Arc’s post-quantum roadmap covers wallet signatures, validator authentication,
private smart contract state, and offchain infrastructure.
Post-quantum features are on the roadmap and not yet available on Arc.
Why post-quantum security matters
Most public-key cryptography used today is vulnerable to large-scale quantum
computers. If those computers become practical, blockchains face two risks:
- Signature forgery. A quantum computer that breaks public-key cryptography
can forge signatures that secure wallets, authorize transactions, and
authenticate network participants.
- Harvest-now, decrypt-later attacks. Encrypted data captured today can be
stored and decrypted later when quantum attacks become practical, exposing
private transaction details, balances, and other sensitive data.
Because blockchain data is long-lived, post-quantum protections need to be in
place before quantum attacks are widely available.
Post-quantum roadmap
Arc’s roadmap phases each layer in a production-aligned sequence.
Post-quantum wallet signatures
Arc introduces beta support for a post-quantum wallet signature based on
SLH-DSA-SHA2-128s at mainnet launch. Adoption is opt-in.
Ecosystem constraints to keep in mind:
- Hardware wallet support will take time to mature.
- Post-quantum standards are still evolving, so long-term signature choices may
change.
Expect a transition period as tooling, wallet support, and integrations
mature.
Post-quantum privacy
Arc Privacy addresses the harvest-now,
decrypt-later threat. When Arc Privacy launches, encrypted state and private
transaction flows use post-quantum cryptography. In practice, public-key
encryption uses X-Wing KEM (combining X25519 and ML-KEM-768) with HKDF-SHA256
and AES-256-GCM.
Attackers can capture encrypted data today and attempt to decrypt it later when
quantum attacks become practical. Post-quantum encryption at the platform level
protects sensitive balances, transaction details, and recipients without
requiring you to implement custom post-quantum cryptography.
Post-quantum validator signatures
Validator authentication also requires post-quantum protection to keep the
ledger resilient. Arc adds post-quantum validator signatures in a later phase.
This sequencing is intentional: validator upgrades must be introduced carefully
to preserve throughput, latency, and operational reliability. Because Arc uses
sub-second finality, the window to exploit validator signatures is narrower than
the wallet-signature risk, making wallets the higher-priority target.
Offchain infrastructure
Quantum resilience extends beyond the chain itself. Circle’s roadmap includes
upgrading node-to-node communication to TLS 1.3 with the X25519MLKEM768 hybrid
key agreement, as well as encrypted data flows, access controls, cloud
environments, and other operational systems that support Arc.
Offchain traffic and stored data face the same post-quantum threat vectors as
onchain data when vulnerable cryptography remains in use. 
