Zap: Bitcoin Lightning Wallet


Wallet Logo

This Android app currently has more than 5000 downloads and the latest release is version Varies with device.

Our last analysis was done on 30th December 2019 based on data found in their Google Play description and their website and their source repository. We discuss issues with the provider here. Our verdict was Not reproducible from the source provided (details below).

We found these ways of contacting the developers:

Help spread awareness for build reproducibility

Please help us spread the word, asking Zap: Bitcoin Lightning 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

Their description

Manage your private keys, multiple wallets, and open channels, to get connected with peers on the Lightning Network and start transacting today.

sounds non-custodial.

On their website we find their GitHub repository and there a bit hidden, the build instructions.

So let’s try this without Android Studio, as we don’t want to automate clicking buttons in Android Studio …

For my phone Google Play offers to download version 0.2.11-alpha.

$ cd zap-android/
$ git tag | grep 0.2.11
$ git checkout v0.2.11-alpha 
$ docker run --rm -it --volume=$PWD:/mnt --workdir /mnt mreichelt/android:latest bash
root@84c836f4577a:/mnt# ./gradlew bundleRelease
root@84c836f4577a:/mnt# mv app/build/outputs/apk/release/zap-android-0.2.11-alph* .
root@84c836f4577a:/mnt# exit
$ ls *.apk
'zap-android-0.2.11-alpha(17)-arm64-v8a-release-unsigned.apk'  'zap-android-0.2.11-alpha(17)-armeabi-v7a-release-unsigned.apk'

So … this is a problem. The version “Varies with device” as we already noticed on the Playstore description. App providers can publish a different app for you than they publish for me, so me verifying a build gives you not much of information. This is why we are also working on a tool to collect APKs that hopefully soon will detect which version you downloaded, check if it was already verified to match the published code and upload it to us if not.

Should we be able to verify the one APK but naturally not the other, this should be our top priority to work on.

$ apktool d -o fromBuild-arm64-v8a 'zap-android-0.2.11-alpha(17)-arm64-v8a-release-unsigned.apk'
$ apktool d -o fromBuild-armeabi-v7a 'zap-android-0.2.11-alpha(17)-armeabi-v7a-release-unsigned.apk'
$ apktool d -o fromPlay Zap\ 0.2.11-alpha\ \(zapsolutions.zap\).apk 
$ diff --brief --recursive fromPlay/ fromBuild-armeabi-v7a/
Files fromPlay/apktool.yml and fromBuild-armeabi-v7a/apktool.yml differ
Only in fromPlay/lib: arm64-v8a
Only in fromBuild-armeabi-v7a/lib: armeabi-v7a

… so my phone installed the arm64 version but as

$ diff --brief --recursive fromPlay/ fromBuild-arm64-v8a/
Files fromPlay/apktool.yml and fromBuild-arm64-v8a/apktool.yml differ
Files fromPlay/lib/arm64-v8a/ and fromBuild-arm64-v8a/lib/arm64-v8a/ differ
Files fromPlay/lib/arm64-v8a/ and fromBuild-arm64-v8a/lib/arm64-v8a/ differ
Only in fromPlay/original/META-INF: CERT.RSA
Only in fromPlay/original/META-INF: CERT.SF
Files fromPlay/original/META-INF/MANIFEST.MF and fromBuild-arm64-v8a/original/META-INF/MANIFEST.MF differ
Files fromPlay/res/drawable-hdpi/ic_icon_modal_on_chain.png and fromBuild-arm64-v8a/res/drawable-hdpi/ic_icon_modal_on_chain.png differ
Files fromPlay/res/drawable-ldpi/ic_icon_modal_on_chain.png and fromBuild-arm64-v8a/res/drawable-ldpi/ic_icon_modal_on_chain.png differ
Files fromPlay/res/drawable-mdpi/ic_icon_modal_on_chain.png and fromBuild-arm64-v8a/res/drawable-mdpi/ic_icon_modal_on_chain.png differ
Files fromPlay/res/drawable-xhdpi/ic_icon_modal_on_chain.png and fromBuild-arm64-v8a/res/drawable-xhdpi/ic_icon_modal_on_chain.png differ
Files fromPlay/res/drawable-xxhdpi/ic_icon_modal_on_chain.png and fromBuild-arm64-v8a/res/drawable-xxhdpi/ic_icon_modal_on_chain.png differ
Files fromPlay/res/drawable-xxxhdpi/ic_icon_modal_on_chain.png and fromBuild-arm64-v8a/res/drawable-xxxhdpi/ic_icon_modal_on_chain.png differ
Files fromPlay/res/raw/country_list.json and fromBuild-arm64-v8a/res/raw/country_list.json differ
Files fromPlay/res/raw/currency_list.json and fromBuild-arm64-v8a/res/raw/currency_list.json differ
Files fromPlay/smali/com/squareup/okhttp/internal/DiskLruCache$2.smali and fromBuild-arm64-v8a/smali/com/squareup/okhttp/internal/DiskLruCache$2.smali differ
Files fromPlay/smali/com/squareup/okhttp/internal/framed/FramedStream$FramedDataSource.smali and fromBuild-arm64-v8a/smali/com/squareup/okhttp/internal/framed/FramedStream$FramedDataSource.smali differ
Files fromPlay/smali_classes2/io/grpc/internal/DelayedStream$DelayedStreamListener.smali and fromBuild-arm64-v8a/smali_classes2/io/grpc/internal/DelayedStream$DelayedStreamListener.smali differ

contains more than the expected two to three files about the signature, this is not a clean reproducible build.

Our verdict: not verifiable.

Verdict Explained

Not reproducible from the source provided The app provider also shares code but we could so far not verify that the published code matches the published app!

This verdict means that the provider did share some source code but that we could not verify that this source code matches the released app. This might be due to the source being released later than the app or due to the provided instructions on how to compile the app not being sufficient or due to the provider excluding parts from the public source code. In any case, the result is a discrepancy between the app we can create and the app we can find on GooglePlay 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.

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.