Sei Network Goes Post-Quantum: What is SIP-5?

SIP-5 is a draft proposal from Sei Labs (@Sei_Labs) that gives every EVM account on Sei Network (@SeiNetwork) a ready-made path to quantum-safe security, without changing addresses, balances, or transaction history. The proposal was filed on July 27, 2026, and announced a day later. No quantum computer capable of breaking Sei's cryptography exists today, and that is exactly the point: build the fire escape before anyone smells smoke.

Sei confirmed the release on X with a short message: "The first proposed plan for Sei to become quantum-secure is live."

Why Would a Blockchain Need Quantum Protection?

Sei, like every EVM chain, secures user accounts with ECDSA signatures on the secp256k1 curve. That scheme has one theoretical weak spot. Once an account's public key appears on-chain, a sufficiently powerful quantum computer running Shor's algorithm could work backward to the private key and forge transactions from that account.

Nobody has built that machine, but Sei Labs notes many experts believe the timeline for one is accelerating. The SIP's authors, Maja Lie and Benjamin Marsh, argue that a migration performed only after a credible attack becomes public would be a race between account holders and attackers. The mechanism has to exist before the emergency does.

How Does SIP-5 Work?

The core idea is a registry that sits alongside the existing account model, designed so validators can verify a post-quantum transaction with one address lookup and one signature check. Nothing about the EVM address format changes. Instead:

• Users bind a post-quantum verification key to their existing address. The first supported algorithm is ML-DSA-44, a lattice-based signature scheme standardized by NIST in FIPS 204.
• Everything the account already has is preserved: address, balance, nonce, transaction history, token approvals, and contract relationships. No funds move and no chain reset happens.
• Accounts choose how to transition. DUAL mode accepts both classical and post-quantum signatures during a window, while SOLO mode switches to post-quantum only right away.
• A future governance vote can set a global cutoff height, called H_Q in the spec, after which classical signatures stop working network-wide. No cutoff is currently scheduled.
• After a cutoff, accounts that never registered a quantum-safe key can no longer send transactions, but they keep their full state and can still receive funds and be called by contracts.
• New accounts can still be created after the cutoff through sponsored transactions that register and fund a post-quantum address in one atomic step.

An algorithm identifier is built into the registry, so future signature schemes can be added or retired without redesigning the system.

What Are the Trade-Offs?

Post-quantum cryptography is heavy. An ML-DSA-44 public key is 1,312 bytes and a signature is 2,420 bytes, against 65 bytes for a classical ECDSA signature. That means more bandwidth, higher gas costs, and lower throughput if large numbers of accounts switch over. The draft also caps how many post-quantum authentication bytes can go into a single block, so the heavier signatures cannot crowd out ordinary transactions.

Sei Labs is upfront about this. SIP-5 is positioned as an emergency option rather than the end state, and the team says it is researching higher-performance post-quantum schemes that could eventually replace it. The draft also flags its own limits: it covers EVM account authorization only, while consensus keys and bridge or contract-level authentication would need separate migration plans.

What Happens Next?

SIP-5 sits in Draft status as a Standard (Core) proposal, reviewed by Philip Su and open for community discussion on GitHub. The rollout, if approved, comes in stages: registration support first, then a migration window with wallet and explorer tooling, and only after audits and monitoring an optional cutoff decision by governance.

Sei Labs co-founder Jayendra Jog (@jayendra_jog) framed the proposal on X as insurance rather than alarm, writing that "every account on @SeiNetwork has a route to become quantum-secure" if a threat appears, while the team works in parallel on faster signature schemes.

SIP-5 answers what Sei will do if quantum computing arrives ahead of schedule. Whether accounts ever need to use it, and whether a lighter scheme replaces ML-DSA-44 before they do, now sits with the community review that opened this week.

Sources:

• Sei Labs Blog Official announcement post explaining SIP-5 in plain language.
• Sei Protocol GitHub Full SIP-5 draft with the technical specification and security considerations.
• Sei Research Simplified explainer of the proposal.
• Sei Network on X Announcement post confirming the proposal is live for review.