Ethereum specialists are proposing to reconstitute the contract which gives validators the possibility of depositing their ETH. Their intention is to authorize new cryptographic systems in order to abandon the BLS signatures currently employed. Nearly 42.4 million ETH, valued at nearly $104 billion, depends on this format. The project nevertheless remains a working document. It does not choose any post-quantum algorithm and does not yet ensure the protection of the network against any attack.
In brief
- The new contract would accept multiple cryptographic key formats.
- Current BLS signatures would temporarily retain compatibility.
- An irreversible mechanism would then make it possible to block new BLS deposits.
- No quantum computer can currently compromise Ethereum.
The current deposit contract blocks any rapid migration
On August 24, three researchers submitted a draft deposit contract dedicated to Ethereum validators. Indeed, Kevaundray Wedderburn, Tom Wambsgans and Thomas Coratger wish to prepare staking for the future adoption of signatures robust to quantum computers.
It should be noted that the deposit contract is the entry point for staking. The investor locks his ETH there before his validator can join the network, carry out transaction verifications and participate in the consensus. This procedure currently approves public keys as well as BLS signatures whose size is determined in advance.
The BLS public key used by Ethereum takes up 48 bytes, while the size of a signature is 96 bytes. This configuration offers a major advantage. Various signatures can be brought together without their size increasing correlatively with the number of validators. Thus, Ethereum could effectively carry out votes useful for the operation of his channel Beacon.
This dependency may, however, become a limiting thing during a future crypto migration. Post-quantum systems generally use massive keys and signatures. Therefore, it will be complicated for the current contract to accept them without modification, even if the researchers immediately agree on a replacement algorithm.
This difficulty affects a significant part of the ecosystem. Nearly 42.4 million ETH are currently staked, or around $104 billion. Capital is not currently under threat, however the validators who ensure their security use cryptography which would become fragile in the long term.
An identifier would allow you to change cryptographic systems
The contract submitted by the developers could accept public keys, signatures as well as metadata of variable length. Thus, each deposit would also contain an identifier which would specify the cryptographic system used by the validator. The number zero would be reserved for the current BLS format to ensure compliance during the transition.
Future identifiers would potentially be compatible with post-quantum signatures or other devices still in development. This structure could give Ethereum a form of cryptographic flexibility. The blockchain would add a new architecture without having to reconstitute the entire deposit contract.
However, it is not up to the project to choose a post-quantum algorithm. It only designs the infrastructure capable of hosting one. A new protocol modification will be necessary to define the rules for verification, aggregation and processing of new signatures at the consensus level.
The various data relating to the deposit could also pass through requests from the execution layer. Introduced by the EIP-7685this mechanism ensures the transmission of certain operations from this execution layer to the consensus layer. Note that Ethereum already uses it for deposits, withdrawals caused from the execution layer and the consolidation of validators.
The change would replace the historic architecture based on a Merkle tree. It would then bring together future post-quantum deposits of the structure already adopted for multiple operations relating to staking.
Ethereum could permanently close the door to BLS deposits
Various could follow this migration. The contract would first accept BLS filings while gradually incorporating new signature formats. Ethereum clients, validators and staking operators would thus benefit from time to adapt the different tools.
A future decision by the protocol would contribute to the deactivation of new deposits employing the BLS system. This mechanism could be irreversible in the current version of the project. When this mode is activated, it is no longer possible for a validator to join Ethereum using a key that falls under the old format.
BLS validators already active could not be immediately deleted by this closure. Indeed, additional rules would be useful to govern the migration of their keys, their exits or the change of their withdrawal identifiers. The document then fundamentally deals with the arrival of future validators, not the complete migration of present operators.
Such a proposal does not take into account users’ wallets. While validators rely on BLS, conventional Ethereum accounts use ECDSA signatures. Accounts, KZG commitments employed for data, and some zero-knowledge proof systems require their own post-quantum solutions.
The new contract cannot be presented as a general protection of Ethereum because of such a distinction. This is one piece of a larger migration that will affect multiple layers of the protocol and much of its infrastructure.
Full protection remains scheduled for around 2029
A team exclusively dedicated to post-quantum security was set up last January by the Ethereum Foundation. His official action plan aims to gradually put in place essential protections during the year 2029. This deadline remains a planning objective, and not a guaranteed date.
For the modification of BLS signatures, the developers operate in particular on leanXMSS. It is a system that relies on hash functions considered resistant to quantum attacks. However, the signatures are much larger than those currently used, which poses a bandwidth and processing problem.
This increase must be compensated by the LeanVM project. This type of specialized virtual machine could group post-quantum signatures using cryptographic proofs. L’EIP-8292 makes the proposal to entrust this task to aggregators who have the necessary equipment, without imposing this burden individually on all validators.
The infrastructure itself designs new trade-offs. The evidence will therefore be produced within a very short time by the aggregators. The latter will have greater computing power than that of an individual staker. Researchers will therefore be called upon to prevent such a function from consolidating the centralization of the network.
The immediate threat is not yet quantum risk. Thus, the official Ethereum documentation predicts that no current quantum computer can break the network’s cryptographic systems. Users and validators do not have to perform any urgent operations.
The project must now obtain the agreement of the publishers, be the subject of a technical discussion, receive an official number and pass the controls for the submission of EIPs. Customer implementations, audits, testing on experimental networks and selection for a future hard fork will then be necessary. Until these steps are taken, the new contract remains a first preparation, not an already active protection.
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