Help spread awareness for build reproducibility
Please help us spread the word, asking HODLER Open Source Multi-Asset Wallet to support reproducible builds via their Twitter!
Do your own research!
Try out searching for "lost bitcoins", "stole my money" or "scammers" together with the wallet's name, even if you think the wallet is generally trustworthy. For all the bigger wallets you will find accusations. Make sure you understand why they were made and if you are comfortable with the provider's reaction.
The Analysis ¶
So their website … is for sale:
Buy Hodler.tech For USD 3,799
but according to Play Store, it features BTC and is open source:
We’d like to introduce the only fully Open Source, free multi-asset and multi-platform cryptocurrency wallet in the world.
In the description they link to this steemit article on why HODLER is open source and cite security thanks to auditability but do not mention reproducibility even though they mention that a malicious site could provide bad binaries. Their proposal: Compile it yourself.
In the description they claim:
Transactions are always generated and signed on your device. No sensitive data is ever send to an external server.
In the issues section this issue stands out:
Actually a one word mnemonic seed is accepted, and it most definitely should not.
However, like your project!
Yes, a single word is definitely not a BIP39 backup. That sounds scary! They might be inventing their own crypto here which means that restoring your account on a different product might not be straight forward in case their servers go down.
Else it checks all the boxes: BTC, self custodial, public source but what about reproducibility? Let’s see:
The Build Instructions are … not straight forward.
Biggest hurdles are the need to use commercial or trial licensed compilers and graphical tools which is hard to automate and run in a docker container.
Poking around in the repository I also found for example the folder homeAndroid which contains huge “fmx” files for not only Android. Those files are 1MB each while kind of human readable (there is binary embedded. PNGs for example), they are not what the developer is working on. Then commit messages like autocommit on build sound not like any coding I’ve done so far but more like a Powerpoint document that auto-saves from time to time. This commit for example changes 30 files with 8,301 added and 2,188 deleted lines, including the addition of binary files of undocumented origin.
All in all I’d like to understand more what’s going on but as the project has only 1000 downloads, a rather unconventional code base and basically two years of silence on all levels, I won’t dig deeper for now and file it as not verifiable.
We could not verify that the provided code matches the binary!
As part of our Methodology, we ask:Is the published binary matching the published source code? If not, we tag it
Published code doesn’t help much if it is not what the published app was built from. That is why we try to reproduce the binary. We
- obtain the binary from the provider
- compile the published source code using the published build instructions into a binary
- compare the two binaries
- we might spend some time working around issues that are easy to work around
If this fails, we might search if other revisions match or if we can deduct the source of the mismatch but generally consider it on the provider to provide the correct source code and build instructions to reproduce the build, so we usually open a ticket in their code repository.
In any case, the result is a discrepancy between the app we can create and the app we can find on the app store and any discrepancy might leak your backup to the server on purpose or by accident.
As we cannot verify that the source provided is the source the app was compiled from, this category is only slightly better than closed source but for now we have hope projects come around and fix verifiability issues.
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