Btcd: A Full Alternative Bitcoin Implementation, Written In Go

http://bitcoinmagazine.com/btcd-a-full-bitcoin-alternative-written-in-go/

by waterlesscloud • 13 years ago

150 56 13 years ago

saurik2• 13 years ago

> The implementation is not yet entirely done, but most core features such as transaction verification, database interaction and network connectivity are tested as working, and the company has released one component of the system for public review...

I have a different definition of "full".

jeffasinger• 13 years ago

I think full here may mean in the sense that it actually verifies the entire blockchain, rather than relying on an instance of bitcoind to do that.

saurik2• 13 years ago

I am willing to re-state "I have a different definition of 'implementation'"? It actually occurred to me that that is how "full" might be being used in this context (I spent some time recently learning about bitcoin and even ran a class on it a few days ago, and had run into the distinction), but if I were to say I had "an end-to-end website rendering engine written in Erlang" would you not also feel a little disappointed when you got to my page and found only that "most of the core pieces, such as CSS3 selectors, DOM event bubbling, and network connectivity are done and we've open sourced the HTML parser"?

conformal• 13 years ago

i think there has been some confusion in links and titles: btcd is a full-node alternative implementation of the bitcoin protocol. this was not meant to be misleading and you are right to point out that the btcwire package is far from the entire piece of software.

in another few weeks all the pieces will be public and it will be closer to a full implementation, per my interpretation of your use of the word full.

jimrandomh• 13 years ago

Some variety in Bitcoin software could be a good thing. However, I'd just like to leave a reminder here that beta-level software is not something you should trust significant amounts of Bitcoins to, or build a business on, until it stops being beta-level.

tptacek• 13 years ago

Yeah, not like bitcoind.

swhitt• 13 years ago

When this was posted on reddit there was a bit of confusion as the title lead people to believe this was about an alternate cryptocurrency (like litecoin, feathercoin, etc).

It's actually a complete reimplementation of the Bitcoin protocol, which can be used as an alternative to the bitcoind/bitcoin-qt (the official Bitcoin p2p clients) JSON-RPC interface.

DanielBMarkham• 13 years ago

Speaking as a Bitcoin skeptic, the really cool thing about it is that it opens up a world of virtual collectibles.

Bitcoin isn't the future of money, it's more like Netscape -- a new way of doing things we haven't thought of before. The follow-on products should truly be amazing. Good to see this.

michielvoo• 13 years ago

Not sure from your comment if you got the gist of it... but this is not an alternative to Bitcoin, the currency. It's an alternative to bitcoind, the library.

If anything, the article suggests, the rise of such alternative implementations of the same protocol could make the network as a whole more resilient and stable.

Guvante2• 13 years ago

Why does that disagree with what he said? Netscape understood the same protocols all future browsers did, with only some feature misalignment, yet eventually disappeared.

I think he is saying the same thing to could happen to Bitcoin, the current use cases of the currency may be only the beginning.

DennisP• 13 years ago

True, but if the code ends up easier to understand, it might well make it easier to create alternatives to Bitcoin, the currency.

SomeoneWeird• 13 years ago

This is ridiculous, it's not even a partial implementation, it's just a serialization library, at the moment. People should get their facts straight :)

whaevr2• 13 years ago

Interesting, one question though. Who thought orange text on white background was a good idea? Ow

maaku• 13 years ago

Discuss the topic please.

whaevr2• 13 years ago

? It is related to the topic. Maybe not specifically the article but the website in question that was linked. I thought it was a pretty odd choice, and website design is definitely relevant to HN

patio112• 13 years ago

Interestingly, the main bitcoin developers generally treat other implementations of the protocol as being suspect and more-than-possibly threatening, since if you're not bug-for-bug compatible with the satoshi client that is a security risk. This remains true even if you improve upon the satoshi client with regards to, for example, hewing closer to the published spec.

This might come as something of a surprise to many HNers, who would think "But wait. The Internet would sort of suck if HTML5 were a purely advisory document and failing to match IE6's actual behavior 100% of the time was a fatal flaw in a browser." But, to quote a fairly representative post from their forums:

Any implementation needs to specifically test for uniformity with the network: Bitcoin is a distributed consensus algorithm and differences in what nodes accept or reject in the blockchain— things which would be minor harmless behavioral differences in most software— can often result in fatal security flaws where an attacker can move the nodes in question onto a separate fork and double-spend their funds away or partition the network. This requires a unusual level of care and system level tests.

Many of the most interesting cases are the great many things which must be rejected as no amount of exposure to the live network will trigger those cases (until an attacker exploits them to partition the network). (cite: https://bitcointalk.org/index.php?topic=192880.0)

mseebach2• 13 years ago

How can a bug in the implementation be a security risk? Aren't the artefacts of bitcoin (I don't know the correct terminology) cryptographically unambiguous, completely independent of the implementation used to create them?

The "problem" with HTML incompatibilities is that there is room for plenty of ambiguity in both standard and implementation, without compromising the fundamental mission of the users of the protocol (rendering web content).

Strilanc• 13 years ago

If one type of client accepts a particular block and another doesn't, the block chain splits and things go badly.

This literally happened one month ago, because of a bug being fixed: https://bitcointalk.org/index.php?topic=152030.0

zoul• 13 years ago

A bug in the implementation could affect the consensus about the largest chain, just as happened with the official client recently. That’s a security risk.

patio112• 13 years ago

How can a bug in the implementation be a security risk?

This gets a little complicated. "Bitcoin" is a commodity, a protocol (series of promises), a protocol (computer code to implement that series of promises), a particular distributed ledger, a network (of computers implementing the computer code implementing the series of promises with regards to one consensus distributed ledger), etc etc.

Consider bitcoin the series of promises. One such promise is under what circumstances opcode 32 causes a transaction to be marked as invalid. (Don't bother looking it up -- you'll have to go down a rabbit hole for a while.) It is critically important that all code implementing opcode 32 comes to the same conclusion regarding every transaction in history and every transaction in the future.

Consider an edge case for opcode 32, occurring in a transaction that I'll call T, two years ago. T is, as of right now, accepted as valid in the history that bitcoin (as you understand that term) accepts as correct. If a malfunctioning bitcoin client were to reject T, they would reject large portions of history after T, because they'd be predicated on an invalid series of transactions. Following me so far?

So the more interesting case isn't when there is a difference of opinions in the past, it is when there is a predictable difference of opinions in the future. In this case, one set of clients starts building a transaction ledger B, and one starts building a transaction ledger B'. They are different transaction ledgers. People subscribing to either ledger, which they think of as The One True Bitcoin Ledger, will be mighty pissed when other people in The One True Bitcoin Economy tell them that their unforgeable, unloseable, ungovernable units of crypocurrency are actually worthless bits.

This is called a blockchain fork. Bitcoiners are terrified of it happening again. (Yes, it has already happened at least once. Long story. "No harm, no foul, he wasn't trying to crash our entire economy so we dodged a bullet." is pretty much the consensus among Bitcoiners who actually understand what happened there.)

wcoenen• 13 years ago

A bitcoin node tries to determine what the consensus is about the bitcoin ledger by looking for the longest block chain.

However, in order to do that it must first collect blocks from other nodes and reject any invalid ones. If a certain implementation disagrees with the rest of the network about the validity of a block, then it will disagree with the rest of the network about the state of the ledger. This can then be exploited by an attacker, e.g. by paying a merchant with a transaction that seems to OK to him but is not accepted by the rest of the network.

I don't think that this is a big problem though. A node knows that it is no longer in agreement with the majority of the network when it sees an "invalid" block chain that has the most proof of work done on it. In this case it should shut itself down.

betterunix6• 13 years ago

"How can a bug in the implementation be a security risk?"

It could fork the block chain:

http://bitcoin.org/chainfork.html

evv• 13 years ago

More importantly, I believe, is the fact that nobody can stop alternative implementations from existing on the network.

Attackers are probably already tinkering with custom BTC clients, attempting to abuse the system. If this were really a concern, it is far too late.

The smart bitcoin users will choose the best client available, not just the default one.

betterunix6• 13 years ago

"The smart bitcoin users will choose the best client available, not just the default one."

What you are saying is that the security of Bitcoin depends on everyone other than the smart users. If the block chain is forked because of an incompatibility between two Bitcoin clients, the fact that smart users choose the "best" client is irrelevant; you need most users to choose that client. You should not rely on most of the users of a cryptosystem to be "smart" about using it:

http://www.securius.com/newsletters/Security_Through_Usabili...

vbuterin• 13 years ago

Hi there, original author of the article here.

Many Bitcoin developers are actually quite positive to the idea of alternative implementations; all they're saying is "be careful".

> Gavin wrote to me only days after the BitCoinJ release to tell me how happy he was to see an alternative implementation. Satoshi expressed very similar sentiments. Nobody is against alternative implementations. > What some people, especially Satoshi, have said is that there’s an unusual amount of risk involved with reimplementing the full system and using that reimplementation to mine. Bitcoin is very complex and if you aren’t skilled and very thorough you are likely to diverge from its behavior in small, hard to detect ways. This can fork the chain and split the economy. It’s one of the few things that could instantly kill Bitcoin beyond legal harassment of its users.

- Mike Hearn 2011

> part of the solution is to encourage alternative implementations that make different trust/convenience tradeoffs than the reference implementation. There has been a lot of behind-the-scenes work on cross-implementation testing (the “testnet3″ blockchain contains hundreds of transaction validation test cases, for example), and new features are being added to the protocol to support alternative implementations

-Gavin Andresen, late 2012

If you're not mining, I personally would say it can only be good if you just follow the protocol spec and try to implement Bitcoin from there. If you fall off the main chain and it's not obviously your fault, then either the protocol spec was unclear and can get improved or the original client has a bug, in which case there are ways to carefully phase the bug out of existence with a patch.

shazow• 13 years ago

I probably haven't been keeping up with the bitcointalk forums as much as yourself, but I haven't gotten the impression that the main bitcoin developers treat alternative implementations as threatening.

There are already several moderately-popular alternative implementations in the wild. Bitcoinj is used by pretty much every Android-based Bitcoin app. Electrum (a popular thin-client) is using a custom implementation on their backends, too.

Every time I ask or see a question from people who are working on alternative clients, the developers have always been supportive and informative.

The biggest problem, and possibly the underlying spirit of the warning you quoted, is that the current version of the protocol is not super-well documented. Some data structures are undefined and need to be reverse-engineered from other implementations (such as net_time), others are ambiguously defined.

My takeaway from the thread you linked is closer to this quote:

"Yes, please, feedback from re-implementors is very helpful." — Gavin Andresen, lead Bitcoin developer.

nwh• 13 years ago

> Electrum (a popular thin-client) is using a custom implementation on their backends, too.

The Electrum server doesn't do any network communication of it's own, it's a bunch of external databases that does it's communication though a standard bitcoind.

GigabyteCoin• 13 years ago

I think you are misinformed.

There are links to multiple Bitcoin clients on bitcoin.org which is controlled by "the main Bitcoin developers": http://bitcoin.org/en/choose-your-wallet

Where did you get the impression that the Bitcoin devs treat other clients as "suspect and more-than-possibly threatening"?

gojomo• 13 years ago

The early days of the web were similar; that's how you get rapid evolution in a decentralized system.

The whole Bitcoin ecosystem is learning by doing, with lots of precocious amateur participation, under intense pressure. Ultimately that may make it stronger.

Those who prefer spec stability should stick to systems built by government/defense contracting.

dennisgorelik• 13 years ago

Why do you even discuss technical side of bitcoin if you find the whole bitcoin business concept flawed?

Sami_Lehtinen• 13 years ago

Also see: https://blog.conformal.com/btcd-a-bitcoind-alternative-writt... Btw, this original link was posted here full week ago.

kellros• 13 years ago

Should definitely build this with the gcc go compiler (which featured a couple of days ago on HN) that produces larger binaries but faster code :)

Btcd: A Full Alternative Bitcoin Implementation, Written In Go

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