin has been seamlessly transferred using implementations from Lightning Labs, Blockstream, and ACINQ, all of which work together. An ACINQ engineer swiftly sent 0.000001 bitcoin (equivalent to about $0.01) from an eclair node to an lnd node through a c-lightning node:
To evaluate the improvement, we attempted a similar transaction on the Bitcoin blockchain using the GreenAddress mobile wallet app. The app recommended a miner fee of 0.00001907 BTC ($0.19), a staggering 1,907% fee. The confirmation time likely spanned six blocks, approximately an hour, though confirmation specifics remained unclear.
We couldn’t determine the actual transaction duration, as an error message indicated that “outputs below 546 satoshis [$0.05] are deemed uneconomic dust by Bitcoin. Please increase the value.”
Incidentally, some funds were temporarily lost to a c-lightning bug on the mainnet, but Christian Decker of Blockstream assured that most were eventually recovered. Nonetheless, Lightning Labs is diligently working on these issues.
So, what’s the mechanism behind the lightning network?
The solution relies on two-way, off-chain payment channels. For instance, Alice and Bob make frequent, minor transactions with each other. On-chain payments are impractical due to high fees and lengthy confirmation times, prompting them to open a channel for swift, fee-less Bitcoin exchanges.
Interchanging Channels
Alice and Bob aim to conduct transactions with various parties. Establishing channels with each would be infeasible. Despite having simplified interfaces, users would need substantial liquidity to engage Bitcoin in numerous channels.
However, complexity can be minimized. The principle of six degrees of separation allows users to transmit payments through intermediaries, forming a network of channels. Small fees encourage nodes to sustain open channels. Privacy is safeguarded through onion routing, similar to the TOR browser, which obscures the complete transaction path.
It remains to be seen how effectively this channel network will operate. Excessive “hops” between intermediaries may incur high cumulative fees.
Critics highlight today’s channel limitation: the initial funding transaction dictates the channel’s total Bitcoin capacity.
Users face a choice: allocate significant Bitcoin amounts to channels for unfettered transactions or opt for smaller channels, retaining accessible Bitcoin. Thanks to linked channels, a user need only maintain a few open channels.
The decision involves choosing between channel liquidity and on-chain liquidity. If solutions like watchtowers ensure fund security, channels may dominate Bitcoin usage. As channels transform into “rechargeable debit cards,” the main chain becomes akin to a savings reserve, as Decker describes.
Stark echoes this sentiment: while channel funding limits other Bitcoin uses, it enables transactions across a network of nodes with swift, low-fee Bitcoin acceptance. She foresees more utility in Lightning channels than on-chain transactions due to speed and reduced costs.
Maintaining Trust in Lightning
Bob wants to send Alice 0.1 BTC through their open channel; updating the commitment transaction suffices, avoiding miner intervention. The balance shifts to 0.6 BTC for Alice and 0.4 BTC for Bob.
Securing this process is challenging. With exchanged signatures on initial transactions, Bob could exploit this to receive 0.5 BTC, disregarding agreed terms. This could lead to a potential $1,000 loss for Alice. Trust isn’t a reliable solution—it’s antithetical to Bitcoin’s purpose.
Cryptographic measures can prevent old transactions from recording outdated channel states. Using RSMC, parties can impose time limitations on one output for revocation, ensuring financial assurance without instant access.
This mechanism deters duplicity. If Bob attempts deceit, Alice can reclaim what Bob tried to misappropriate, effectively seizing the entire channel upon detecting dishonesty.
This enforcement relies on breach remedy transactions, promising not to broadcast obsolete commitments. The breach remedy agreement allows either party to penalize fraudulent attempts, securing the channel’s integrity.
Alice must monitor her channels vigilantly, or Bob might exploit her inattention for up to 1,000 blocks. Poon and Dryja propose third-party agents to execute breach remedies, rewarding this service via penalty fees.
Olaoluwa Osuntokun, Lightning Labs’ CTO, is developing “watchtowers” to enforce such measures. Though some worry about these nodes’ potential as trusted parties, Osuntokun asserts that a single honest watchtower suffices for a channel.
Christian Decker notes that fraud is unlikely, as the risk of losing an entire channel’s funds deters attempts. The gamble that the counterpart won’t verify weekly isn’t worth the consequences.
The Concept of Hubs
Selecting parties to open channels with involves economic decisions. Critics suggest that centralized “hubs,” financially robust nodes, might emerge as major channel operators.
The prospect of an off-chain Bitcoin banking industry concerns Bitcoin purists, who fear network centralization.
Stark dismisses this notion, highlighting that numerous users operate full Bitcoin nodes and are likely to manage Lightning nodes as well. Her team is working on “splicing,” facilitating channel replenishment from the main chain, potentially balancing Bitcoin allocation between the network and individual channels.
Decker anticipates a “two-tier network” with dependable nodes supporting the network’s backbone. These nodes are expected to be merchants, not exclusive hubs, as providing liquid channels would necessitate high fees, making them less competitive.
ACINQ CEO Pierre-Marie Padiou acknowledges the unpredictable future of the lightning network. The equilibrium between centralization and decentralization remains uncertain, with outcomes hinging on node configurations.
Poon and Dryja believe the network can support billions of daily transactions using current computing power, though fewer than 1,000 mainnet lightning nodes currently exist. This debate involves groups like Bitcoin Cash supporters, lightning advocates, and others, each championing their approach to scalability.
Regardless, the lightning network presents a hopeful solution to the scalability issue haunting Bitcoin since 2008.
Initiating a Channel
To commence a channel, Alice and Bob contribute Bitcoin to a special address via a funding transaction. Suppose Alice allocates 1 BTC, sending it to a 2-of-2 multisig address, necessitating both parties’ cryptographic signatures for any transactions.
It’s crucial the funding transaction remains unsigned and unbroadcasted until all steps are finalized.
All images sourced from relevant repositories.
Alice and Bob then create a “commitment transaction” from the funding transaction, utilizing its 1 BTC output to allocate 0.5 BTC each. Soft forks in Bitcoin’s protocol allow such transactions to exist pre-signature confirmation.
Alice signs Bob’s 0.5 BTC allocation, and Bob reciprocates. Both then finalize and broadcast the funding transaction, etching it into the Bitcoin blockchain, subject to fees and confirmation times.
Their open payment channel now facilitates instant, free Bitcoin transfers. Either can close it anytime, reclaiming their respective shares. As transactions occur, channel balances update accordingly.
Understanding Channel Initiation
For newcomers to the lightning network, the process can seem convoluted with its steps of “sign here, initial there.” A more conceptual description might help clarify.
The funding transaction establishes channel funds, setting a cap that prevents either party from exceeding the initial amount. Broadcasting the funding transaction without prior steps accomplishes nothing more than a standard Bitcoin transaction.
Leaving the funding transaction open, then inserting a commitment transaction—which acts as a smart contract—allows for flexible Bitcoin transfers along predefined routes without mining delays or costs.