So, why don't regular transfer transactions get sniped, but transactions for listing Ordinals NFTs do? The core reason lies in the asynchronous nature of matching sellers and buyers in listing transactions. After a seller lists an NFT, they have to wait for a buyer to come and complete the purchase. The waiting time is uncertain, and the seller doesn't know the buyer's address and signature when listing. This scenario is well-suited for using pre-signed technology.

Pre-signed transactions allow sellers to create and sign sell orders in advance, storing them locally or in other secure places until a buyer makes a purchase and broadcasts it to the blockchain network. When a buyer purchases an Ordinals NFT and broadcasts it to the Bitcoin network, the seller's pre-signed information is already available. At this point, anyone can use the UTXO to obtain the seller's pre-signed information and restructure a new buy transaction with their signature. The Bitcoin network packages "unconfirmed" transactions based on gas fees, so the restructured transaction must offer a higher gas fee to outpace the original purchase transaction. In this scenario, MagicEden introduced the Mempool Protection feature, which automatically restructures the transaction with a higher gas fee to compete with users attempting "mempool sniping."

As a stablecoin protocol running on Bitcoin Layer 1, Shell Finance requires users to broadcast transactions on-chain for borrowing, repaying, and liquidation scenarios. However, Shell Finance doesn't face "mempool sniping" issues in these scenarios. Shell Finance operates on a peer-to-pool mechanism, where users interact with Shell Finance for borrowing, repaying, and liquidation in a synchronous transaction signing process. Without asynchronous transactions, there is no need for pre-signed technology, and thus the "mempool sniping" vulnerability does not exist.

Discreet Log Contracts (DLCs), an MIT invention that became possible with Taproot’s introduction of Schnorr signatures. DLCs were originally proposed by Tadge Dryja, the co-creator of the Lightning Network, as a way to enable smart contracts to conditionally move Bitcoin. This innovative approach allows for creating financial contracts that depend on external events, which is crucial for implementing complex DeFi functionalities directly on the Bitcoin blockchain.

DLC in Shell Finance

In Shell Finance, DLC is implemented as the core technology for the liquidation process. DLC ensures that the liquidation process in a trustless way without any centralizd third party. Here’s how DLC is used in practice:

• Loan Initiation: When a user initiates a loan by collateralizing Bitcoin inscription assets (such as Ordinals, Runes, Atomicals, and BRC-20), Shell Finance calculates the loan amount based on the collateral value. A DLC contract is then set up, initializing a secret value used for future liquidation scenarios.

• Loan Adjustment: Users can adjust their collateral or debt amounts throughout the loan's lifecycle. Each adjustment recalculates the collateral ratio using real-time data from Oracle, ensuring the loan remains properly collateralized. The DLC is updated accordingly to reflect any changes.

• Liquidation: The most critical application of DLC in Shell Finance is during liquidation process. If the collateral value drops below the required minimum collateralization ratio (MCR), the DLC allows for the automatic liquidation of the position. Here’s how it works:

1. The oracle provides a price update indicating that the collateral value has fallen below the liquidation threshold.

2. This triggers the disclosure of the secret value within the DLC, enabling the protocol to execute the liquidation.

3. The assets are then auctioned off in a Dutch auction style, with the proceeds used to repay the debt and any excess added to Shell Finance’s insurance fund.

DLC in DLC.Link

DLC.Link’s platform enables the user to lock BTC into a DLC to mint dlcBTC. The DLC itself is a special multisig UTXO where users retain one key. This innovative design safeguards Bitcoin deposits with the full hashrate of the Bitcoin network. Furthermore, in the DLC, payout addresses are predetermined and locked in during the deposit phase. This means that in the event of a breach, hackers are unable to redirect or steal the deposits. This innovation makes dlcBTC a “theft-proof” Bitcoin bridge.

Attestor Model Ensures Bitcoin Stays Yours, No Custody Required

With a traditional bridge, deposits are locked into a validator network, and are kept in pools in various wallets. In stark contrast, DLC.Link's Attestor system enforces the DLC locking mechanism without ever taking possession of user keys or assets. dlcBTC is set to revolutionize the way Bitcoin is utilized in the world of DeFi. This platform is not just another bridge; it offers a secure, impenetrable structure that respects the sanctity of user sovereignty and eliminates the common vulnerabilities associated with custodian-based bridges.

About Shell Finance

Shell Finance is a trustless lending and stablecoins protocol built on the Bitcoin L1, supporting Bitcoin and Bitcoin layer1 assets like Ordinals NFT, BRC-20, ARC-20, Runes as collateral.

About DLC.Link

DLC.Link harnesses the power of Discreet Log Contracts (DLCs) to establish a trustless bridge between Bitcoin and Ethereum. DLC.Link launched dlcBTC, enabling depositors to self-wrap their Bitcoin for DeFi on Ethereum while retaining full custody of their assets.

Financial asset transactions require at least two parties with opposite directions and matching needs. The core of financial services is to enhance the efficiency of matching these parties while reducing the frictional costs of participation.

P2P trading has been widely applied in spot markets, loans, and futures. ETHLend, the precursor to the largest lending protocol, AAVE, raised over $16 million through an ICO in 2017. Their goal was to achieve decentralized peer-to-peer lending matches through the Ethereum network. According to ETHLend’s product vision, borrowers and lenders could post their requirements on-chain, customizing loan rates, collateral types, and collateral-to-loan ratios. Borrowers and lenders could then find and match suitable orders directly on the platform.

However, the Peer-to-Peer lending model also revealed several critical issues:

• Difficulty in Matching Needs: As a two-sided market, users often spend significant time finding appropriate counterparts. Borrowers might find an order matching their loan amount but not their desired interest rates or loan durations.

• Fragmented Liquidity: The liquidity of both parties was fragmented across highly varied order requirements. Funds were often locked for extended periods due to unmatched orders, leading to inefficient capital utilization.

• High Loan Rates: Low efficiency in fund utilization translated into high frictional and temporal costs, which were passed onto the operational costs of both parties, leading to elevated loan interest rates.

Given that smart contracts can act as a trustless ledger while also managing interest rate calculations and asset custody, why not use them as a medium for liquidity between lenders and borrowers for more efficient demand matching?

ETHLend developers, learning from Compound, used smart contracts to create a liquidity pool. This allowed lenders to deposit assets for passive income based on market demand, while borrowers could secure loans by mortgaging assets and paying interest.

With the Peer-to-Pool design, the user experience for both parties improved dramatically:

• Flexible Loan Parameters: Both parties could independently decide their loan amounts and durations, with the liquidity pool automatically adjusting interest rates based on market conditions.

• Reduced Friction Costs: The bi-directional liquidity was effectively consolidated within the liquidity pool, allowing users to transact directly with the pool. This significantly reduced frictional costs and led to more reasonable interest rates. For instance, in the Bitcoin ecosystem, the P2P lending protocol Liquidium saw annual interest rates as high as 65% for a 16-day loan of BTC against NodeMonke collateral; in contrast, the annual interest rate for lending ETH on AAVE was only 2.54%.

• Instant Loans: Borrowers and lenders could initiate transactions instantly based on current market rates, enabling an "anytime, anywhere" borrowing experience.

What about Lending on the Bitcoin Network?

Lending in the Bitcoin Network In the Bitcoin network, due to the stateless nature of the UTXO model, there are no accounts or balances on-chain, making it impossible to implement programmable state data similar to Ethereum smart contracts. Clearly, the P2Pool lending model, easily implemented on Ethereum, cannot be directly transferred to the Bitcoin network. So, how can an equivalent Peer-to-Pool lending model be realized on Bitcoin? The solution hinges on who assumes the role of the liquidity pool.

Returning to the fundamental functions of a liquidity pool:

• Custody of Collateral and Loan Funds

• Interest Rate Calculations Combining Collateral Ratios and Asset Values

• Passive Position Liquidation

In the Bitcoin network, collateral (such as inscribed assets) and BTC, as native UTXO assets, can be effectively managed by Taproot Script. Interest rate calculations are typically performed off-chain, and users can verify the legitimacy of these calculations through the PSBT signing scheme. Additionally, trustless liquidation is achievable by relying on DLCs. The combination of on-chain and off-chain logic necessary for these operations often presents a high barrier for many users. How can protocols encapsulate and abstract these complex processes to offer easy-to-use lending services?

We'll discuss the concept of Lightning Service Providers (LSPs), a technology widely applied in the Bitcoin Lightning Network payments sector. Given the high threshold for using the Lightning Network and the complexity of connecting to it, which exceeds many end users' tolerance, there is a demand for Lightning Network-related services, fostering the LSP market. LSPs offer services, including opening user payment channels, ensuring sufficient incoming liquidity, routing payments, and maintaining stable network connections. This is similar to how most people prefer to connect to the Internet through Internet Service Providers (ISPs), who handle complex technical issues and charge for the convenience of Internet services.

As a Bitcoin Finance protocol serving as a financial service provider on the Bitcoin network, it too needs to abstract and encapsulate complex on-chain and off-chain calculations, Taproot Script signings and other business logistics to provide users with a "one-click" operational experience that surpasses the convenience of traditional financial markets, truly realizing Protocol as a Service (PaaS).

How does it work in Shell Finance?

Shell Finance, a lending protocol on the Bitcoin layer-one network, introduces vaults as the unit for each loan. This allows the protocol to connect borrower and lender markets, creating a unique Peer-to-Protocol lending structure.

Through this design, the protocol builds independent lending relationships with each borrowing position in the loan-side market, meeting diverse borrowing needs; simultaneously, it maintains the price balance between $BTC and $BTCx through the protocol and liquidity pool, absorbing liquidity from the lender market. The efficient characteristics of a fund pool are simulated on the UTXO model basis, enhancing the matching efficiency and capital utilization of the dual-sided market.

Through Shell Finance, users can experience the same transaction experience as with Peer-to-Pool lending protocols:

• Instant Lending Liquidity

• Diverse Collateral Options

• Low Loan Costs

Importantly, the protocol internally packages the BTC/BTCx trading pool module, price oracle DLC liquidation module, liquidation auction module, vault module, and more. It coordinates the calling and collaboration among these modules based on user needs, providing a simple, easy-to-use lending service.

Outlook for the Future of Bitcoin Finance

Outlook for the Future of Bitcoin Finance Looking back from 2024 at the outstanding DeFi protocols on the Ethereum network, each one cleverly utilizes paradigm shifts to offer more efficient financial services to users. Uniswap, by building spot liquidity pools and leveraging constant function market-making curves, has provided a new paradigm for DEXs; AAVE and Compound introduced the concept of borrowing liquidity pools, taking the decentralized lending market to new heights through the Peer-to-Pool model. Indeed, liquidity pools themselves are one of the most important financial primitives in the crypto world, and they apply to BiFi as well.

Though limited by the UTXO structure and data capacity, Bitcoin script programming is also explored based on the liquidity pool concept. OP_VAULT, proposed as a BIP specifically for constructing "vault contracts," aims to provide a safer, more advanced form of fund custody. The implementation scheme of OP_VAULT allows a new transaction to input parameters to a pre-committed opcode, thus updating the entire script's leaf; this moves beyond "verifying incoming data under certain conditions" to "generating new, meaningful data from incoming data." This data update provides a foundation for more intelligent asset management schemes and brings us closer to a true native liquidity pool.

Looking further into the future of the Bitcoin ecosystem, various second-layer solutions based on the Bitcoin network are also flourishing. With the emergence of Bitcoin second-layer networks equipped with Turing-complete virtual environments like AVM and BVM, BiFi is poised to expand into more complex and advanced financial experiments, and the massive financial reserves in the Bitcoin network will provide continuous momentum for the development of the BiFi ecosystem.

DLCs enable Bitcoin to utilize off-chain data by using adaptor signatures. These signatures ensure that the contract outcomes are verifiable and enforceable only when specific conditions provided by an oracle are met. In Shell Finance, this powerful technology forms the backbone of the lending protocol’s liquidation module.

What is DLC?

DLC is a cryptographic technique that uses adaptor signatures to create programmable financial contracts on Bitcoin. Its core functionality allows Bitcoin to securely utilize off-chain data provided by oracles, trusted entities that supply external information such as market prices, weather data, or sports scores. This integration allows Bitcoin to perform complex operations that typically require a more flexible execution environment like Ethereum's.

DLC in Shell Finance

In Shell Finance, DLC is implemented as the core technology for the lending protocol’s liquidation mechanism. This application ensures that collateralized loans are managed transparently and securely, leveraging off-chain data to determine the state of each lending position. Here’s how DLC is used in practice:

• Loan Initiation: When a user initiates a loan by collateralizing Bitcoin inscription assets (such as Ordinals, Runes, Atomicals, and BRC-20), Shell Finance calculates the loan amount based on the collateral value and the current market price provided by an oracle. A DLC contract is then set up, initializing a secret value used for future liquidation scenarios.

• Loan Adjustment: Users can adjust their collateral or debt amounts throughout the loan's lifecycle. Each adjustment recalculates the collateral ratio using real-time data from Oracle, ensuring the loan remains properly collateralized. The DLC is updated accordingly to reflect any changes.

• Liquidation: The most critical application of DLC in Shell Finance is during liquidation. If the collateral value drops below the required minimum collateralization ratio (MCR), the DLC allows for the automatic liquidation of the position. Here’s how it works:

  1. The oracle provides a price update indicating that the collateral value has fallen below the liquidation threshold.

  2. This triggers the disclosure of the secret value within the DLC, enabling the protocol to execute the liquidation.

  3. The assets are then auctioned off in a Dutch auction style, with the proceeds used to repay the debt and any excess added to Shell Finance’s insurance fund.

Practical Operation

Consider a user who has collateralized $ORDI to borrow $BTCX in a practical scenario. The following steps outline the DLC-driven liquidation process:

1. Monitoring: The oracle continuously monitors the market price of $ORDI.

2. Triggering Liquidation: If the price drops below 225,000 SATS/ORDI, the oracle signals the protocol.

3. Executing Liquidation: The secret value is revealed, and the DLC signatures are completed to liquidate the position.

4. Auction: The collateral is auctioned, and the proceeds are used to cover the debt and any liquidation penalties.

By integrating DLC with Oracle technology, Shell Finance ensures a trustless and automated liquidation process, enhancing security and efficiency in its lending operations. This innovative use of Bitcoin Layer 1 capabilities sets a new standard for DeFi protocols, bringing sophisticated financial services directly onto the Bitcoin network.

In blockchain networks, the core of each layer of applications is built to capture the liquidity value from the layer above it. Ethereum, as a public blockchain platform with smart contract capabilities, established the ERC-20 token standard since its inception in 2015:

• Builders are not satisfied with simple asset trading. To capture the liquidity value of both the native token $ETH and the proliferation of ERC-20 tokens, a plethora of excellent DeFi projects, such as DEXs, stablecoins, and lending platforms, emerged.

• Similarly, the ERC-721 market, with its significant capital accumulation, gave rise to numerous NFTFi projects focusing on lending and fractional ownership.

As for the Bitcoin network, originally designed as a peer-to-peer electronic cash system, its primary purpose is to facilitate the easy transfer of $BTC among users. Innovative applications like the Lightning Network are built on top of $BTC. However, this situation changed with the emergence of tokens on Bitcoin:

• The popularity of Bitcoin-incribed assets provides a good opportunity to activate the liquidity value of the vast capital within the Bitcoin network. The emergence of token protocols and assets attracts many OTC funds and Bitcoin holders.

• Similarly, the token market on Bitcoin is not limited to simple asset trading, necessitating a plethora of BeFi (Bitcoin Finance) projects to provide users with high-quality leverage and lending scenarios.

The bitcoin-inscribed asset market encompasses fungible token standards (such as BRC-20, ARC-20, SRC-20, etc.) and non-fungible token standards like Ordinals NFT, Bitmap, etc. Because these token standards derive their underlying logic from Ordinals, their trading paradigms and liquidity characteristics are very similar, and their user bases heavily overlap. Therefore, when discussing BeFi (Bitcoin Finance), the market scope includes the entire Bitcoin-inscribed asset market. This market has rapidly grown into a multi-billion-dollar market.

Due to the unique nature of the Bitcoin network, existing infrastructure and applications from other layer-one networks cannot be quickly migrated. Therefore, the BeFi infrastructure in the Bitcoin ecosystem (including DEXs, stablecoins, lending platforms, etc.) is severely lacking. The emergence of Shell Finance is expected to fill the gap in the token lending market on Bitcoin, becoming an essential piece in the puzzle of the new wave of the BTC ecosystem.

BiFi: Coin-Based Products

Protocols and applications should be designed to align with the user habits of upper-layer networks to capture the value of assets better.

Due to its design as a smart contract platform, Ethereum has a highly diverse user base. Differences between new and experienced users lead to the coexistence of both ETH-based and USDT-based user groups. Despite this, most NFT projects still use ETH as the base currency. Because of this community culture and user habits, NFTFi projects will continue to use ETH as the base currency, aiming to lower the barrier to user acquisition.

On the other hand, the Bitcoin network is a single-asset network, with a highly unified user base accustomed to a single asset valuation standard. The value is priced only in Bitcoin in the world created by Bitcoin. Due to this inherent habit of pricing assets in Bitcoin, even in the flourishing marketplace of tokens on Bitcoin, the valuation of tokens remains in BTC terms (satoshis terms). Therefore, the pricing logic of BeFi projects in the token market should respect this highly overlapping user habit. This is also the fundamental reason why Shell Finance chooses $BTCX, a synthetic asset anchored to the value of BTC, as the basis for valuation. Moreover, from an engineering standpoint, using BTC-based valuation allows the entire business process to be conducted according to the native token transfer method without introducing additional system complexity.

Peer-to-Protocol: Combination of Peer-to-Peer and Peer-to-Pool

In the cryptocurrency lending market, the two most common matching methods are:

• Peer-to-Peer (P2P): In P2P lending, bilateral participants in the market, borrowers and lenders, are directly paired. When the required parameters are met, the lending relationship can occur.

• Peer-to-Pool (P2Pool): P2Pool lending allows users to borrow and lend assets without the need to trust a third party. The lending platform charges borrowers borrowing costs and offers interest incentives to lenders based on liquidity and market conditions.

Peer-to-peer lending protocols are relatively inefficient. Borrowers and lenders need time and effort to find suitable counterparties and offers. Also, the liquidity in the lending bilateral market is fragmented, making it difficult to match user demands precisely. In the Bitcoin network, due to the stateless nature of the UTXO model, there are no concepts of accounts and balances on-chain, making it impossible to implement programmable state data similar to Ethereum smart contracts. Peer-to-pool lending, easily achievable on Ethereum, cannot be directly applied to the Bitcoin network.

Shell Finance focused on solving the key problem of achieving efficient features similar to peer-to-peer on the UTXO model from the outset of its design. The core solution lies in introducing Vaults as the unit of each lending, allowing the protocol to act as a connector between the borrowing and lending markets, thereby constructing a unique lending structure called Peer-to-Protocol.

With this design, the protocol establishes independent lending relationships with each borrowing position in the borrowing market, thereby meeting diverse borrowing needs. Meanwhile, by actively maintaining the price balance between $BTC and $BTCX through the protocol and liquidity pools, the protocol absorbs liquidity from the lending market. Simulating the efficient characteristics of lending pools on the UTXO model greatly improves bilateral markets' matching and capital utilization efficiency.

Lending on Bitcoin Is Cheaper than Ethereum L1.

The operating costs on the Bitcoin mainnet are often overestimated, which may stem from misconceptions arising from the high value of Bitcoin itself and the lack of on-chain applications. However, the reality is that due to the characteristics of the UTXO model, all computations and verifications occur off-chain, making transactions both the result and the proof. Therefore, the data carried by UTXOs is very limited, and the on-chain operating costs are not high.

Here, we illustrate this with a simple comparison: Assuming the current price of Bitcoin is approximately $65,000, and the network's Gas Price is 50 sats/vB. Taking an example operation in Shell Finance where collateralizing $ORDI to borrow $BTCX, the data size required to be sent to the chain is approximately 600 Bytes, according to the formula:

$$Cost = v_{byte} * Price_{gas} * Price_{satoshi}$$

We estimate that this operation will cost approximately $20. Similarly, we can calculate the cost of redeeming $ORDI to repay the $BTCX loan, which is approximately $21.

As shown in the table, for operations involving ARC-20 and Ordinals NFT as collateral, the on-chain data size is smaller (about 400 Bytes per transaction), resulting in lower gas costs, with each operation costing only $12 to $14:

In contrast, looking at lending protocols on Ethereum, taking AAVE as an example (with Ethereum price at approximately $3,800 and Gas Price around 70 Gwei):

• The cost of lending out $USDT 0xb4cb51a...ba94629 through AAVE is approximately 0.028 ETH, equivalent to $109.17.

• While the cost of repaying the $DAI debt 0xb0833ae...54d84fc is about 0.016 ETH, equivalent to $63.85. It can be seen that even with such a high Bitcoin price, the typical user operation costs on Shell Finance are significantly lower than similar products on Ethereum, saving nearly 75-80% of gas expenses.

What Are We Building?

Shell Finance is a trustless peer-to-protocol lending protocol built on the Bitcoin network, which utilizes PSBT and DLC technologies to achieve trustless lending and liquidation processes. The protocol consists of two key modules: first, its synthetic asset $BTCX, which is pegged to the value of BTC; second, the lending protocol that supports various script assets (including Ordinals, Runes, Atomicals, Stamp, etc.) as collateral to borrow $BTCX. It provides the following core functionalities:

• Trustless: Shell Finance leverages PSBT and DLC script contracts to enable secure trading of inscribed assets directly on Bitcoin Layer 1.

• Peer to Protocol: Enhancing market matching and fund utilization efficiency in the lending market through Peer-to-Protocol strategies.

• 0% Interest Loans: Shell Finance charges a one-time fee of 1% for borrowing BTCX, instead of highly fluctuating interest rates.

Users can gain more liquidity through collateralized borrowing, converting lower-liquidity script assets into higher-liquidity Bitcoin synthetic assets, $BTCX, at a lower cost, thus achieving true financial leverage. Moreover, when users borrow $BTCX, whether they swap it back to $BTC for further trading or provide liquidity for BTCX/BTC trading pairs, they can generate additional profits.

How Shell Finance Works?

We know that the Bitcoin network lacks a Turing-complete virtual execution environment like the EVM, making it unable to handle complex business logic through smart contracts. Currently, most projects in the market choose to move to more developer-friendly layer 2 solutions or other networks through cross-chain interoperability. However, the trust assumptions and security risks introduced by cross-chain solutions have become the Achilles' heel they cannot avoid.

Based on the principle of minimizing trust, Shell Finance utilizes PSBT technology to conveniently collect multi-party signatures when dealing with scenarios involving borrowers, liquidators, and the protocol, ensuring the security of user and protocol funds while achieving atomic asset swaps. Additionally, due to the inability to deploy smart contracts to manage users' collateral funds on the Bitcoin network, protocols such as lending, options, and futures that require liquidation based on Oracle prices unavoidably need the protocol to retain operational control over user assets, increasing unnecessary trust costs. Shell Finance addresses this issue by introducing Discreet Log Contracts (DLC), enabling a trustless liquidation mechanism.

Take a common Shell Finance scenario as an example: Suppose Alice collateralizes 100 $ORDI tokens to borrow 0.15 $BTC worth of $BTCX, calculated based on a minimum collateralization ratio of 150%. Only when the Oracle quotes for $ORDI fall below 225,000 SATS/ORDI, does the borrowing position transition to a pending liquidation state. In this scenario, we want liquidators to be able to liquidate the position without permission while ensuring that nobody can manipulate the user's collateral assets until the price reaches the liquidation threshold. DLC is introduced to address this requirement.

In the scenario described above, when Alice establishes the borrowing relationship, she requests a price oracle to generate a secret value pair and initialize the DLC. This DLC is used to stipulate an agreement between Alice and the protocol regarding the price of $ORDI:

• If the price falls below 225,000 SATS/ORDI, the protocol can liquidate Alice's collateral according to the prearranged DLC contract.

• If the price is greater than or equal to 225,000 SATS/ORDI, nothing happens, and asset ownership remains unchanged.

Once the DLC is established, Alice and the protocol must create a commitment transaction for the agreed-upon outcome. However, the signatures exchanged between the parties cannot be directly used to unlock the funds locked in the DLC. Instead, they must wait for the oracle to reveal a secret value. Therefore, in this case, we only need the oracle to commit to publishing the secret value when the price falls below 225,000 SATS/ORDI. Upon a successful auction by a liquidator, the protocol can utilize this secret value to complete Alice's signature and signature, making the transaction valid and broadcast to the network, triggering the liquidation effect.

DLC allows users and protocols to enter into agreements using the Bitcoin blockchain as a platform, with both parties locking funds in a multi-signature address to construct the DLC script. These funds can only be utilized and redistributed according to certain rules when the oracle publishes specific information at a specified time. In Shell Finance, the protocol utilizes DLC to implement a liquidation mechanism involving external price oracles without requiring users to trust any entity.