Ark: Layer 2 Protocol For Cheap, Anonymous Off-chain Payments

"Ark allows recipients to receive payments without acquiring inbound liquidity while preserving their receiver privacy. Ark is as private as WabiSabi, as convenient as on-chain, and as cheap as Lightning."

Ark: Layer 2 Protocol For Cheap, Anonymous Off-chain Payments

Bitcoin developer Burak wrote a blog post clarifying his thought process behind the proposal of Ark.

  • "I named it Ark because it resonated with Noah's Ark to save plebs from chain analysis companies and custodians. Self-custodial Lightning doesn't work for obvious reasons, and chain analysis companies significantly threaten user privacy."
"The ideal self-custodial end-user experience has to be frictionless. If something works %95 of the time, it's not considered working. Users should be able to simply push a magical button to receive sats and another button to send sats, just like how on-chain funds flow."
  • "Ark enables anonymous, scalable off-chain payments through an untrusted intermediary called the Ark Service Provider (ASP). ASPs are always-on servers that provide liquidity to the network, similar to how Lightning service providers work."
"Ark is a trustless, distinct layer two protocol with unilateral exit. ASPs cannot steal users' funds or link senders & receivers. Users retain self-custody and can revert their funds to the base layer if something goes wrong on the second layer."
  • "Ark has a utxo set that lives off the chain. These utxos are referred to as virtual utxos or vtxos in short. Existing virtual utxos are destroyed, and new virtual utxos are created on an ongoing basis, similar to how on-chain funds flow."
  • "Ark payments settle every 5 seconds and final in every block. Users need to wait for on-chain confirmations to consider a payment 'final'. However, this doesn't prevent them from paying invoices with their zero-conf coins. Ark has immediate availability with delayed finality."
  • "Ark ensures "absolute atomicity" by using ATLCs instead of HTLCs. Users can receive payments and forward them further without waiting for confirmations. A mempool-level double-spend breaks the atomicity. ASPs cannot redeem senders’ vTXOs if they double-spend recipients' vTXOs."
  • "Ark provides an order of magnitude greater level of privacy compared to Lightning. Every payment on the protocol takes place in a coinjoin round. This obfuscates the trace from the sender to the receiver. The anonymity set is everyone who involves in a payment."
"Numbers tell us it would take +100 years to onboard the whole population into lightning in a non-custodial way, assuming it takes 4 channels per human and an average channel opening consumes a few hundred vBytes."
  • "You may say okay, channels can be batched under a coinpool or a factory, but still, you have to "touch" the chain very often to close channels. Bitcoin backspace cannot handle channel closings at a scale of ~150,000 people dying daily, considering closings are TLUV-style."
  • "Ark kind of checks all the boxes; maybe I'm just biased. It preserves receiver privacy, has no entry barrier to onboarding, and is convenient to use. Ark may in theory onboard the whole population to Bitcoin in a self-custodial way."

Burak also shared his view on the best approach for implementing Ark.

  • A deep dive into Ark proposal can be found here.

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