[bitcoin-dev] Why SegWit Anyway?

Praveen Baratam praveen.baratam at gmail.com
Mon Nov 20 18:07:40 UTC 2017

BIP 140 looks like it solves Tx Malleability with least impact on current
practices. It is still a soft fork though.

Finally, if we were to create an alternative cyptocurrency similar to
Bitcoin, a Normalized Tx ID approach would be a better choice if I get it

On Mon, Nov 20, 2017 at 11:15 PM, Johnson Lau <jl2012 at xbt.hk> wrote:

> We can’t “just compute the Transaction ID the same way the hash for
> signing the transaction is computed” because with different SIGHASH flags,
> there are 6 (actually 256) ways to hash a transaction.
> Also, changing the definition of TxID is a hardfork change, i.e. everyone
> are required to upgrade or a chain split will happen.
> It is possible to use “normalised TxID” (BIP140) to fix malleability
> issue. As a softfork, BIP140 doesn’t change the definition of TxID.
> Instead, the normalised txid (i.e. txid with scriptSig removed) is used
> when making signature. Comparing with segwit (BIP141), BIP140 does not have
> the side-effect of block size increase, and doesn’t provide any incentive
> to control the size of UTXO set. Also, BIP140 makes the UTXO set
> permanently bigger, as the database needs to store both txid and normalised
> txid
> On 21 Nov 2017, at 1:24 AM, Praveen Baratam via bitcoin-dev <
> bitcoin-dev at lists.linuxfoundation.org> wrote:
> Bitcoin Noob here. Please forgive my ignorance.
> From what I understand, in SegWit, the transaction needs to be serialized
> into a data structure that is different from the current one where
> signatures are separated from the rest of the transaction data.
> Why change the format at all? Why cant we just compute the Transaction ID
> the same way the hash for signing the transaction is computed?
> --
> Dr. Praveen Baratam
> about.me <http://about.me/praveen.baratam>
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> bitcoin-dev at lists.linuxfoundation.org
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Dr. Praveen Baratam

about.me <http://about.me/praveen.baratam>
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