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Bitcoin Cash contributor mainnet_pat’s CHIP-2026-06 proposes an opcode that exposes the transaction digest already used in signature checks, making it easier to build contracts for alternative and hybrid signature schemes. The proposal is under review, with a potential lock-in date of Nov. 15, 2026, and mainnet activation targeted for May 15, 2027; neither milestone is confirmed.
Bitcoin Cash developers are reviewing CHIP-2026-06, a proposal to add an OP_SIGHASH opcode that could make it easier for transaction contracts to use post-quantum and hybrid signatures. The proposal remains open for review, with a potential lock-in date of Nov. 15, 2026, and mainnet activation targeted for May 15, 2027; both dates depend on the community’s upgrade process and are not confirmed outcomes.
Introduced in June by Bitcoin Cash contributor mainnet_pat, the proposal would expose a transaction’s 32-byte signature hash—the digest used in signature verification—to the Bitcoin Cash virtual machine. According to the proposal, the opcode would use the same algorithm, flags and script conventions as existing OP_CHECKSIG operations. It does not introduce a new signature algorithm or change how the digest is calculated.
The stated goal is to reduce the work and potential for errors when developers build contracts around signature schemes other than current secp256k1-based ECDSA and Schnorr signatures. The source report says contracts can currently reconstruct the signature hash manually in Script, including handling details such as SIGHASH_SINGLE, ANYONECANPAY, ForkID and UTXOS. OP_SIGHASH would make the already calculated digest available directly, rather than requiring each contract to reproduce those rules.
CHIP-2026-06 describes a registry-based approach in which a public key’s first byte identifies its signature scheme. The proposal names existing secp256k1 schemes and possible additions including SPHINCS+ and Falcon-512. For a hybrid key, both classical and post-quantum components would have to verify for a spend to be valid. Its authors say these keys could use ordinary P2PKH outputs and existing address formats, rather than requiring new output types. The report says Bitcoin Cash Node developers have opened a merge request to implement the opcode; that work is not itself evidence that the proposal has been adopted or activated.
The proposed change focuses on making advanced signature contracts less complex, not replacing the signatures used in routine transactions. By exposing the digest that nodes already calculate, OP_SIGHASH could give contract developers a common input for alternative verification methods and reduce the chance that independently written scripts mishandle transaction-hash rules. The proposal’s supporters describe this as a way to make such contracts easier to build and review.
The hybrid design also offers a possible migration path: a transaction could require both a familiar classical signature and a post-quantum signature. Under the proposal’s stated AND rule, failure of either check would invalidate the spend. That could let users and developers test additional cryptographic protections without immediately abandoning existing schemes. It would not, by itself, prove that a selected post-quantum algorithm is suitable for every use or that future quantum computers pose an immediate threat.
Keeping ordinary P2PKH outputs and address formats, as the proposal intends, could limit disruption to wallets and existing tools. However, compatibility claims still need to be evaluated through implementation and review. If adopted, the opcode could also support other contract patterns that combine a transaction digest with additional data, including covenants and oracle-related applications.
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How CHIP-2026-06 Fits BCH Upgrades
The proposal builds on capabilities delivered in the May 2026 Layla upgrade, which, according to the source report, added Loops, Functions, Bitwise operations and Pay-to-Script functionality. The report also says script-level options such as Quantumroot vaults were already live on Bitcoin Cash mainnet after Layla. CHIP-2026-06 is presented as an additional route at the signature-verification layer, rather than the first possibility for post-quantum protections on the network.
Bitcoin Cash changes are handled through the Cash Improvement Proposal process. CHIP-2026-06 remains under discussion and implementation review, and its suggested schedule is prospective: possible lock-in on Nov. 15, 2026, followed by a target activation date of May 15, 2027. The report says the network had completed six consecutive annual upgrades from 2021 through 2026 without chain splits; that record is context, not a guarantee that this proposal will pass or follow the proposed dates.
“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
The proposal is still open for review, refinement and stakeholder statements. It is not yet clear whether it will meet the conditions for lock-in, whether the suggested dates will hold, or what final wording and implementation will be accepted. The reported Node implementation merge request is a development step, not confirmation of network-wide consensus or activation.
The initial post-quantum schemes and their parameter sets also remain subject to discussion, according to the source material. The proposal favors hash-based, stateless SPHINCS+ / SLH-DSA as an initial target, while listing Falcon-512 as a possible scheme. The available report does not provide final scheme parameters, performance measurements, wallet support status, or a complete account of operational trade-offs. It also does not establish when a cryptographically relevant quantum computer might exist or quantify the urgency of migration.
Review Before the November Milestone
Stakeholders, wallet developers, node implementers and other community members are being invited to review the CHIP and comment on the proposed signature schemes and parameters. The next stated milestone is a potential Nov. 15, 2026, lock-in. If the proposal proceeds through the upgrade process, its authors target mainnet activation for May 15, 2027. Until the review and consensus process concludes, those dates should be treated as targets rather than a confirmed deployment schedule.
Key Questions
What does CHIP-2026-06 propose?
It proposes an OP_SIGHASH opcode that would place the transaction’s existing 32-byte signature hash on the Script stack, helping contracts use alternative signature-verification schemes.
Does the proposal add a new post-quantum signature algorithm?
No. The proposal exposes a digest already calculated during signature verification. It describes a dispatch mechanism for signature schemes, with post-quantum options such as SPHINCS+ and Falcon-512 discussed as possible additions.
How would a hybrid signature work?
Under the proposal’s design, a hybrid key combines classical and post-quantum components, and both checks must pass for the transaction to be valid.
When could the change activate?
The proposal lists a potential lock-in date of Nov. 15, 2026, and a mainnet activation target of May 15, 2027. These are proposed milestones, not confirmed dates for an activated change.
Has Bitcoin Cash adopted the proposal?
No adoption or activation is confirmed in the source report. CHIP-2026-06 is under review, and the reported implementation merge request does not establish that the network has approved the change.
Source: thequantuminsider.com
