Circle details Arc’s roadmap for quantum-resistant blockchain security, addressing the 'harvest now, decrypt later' threat to digital assets.

The company plans a phased rollout of security measures, starting with quantum-resistant signatures and wallets at the mainnet launch in 2026, with the solution being voluntary. Subsequent phases will cover validators, infrastructure, and data protection.

Arc, which is already operating on a public testnet, aims to provide corporate access to blockchain applications through assets like USDC.

The Risk Begins Before Q-Day

Circle emphasized that the threat does not start with the so-called “Q-Day”—the moment quantum computers can break public-key cryptography—but much earlier. The “harvest now, decrypt later” concept, described by the National Institute of Standards and Technology, suggests that attackers may already be collecting encrypted data for the purpose of future decryption.

This creates a specific risk for blockchain ecosystems, where public keys, signed transactions, and offline infrastructure could be exposed to future attacks. Addresses that have already conducted transactions and revealed their public keys are particularly vulnerable.

Migration: The Greatest Challenge

According to Circle, the transition to post-quantum security will be a long-term and complex process that could take years. It is not just about wallets; it involves the entire ecosystem—validators, smart contracts, key management systems, cloud infrastructure, and even the cryptographic assumptions behind ZK technologies.

Some estimates reveal that simply migrating all Bitcoin UTXO addresses to quantum-resistant solutions could take months of continuous processing—a scale that underscores the systemic risk to the industry.

An additional complication is the size of post-quantum signatures, which are significantly larger than current standards, increasing requirements for storage and computational power.

Industry Responds, but Consensus is Lacking

The growing risk is already triggering action across the sector. Google and experts from the California Institute of Technology warn that quantum breakthroughs may occur sooner than expected.

Some blockchains, such as Algorand, are considered better prepared, while Ethereum and Solana are actively developing solutions. At the same time, the Bitcoin community lacks a unified opinion. Adam Back of Blockstream considers the risk exaggerated, while other researchers insist on rapid protocol changes.

Arc Bets on Proactive Preparation

The advantage of Arc, according to Circle, is that it was designed with the quantum threat in mind from the very beginning. Instead of forced migration, the platform offers a phased, compatible approach that allows the ecosystem to adapt over time.

In the shorter term, the focus is on protecting wallets and confidential data, while the medium and long-term horizons will address infrastructure and validators.

For institutions—including banks, fintech companies, and digital asset issuers—this sets a new standard: cryptographic resilience must match the lifecycle of the assets.

Against this backdrop, Circle’s strategy highlights a broader industry trend—a shift from theoretical discussions to real infrastructure solutions before the quantum risk becomes inevitable.