Zcoin implementation bug enabled attacker to create over 500K Zcoins

Post by jacquesm » Tue, Mar 07, 2017, 6:50 AM UTC

pilif wrote: post #67

jacquesm wrote: post #52

Earlier quoted context omitted.

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.

-Wall sure (also, it should really enable all warnings, just as the name implies. Currently it doesn't) -Werror, I'm not sure. During development and on CI systems it makes sense. But if you intend to ship source code, it's probably best left off. Other people might be using different compilers that emit warnings for things yours didn't. You don't want the build to fail for those people.

Post by repomies6991 » Tue, Mar 07, 2017, 6:55 AM UTC

seibelj wrote: post #2

> If the attacker managed to liquidate their Zcoins at an average price of $1.25, they may have netted themselves upto USD 750,000. If you are a skilled programmer / security expert / mathematician, crypto currency exploit creation seems to be an extremely lucrative hobby.

Post by willtim » Tue, Mar 07, 2017, 7:00 AM UTC

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…

Post by xroche » Tue, Mar 07, 2017, 7:08 AM UTC

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.

Post by iopq » Tue, Mar 07, 2017, 7:24 AM UTC

NKCSS wrote: post #79

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 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).