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Key Takeaways
- MIT’s Muriel Médard warns that adversaries are already harvesting encrypted blockchain data to decrypt once quantum computers mature.
- She argues full-scale post-quantum encryption is unnecessary; encrypting roughly 10% of coded data via Random Linear Network Coding can protect an entire dataset.
- Ethereum-linked researchers and Algorand are already adopting post-quantum measures, signaling early industry movement toward quantum resistance.
Blockchains face a data-harvesting threat that predates any working quantum computer, according to Muriel Médard, an MIT professor and co-founder of network-coding firm Optimum. In her view, defending against it will come down to better math rather than new hardware.
The “Harvest Now, Decrypt Later” Problem
Médard argues that sophisticated actors, including nation-states, are already collecting encrypted data with a specific goal: decrypting it once quantum computers become powerful enough to break today’s cryptography.
She points to legal requirements that organizations retain identity logs and sensitive records for years, which she says leaves that stored data exposed to future decryption even though it is secure now. She states:
“Blockchains carry a particular version of this risk. Unlike messaging platforms where data can expire, blockchains are designed to permanently record money, identity, contracts, and governance decisions.”
Médard contends that without defenses built in now, that permanence could leave decentralized systems open to attacks that do not yet exist but are being prepared for.
How Post-Quantum Cryptography Emerged
The concern traces back to 1994, when mathematician Peter Shor showed that a quantum computer could solve the large-number factoring problems underlying cryptographic systems like RSA far faster than a classical computer, turning a computationally “hard” puzzle into a solvable one.
That result spurred the development of post-quantum cryptography, an approach that protects data by forcing an attacker to make an infeasible number of guesses rather than relying on a single hard problem. Médard writes:
“One long-standing method, the McEliece cryptosystem introduced in 1978, is still regarded as one of the stronger post-quantum approaches. However, it carries a significant cost: encrypting and decrypting all data under the scheme is computationally heavy enough to strain the systems meant to use it.”
Some blockchain projects have already begun adapting. A research group backed by the Ethereum Foundation is developing open-source post-quantum tools that the group has said could cut gas fees by as much as 12 times while preparing Ethereum for quantum-era threats.
Algorand has said it is securing its full chain history using FALCON signatures, a post-quantum signature scheme.
A Coding-Based Alternative
Médard’s central argument is that full encryption of all blockchain data is not necessary to achieve quantum safety. She points to Random Linear Network Coding, a method developed over roughly two decades in her MIT lab, as an alternative that splits data into coded equations that can be mixed and recombined as they move through a network.
Applied to post-quantum cryptography, this approach only requires encrypting a fraction of the coded equations, for example one out of ten, for the entire dataset to inherit quantum-resistant protection, according to Médard.
“Encrypting roughly 10% of the data can protect the full dataset while cutting about 90% of the computational load compared with full encryption.”
Because the method works by encoding and decoding data into packets, Médard says it could be applied at different levels of a blockchain’s technology stack. According to her:
“At the software layer, the approach could be deployed relatively quickly since it would be managed locally within existing applications. At the infrastructure level, implementing the coding method directly in hardware chips could extend quantum-safe protection into blockchain nodes themselves.”
Médard and colleagues at MIT have published research on this, and Médard also frames the approach as a potential “quantum-safe memory layer” that blockchains could use to protect how data is propagated, stored, and written to a chain without requiring end-to-end encryption of every transaction.
The Case for Acting Before Quantum Computers Arrive
Médard’s broader argument is that institutions will not commit financial, identity, or governance systems to public blockchains unless those systems can demonstrate quantum resistance in advance.
She argues that waiting until quantum computers are operational is too late, since data harvested under the “harvest now, decrypt later” strategy would already be exposed by that point. She characterizes post-quantum security as a matter of classical mathematics and coding, not quantum technology itself, and argues that blockchains do not need quantum hardware to defend against quantum-era threats.
Her position is that coding methods like RLNC offer a practical path to that protection without the performance costs associated with full-scale post-quantum encryption schemes.
