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Date: Thu, 26 Apr 2012 10:59:45 -0700 (PDT)
From: Amir Taaki <zgenjix@yahoo.com>
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Subject: Re: [Bitcoin-development] Trusted identities
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look at the first line of the if statement=0A=0A=0A=A0=A0=A0=A0// Check for=
conflicts with in-memory transactions=0A=A0=A0=A0=A0CTransaction* ptxOld =
=3D NULL;=0A=A0=A0=A0=A0for (unsigned int i =3D 0; i < tx.vin.size(); i++)=
=0A=A0=A0=A0=A0{=0A=A0=A0=A0=A0=A0=A0=A0=A0COutPoint outpoint =3D tx.vin[i]=
.prevout;=0A=A0=A0=A0=A0=A0=A0=A0=A0if (mapNextTx.count(outpoint))=0A=A0=A0=
=A0=A0=A0=A0=A0=A0{=0A=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0// Disable replac=
ement feature for now=0A=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0return false;=
=0A=0A=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0// Allow replacing with a newer v=
ersion of the same transaction=0A=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0if (i =
!=3D 0)=0A=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0return false;=0A=
=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0ptxOld =3D mapNextTx[outpoint].ptx;=0A=
=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0if (ptxOld->IsFinal())=0A=A0=A0=A0=A0=
=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0return false;=0A=A0=A0=A0=A0=A0=A0=A0=
=A0=A0=A0=A0=A0if (!tx.IsNewerThan(*ptxOld))=0A=A0=A0=A0=A0=A0=A0=A0=A0=A0=
=A0=A0=A0=A0=A0=A0=A0return false;=0A=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0fo=
r (unsigned int i =3D 0; i < tx.vin.size(); i++)=0A=A0=A0=A0=A0=A0=A0=A0=A0=
=A0=A0=A0=A0{=0A=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0COutPoint o=
utpoint =3D tx.vin[i].prevout;=0A=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=
=A0=A0if (!mapNextTx.count(outpoint) || mapNextTx[outpoint].ptx !=3D ptxOld=
)=0A=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0return fals=
e;=0A=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0}=0A=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=
=A0=A0break;=0A=A0=A0=A0=A0=A0=A0=A0=A0}=0A=A0=A0=A0=A0}=0A=0A=0A__________=
______________________=0AFrom: Peter Vessenes <peter@coinlab.com>=0ATo: Pet=
er Todd <pete@petertodd.org> =0ACc: bitcoin-development@lists.sourceforge.n=
et =0ASent: Thursday, April 26, 2012 6:11 PM=0ASubject: Re: [Bitcoin-develo=
pment] Trusted identities=0A=0A=0AThese are interesting thoughts, karma for=
bitcoins essentially.=0A=0AI would like CoinLab to publish a 'cost of subv=
erting 1-n transactions with 90% probability' metric soon, and I think it w=
ould help everyone to understand what that number is.=0A=0AWhen we started =
out, you probably needed to wait 5 blocks for $10 or $20 of bitcoin value t=
ransfer.=0A=0ANow, I'd happily accept a $1k transaction with 1 confirmation=
.=A0=0A=0AMore difficulty shortens the safe time we can transact large volu=
mes in, which is good for the network.=0A=0AI'm not sure of the current imp=
lementation of replacement transactions, can anyone on the core team speak =
to this? Can I replace transactions, or is that part of the spec unimplemen=
ted or deprecated right now?=0A=0APeter=0A=0A=0A=0AOn Thu, Apr 26, 2012 at =
8:49 AM, Peter Todd <pete@petertodd.org> wrote:=0A=0AIt recently occured to=
me that we can use the public nature of the block=0A>chain to create trust=
ed identities, for a specific form of trust.=0A>=0A>Lets suppose Alice has =
some bitcoins held at bitcoin address A. She=0A>wants to establish trust in=
the "identity" associated with the ECC=0A>keypair associated with A, for i=
nstance for the purpose of having other=0A>users trust her not to attempt t=
o double spend. Since the trust she=0A>seeks is financial in nature, she ca=
n do this by valuing the identity=0A>associated with A, by delibrately thro=
wing away resources. A simple way=0A>to do this would of course be to trans=
fer coins to a null address,=0A>provably incurring a cost to her.=0A>=0A>A =
more socially responsible way would be for her to create a series of=0A>tra=
nsactions that happen to have large, and equal, transaction fees.=0A>Bitcoi=
n makes the assumption that no one entity controls more than 50%=0A>of the =
network, so if she makes n of these transactions consecutively,=0A>each spe=
nding m BTC to transaction fees, there is a high probability=0A>that she ha=
s given up at least n/2 * m BTC of value. This of course is=0A>all public k=
nowledge, recorded in the block chain. It also increases the=0A>transaction=
fees for miners, which will be very important for the=0A>network in the fu=
ture.=0A>=0A>Now Bob can easily examine the block chain, and upon verifying=
Alice's=0A>trust purchase, can decide to accept a zero-confirmation transa=
ction at=0A>face value. If Alice breaks that promise, he simply publishes h=
er signed=0A>transaction proving that Alice is a fraudster, and future Bob'=
s will=0A>distrust Alice's trusted identity, thus destroying the value need=
ed to=0A>create it.=0A>=0A>In effect, we now have a distributed green addre=
ss system.=0A>=0A>Now Alice could try to mount a double-spend attack on a w=
hole bunch of=0A>people at once, hoping to have them all accept the transac=
tion. However=0A>as it is the "just trust them" model works pretty well alr=
eady.=0A>=0A>=0A>A good usecase for this idea, beyond the obvious fast paym=
ents=0A>application, is a distributed anonymizer. Alice can now publish her=
=0A>request to anonymize coins, and other trusted identities can make their=
=0A>bids. If Alice accepts a bid from Bob, she will want Bob to send her th=
e=0A>anonymized coins *prior* to her transaction going through, thus breaki=
ng=0A>the temporal connection between the transactions. Now Alice can give =
Bob=0A>the signed payment transaction, and Bob can submit his payment=0A>tr=
ansaction to the network first, knowing that Alice isn't going to try=0A>to=
rip him off. Bob can also have a trusted identity which signed the=0A>cont=
ract for the anonymizer transaction, and similarly if he rips Alice=0A>off,=
she can publish it for the world to see.=0A>=0A>A more subtle effect, is t=
his makes sybil attacks more difficult. To=0A>pretend to be a thousand iden=
tities is going to now require 1,000 * n=0A>coins, and attempting to pull t=
his attack off inherently strengthens the=0A>bitcoin network. Obviously we =
can apply this principle to other things=0A>like tor nodes as well.=0A>=0A>=
--=0A>http://petertodd.org 'peter'[:-1]@petertodd.org=0A>=0A>-----BEGIN PGP=
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----------------------------------------------------------------------=0A>L=
ive Security Virtual Conference=0A>Exclusive live event will cover all the =
ways today's security and=0A>threat landscape has changed and how IT manage=
rs can respond. Discussions=0A>will include endpoint security, mobile secur=
ity and the latest in malware=0A>threats. http://www.accelacomm.com/jaw/sfr=
nl04242012/114/50122263/=0A>_______________________________________________=
=0A>Bitcoin-development mailing list=0A>Bitcoin-development@lists.sourcefor=
ge.net=0A>https://lists.sourceforge.net/lists/listinfo/bitcoin-development=
=0A>=0A>=0A=0A=0A-- =0A=0APeter J. Vessenes=0ACEO, CoinLab=0AM: 206.595.983=
9=0ASkype: vessenes=0AGoogle+ =0A=0A---------------------------------------=
---------------------------------------=0ALive Security Virtual Conference=
=0AExclusive live event will cover all the ways today's security and =0Athr=
eat landscape has changed and how IT managers can respond. Discussions =0Aw=
ill include endpoint security, mobile security and the latest in malware =
=0Athreats. http://www.accelacomm.com/jaw/sfrnl04242012/114/50122263/=0A___=
____________________________________________=0ABitcoin-development mailing =
list=0ABitcoin-development@lists.sourceforge.net=0Ahttps://lists.sourceforg=
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