Ethereum developers are considering a new approach that could let validators use quantum-resistant keys while gradually eliminating the BLS signature format that secures validator deposits today.

A group of Ethereum researchers has drafted a proposal to redesign the network’s deposit contract, which users rely on when locking ETH to become validators. The changes are intended to prepare Ethereum for the possibility of quantum computers eventually being capable of attacking its existing cryptographic protections.

The proposal would add a mechanism to the deposit contract that could eventually prevent new deposits from using the signature format currently supported by the network.

Ethereum’s BLS Keys Could Limit a Quantum-Safe Upgrade

The existing deposit contract hard-codes the size of BLS key pairs, creating a technical barrier to adopting alternative cryptography. Without modifying the contract, Ethereum would not be able to accept a quantum-resistant signature scheme even after developers selected a suitable replacement.

Approximately 42.4 million ETH is currently staked on Ethereum, worth around $104 billion at prevailing prices. Those funds are secured by validators using the BLS-based key format that the proposal would eventually phase out.

The proposal remains a draft and is awaiting further review. It currently carries a temporary identifier, while one repository maintainer has proposed EIP-8394 as its eventual number.

The plan would also retire Ethereum’s original deposit-processing system, which has been in use since staking began in 2022. Deposits would move to the newer framework that already handles withdrawals and validator-related changes.

New Deposit Design Could Support Multiple Signature Schemes

Ethereum validators currently use BLS signatures to participate in consensus. The system is efficient because many validator signatures can be combined into a single signature, helping reduce the resources required to operate the network.

The underlying cryptography, however, relies on elliptic-curve mathematics that a sufficiently advanced quantum computer could potentially defeat using Shor’s algorithm. Such an attack could give an attacker the ability to forge validator signatures.

The proposed deposit contract would remove the restriction to a single key format by supporting different key sizes. Each deposit would carry a tag identifying the cryptographic scheme it uses. Existing BLS deposits would be assigned tag zero, while future tags could be allocated to quantum-resistant alternatives.

If adopted, the updated system could initially accept BLS deposits alongside newer signature formats. Ethereum developers could later activate a rule preventing any additional BLS deposits. Validators already using BLS keys would continue operating, but new participants would have to use an alternative supported scheme.

Another protocol change would then be necessary to establish how Ethereum validators verify signatures produced by the new cryptographic systems.

Quantum Resistance Is Becoming a Larger Ethereum Priority

The deposit-contract proposal is part of Ethereum’s broader effort to prepare for quantum computing. EIP-8141, or the Frame Transactions proposal, is another piece of that strategy and is being considered for the Hegotá upgrade expected later this year.

Frame Transactions would allow regular Ethereum accounts to change the cryptographic method used to authorize transactions without requiring users to transfer their assets to a different address.

The issue gained additional attention after Google Quantum AI research published in March identified five potential ways quantum computing could be used to attack Ethereum. The research estimated that more than $100 billion in assets could be exposed across wallets, staking, smart contracts and layer-2 networks.

The Ethereum Foundation is aiming for around 2029 to complete the core protocol changes needed to strengthen the network against potential quantum attacks.