Ethereum developers have proposed a new deposit contract plan to prepare for the threat of quantum computers breaking signatures.

On Aug. 25, blockchain outlet CoinPost reported that the proposal was filed in the GitHub EIP repository under the provisional designation EIP9999 and is designed to process variable-length public keys and authentication data. The key point is that the current Ethereum deposit contract assumes fixed BLS12-381 public key and signature sizes, making it unable to accept larger post-quantum keys.

The new contract structure assigns an identifier called a "schema" for each deposit. Schema 0 refers to existing BLS (Boneh-Lynn-Shacham) signatures, while other values are reserved for future assignment to different cryptographic methods. Deposit data is delivered to the consensus layer as a request based on the EIP-7685 structure.

The contract structure also changes. The Merkle-tree method used by the existing contract is removed, and the design follows the log-based verification method introduced in EIP-6110. The verification hash field required under the previous method is also dropped. The deposit function is designed to take 4 arguments: "schema", "public key", "withdrawal credentials" and "credential metadata".

The developers also presented a phased shutdown procedure for the BLS method. The proposal manages contract status in a three-stage mode. It starts in an invalid state that rejects deposits immediately after introduction, then accepts the existing BLS method in an operational stage. In the final stage, it moves to a deprecation state that stops new BLS submissions.

The transition is designed to be irreversible. The mode moves in only one direction, and once it shifts to the deprecation state, new BLS registrations cannot be allowed again.

The timing for actual application has not been set. Both the activation timing and the timing for BLS deprecation are undecided, and the proposal also specifies dependencies on existing proposals such as EIP-6110 and EIP-7251. As a result, the plan is closer to a draft that lays out an approach to responding to quantum computing.

The current stage is also at an early review level. EIP9999 is still in draft form, and no official review by core developers or agreement on adoption has been reached. The provisional number 9999 is also a temporary label before formal registration. The formal EIP number and implementation schedule have not been confirmed.

In this situation, the proposal is expected to be a starting point for assessing whether Ethereum can change its staking deposit structure to fit future cryptographic systems. In particular, the design that keeps the existing BLS system while leaving room to assign new cryptographic methods if needed, and the transition condition that permanently blocks new BLS registrations, are expected to be central to future discussions.