What are Discreet Log Contracts (DLCs) on Bitcoin?

Discreet Log Contracts (DLCs) enable private, trustless Bitcoin smart contracts using oracles and adaptor signatures for conditional off-chain agreements.

Jul 14, 2025 at 12:56 pm

What Are Discreet Log Contracts (DLCs)?

Discreet Log Contracts (DLCs) are a type of smart contract protocol designed to operate on the Bitcoin blockchain. They enable trustless conditional payments based on external data, often referred to as oracle-provided outcomes. Unlike traditional smart contracts found in platforms like Ethereum, DLCs work within Bitcoin’s more limited scripting capabilities by using cryptographic techniques and off-chain computation.

The primary innovation behind DLCs is their ability to execute agreements without revealing the terms or conditions on the blockchain. This allows for privacy-preserving financial instruments, such as bets, insurance contracts, or derivatives, to be implemented securely using Bitcoin.

How Do Discreet Log Contracts Work?

At the core of DLCs is the use of adaptor signatures and oracles. An oracle is a trusted third-party entity that provides real-world data (e.g., sports results, stock prices) needed to settle the contract. The oracle does not have control over funds but provides a signed outcome that participants can verify.

• Contract Setup: Two parties agree on a condition tied to an oracle's future output.
• Fund Locking: Both parties lock Bitcoin into a 2-of-2 multisignature address.
• Oracle Signing: After the event occurs, the oracle signs the outcome using its private key.
• Payout Execution: Participants use the oracle’s signature along with their own to unlock the funds according to the agreed-upon condition.

This process ensures that only the involved parties know the exact details of the contract, while the blockchain only sees a standard transaction.

Privacy Benefits of Using DLCs

One of the most significant advantages of DLCs is enhanced privacy. Traditional smart contracts on other blockchains expose all logic and conditions publicly. In contrast, DLCs keep the actual contract logic off-chain, revealing only the final outcome.

• No On-Chain Conditions: Only the final transaction appears on the blockchain, indistinguishable from any other.
• Confidential Agreements: Parties can negotiate complex financial instruments without exposing their strategies or positions.
• Minimal Oracle Exposure: Oracles do not learn which contracts they are influencing, preserving the anonymity of users.

This makes DLCs particularly appealing for institutional applications, where confidentiality and plausible deniability are crucial.

Role of Oracles in DLCs

Oracles play a pivotal role in the execution of DLCs. However, unlike centralized oracle models, DLCs minimize trust requirements through cryptographic assurances.

• Non-Custodial Role: Oracles never hold or control funds. They only provide signed data points.
• Deterministic Signing: Oracles must sign outcomes using a known public key, ensuring verifiability.
• N-of-N Trust Model: Multiple oracles can be used to reduce single points of failure, though this increases complexity.

It’s important to note that oracles cannot alter the outcome or steal funds, even if malicious. Their role is strictly informational, and users can choose trusted sources or aggregate multiple feeds to mitigate risk.

Use Cases for Discreet Log Contracts

DLCs open up a wide array of decentralized financial tools that were previously difficult or impossible to implement on Bitcoin.

• Prediction Markets: Users can bet on real-world events (e.g., elections, sports) without relying on centralized bookmakers.
• Insurance Contracts: Automate payouts based on weather data, flight delays, or other measurable events.
• Options and Derivatives: Create decentralized options markets where counterparties can hedge exposure using BTC.
• Automated Escrow: Facilitate peer-to-peer trades where release of funds depends on verified delivery or performance.

Each of these applications leverages Bitcoin’s security model while introducing programmable logic via off-chain computation and oracle inputs.

How to Create a Basic DLC

Creating a DLC involves several technical steps, primarily handled by software libraries or wallets supporting DLC functionality.

• Agree on Terms: Define the event and possible outcomes (e.g., "Team A wins" or "Team B wins").
• Select an Oracle: Choose a reliable source that will publish a signed outcome after the event.
• Generate Keys: Each party creates a key pair and exchanges public keys.
• Build Contract Transactions: Construct two transactions: one for each outcome. These are signed with adaptor signatures involving the oracle’s public key.
• Fund the Contract: Both parties fund a 2-of-2 multisig address.
• Wait for Oracle Data: Once the event concludes, the oracle publishes the signed outcome.
• Claim Funds: Use the oracle’s signature to finalize the appropriate transaction and claim winnings.

These steps are typically abstracted away by user-friendly interfaces, but understanding them helps users assess trust assumptions and risks.

Frequently Asked Questions (FAQ)

Q1: Can DLCs Be Used Without Trusted Oracles?

While DLCs rely on oracles for real-world data, they do not require full trust. As long as the oracle’s public key is known and it signs outcomes deterministically, users can verify the authenticity of the data without trusting the oracle with funds or decision-making power.

Q2: Are DLCs Compatible With Lightning Network?

Yes, DLCs can be integrated with the Lightning Network. By keeping contract interactions off-chain, users can achieve faster settlements and lower fees, further enhancing scalability and privacy.

Q3: What Happens If the Oracle Fails to Provide a Signature?

If an oracle becomes unresponsive or refuses to sign, the DLC may remain unresolved. To mitigate this, some implementations allow for fallback mechanisms or multi-oracle setups, although these add complexity.

Q4: How Do DLCs Compare to Other Smart Contract Solutions Like RSK or Stacks?

Unlike RSK or Stacks, which offer Turing-complete smart contracts, DLCs are purpose-built for conditional payments. They prioritize privacy, simplicity, and Bitcoin-native execution, avoiding the need for sidechains or new consensus layers.