Bitcoin Magazine
Not ECDSA. Not Schnorr. Meet DahLIAS.
Aggregate signatures aren’t new. They’ve been round for the reason that early 2000s. But constructing one that really works in Bitcoin’s safety mannequin, with Bitcoin’s elliptic curve, has by no means been confirmed. Developers speculated it may be attainable. They shared hand-wavy sketches and stated, “maybe it’d work like MuSig2, but across transaction inputs.” The thought lingered for years as developer folklore, shut, by no means provably confirmed.
That modified lately, when Jonas Nick and Tim Ruffing of Blockstream Research, along with Yannick Seurin of Ledger, revealed a paper that turned this cryptographic ghost story right into a concrete, provable consequence. DahLIAS is the primary formal, safe development of a full constant-size combination signature (CISA) scheme that works on Bitcoin’s native curve!
But that’s a whole lot of phrases, so let’s break that down:
- Full aggregation: Multiple signatures throughout totally different inputs are mixed into one — and the result’s a 64 byte signature whose dimension stays fixed, regardless of what number of signers or inputs.
- Cross-input: Each signer can authorize totally different inputs, and all mix into one signature.
It provides no vital new assumptions past these already relied on by Bitcoin. DahLIAS builds a brand new cryptographic primitive utilizing the identical math Bitcoin already depends on, unlocking a completely new sort of signature.
Let’s Talk About Curves and Signatures
Digital signatures are how Bitcoin proves {that a} person has approved a transaction. When you go to spend bitcoin, your pockets makes use of a personal key to signal a message, and the community verifies that signature utilizing the matching public key.
Bitcoin makes use of the secp256k1 curve. It is quick, environment friendly, and has been battle-tested over time. It helps signature schemes like ECDSA (Bitcoin’s authentic signature algorithm) and Schnorr (added via Taproot in 2021), that are at the moment the one signature schemes permitted by Bitcoin consensus.
Traditionally, full signature aggregation relied on mathematical operations not supported by Bitcoin’s curve, secp256k1, which made it appear out of attain. These options have usually relied on different varieties of elliptic curves. For instance, BLS (Boneh–Lynn–Shacham) signatures use a particular sort of curve referred to as a pairing-friendly curve, which allows superior operations like combining many signatures, even on totally different messages, into one.
The drawback is that BLS signatures don’t work on secp256k1. While Schnorr was a pure improve from ECDSA, since each depend on the identical sort of elliptic curve, including BLS could be a a lot larger leap and a departure from Bitcoin’s present safety mannequin. Though technically attainable, it might introduce new cryptographic assumptions and add vital complexity to the protocol. Supporting a curve that’s pairing-friendly, like BLS12-381, could be a significant change for Bitcoin.
This is a part of why full signature aggregation has by no means been carried out on secp256k1.
Until now.
What Aggregate Signatures Actually Do
Most Bitcoin customers are aware of multisignatures. In a multisig pockets, a number of individuals collectively authorize the spending of a single UTXO or some particular “coin”. Everyone indicators the identical enter information. This setup is beneficial for issues like shared custody wallets.
Aggregate signatures work otherwise. Instead of a number of individuals signing the identical enter or coin, every signer authorizes a distinct UTXO in a transaction. These separate signatures are then compressed into one compact proof. With DahLIAS, which means a single 64-byte signature on Bitcoin’s secp256k1 curve that verifies all inputs directly.
That means you probably have 5 inputs from 5 totally different individuals, the transaction wants 5 totally different signatures. With an combination signature, all of these might be bundled into one. Even if every signer is spending a distinct enter and signing a distinct a part of the transaction, the result’s one signature that proves your complete transaction was correctly approved.
It’s like zipping a complete checklist of approvals into one file. The signature is compact, however nonetheless verifiably proves that every signer approved their particular UTXO.
Instead of verifying 10 separate signatures, you confirm one.
This helps realign incentives for privateness. By lowering the signature overhead to a single 64-byte proof, DahLIAS lowers the price of combining inputs in CoinJoins, making it financially smarter to decide on privateness than to go with out it.
Why Half-Aggregation Got Close
Shortly after Schnorr signatures have been launched on Bitcoin, builders explored half-aggregation, as a strategy to compress a number of signatures however they weren’t fastened dimension. Each enter contributes to the dimensions of the signature, so the transaction nonetheless grows with each participant. DahLIAS fixes this by enabling full-aggregation throughout inputs and signers. No matter how many individuals are concerned or what they’re signing, all their signatures compress into one constant-size, 64-byte proof.
What DahLIAS Actually Unlocks
The most important profit right here is that DahLIAS are lowering the dimensions of complicated transactions.
DahLIAS makes use of a two-round interactive signing course of. It’s just like MuSig2 in that regard, nevertheless it isn’t a multisignature protocol as a result of it doesn’t require all individuals to co-sign the identical message. Instead, it aggregates totally different signatures on totally different messages throughout the transaction.
DahLIAS can be quicker to confirm than checking every signature individually, as much as twice as quick in some instances. Lower verification prices make it simpler for extra individuals to run full nodes, which helps protect Bitcoin’s decentralization over time.
Importantly, DahLIAS comes with robust cryptographic ensures. The scheme consists of formal safety proofs. Earlier ‘folklore’ approaches to full signature aggregation lacked this, and a few have been even later proven to be insecure. Fortunately they weren’t adopted prematurely.
It’s value repeating: DahLIAS just isn’t a multisig protocol. It isn’t corresponding to MuSig2 or FROST from a purposeful standpoint, even when it shares related cryptographic constructing blocks. It serves a distinct objective. It affords a brand new strategy to encode many unbiased approvals into one clear, verifiable package deal.
Future Directions
You would possibly suppose: if DahLIAS is so highly effective, why isn’t it a BIP? Why not suggest it for Bitcoin consensus?
DahLIAS signatures don’t appear like Schnorr or ECDSA signatures. The verification algorithm is totally different. Instead of taking a single public key, message, and signature, a DahLIAS verifier takes lists of public keys and messages, and a single 64-byte proof.
This makes DahLIAS incompatible with Bitcoin’s present consensus guidelines. Supporting it on the base layer would require a consensus change. This paper doesn’t suggest that change, nevertheless it does one thing equally essential.
This paper exhibits {that a} full signature aggregation scheme for Bitcoin’s native curve is feasible.
That alone is a significant step ahead.
To make DahLIAS a part of Bitcoin, somebody would want to put in writing a Bitcoin Improvement Proposal (BIP), perhaps even utilizing secp256k1lab. That means specifying the scheme intimately, contemplating its implications for consensus and implementation, and constructing neighborhood assist. This paper lays the cryptographic basis for that dialog.
The actual worth of the DahLIAS paper is what it proves. Full signature aggregation on secp256k1 is not only a thought experiment. It’s concrete. It’s environment friendly. It’s safe. For years, the thought lived in developer folklore. Now, it’s written down, analyzed, and confirmed. All that’s left is to convey it to Bitcoin—if we would like it.
This is a visitor publish by Kiara Bickers. Opinions expressed are fully their very own and don’t essentially replicate these of BTC Inc or Bitcoin Magazine.
This publish Not ECDSA. Not Schnorr. Meet DahLIAS. first appeared on Bitcoin Magazine and is written by Kiara Bickers.
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