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papers/lux-threshold-mpc/sections/09-comparison-with-alternatives.tex
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\section{Comparison with Alternatives}
\label{sec:comparison}
% ============================================================
We compare the FROST+CGGMP21 approach against three deployed alternatives for
cross-chain custody.
\begin{table*}[t]
\centering
\small
\begin{tabular}{@{}p{2.8cm}p{2.5cm}p{2.5cm}p{2.5cm}p{2.5cm}@{}}
\toprule
\textbf{Property} & \textbf{FROST + CGGMP21} (Teleport) & \textbf{BLS Aggregation} (Wormhole) & \textbf{TSS GG20} (tBTC v2) & \textbf{Multisig} (Gnosis Safe) \\
\midrule
Sig. scheme & Schnorr + ECDSA & BLS12-381 & ECDSA (GG20) & ECDSA \\
On-chain format & Native single sig & Custom verifier & Native single sig & $k$ sigs + contract \\
Verify cost (EVM) & 3,000 gas & 180,000 gas & 3,000 gas & $3{,}000k$ gas \\
Chain coverage & 17 families & EVM + custom & secp256k1 only & EVM only \\
Rounds (signing) & 2 (FROST) / 1+pre (CGGMP) & 1 & 8 & 0 (async) \\
Identifiable abort & Yes (CGGMP21) & No & No (GG20) & N/A \\
Key refresh & Yes & No (fixed keys) & Yes & N/A \\
Bitcoin Taproot & Yes (native) & No & No & No \\
Ed25519 chains & Yes (native) & No & No & No \\
Corruption threshold & $t{-}1$ of $n$ & $t{-}1$ of $n$ & $t{-}1$ of $n$ & $k{-}1$ of $n$ \\
\bottomrule
\end{tabular}
\caption{Comparison of threshold/multisig schemes for cross-chain custody.}
\label{tab:comparison}
\end{table*}
\paragraph{BLS Aggregation (Wormhole-style).}
Wormhole~\cite{wormhole2023} uses BLS12-381 aggregate signatures from a guardian set.
BLS aggregation provides compact multi-signer proofs but requires a custom on-chain
verifier (BLS precompile or Solidity implementation) costing 180,000+ gas on EVM.
BLS12-381 is not natively supported on any major chain except Ethereum (EIP-2537).
Coverage is limited to chains where the verifier can be deployed.
\paragraph{TSS GG20 (tBTC v2).}
tBTC v2~\cite{tbtc2022} uses the GG20 protocol~\cite{gennaro2020} for threshold
ECDSA. GG20 requires 8 rounds of communication (vs.\ CGGMP21's offline+1 or FROST's
2 rounds) and lacks identifiable abort---a malicious party can cause signing to fail
without detection. GG20 covers only secp256k1 chains. No Ed25519 or Taproot support.
\paragraph{Multisig (Gnosis Safe).}
On-chain multisig is the simplest approach but has fundamental limitations: (1)~gas
cost scales linearly in the number of signers $k$; (2)~threshold changes require
contract transactions; (3)~not available on chains without smart contracts
(Bitcoin, Stellar); (4)~reveals the threshold structure on-chain.
\subsection{Security Property Comparison}
\begin{table}[H]
\centering
\small
\begin{tabular}{@{}lcccc@{}}
\toprule
\textbf{Property} & \textbf{Ours} & \textbf{BLS} & \textbf{GG20} & \textbf{Multisig} \\
\midrule
EUF-CMA & \checkmark & \checkmark & \checkmark & \checkmark \\
Id. abort & \checkmark & -- & -- & N/A \\
Key refresh & \checkmark & -- & \checkmark & -- \\
Forward sec. & \checkmark & -- & \checkmark & -- \\
Privacy${}^*$ & \checkmark & -- & \checkmark & -- \\
UC security & \checkmark${}^\dagger$ & \checkmark & -- & N/A \\
\bottomrule
\end{tabular}
\caption{Security properties. ${}^*$Privacy = threshold structure not revealed on-chain.
${}^\dagger$CGGMP21 is UC-secure; FROST is proven in the ROM.}
\label{tab:security}
\end{table}
% ============================================================