Leilão de Vickrey Confidencial com FHE em Blockchain Pública

• Thiago Rocha Duarte CEFET/RJ
• Thiago Delgado Pinto CEFET/RJ
• Diogo Silveira Mendonça CEFET/RJ

DOI: https://doi.org/10.5753/webmedia_estendido.2026.34243

Resumo

Sealed-bid auctions assume that each participant decides their bid without knowing the others’, but public blockchains expose every transaction in the mempool and in the permanent history, enabling frontrunning and strategy leakage. The prevailing workaround, the commit-reveal scheme, requires two transactions and reveals the losing bids at the end. This paper presents the implementation of a Vickrey (second-price sealed-bid) auction on Fhenix CoFHE, a Fully Homomorphic Encryption (FHE) platform for smart contracts, in which bids remain encrypted end to end. An incremental top-2 pattern solves the homomorphic computation of the second price with constant cost and storage per bid, handling ties with no additional structures. The evaluation on a public testnet (Arbitrum Sepolia) measures gas, calldata, and latency with 3, 5, and 10 participants, compares the pattern against an𝑂(𝑁) homomorphic-mask baseline implemented and measured in the same environment, and a leakage analysis quantifies in bits the adversary’s residual uncertainty: about 95% of the uncertainty over the unrevealed bids survives settlement. The contract, the web interface with in-browser encryption, and the measurement data are public and reproducible.

Palavras-chave: Vickrey auction, Fully Homomorphic Encryption, blockchain, privacy, smart contracts

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