USDC quantum safety depends on slowest wallet, bridge or blockchain, Circle warns
USDC’s quantum security hinges on coordinated upgrades
Circle has warned that the security of its USDC stablecoin against future quantum computing attacks depends on the slowest participant in its ecosystem to upgrade. The company highlighted that wallets, bridges, custodians, and all 37 host blockchains must adopt quantum-resistant cryptography to fully protect the stablecoin, which holds a market value of about $73.6 billion.
A stablecoin is a type of cryptocurrency designed to maintain a stable value, often pegged to a traditional currency like the US dollar.
Why the 813-qubit record matters
Circle pointed to a recent record of 813 logical qubits in a quantum circuit as evidence that attacks on widely used blockchain signatures are becoming more feasible. However, the company clarified that this number alone does not predict when such an attack, known as Q-day, will occur. Instead, it signals the need for urgency in upgrading cryptographic systems.
The 813-qubit figure comes from a challenge optimizing circuits for secp256k1, the cryptographic curve used by Bitcoin and Ethereum. While it shows progress in reducing the resources needed for an attack, it does not account for factors like circuit depth, error correction, or physical hardware requirements. A March 2026 research paper estimated that a full attack on 256-bit elliptic curve cryptography could require fewer than 1,200 logical qubits and 90 million Toffoli gates, but this remains theoretical.
Circle’s limited control over the upgrade process
Circle can upgrade its own infrastructure, including its Arc blockchain, which supports post-quantum cryptography like SLH-DSA. However, the company cannot force upgrades on third-party wallets, custodians, or the 37 host blockchains where USDC operates, such as Ethereum, Solana, and XRPL. Each of these networks must independently adopt quantum-resistant signature schemes to prevent vulnerabilities.
Arc currently allows for post-quantum signature verification but still relies on traditional ECDSA signatures for transaction authorization. Circle’s roadmap includes testing hybrid systems that combine classical and post-quantum cryptography during the migration period.
What is confirmed
- Circle has warned that USDC’s quantum safety depends on all parts of its ecosystem upgrading, including 37 host blockchains.
- An 813-logical-qubit circuit record shows progress in quantum attack efficiency but does not set a timeline for Q-day.
- Circle’s Arc blockchain supports post-quantum signature verification but has not finalized its transaction-signature scheme.
- USDC’s market value was approximately $73.6 billion as of September 2, 2026.
Why this matters
The warning highlights a coordination challenge: even if Circle secures its own systems, USDC remains vulnerable if any wallet, bridge, or blockchain in its network fails to upgrade. This could leave parts of the ecosystem exposed to future quantum attacks, which could compromise transaction security.
