Bitcoin Cash quantum signatures: lock-in due November 15 - CryptoTicker.io

The proposal, known as CHIP-2026-06, would modify Bitcoin Cash's signature verification to include post-quantum cryptographic schemes that can withstand attacks from powerful quantum computers. According to The Quantum Insider, lock-in is scheduled for November 15, 2026, with mainnet activation planned for May 15, 2027. Both milestones depend on developers completing their review without objections.

The price of Bitcoin Cash has been struggling amid this development. Trading at $229.48 on November 12, BCH is approximately 19% below its level from the previous week. With a market capitalization of $4.6 billion, it ranks 22nd among the largest cryptocurrencies.

Quantum-resistant signatures

CHIP stands for Cash Improvement Proposal, which are proposed changes to Bitcoin Cash's consensus rules. Published on June 10, 2026, by developer mainnet_pat, the technical core involves modifying script opcodes to distinguish between multiple signature schemes. The first byte of the public key will indicate which scheme applies, with a registry that currently only contains secp256k1 but will later include post-quantum schemes.

Post-quantum schemes are signature methods whose security doesn't rely on mathematical problems that quantum computers could solve with Shor's algorithm. The proposal also introduces a new opcode called OP_SIGHASH that pushes the signature hash of a transaction onto the stack. Importantly, the draft states that the proposal introduces no new cryptography.

Hybrid keys approach

The most innovative aspect of the proposal is composite keys, which combine two signature schemes with an AND condition. For example, a hybrid key might pair secp256k1 with a post-quantum scheme, requiring both signatures to be valid for a payment to process. This approach provides a safety net—if one cryptographic method is compromised, the other continues to protect the coins.

Practically, hybrid and pure post-quantum keys can be spent from ordinary P2PKH outputs, the address type most wallets have used for years. This means no new output type is needed, and address formats and wallet software could largely remain unchanged. The hybrid approach offers a gradual transition, avoiding the need to move all coins to new addresses simultaneously.

Signature schemes and concerns

The proposal suggests starting with SPHINCS+ and its hybrid variant. SPHINCS+ is a hash-based signature scheme standardized by NIST as FIPS 205 (SLH-DSA). Its security depends only on hash function strength and is stateless, allowing a key to sign any number of times without counting. Falcon-512, a lattice-based scheme with smaller signatures, has also been mentioned in discussions.

However, the proposal faces criticism, primarily regarding signature size. A SPHINCS+ signature is approximately 8 kilobytes, compared to 64 bytes for a current Schnorr signature. This could increase block sizes and fees by 80-160 times if all users switched. Forum participant moonsettler considers SPHINCS+ "way overkill" for the transition period, preferring more flexible constructions based on Merkle trees.

Bitcoin Cash shares its quantum vulnerability with Bitcoin due to their shared use of the secp256k1 signature curve. While Bitcoin Cash has a more predictable upgrade cycle and already has Quantumroot vaults on mainnet, the quantum-resistant upgrade would require users to actively move their coins to hybrid or quantum-resistant keys for full protection.