Blockstream CEO Adam Back supports Ethereum’s shift to established hash standards

Ethereum abandons Poseidon after long investment

After dedicating eight years and significant resources to the integration of the highly specialized Poseidon hash function, Ethereum is now refocusing on traditional cryptographic approaches. The network plans to implement the SHA or BLAKE2s hash standards at its base layer, reversing its earlier strategy that had prioritized efficiency for zero-knowledge (ZK) cryptography systems.

Commenting on these developments, Adam Back questioned the wisdom of using custom, less-studied algorithms, particularly in high-value systems. He noted that experimental, ZK-optimized algorithms had received insufficient scrutiny from the global cryptography community. Back stated that he had “never liked prover-friendly hashes anyway,” suggesting that such approaches result in “an under-reviewed quirky hash.”

Back maintained that, even in the early days of ZK system development, he favored standard hash algorithms, accepting higher computational expense to reduce security risk, rather than depend on new and unproven cryptographic constructions.

The move away from Poseidon stems largely from recent technical progress in cryptography and computer science. For years, conventional hash algorithms were seen as too computationally intensive for ZK systems, prompting development of new solutions like Poseidon. However, breakthroughs in binary-field mathematics changed the landscape by making standard algorithms more practical for ZK proofs.

Breakthroughs in cryptography reshape industry best practices

In 2023, the Binius proof system was introduced, followed by the launch of Flook in 2024. These systems were designed to efficiently process large volumes of conventional cryptographic hashes, reaching speeds of up to one million hashes per second on standard consumer laptops. The advancements significantly reduced the performance gap between established and experimental hash algorithms.

This rapid progress in proof technology rendered custom solutions such as Poseidon unnecessary, undercutting their primary justification. As a result, Ethereum decided to discontinue further investment in the project and realign with industry-standard hash functions. This decision has been viewed as a validation of Back’s longstanding conservative stance on cryptographic security.

Mini dictionary: Binius and Flook—Binius is a proof system introduced in 2023 that increases the efficiency of zero-knowledge proofs by optimizing binary field arithmetic. Flook, developed in 2024, further enhances cryptographic computation, making standard hash functions feasible for high-throughput ZK applications.

According to a timeline approved by the Ethereum Foundation, the start of new post-quantum security measures is scheduled for 2027 with the launch of the LeanVM virtual machine. Full network-wide implementation at Ethereum’s base layer is targeted for completion in 2028.

The shift marks an industry-wide move toward established cryptographic standards, echoing Adam Back’s caution and commitment to long-term security, while also recognizing Ethereum Foundation’s willingness to adapt in light of breakthrough research.