Bitcoin’s Signing Gap and How Cadena Bitcoin Is Built Differently
Bitcoin Core just fixed a flaw that could let a valid signature redirect funds to the wrong address. See how Cadena Bitcoin’s design handles this risk.
Bitcoin Core developers merged a safeguard that closes a narrow but serious gap in how certain transactions get signed. No private key was ever exposed. Under a specific set of conditions, the flaw let a technically valid signature survive even when the actual payment destination had been changed.
Picture signing a check with the amount filled in correctly but the payee line left blank because of a form error. Your bank still honors your signature, the money still leaves your account, and nothing about your handwriting was forged. The question is simply who ends up holding the check. That is close to the gap Bitcoin Core just closed, and it points to a deeper lesson than any single bug: a valid signature only protects you if it is also bound to the correct destination. That exact discipline, fixing every payout to a destination agreed in advance, is central to how Cadena Bitcoin is built. Before getting into why that matters, it helps to walk through what Bitcoin Core actually fixed.
What Bitcoin Core Actually Fixed
The flaw lives inside Partially Signed Bitcoin Transactions, or PSBTs, the standard format wallets use to pass an unfinished transaction between different pieces of software before it is broadcast. Think of a PSBT as an order form that moves between departments. One program fills in the details of what is being spent and who should receive it. A separate device, often a hardware wallet kept deliberately simple and offline, adds the final signature without otherwise being able to see or move funds on its own. That separation is good for security, but it only works if the signer can trust that the form it is given is complete and honestly filled in.
The gap involved a signing mode called SIGHASH_SINGLE, which is meant to tie a specific input, meaning a specific coin being spent, to the output sitting in the matching position on the form. Normally that works fine. The problem shows up when the form is missing an output at that position entirely. For older, legacy coins, Bitcoin Core developers found that the missing output case could produce a signature over a fixed, predictable value, one that could potentially be reused against other coins controlled by the same key under the same conditions. For newer SegWit coins, the signature still proves exactly which coin is being spent and for how much, but the box naming the destination can be left unbound, meaning it is not locked down by the signature at all.
Put simply, a wallet’s screen could show you one recipient while the underlying signature did nothing to cryptographically guarantee that recipient would not change before the transaction settled. The signature proved you approved spending a particular coin. It did not always prove you approved where that coin would land.
Why a Correct Signature Does Not Always Mean the Right Address
This is the detail worth sitting with. Bitcoin’s entire reputation rests on cryptographic proof: if a signature is valid, the spend was authorized. That remains true in the narrow sense. What this gap revealed is that authorized to spend and authorized to pay a specific recipient are two different guarantees, and a system can quietly satisfy the first while leaving the second open.
Bitcoin Core’s raw transaction signing path had already rejected this edge case. The PSBT path, the one most wallets, hardware signers, and multi-party tools actually use, had not. The fix moves the check into Bitcoin Core’s shared signing logic, so an affected input is refused rather than signed, while any other valid inputs in the same transaction can still proceed normally.
The Fix Is Not in Your Wallet Yet
As of October 4, the change sits only in Bitcoin Core’s development branch. There is no confirmed release version or backport yet, as Bitcoin Optech noted when it flagged the update. That leaves every wallet provider, hardware signing integration, and multi-party protocol in an awkward window: the protocol-level protection exists, but it has not shipped to the software people actually use. Until it does, anyone building or signing PSBTs with SIGHASH_SINGLE needs to review their own handling of the missing output case directly rather than assume Bitcoin Core’s eventual release will cover them automatically.
Get Cadena Bitcoin’s stories in your inbox
Join Medium for free to get updates from this writer.
It is a useful reminder that a fix merged into a development branch is not the same as a fix running on your device, in the same way a recall notice is not the same as the part actually being replaced in your car.
How Is Cadena Bitcoin’s Infrastructure Built to Safeguard Your Assets?
This particular gap matters most for exactly the category of software Cadena Bitcoin operates in. Non-custodial, multi-party Bitcoin protocols depend on counterparties proposing transactions for each other to sign, which is precisely the setup where a malformed or dishonestly built form could matter. Cadena’s answer is to remove the ambiguity this gap exploited, by design, rather than patch around it after the fact.
A Bitcoin-backed loan on Cadena settles through a fixed-term Discreet Log Contract, or DLC, on Bitcoin’s base layer. Every possible outcome of that contract, meaning every address that could ever receive funds and under what condition, is specified and agreed by both the borrower and the lender at the moment collateral is locked, not assembled later by a wallet filling in a form on the fly. At settlement, an independent price feed called an oracle reports which pre-agreed outcome occurred. The oracle only reports facts. It cannot redirect a payout to an address nobody agreed to, because no such address was ever left open to begin with.
That is the direct answer to the lesson in Bitcoin Core’s fix. The flaw existed because a signature could be valid while the destination remained unbound. Cadena’s contracts are built so the destination is bound before anything is signed at all, with every outcome fixed in advance rather than filled in at the last step.
However, no design is immune to every implementation detail, and a protocol-level principle is only as good as the code that enforces it.
Borrow Against Bitcoin Without Leaving the Destination Open
Bitcoin Core closing this gap is a reminder that security on Bitcoin is not just about who can see your private key. It is about whether every payout is bound to a destination that was actually agreed upon, at every step, by every piece of software that touches the transaction.
Cadena Bitcoin exists to hold that standard by default. Lock your Bitcoin as collateral, access dollar liquidity, and settle against outcomes that were fixed before a single signature was ever produced. Non-custodial, peer-to-peer, settled on Bitcoin’s base layer, with no destination left open for anyone to redirect.
Register now: cadenabitcoin.com
Follow us on socials:
X: https://x.com/cadenabitcoin
YouTube: https://youtube.com/@cadenabitcoin
