Hi All,
I'd like to propose a BIP to normalize transaction IDs in order to address transaction malleability and facilitate higher level protocols.
The normalized transaction ID is an alias used in parallel to the current (legacy) transaction IDs to address outputs in transactions. It is calculated by removing (zeroing) the scriptSig before computing the hash, which ensures that only data whose integrity is also guaranteed by the signatures influences the hash. Thus if anything causes the normalized ID to change it automatically invalidates the signature. When validating a client supporting this BIP would use both the normalized tx ID as well as the legacy tx ID when validating transactions.
@gmaxwell: I'd like to request a BIP number, unless there is something really wrong with the proposal.
In addition to being a simple alternative that solves transaction malleability it also hugely simplifies higher level protocols. We can now use template transactions upon which sequences of transactions can be built before signing them.
I hesitated quite a while to propose it since it does require a hardfork (old clients would not find the prevTx identified by the normalized transaction ID and deem the spending transaction invalid), but it seems that hardforks are no longer the dreaded boogeyman nobody talks about.
I left out the details of how the hardfork is to be done, as it does not really matter and we may have a good mechanism to apply a bunch of hardforks concurrently in the future.
I'm sure it'll take time to implement and upgrade, but I think it would be a nice addition to the functionality and would solve a long standing problem :-)
Please let me know what you think, the proposal is definitely not set in stone at this point and I'm sure we can improve it further.
Regards,
Christian