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Bitcoin Cash developers are reviewing CHIP-2026-06, a proposal to add an opcode that exposes a transaction signature hash for alternative signature schemes. It could support post-quantum and hybrid signatures without changing existing address formats, but the proposal is still under review and has not been activated.
Bitcoin Cash developers are reviewing CHIP-2026-06, a proposal to add an OP_SIGHASH opcode that could make it easier for transactions to use post-quantum and hybrid signatures. The proposal has not been adopted: its authors are seeking feedback ahead of a potential Nov. 15, 2026, lock-in, with mainnet activation targeted for May 15, 2027.
Introduced by contributor mainnet_pat in June 2026, the Cash Improvement Proposal would let Bitcoin Cash’s virtual machine place a transaction’s 32-byte signature hash, or sighash, on the script stack. The proposal describes this as exposing a calculation already performed during signature verification, rather than introducing a new cryptographic algorithm or changing the existing sighash rules.
The opcode is intended to reduce the work needed for contracts that verify signatures using schemes beyond current Bitcoin Cash signatures. According to the proposal, scripts that now reconstruct transaction data and sighashes themselves can be substantially shorter, while relying on the same digest calculation used by node software. That could also reduce errors around existing sighash options and rules.
The proposal outlines a public-key format in which a leading byte identifies the signature scheme. Existing secp256k1 signatures would remain supported, while post-quantum algorithms could be added through a registry. For a hybrid key, both the classical and post-quantum signature checks must pass. The proposal says these keys could spend from ordinary Pay-to-Public-Key-Hash outputs, retaining existing address formats and avoiding new output types.
A Gradual Route to Quantum Resistance
The proposal addresses a long-term protocol concern: a sufficiently capable quantum computer could threaten public-key cryptography used by current digital signatures. No such machine is identified in the proposal as an immediate threat, and the suggested change is framed as preparation rather than a response to a present-day break.
For users and wallet developers, the proposed hybrid approach could offer a way to require both a conventional signature and a post-quantum one, rather than forcing an abrupt switch away from current cryptography. If implemented as described, keeping familiar address formats could lower some migration friction. However, actual compatibility would still depend on software support and how wallets handle the new key and signature schemes.
The opcode may also matter beyond quantum resistance. The proposal’s author says providing the node-calculated sighash directly to scripts could help developers build covenants, oracle applications, and other contract patterns without duplicating complex transaction-hash logic. Those are potential uses, not outcomes established by an activated change.
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From Layla to CHIP-2026-06
The proposal follows Bitcoin Cash’s May 2026 Layla upgrade, which, according to the source report, added features including loops, functions, bitwise operations, and Pay-to-Script. The report says these features have enabled script-level approaches such as Quantumroot vaults, described as already live on mainnet. CHIP-2026-06 would add a separate path at the signature-verification layer; it is not presented as a replacement for those scripts.
Bitcoin Cash uses the Cash Improvement Proposal (CHIP) process to discuss and coordinate protocol changes. The source report says Bitcoin Cash Node developers have opened a merge request implementing OP_SIGHASH, but a merge request is not the same as consensus approval or activation. The proposal remains open for review, including discussion of which signature schemes and parameter sets should be supported first.
The proposal favors stateless post-quantum schemes for the signature-checking path. The source material names SPHINCS+ (also known as SLH-DSA) and Falcon-512 as possible schemes, while noting that the initial selection remains subject to stakeholder review. It also argues against putting stateful signature schemes in the core check-signature path because key reuse can create risks for those schemes.
“This completes a useful unbundling of checksig functionality and gives every builder the same battle-tested sighash the nodes already use.”
— Bitcoin Cash Research forum discussion, as quoted in The Quantum Insider report
Approval and Scheme Choices Remain Open
CHIP-2026-06 is still under discussion, and the proposed dates are milestones rather than guaranteed outcomes. The source report says lock-in could occur on Nov. 15, 2026, and activation is targeted for May 15, 2027, but it does not establish that the necessary stakeholder decisions or implementation work will be complete by those dates.
The final set of supported post-quantum schemes, their parameter choices, and the timing for adding them are not settled in the supplied material. It also does not provide independent testing results, performance measurements, or a detailed account of wallet readiness. Preserving address formats would not, by itself, confirm that existing wallets can create or verify the proposed signatures.
The proposal is preparation for a possible future cryptographic risk. The source material does not specify when a cryptographically relevant quantum computer might be available, nor does it provide a quantified risk assessment for Bitcoin Cash transactions today.
Review Before the November Milestone
Developers, wallet teams, node implementers, and other stakeholders are being asked to review the specification and comment on the initial signature schemes and parameter sets. The proposal’s next stated milestone is the potential Nov. 15, 2026, lock-in. Whether it reaches that milestone depends on the ongoing CHIP review and implementation work.
If the proposal is locked in and later activated as targeted, the planned mainnet date is May 15, 2027. Until approval and activation occur, OP_SIGHASH and the proposed signature-dispatch mechanism should be treated as a proposal, not a currently available Bitcoin Cash consensus feature.
Key Questions
What would OP_SIGHASH do?
It would put the transaction’s 32-byte sighash on the script stack, allowing scripts to use the same digest calculation that signature verification already performs.
Does Bitcoin Cash support these proposed signatures now?
The proposal is still under review. The supplied report says a node implementation merge request has been opened, but that does not mean the change is active on mainnet.
How would hybrid signatures work?
Under the proposal, a hybrid key combines classical and post-quantum schemes. A transaction would be valid only if both signature checks succeed.
Would users need a new address format?
The proposal says post-quantum and hybrid keys could use ordinary Pay-to-Public-Key-Hash outputs, preserving existing address formats. Wallet support and practical compatibility remain to be established.
When could the change take effect?
The proposal lists a potential Nov. 15, 2026, lock-in and a target mainnet activation date of May 15, 2027. Both depend on review and approval; neither date is a confirmation that activation will happen.
Source: thequantuminsider.com
