Re: [bitcoin-dev] Why is deriving public key from the signature not used in Segwit?

From: Aymeric Vitte <vitteaymeric@gmail•com>
To: "Gregory Maxwell" <greg@xiph•org>,
	"Bitcoin Protocol Discussion"
	<bitcoin-dev@lists•linuxfoundation.org>,
	"Артём Литвинович" <theartlav@gmail•com>
Subject: Re: [bitcoin-dev] Why is deriving public key from the signature not used in Segwit?
Date: Wed, 24 Jan 2018 11:24:55 +0100	[thread overview]
Message-ID: <41d8ff42-106f-45b9-cc70-507982c7336b@gmail.com> (raw)
In-Reply-To: <CAAS2fgQmKY5206-ko9ttV4K_4aPfoWh7Jrx=XYetXLeknU30iw@mail.gmail.com>

34 bytes in fact

I have asked already the question at least twice on this list pointing
out the fact that pubkey is there now even for standard p2pkh
transactions and it was not the case some time ago

But I never got any answer regarding what motivated this change
(compared to the previous behavior) and when, so whether I am missing
something obvious, whether nobody wants to answer

Txs without pubkey are now rejected then what is the element in the code
(protocol, version, etc) that "decided" this?

Le 24/01/2018 à 05:25, Gregory Maxwell via bitcoin-dev a écrit :
> On Wed, Jan 24, 2018 at 3:50 AM, Артём Литвинович via bitcoin-dev
> <bitcoin-dev@lists•linuxfoundation.org> wrote:
>> Greetings.
>>
>> I wanted to ask what was the rationale behind still having both public
>> key and signature in Segwit witness?
>>
>> As is known for a while, the public key can be derived from the
>> signature and a quadrant byte, a trick that is successfully used both
>> in Bitcoin message signing algorithm and in Ethereum transaction
>> signatures. The later in particular suggests that this is a perfectly
>> functional and secure alternative.
>> Leaving out the public key would have saved 33 bytes per signature,
>> which is quite a lot.
>>
>> So, the question is - was there a good reason to do it the old way
>> (security, performance, privacy, something else?), or was it something
>> that haven't been thought of/considered at the time?
> It is slow to verify, incompatible with batch validation, doesn't save
> space if hashing isn't used, and is potentially patent encumbered.
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