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Zcoin implementation bug enabled attacker to create over 500K Zcoins

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Re: Zcoin implementation bug enabled attacker to create over 500K Zcoins

#91

Post by im3w1l »

robertgraham wrote: post #89
yjgyhj wrote: post #71

The point I'm about to make in this comment is so old and has been said so many times that we all are tired of hearing it. But why do we use a language like C++ to implement something where we don't wish to have bugs? C++ is not memory-safe (no GC or whatever Rust does), it's not type safe (in the ML sense), it relies on writing to memory a lot (instead of having pure functions). Had this program been written in Ocam…

It's an absurd point. ZCash was built upon the Bitcoin codebase. This inherits a lot of bad decisions. Moral purity, demanding they start over again from scratch, just isn't practical. The bug in question could have been solved had the simply compiled with minimal static analysis -- by which I mean -Wall. C/C++ is memory safe if you turn on dynamic checking. Sure, it's twice as slow as C/C++, but still tons faster th…

> C/C++ is memory safe if you turn on dynamic checking.

Is anyone here doing this? Would be interesting to hear your experience.

Re: Zcoin implementation bug enabled attacker to create over 500K Zcoins

#92

Post by NKCSS »

iopq wrote: post #80
NKCSS wrote: post #79

Earlier quoted context omitted.

Because old habits die hard. Using 'unmanaged' languages for 'performance' reasons is no longer a good reason, because the likes of C# have shown multiple times that there is no reason to choose C++ over C# if you look at performance alone (difference is neglible).

The difference is not negligible: http://benchmarksgame.alioth.debian.org/u64q/compare.php?lan... Sure, it's silly benchmarks, so I wouldn't take the results as gospel. But the fact is, nobody who writes C# managed to produce a benchmark yet that beats a C++ program. Fast languages like Rust have managed to at least match the performance of C in some benchmarks (and even beat it in others).

If they were properly written, I'd accept that, but just take a look at how vastly different things these two are doing:

http://benchmarksgame.alioth.debian.org/u64q/program.php?tes... http://benchmarksgame.alioth.debian.org/u64q/program.php?tes...

Re: Zcoin implementation bug enabled attacker to create over 500K Zcoins

#93

Post by dEnigma »

gspetr wrote: post #43
kolinko wrote: post #35

Earlier quoted context omitted.

Depends on a country. In Poland, if a company sends you money, once you spend it, they have no right to get it back. The reasoning being that you have a right to assume companies know what they are doing. If a private person sends you money, you have to give it back.

This seems very surprising to me. And it also seems criminally exploitable. So if a bank in Poland sends you a million dollars by mistake, is it yours? What would happen if someone stole it and transferred it to your account, does that make you a criminal? And even more interestingly, if a malicious bank programmer (who's in league with you) introduced a bug on purpose (let's suppose we cannot prove the intent here,…

I don't know about Poland, but in Austria there is a similar law (IANAL but my lawyer friend told me about it), and banks are excepted from it. So if a company sends you money by mistake you can spend it and don't have to give it back after that, but if a bank makes a mistake in your favour, you have to return it in any case. Happened to my lawyer friend's mother.

Re: Zcoin implementation bug enabled attacker to create over 500K Zcoins

#94

Post by barking »

WalterBright wrote: post #42

The error is here: https://github.com/zcoinofficial/zcoin/blob/81a667867b5d8489... and the line of code: zccoinSpend.denomination == libzerocoin::ZQ_LOVELACE; In other words, a statement with no effect. In D, such a line gives an error, not a warning: Error: == has no effect in expression You can force the statement to be accepted by casting it to void. It's really past time for languages to not accept such code any…

Sorry if this is stating the obvious.

I'm guessing that this was meant to be a single equals sign for an assignment rather than a double equals for an equality test?

Re: Zcoin implementation bug enabled attacker to create over 500K Zcoins

#95

Post by Sanddancer »

yjgyhj wrote: post #71

The point I'm about to make in this comment is so old and has been said so many times that we all are tired of hearing it. But why do we use a language like C++ to implement something where we don't wish to have bugs? C++ is not memory-safe (no GC or whatever Rust does), it's not type safe (in the ML sense), it relies on writing to memory a lot (instead of having pure functions). Had this program been written in Ocam…

Because pretty much any language that's been touted as a replacement has problems which need solved before they'd really be viable. They're either single vendor with no independent standardization, like Rust or D, or have lower performance like go, or both. Once both problems are fixed, it'll be a lot easier to start looking at alternatives. Until then, there's not a language that settles into a lot of the niches C and C++ operate in.

This case specifically, a lot of the issues that allowed this to happen were logic errors which would have been valid in most languages. A functional language would not have helped very much here.

C and C++ are still used because they work, and have huge ecosystems around them. There's a lot of tooling around them, the compilers build fast, code, and are available for pretty much every planet under the sun. This particular case, it would have helped a lot if the developers looked at the warnings of the questionable code they had made, but they seem to be of the "it compiles, ship it" type that would have let those things fly regardless of the language.

Re: Zcoin implementation bug enabled attacker to create over 500K Zcoins

#96

Post by petters »

yjgyhj wrote: post #71

The point I'm about to make in this comment is so old and has been said so many times that we all are tired of hearing it. But why do we use a language like C++ to implement something where we don't wish to have bugs? C++ is not memory-safe (no GC or whatever Rust does), it's not type safe (in the ML sense), it relies on writing to memory a lot (instead of having pure functions). Had this program been written in Ocam…

As far as I can tell, this bug has nothing to do with memory-safety. And I don't think C++ is to blame here.

It's just a lot of untested code. Surely even Ocaml and Haskell need tests.

Re: Zcoin implementation bug enabled attacker to create over 500K Zcoins

#97

Post by Freak_NL »

barking wrote: post #94
WalterBright wrote: post #42

The error is here: https://github.com/zcoinofficial/zcoin/blob/81a667867b5d8489... and the line of code: zccoinSpend.denomination == libzerocoin::ZQ_LOVELACE; In other words, a statement with no effect. In D, such a line gives an error, not a warning: Error: == has no effect in expression You can force the statement to be accepted by casting it to void. It's really past time for languages to not accept such code any…

Sorry if this is stating the obvious. I'm guessing that this was meant to be a single equals sign for an assignment rather than a double equals for an equality test?

Yep. That's all there is to it.

Re: Zcoin implementation bug enabled attacker to create over 500K Zcoins

#98

Post by Sanddancer »

jacquesm wrote: post #52
WalterBright wrote: post #42

The error is here: https://github.com/zcoinofficial/zcoin/blob/81a667867b5d8489... and the line of code: zccoinSpend.denomination == libzerocoin::ZQ_LOVELACE; In other words, a statement with no effect. In D, such a line gives an error, not a warning: Error: == has no effect in expression You can force the statement to be accepted by casting it to void. It's really past time for languages to not accept such code any…

You're absolutely right (to my surprise), it gives: test.cpp: In function ‘int main()’: test.cpp:13:11: warning: statement has no effect [-Wunused-value] a == b; ^ But only after enabling a warning that is not on by default. -Wall and -Werror should be the default.

It gets worse for this particular project. They do build with -Wall and -Wextra, but they ignore many warnings that the compiler does emit, and a lot of them are adding/removing a single word. Also, compilers have different default warnings. Gcc doesn't emit a warning on that code, but clang does, for example.

Re: Zcoin implementation bug enabled attacker to create over 500K Zcoins

#99

Post by jhasse »

im3w1l wrote: post #91
robertgraham wrote: post #89

Earlier quoted context omitted.

It's an absurd point. ZCash was built upon the Bitcoin codebase. This inherits a lot of bad decisions. Moral purity, demanding they start over again from scratch, just isn't practical. The bug in question could have been solved had the simply compiled with minimal static analysis -- by which I mean -Wall. C/C++ is memory safe if you turn on dynamic checking. Sure, it's twice as slow as C/C++, but still tons faster th…

> C/C++ is memory safe if you turn on dynamic checking. Is anyone here doing this? Would be interesting to hear your experience.

If valgrind counts, then yes.

Re: Zcoin implementation bug enabled attacker to create over 500K Zcoins

#100

Post by zuzun »

yjgyhj wrote: post #71

The point I'm about to make in this comment is so old and has been said so many times that we all are tired of hearing it. But why do we use a language like C++ to implement something where we don't wish to have bugs? C++ is not memory-safe (no GC or whatever Rust does), it's not type safe (in the ML sense), it relies on writing to memory a lot (instead of having pure functions). Had this program been written in Ocam…

You are looking at a 1k LOC function in a 7k LOC file with a bug that can be easily spotted by -Wall and you think it's the fault of the programming language? The only thing irresponsible is putting your hard-earned money into the 100th Bitcoin fork maintained by some guy with an Anime avatar. Once you stop trusting the developers it essentially becomes an underhanded ... contest and no language wins.
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