The Lava Loans Protocol (v2): A Trustless Bitcoin Collateralized Loan System

The Lava Loans protocol (v2) is a scheme designed by Lava building upon Discreet Log Contracts (DLCs) to facilitate a trustless Bitcoin collateralized loan system.

The Lava Loans protocol (v2) is a scheme designed by Lava building upon Discreet Log Contracts (DLCs) to facilitate a trustless Bitcoin collateralized loan system. The huge implosion in the market last cycle caused by centralized platforms facilitating Bitcoin backed loans showed that left unchecked, such products and services can present a massive systemic risk to the entire market in the ecosystem.

Lava seeks to provide the same utility users of such centralized platforms sought in a decentralized and atomic fashion, using DLCs.

DLCs, for those unfamiliar with the concept, are a smart contract designed to settle a certain way depending on the outcome of some event outside of the Bitcoin protocol, i.e. the price of Bitcoin, the outcome of a sports game, etc. This is done by depending on an oracle, or a set of multiple oracles, who sign a message attesting to the actual outcome of the real world event. These signed messages are used as the basis for adapter signatures that unlock specific pre-signed transactions that settle the contract a certain way.

The benefit of DLCs is they can be done privately. As long as the oracle(s) publish the keys they will use to sign outcomes for specific events at specific times, any user can take that information and construct pre-signed transactions to settle correctly based on the range of possible outcomes without the oracle ever knowing that a contract exists. The oracle simply publicly broadcasts the signed message at the appropriate time, and that gives both users all the needed information to settle the contract correctly.

Lava is designed to make use of a modified variant of DLCs, in addition to stablecoins on other networks, to facilitate a bitcoin collateralized loan that can be entered into atomically and trustlessly (i.e. guaranteeing that the lender cannot gain control of bitcoin without releasing control of the stablecoin to the borrower).

Instantiation

The funding of the DLC is a two step process in the Lava protocol, given the requirement that the stablecoins given in exchange for the collateral being locked in the contract must be atomic. In the first phase, the borrower creates a script that allows them to claim their coin back after a timelock, or allows the lender to complete the funding with a hash preimage and signature from the borrower. They then sign a transaction that moves the coins from this staging address into the DLC. The lender then exchanges a hashlock for use later in the protocol with the borrower.

From this point, the lender needs to fund a similar atomic exchange contract with the borrower on the chain hosting the stablecoin. This contract allows the borrower to claim the stablecoins with the same preimage used to finalize the DLC on Bitcoin, or the lender to reclaim the stablecoins after a timeout. The contract on the alt-chain is also collateralized with extra stablecoins that remain in the contract, and cannot be claimed back by the lender until after the completion of the contract. This will be explained later.

After the setup phase, the borrower releases the preimage to the hashlock, claims the stablecoins, and enables the lender to move the bitcoin from the staging address into a finalized DLC. At this point the contract is active.

Execution

During the lifetime of the contract there are three ways that the loan can be settled, either at expiry or during its lifetime. Firstly, the lender can execute the DLC with the borrower’s adaptor signature, and an attestation of the current price from the oracle(s). Secondly, the borrower can execute with the lender’s adaptor signature and an attestation from the oracle(s). Lastly, the borrower can repay the loan on the alt-chain, enabling them to claim back bitcoin collateral when the lender claims their repayment and stablecoin collateral. All of these execution paths disperse the appropriate amount of bitcoin to both parties based on the market price attested to by the oracle(s).

The repayment path makes use of the second hash preimage that the lender generated during the setup. The DLC script is modified allowing the borrower to claim back the collateral at any time during the contract lifetime as long as they have the preimage to that the lender has generated. On the alt-chain, the stablecoin contract is also established to require the lender to reveal that preimage to claim back their repayment and collateral.

This construction for repayment is added to deal with the incentive where a repayment is made, but the lender does not finalize the repayment because the interest payment on the loan outstanding is greater than the interest that could be earned from them issuing a new loan. This is also the reason that the lender is required to collateralize the alt-chain contract with extra stablecoins, creating an incentive for them to redeem a repayment. Without doing so, they cannot claim the collateral back, thereby creating an incentive for them to honor the repayment and release the bitcoin collateral even when there is a financial incentive due to the interest payments to not do so.

Once the lender releases the preimage to claim back the repayment and the stablecoin collateral, the borrower is then capable