This app was first launched on 15th January 2018 and currently has more than 100000 downloads, a 4.5 stars rating from 1698 users and the latest APK is version 3.0.9.
We found these ways of contacting the developers:
Help spread awareness for build reproducibility
Please help us spread the word, asking Lumi Bitcoin and Crypto Wallet to support reproducible builds via their Twitter!
The following Analysis is not a full code review! We plan to make code reviews available in the future but even then it will never be a stamp of approval but rather a list of incidents and bad coding practice. We cannot find and tell you all the dark secrets the wallet providers might have.
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.
Update: Following a conversation on Twitter we checked again and also added statements of being Open Source and our take to those.
The description on their Playstore listing gets straight to the point:
With Lumi Wallet, you are the only one in charge of your funds. Your private keys are stored on your device, and the funds are protected with a 12-word mnemonic.
So they are not custodial but can we verify this?
On their website we find no link to the wallet’s source code although they claim:
Open-source We’re ready to prove our reliability that’s why our code is publicly available.
In their FAQ we find:
Is Lumi open-source?
Open-source is one of the major concepts in the cryptocurrency space as the whole industry basically grew up on it. Nowadays, building a crypto project without publishing at least a part of your code on GitHub is considered to be bad manners.
We are proud to say that our core wallet technology is open-source. You can view the libraries (for Android, iOS and Web) that we use to generate private keys and sign the transactions.
We use these libraries in our apps and in the web version of the wallet. You are welcome to see and review it anytime via this link.
Public source is not about good or “bad manners”. and “publishing at least a part of your code” achieves nothing at all in terms of security of the app in Google Play.
“We are proud to say that our core wallet technology is open-source.” … this
in turn is indeed something to proudly announce: The code they have on GitHub is
not only public but also Open Source. Their
lumi-android-core for example is
released under the very permissive MIT license. Kudos to their contribution!
For peace of mind that the wallet doesn’t contain backdoors though, publishing libraries that are used by the wallet, without also publishing the wallet’s code itself is not enough and until that code is public at least under a less permissive license, we have to remain with our verdict: not verifiable
Not verifiable: No Source Code found
This verdict means that we could not find any source to compile the app from. Internally the company might do everything right but as we can't verify it, there is nothing protecting the user from an exit-scam where the provider releases an app that leaks the keys to the servers.
The app cannot be independently verified. If the provider puts your funds at risk on purpose or by accident, you will probably not know about the issue before people start losing money. If the provider is more criminally inclined he might have collected all the backups of all the wallets, ready to be emptied at the press of a button. The app might have a formidable track record but out of distress or change in management turns out to be evil from some point on, with nobody outside ever knowing before it is too late.