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89 lines
4.0 KiB
TeX
89 lines
4.0 KiB
TeX
\section{Blockchain-Specific Attack Vectors}
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\label{sec:attack-vectors}
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\subsection{Attack 1: Mempool Key Exposure}
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When a user broadcasts a transaction, the transaction includes a signature from which
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the public key can be recovered (ECDSA recovery) or is explicitly included. Between
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broadcast and confirmation (typically 2--30 seconds on modern chains), the public key
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is visible in the mempool. A quantum adversary monitoring the mempool can:
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\begin{enumerate}[leftmargin=2em]
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\item Observe the public key in the pending transaction.
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\item Compute the private key via Shor's algorithm.
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\item Broadcast a competing transaction draining the account with higher gas.
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\item The competing transaction confirms first (front-running).
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\end{enumerate}
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This attack requires completing Shor's algorithm within the block time. Current
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estimates suggest this is infeasible with near-term quantum computers (hours per key
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recovery), but may become feasible as quantum hardware improves.
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\textbf{Mitigation}: Commit-reveal transaction schemes, where the transaction is
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committed (hash only) before revealing the public key. However, this doubles latency
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and is not backward compatible with existing EVM transaction formats.
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\textbf{Better mitigation}: Post-quantum signatures. If the signature scheme is
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quantum-resistant, public key exposure in the mempool is not a threat.
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\subsection{Attack 2: Validator Signature Forgery}
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Validator BLS keys are published in the validator set and remain static for the
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validator's entire stake duration. A quantum adversary can:
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\begin{enumerate}[leftmargin=2em]
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\item Recover any validator's BLS private key from their published public key.
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\item Forge signatures for arbitrary blocks, including blocks that conflict with
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the canonical chain.
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\item Create a forged finality certificate (aggregate signature) for a conflicting
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chain, violating the safety property of the consensus protocol.
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\end{enumerate}
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This is the most severe quantum attack on proof-of-stake blockchains: it breaks
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\emph{finality}, the property that confirmed transactions cannot be reversed.
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\subsection{Attack 3: Retroactive Chain Compromise}
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The permanent, public nature of blockchain data enables retroactive attacks:
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\begin{enumerate}[leftmargin=2em]
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\item A quantum adversary recovers private keys from historical public keys
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recorded on-chain.
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\item Transfers all assets from accounts that have ever had their public key
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exposed (any account that has sent a transaction).
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\item For UTXO chains: any output sent to a P2PKH address (public key hash) is
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safe until spent, but any output sent to a P2PK address (raw public key) is
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immediately vulnerable.
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\end{enumerate}
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For account-based chains (Ethereum, Lux C-Chain), every account that has sent at
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least one transaction has its public key permanently recorded on-chain.
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\subsection{Attack 4: Cross-Chain Bridge Key Extraction}
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Cross-chain bridges typically use MPC (multi-party computation) with ECDSA threshold
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signatures. The bridge's public key is on-chain. If the threshold scheme uses a
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$(t, n)$ configuration and the adversary can recover any $t$ individual signer public
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keys, the adversary can recover each signer's private key independently and forge
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bridge signatures.
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This is particularly dangerous because bridge contracts typically hold large asset
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pools: Wormhole (\$2.4B TVL), LayerZero (\$1.8B TVL), and similar systems are
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single-point-of-failure targets.
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\subsection{Attack 5: Oracle Attestation Forgery}
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Price oracles sign attestations with ECDSA or EdDSA keys. A quantum adversary who
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recovers oracle signing keys can forge arbitrary price feeds, enabling:
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\begin{itemize}[leftmargin=2em]
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\item Manipulation of DeFi lending protocol liquidations
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\item Artificial arbitrage through forged price discrepancies
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\item Triggering of options/derivatives at manipulated strike prices
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\end{itemize}
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%% ========================================================================
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%% 5. TIMELINE ESTIMATES
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%% ========================================================================
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