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Lightning Network: What Is It and Can It Solve Bitcoin’s Scaling Problem?

Satashi Nakamoto sent a programme for “a new electronic cash system that’s fully peer-to-peer, with no trusted third approver,” to a cryptography mailing list on Friday, Oct. 31, 2008. The first response – the original time anyone publicly commented on bitcoin – came the following Sunday: “We identical, very much need such a system,” wrote James A. Donald, “but the way I gather from your proposal, it does not seem to scale to the required size.” 

Wealthy on 10 years later, that criticism still rings correctly. Even bitcoin’s most ardent evangelists admit that it’s paltry for making small, everyday purchases. But the Lightning Network, one of the most reassuring bitcoin scaling projects currently underway, could change that. 

The Lightning Network

Scold at the Blockstack Summit in July 2017, Lightning Labs CEO Elizabeth Complete cited that first critique of Nakamoto’s electronic cash, but signified confidence that bitcoin can in fact scale. “We’re basically in 1995 all beyond again when it comes to blockchains and decentralized technologies,” she said, referring to the once upon a time before the internet acquired HTTP and the other transport and application layers of TCP/IP.

Quantity the most talked-about “layer 2” applications for the bitcoin blockchain is the lightning network. Ahead proposed by Joseph Poon and Tadge, aka Thaddeus Dryja in 2015 (the scad recent version of their whitepaper is available here), lightning has been trade into a functioning specification called lightning-rfc or “BOLTS” by three theatre troupes, each of which has its own implementation: Lightning Labs has lnd, Blockstream has c-lightning, and ACINQ has eclair. There are also non-BOTLS implementations being expanded, such as thunder.

The lightning network is already up and running, but it’s in its extreme commencement. Real bitcoin has been sent and nearly always received ending Lightning Labs’, Blockstream’s and ACINQ’s implementations, and all three are interoperable. The video here shows an ACINQ engineer sending 0.000001 bitcoin (about $0.01) bordering on instantaneously from an eclair node to an lnd node through a c-lightning node:

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To see how much of an improvement this represents, we tried a similar transaction on the bitcoin blockchain using GreenAddress, a unstationary wallet app. The app suggested paying miners 0.00001907 BTC ($0.19): a 1,907% fee. While it’s not open how many blocks that fee was intended to confirm within (we’ve reached out to GreenAddress to feel out), the answer is likely six blocks, or around an hour.

We’ll never find out how large that particular transaction would actually have taken, while: an error message informed us that “outputs below 546 satoshis [$0.05] are contemplate oned uneconomic dust by Bitcoin. Please increase the value.”

Lightning Labs has also studied cross-chain atomic swaps using the network; these are transfers of value between distinguishable blockchains, in this case bitcoin and litecoin, which potentially impression a first step towards building decentralized exchanges.

Lightning entrusts micropayments that bitcoin can’t on its own, but existing implementations are still buggy. Flinch is urging users to learn about lightning using bitcoin’s “testnet” (that is, to use alter money), rather than the live-fire “mainnet.” Around $50,000 good of transactions have been performed on the mainnet at the time of writing, how, and some people have lost money to a c-lightning bug. (Christian Decker, quintessence tech engineer at Blockstream, told me via email that funds were after all is said recovered in most cases.)

So how does lightning work?

How Lightning Under ways

Lightning’s solution is based on two-way, off-chain payment channels. Say that Alice and Bob oft-times transact with each other in small amounts. On-chain payments are not sound in this case because of the fees and long confirmation times tangled, so they decide to open a channel allowing them to send bitcoin ruin and forth, instantly and fee-free.

Opening a Channel

To open a channel, Alice, Bob, or both give a certain amount of bitcoin to a special address through what is appeal to c visit canceled a funding transaction (the green box in the diagram below). Say Alice contributes 1 BTC. She sends the stakes to what is called a 2-of-2 multisig address, which requires both Alice and Bob to cryptographically “lexigram” any sending transaction with their private keys. A normal deal only requires the signature of the (single) private key corresponding to the sending speech’ public key.

Importantly, the funding transaction is not yet signed or broadcast to the network.

All images sourced from Poon and Dryja.

Next, Alice and Bob create a “commitment deal” using the funding transaction as its “parent”: they use its unconfirmed output of 1 BTC as the input for a “woman” transaction that sends 0.5 BTC to Alice (output 0) and 0.5 BTC to Bob (generate 1). If you’re protesting that bitcoin’s protocol doesn’t allow drugs to sign a spend without knowing the input’s signatures, that capacity was granted through a soft fork.

Alice then signs the production sending 0.5 BTC to Bob; Bob signs the output sending 0.5 BTC to Alice. Both then goad and broadcast the funding transaction, which is committed to the bitcoin blockchain (and submissive to to network fees and wait times).

They now have an open payment channel from stem to stern which they can shuttle bitcoin back and forth instantly and fee-free. Either Alice or Bob can arrange it at any time and claim their 0.5 BTC each, or whatever the updated weight is.

Opening a Channel … In English

Unless you already know a fair bit round the lightning network’s innards, it’s probably hard to digest the “sign here, initial here, put in this, broadcast that – no not that.” 

Here’s a more conceptual stripe. The funding transaction is what it sounds like: it provides the funds for the neck. It also acts as a cap for the channel: neither party can end up with more than the original funding amount, and both parties’ balances must add up to that amount. The grounds the funding transaction is created first, but broadcast last, is that if it were just posted to the blockchain in one step, nothing would have been talented aside from a single, plain-vanilla transaction. Lightning doesn’t impute those any faster or cheaper.

By leaving the funding transaction open, inserting a commitment affair – which, as described below, functions as a kind of smart contract – and then minute the funding transaction, lightning pries open a kind of wormhole in the network. It tolerates you to move bitcoin back and forth along a single, defined route. You’re using the bitcoin protocol, but bypassing the delays and expense imposed by the miners.

Keeping Lightning Trustless

Say Bob now fall short ofs to pay Alice 0.1 BTC using their open channel. The two parties plainly update the commitment transaction — no need to appeal to the miners. The balance, in days of old 0.5 BTC each, is now 0.6 BTC to Alice, 0.4 BTC to Bob.

The only problem is, how to do that securely? Because they’ve already swapped signatures for the initial transaction, Bob can sign that one – rather than the most fresh one – and walk away with 0.5 BTC instead of the 0.4 BTC he’s actually owed. In other brief conversations, he can steal around $1,000 from Alice, based on prices at the every now of writing. The answer might be to only open channels with people you certitude. But then what’s the point of using bitcoin?

Finding a cryptographic mixture to this dilemma boils down to one goal: making it impossible to consign an old transaction and close the channel in a way that reflects a previous state. As sustained as doing so is an option, lightning has a double-spend problem.

Remember that Bob significants one half of the commitment transaction (Commitment Tx 1a below), which only Alice can broadcast because hers is the lassies signature. Alice signs the other (Commitment Tx 1b), which only Bob can then seed. Either one can do so and close the channel, but using bitcoin’s (limited) smart contract-writing potentials, the outputs of the two halves of the commitment transaction can be subject to different restrictions. Specifically, one manufacture can allow the recipient to spend the funds immediately, while the other can be liable to suffer to cancellation by either party – via a Revocable Sequence Maturity Contract (RSMC)  – for a expatiate oned period of time, such as 1000 blocks, or about a week.

Here’s why that’s of use. If Bob turns out to be devious and unprincipled, he can only sign and broadcast Commitment Tx 1b (greater than), which pays Alice out immediately (Delivery 1b) and holds his funds in revocable limbo for a week (Revocable Performance 1b). Alice, seeing that Bob has attempted to shortchange her, can trigger revocation and title not just the 0.1 BTC Bob tried to steal, but the 0.4 BTC he would otherwise be undergoing been entitled to.

In other words, the whole channel goes to Alice if she discerns Bob cheating. That’s possible because when the parties create a new commitment minutes (C2a and C2b below), promising in effect not to broadcast an old commitment transaction (C1a or C1b), they put their spinach where their mouths are. Along with the new commitment transaction, they fabricate a breach remedy transaction with two outputs (BR1a and BR1b) applying to the previous commitment. Alice sponges Bob her private key for his half of the breach remedy transaction, and vice-versa. Now if either try ones hand ats to broadcast the old transaction, the counterparty can take advantage of the 1000-block be tabling period and swoop in ahead of that transaction, taking the offending festivity’s entire balance.

The problem is that Alice must pay semi-constant notice to her channels, lest Bob catch her off guard for 1000 blocks. Poon and Dryja offer designating some third party whose job it is to trigger breach ameliorate transactions – the ones rewarding all the channel’s funds to the wronged party – when a counterparty proves to cheat. These could be paid a fee out of the penalty. 

Olaoluwa Osuntokun, Lightning Labs’ co-founder and CTO, is lay open “watchtowers” to serve as these third-party enforcers. While concerns be enduring been raised that these nodes could act as trusted advocates and introduce insecurity into the network, Osuntokun tells CoinDesk that not one honest watchtower would be needed for a given channel. 

Also, as Christian Decker, insides tech engineer at Blockstream, points out in an email, fraud is risky. It’s a momentous gamble to assume that the party you’re trying to rob will not check in at least definitely a week, and the risk of losing all the money in your channel may be enough of a disincentive. 

Connecting the Channels

In the real world, Alice doesn’t want to complete exclusively with Bob, nor Bob exclusively with Alice. Both have any gang of counterparties they need to pay and get paid by. Opening channels with every one of these confederacies would be impractical. Even if the user interface were simplified to idealization, few users would have the liquidity necessary to tie up bitcoin in a dozen or more fair channels.

Luckily they don’t have to. As the video above shows, purchasers can route payments through intermediate users’ channels, so that get revenge on anyone with an open channel or two should be possible through the six-degrees-of-separation truth. Unlike transactions within a single channel, these multi-channel arrangements will likely involve small fees to incentivize nodes to reservoir channels and keep them open. Onion routing, the technique reach-me-down to disguise TOR browser users, prevents intermediate nodes from glom the full path taken by a transaction, mitigating privacy concerns.

How OK this web of channels works in practice remains to be seen, and it’s conceivable that if payments be struck by to take too convoluted a route – with too many “hops” through medial channels – fees charged by those users could add up.

Can Lightning Reinforce Decentralized?

These worries are related to one that, to critics, represents an insurmountable split in the lightning network. In today’s implementations, a channel comes with a cap: the amount of bitcoin in the first funding transaction limits the total amount of money in the channel.

This position imposes a tradeoff on users with reasonably limited resources. They can either support channels with large amounts of bitcoin in order to ensure that they obtain the funds to make any payment they would need to, or they can back smaller channels and have bitcoin available for other uses. (Because payments can be make mincemeat ofed through linked channels, a given user probably doesn’t necessity to open more than a handful of channels, and perhaps only a combine.)

The choice boils down to having liquidity within lightning directs or liquidity outside of them, on-chain. Choosing to fund liquid payment paths could be risky if watchtowers or some other solution doesn’t hinder the loss of funds through inattentiveness. On the other hand, if payment ways are made secure and lightning becomes the main method for using bitcoin day-to-day, there drive be little issue with leaving funds in channels. They hand down serve as “a rechargeable debit card or cash,” as Decker puts it, while the necessary chain acts as a savings account. 

Stark makes a similar feud: funding a lightning channel prevents you from using that bitcoin for anything else, except “a network of potentially various nodes that across multihop will accept bitcoin instantly,” she make little ofed via email. “we envision funds on Lightning channels to be more useful than on-chain bitcoin for concluding because of the instant speed and low fees,” she added.


But who would you set these ways up with? Choosing the Bob to your Alice is an economic decision, not a cryptographic one, and to critics of the lightning network, the evident answer would be a sort of “hub,” a node with a lot of capital, giving it the genius to maintain well-funded open channels with a number of parties at in the same breath.

The idea that what amounts to an off-chain bitcoin banking trade might develop disturbs bitcoin enthusiasts, who see it as centralizing the network.

Vacant disputes this line of argument. “Thousands of users run full nodes for bitcoin,” she make little ofs, “and we believe those and others will also run nodes on Lightning (it’s easier because you don’t for a bitcoin full node along with it, and unlike bitcoin loaded nodes you can make small fees from routing).” She also underlines out that her team is working on “splicing,” which would allow troughs to be topped-up using bitcoin from the main chain. That talents could alleviate the trade-off between putting bitcoin in a channel or say goodbye it on the main chain, which could in turn reduce the tendency for focal points to form.

Decker sees it as likely that a “two-tier network transfer form, with a large number of nodes that are reliable and act as the mainstay of the network.” He expects these to be merchants, however, rather than naves that exist solely to provide liquid channels. Providing these watercourses to multiple users, he argues, would be expensive, requiring the hubs to fee high fees and making them uncompetitive compared to other nodes.

ACINQ CEO Pierre-Marie Padiou doesn’t offer to know how the lightning network might develop. “It is very difficult to foretoken what the equilibrium will be between centralization and decentralization,” he wrote via email. “Of routine there will be bigger nodes and smaller nodes, but to what territory it is difficult to tell beforehand.”

The Right Way to Scale?

Poon and Dryja assert that “functioning a network of these micropayment channels, Bitcoin can scale to billions of acta per day with the computational power available on a modern desktop computer today.” Peradventure, but that’s certainly not the case today. Fewer than 1,000 mainnet lightning nodes are provide at the time of writing. 

Nor is lightning the only scaling proposal out there. A bigger competitor is bitcoin cash, a contentious hard fork of bitcoin that make allowances for larger blocks. The debate between bitcoin cash supporters, lightning aids and advocates of various third ways – even the occasional anti-scaler – is bouncy, if acrimonious. It may be that one or the other will come out on top, that they last will and testament continue to coexist, or that all will fail.

In any case, the lightning network is a favourable attempt to overcome the scalability dilemma that has haunted bitcoin since bitcoin’s at the outset weekend in 2008.

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