Bitcoin - Tópico principal

[Incognitus]

$375 ...

[hermes]

Quando só uma pequena base de tecnófilos dá valor à coisa [os especuladores não interessam, pois não estão lá para o longo prazo], há poucos serviços que essa base possa prestar, por isso tal moeda nunca terá grande valor. Este mesmo mecanismo faz com que a moeda não seja sequer um ponto focal, assim nem sequer é atingida uma das condições necessárias para se ser moeda.

[btcmb]

Os preços neste momento dependem muito de quem está a implementar contra medidas a tempo.

Entretanto, uma explicação em mais detalhe sobre o problema...

Ainda não se sabe bem o que se passou, mas tudo começou no principal exchange de Bitcoin(Mt Gox) que se pensa que tenha sido hackado e roubadas Bitcoins, no entanto não há informação oficial a confirmar o roubo. Existe no entanto uma confirmação de roubo de 4500 Bitcoins($2.7 milhões) no chamado Silk Road 2.

O problema da malaebilidade traduz-se no seguinte:

O atacante modifica uma transação de Bitcoin de modo a que a mesma transação fique com um outro hash. As modificações são feitas de forma bastante rápida e logo de seguida enviadas para os mineiros. A transação modificada por vezes fica minada em primeiro lugar, antecipando a operação original. O atacante só pode fazer alterações "triviais" na transação, tão exatamente que a mesma transferência Bitcoin acontece como se pretendia - a mesma quantidade é movida entre os mesmos endereços, de modo que este ataque pareça totalmente sem sentido. No entanto, cada transação é identificada por um hash criptográfico e mesmo uma mudança trivial na transação faz com que o hash de transação mude. E alterando o hash de uma transação pode ter efeitos inesperados sobre o sistema Bitcoin.

Alguns neste momento perguntam-se... “sim... e depois?”

Bem, o problema desta hack é o seguinte, o atacante sabendo o explicado em cima pode alterar transações de modo a que a transação originalmente enviada nunca seja entregue, pois a rede Bitcoin apenas confirmará uma unica transação com a mesma hash(ou idêntica neste caso). O que se passou no roubo do Silk Road 2 foi o seguinte, o atacante conhecendo esta técnica, fazia pedidos de pagamento, alterava a hash e os pagamentos originais que não era minerados primeiro eram pagos de forma repetida...
Para quem quiser ir mais a fundo:

    Problema da malaebilidade explicado a fundo: http://www.righto.com/2014/02/bitcoin-transaction-malleability.html
    Hack ao Silk Road 2 explicado: http://www.deepdotweb.com/2014/02/13/silk-road-2-hacked-bitcoins-stolen-unknown-amount

Nós, não sofremos qualquer ataque ou tentativa porque não funcionamos com "carteiras partilhadas", este problema apenas se coloca em implementações que usam as contas internas.

[Kin2010]

Como é que se pode ter confiança numa moeda se a própria segurança da guarda da mesma depende de detalhes técnicos tão complexos que para os entender é preciso tirar um curso intensivo de software especializado e TI especializada e se há perdas com avarias ou vírus ou piratas informáticos?

[btcmb]

Como é que se pode ter confiança numa moeda se a própria segurança da guarda da mesma depende de detalhes técnicos tão complexos que para os entender é preciso tirar um curso intensivo de software especializado e TI especializada e se há perdas com avarias ou vírus ou piratas informáticos?

Boas Kin2010,

Sim, é verdade que o Bitcoin pode ser extremamente complexo quando se olha para o aspeto técnico, sendo de código aberto e no tema(dinheiro) é quase inevitável que assim o seja. A segurança também tem sido um problema grave, houveram muitíssimos episódios de roubos, inclusivamente empresas que faliram devido a esses roubos.

No entanto o Bitcoin neste momento ainda é uma versão beta. Se isto fosse há uns anos(belos) atrás, certamente que ainda não estaria no mercado dada a sua imaturidade. No entanto as coisas hoje em dia são feitas assim(mal)...

Voltando à segurança e dificuldade em usar... pode ser difícil e perigoso para quem corre um servidor de pagamentos Bitcoin, para o utilizador final é bastante simples, para começar a usar basta isto, http://btcmb.pt/tutoriais-bitcoin/como-obter-um-endereco-bitcoin/

[darkmoon]

destinia.com aceita bitcoins

[amsf]

Não será fácil montar uma loja on-line, sem inventário, em cuja única moeda aceite fosse o bitcoin? Fornecia o bem, recorrendo a outro fornecedor, se a cotação do bitcoin, no espaço de 15 dias, subisse significativamente, se, pelo contrário, a cotação baixasse dava o bem por esgotado e devolvia o bitcoin desvalorizado. Digam lá se não é uma bela forma de ganhar dinheiro e de forma legal!?

[btcmb]

Artigo no zerohedge sobre o Mt. Gox, http://www.zerohedge.com/news/2014-02-20/bitcoin-exchange-mt-gox-finished

[Zel]

mt.gox ja confirmou a bancarrota

[btcmb]

Mt. Gox acaba por declarar bancarrota, http://online.wsj.com/news/article_email/SB10001424052702303801304579410010379087576-lMyQjAxMTA0MDIwNzEyNDcyWj

Cerca de 850 000 Bitcoins perdidas das quais 750000 eram de clientes.

[jeab]

Mt. Gox acaba por declarar bancarrota, http://online.wsj.com/news/article_email/SB10001424052702303801304579410010379087576-lMyQjAxMTA0MDIwNzEyNDcyWj

Cerca de 850 000 Bitcoins perdidas das quais 750000 eram de clientes.

Sou mesmo do século passado ... como se perde uma moeda virtual ? 

[Zel]

ficaram milionarios por paia total e agora perderam tudo por azar

[Incognitus]

Eu acho que foram os próprios do Mount Gox que roubaram aquilo, foi muita bitcoin em falta e não é credível que não tenham reparado mais cedo.

[kitano]

Sou da mesma opinião...tudo desviado!

[Zel]

Karpeles is a self-described PHP programmer. So he could build a website, but he didn't have the skills to program a custom bitcoin wallet, so the one they built had errors, and their trading engine showed strains and backlogs every time trading got busy. The reason for a custom wallet is the one you and I might use is perfectly fine for one person and their PC, but the largest bitcoin exchange had to handle massively more transactions per day, and do it correctly.

His real failure as majority owner was not hiring excellent programmers, IT security, and accounting staff. He was still running like a haphazard couple of people web business (which is exactly what it was in 2010 when it was founded). Therefore their wallet was looking at transaction *numbers* on the bitcoin shared ledger (the Block Chain), rather than the transaction *contents* - the actual addresses and amounts being transferred. Malicious people figured out they could alter the numbers and pass the transaction along, then tell Mt.Gox their withdrawal never appeared. When Mt. Gox checked the number and saw it was not on the Block Chain, they sent the payment again, double paying. Obviously this leads to lost funds.

In paper check terms, this is like only looking at the check number, and not the actual entries on the check. Coupled with a basic failure in double entry-bookkeeping (keeping proper track of internal and customer balances), they didn't know they were leaking bitcoins. This problem is on top of the US government seizing $10 million from their US bank accounts because they failed to fill out their Treasury registration form correctly - as far as I know, that money is still gone, and probably other amateurish business errors that would not have happened if they had people who knew what they were doing working there.

[Zel]

eh possivel que tenham sido eles proprios, nao da para saber

mas acho estranho pois tinham um bom negocio

[btcmb]

Eu tenho uma teoria um bocado rebuscada...

Muito provavelmente tudo começou com roubo de Bitcoins e parece fazer sentido que eles tenham tentado mitigar a coisa de forma a saírem com algum no bolso...

O que pode ter ditado a derrocada antecipada foi a queda de preço, o que de certo fez com que muitos depósitos em BTC tivessem sido convertidos para USD.

Se ainda se recordam, o preço dos Bitcoins no Mt. Gox era sempre mais elevado que em outro lado qualquer. Era quase de caras alguém tentar ganhar dinheiro com a arbitragem, comprando em outro sitio e vendendo no Mt. Gox, fazendo lucro sem correr qualquer risco.

A mim parece-me que o Mt. Gox tenha tentado mitigar a coisa com a ilusão da possibilidade de ganhar $ fazendo arbitragem, tendo o Mt. Gox como destino final e a consequente saída de Bitcoins para Moeda Fiat. O problema era que a conversão para Fiat no Mt. Gox estava a demorar largas semanas o que fazia com que não fosse muito apetecível fazer levantamentos, no entanto entravam grandes quantidades de Bitcoins para o Mt. Gox, pois era o exchange que pagava mais... essas Bitcoins acabavam por ir ficando lá depositadas... enquanto o preço estivesse a subir, não iriam haver muitas conversões de BTC para USD...

Pode-se especular que esta estratégia de acumulação de Bitcoins por parte do Mt. Gox tenha sido a estratégia de saída... do ponto de vista legal, os Bitcoins não são a mesma coisa que $. Muito provavelmente pode ter havido um roubo inicial, mas o grande roubo, muito provavelmente foi feito com a conivência de responsáveis do Mt. Gox.... mesmo o uso do problema da maleabilidade em transações entre endereços na mesma carteira é um bocado estranha, pois já era um problema conhecido há anos... talvez tenha sido a forma que arranjaram para estancar as conversões de BTC para USD e consequente levantamento de dinheiro que eles não tinham...

Apenas uma teoria... pura especulação... pode ser que no futuro se saiba mais alguma coisa do que realmente se passou... 



Parece que o mesmo se aplica a quem tem bancos de Bitcoin... e não é necessário ser assim, uma vez que uma das inovações do Bitcoin é cada pessoa poder ser o seu banco, guardando os Bitcoins ela mesma...

[btcmb]

Artigo muito interessante que especula sobre uma série de teorias sobre o caso Mt. Gox, http://hackingdistributed.com/2014/03/01/what-did-not-happen-at-mtgox/

[btcmb]

Mais uma teoria sobre o que eventualmente aconteceu no caso Mt. Gox, em todo o caso muito próxima da teoria que eu tenho...

Peter R’s Theory on the Collapse of Mt. Gox


TL/DR: A young man had a secret.  To keep it hidden, he kept digging until the hole was a billion dollars deep.  This is a speculative tale of a great bitcoin theft from MtGox in 2011 and the efforts that this man undertook to fix it.  The tale explains the bitcoin bear market of 2011, the explosive rally of 2013, delayed fiat withdrawals, malled transactions, and a bot named Willy.


“By the time you realize that real life has begun, you are already three moves in.”—Author unknown


It was June 19, 2011.  Mark, a 26 year-old young man—a boy really—was ecstatic.  He had recently purchased MtGox—a small, online exchange for trading virtual tokens—and business was booming.   These virtual tokens were called bitcoins and Mark loved them. 

Bitcoins were an obscure curiosity: a peer-to-peer electronic cash system that allowed users to store and exchange credits with any other user in the world, nearly instantly, and without the assistance of a third-party or the permission of an authority.   All that was needed was a 78-digit secret number—a key if you will.

In order for his customers to withdraw their bitcoins over the internet, MtGox stored some of these keys on its online server.   The remaining keys were stored on USB drives and backed up on paper to prevent theft should the server be compromised. 

But theft was hardly a concern.  In October of 2010, bitcoins were trading for $0.10 and the half a million bitcoins held by MtGox was worth only $50,000.   But still Mark took precautions, diligently moving bitcoins to offline storage and leaving only what was necessary for customer withdrawals online.   He truly wanted both his business and bitcoin to succeed. 

By April, the bitcoin price had risen to $1 and by June it had exploded to $30.  Between June 1 and June 15, an additional one million bitcoins were sent to MtGox and immediately sold, crashing the price back to $10.  It was a hectic time, with hundreds of customers needing help, visits from the FBI related to the Silk Road black market, and stress related to the recent market crash.  Young Mark was becoming a victim of his own success: there simply wasn’t enough time to get everything done.  On this very day in June 2011, the keys to the recently-deposited 1,000,000 BTC were still sitting on his server. 

Later this day, a group of hackers gained access to MtGox servers and executed fake trades that the world could see, driving the nominal price of bitcoin near $0.  Mark was frantic.  He quickly regained control of the servers and learned the dark truth: the million bitcoins that had recently flooded in earlier that month were gone.  Mark admitted publically to the hack, rewound the false trades, but kept the truth of the missing coins a secret. 

How could this 26-year old explain to his customers that he had lost their bitcoins?  And if the world found out, would this kill the thing he loved so dearly?  Would he go to jail?  Or worse yet, would someone kill him?  Mark decided that he would do what he thought was right: he would slowly earn back the lost bitcoin with MtGox trading fee profits and eventually make his customers whole again.  He still had over 500,000 BTC left—he moved 424242.42424242 BTC between bitcoin addresses and convinced the community that MtGox was solvent.  As long as withdrawals didn’t exceed deposits over a long period of time, no one would ever find out the truth.  Or so he thought.

Meanwhile, the bitcoin thieves slowly mixed their coins with other coins, obfuscating the chain of ownership, and then re-selling these coins on MtGox using sock-puppet accounts.  Mark tried to stop them, but there was no way he could know for sure which accounts were fraudulent—he even accused innocent people of bitcoin laundering.  The constant selling of these stolen bitcoins drove the price down to $2 in November 2011.  Mark faithfully used all of the MtGox profits to purchase coins back during this decline.  But he would never use customer funds—that was a line he swore not to cross. 

The selling of these stolen bitcoins continued at a diminished rate over 2012, and Mark continually purchased coins using the MtGox trading fees.  The bitcoin economy was growing and new exchanges were opening up across the world.  His bitcoin reserves weren’t building fast enough but the price of bitcoin kept rising (along with the dollar value of the missing bitcoins).  He was worried that other exchanges would suck coins out of Gox and reveal his secret.  He decided he needed to take decisive action: for the first time, he used customer funds to purchase real bitcoins.  These large purchases by Mark further increased demand and ignited the great rally of spring 2013 when the bitcoin price shot from $20 to $266.  Mark had reduced his liability in bitcoins, but in dollar terms the coins that were still missing were worth more than ever before. 

On May 15, 2013 the US Department of Homeland Security seized millions of dollars from the MtGox Dwolla bank account. MtGox dollar reserves were already depleted at this point, and with the recent seizure, Mark could no longer make good on customer withdrawals in US dollars. 

Under the guise of “banking problems,” MtGox slowed US dollar withdrawals to a trickle in the summer of 2013.   Customers became increasingly worried and began to bid up the price of bitcoin on MtGox, as this was the only way to escape with their funds. MtGox had little fiat and very little bitcoins, but it learned one thing: as the price differential between Gox and BitStamp grew, the outwards flow of bitcoin slowed dramatically. 

And so Willy was born.  Willy was a bot, discovered by Wall Observers from bitcointalk.org and named by Opet on Bonavest's trading show, who would consistently purchased bitcoins at regular intervals between November 2013 and February 2014.  Evidence that Willy belonged to Mark was revealed when both web and API trading at Gox was disabled for a brief period of time, exposing Willy as the only one left buying. 

Willy served two purposes: he drove the price of bitcoin on the MtGox exchange high, thereby slowing and sometimes reversing the outward flow of real BTC, and he reduced the number of GoxBTC held by clients.  Of course, this meant that Willy eventually became the owner of a huge number of GoxBTC (that were of course no longer backed by real BTC). 

By December, the situation at MtGox was grim.  In a desperate attempt to attract more funds, Mark offered reduced trading fees under the guise of celebrating their 1,000,000th customer.  This partially worked, but Mark knew it was too late.  If MtGox collapsed, it must appear that he didn’t know about the theft until now—for it was better to appear incompetent than criminal. 

It was time to cover his tracks.

He purposely mixed immature coins into bitcoin withdrawals to delay the outward flow of coins, and later began malling his own transactions.  He added the Gox malleability weakness not as a bug, but as a feature, so that it would seem plausible that outsiders had recently stolen the coins without his awareness.   No coins were actually lost to malleability. 

The MtGox coin supply dwindled to 2,000 BTC and on February 7, 2014 he had no choice but to disable bitcoin withdrawals.   The end was near. 

The problem Mark faced was that his customers had $150,000,000 credited to their accounts, yet the MtGox bank account only contained $38,000,000.  He could blame the missing bitcoins on transaction malleability, but how could he explain where the fiat money went?

He shifted Willy into reverse and cranked the throttle.  Willy relentlessly dumped bitcoins into the open bids.  The price fell further and further, eventually dropping well below the BitStamp price.  But still not enough people were buying!  He needed his customers to buy the GoxBTC.  Willy kept dumping coins until finally the price dropped below $100.  MtGox even acquired new USD bank wires from customers looking to purchase the cheap coins.   By this time, the majority of Gox customers had converted their dollars into bitcoins. 

On February 28, 2014, Mt Gox filed for bankruptcy protection in Tokyo, reporting 6.5 billion yen in liabilities, 3.8 billion yen in assets, and 750,000 of customer bitcoins missing.  Willy had failed to completely close the fiat solvency gap and Mark finally admitted to having lost the coins.

Now we watch the rest of the story unfold.  A story of how an oversight during a hectic period, an untimely theft, and an attempt to cover it up, lead to the greatest loss in the history of bitcoin. 

[Zel]

alguem vai escrever um livro sobre essa historia