HODL Wallet : Bitcoin Wallet

9 minute read


Wallet Logo

This app was first launched on 24th September 2018 and currently has more than 10000 downloads, a 3.9 stars rating from 74 users and the latest APK is version 3.3.5.

Our last analysis was done on 28th December 2019 based on data found in their Google Play description and their website and their source repository. We discuss verification with the provider in this issue.

We found these ways of contacting the developers:

Help spread awareness for build reproducibility

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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.

The Analysis

Update: The developer closed the issue where we asked for help to verify the app build. There appears to be no interest in scrutiny.

The description sounds a bit scary:

Your Bitcoin are stored on your device and backed up to a Backup Recovery Key when you create a wallet. This means HODL Wallet can never stop you from accessing or sending your funds.

So they can’t stop me from sending my funds but can I stop them from sending my funds if they have a backup? Or what is this “Backup Recovery Key” again? I guess that’s just me being paranoid but this could be worded more clearly.

HODL Wallet is free, open source, and doesn’t require you to create an account.

That at least sounds great! :)

Choose to connect to your own node in advance settings

That’s great, especially if it doesn’t talk to a company server after that.

The website is more reassuring:

HODL Wallet does not collect any information at any point in time and all your Bitcoin exist exclusively on your device.

Also do we learn about it supporting the industry standard BIP39, menmonic backups.

Apparently hodl-wallet-android is their repository. It is MIT licensed, which is one of the most permissive licenses.

There, the build instructions are very minimal and involve Android Studio. Let’s see how it goes:

Go to github.co/hodlwallet/breadwallet-android and clone or download the project

Breadwallet? Ok, good to know where the code comes from but this alone lets us doubt a bit how dedicated the team is working on the project. Also: more guessing on our part:

$ git clone git@github.com:hodlwallet/hodl-wallet-android.git
Cloning into 'hodl-wallet-android'...
$ cd hodl-wallet-android/
$ git tag
$ git branch
* develop

Not good. In the history we find no mention of 3.3.2 which would be the version name mentioned on Google.

Looking at the recent history though:

$ tig

2019-04-22 15:49 -0400 Igor Guerrero    o [HEAD] Bump version to `3.3.3
2019-04-22 15:47 -0400 Igor Guerrero    M─┐ Merge pull request #42 from
2019-04-19 16:33 -0400 Igor Guerrero    │ o Bump version
2019-04-19 16:33 -0400 Igor Guerrero     o Add hodlTestnet to the igno
2019-04-18 13:17 -0400 Igor Guerrero     o Add error message when we d
2019-04-17 17:13 -0400 Igor Guerrero     o Fix issue with Java not kno
2019-04-17 13:08 -0400 Igor Guerrero     o Fix problem with regular pa
2019-04-02 11:28 -0400 Igor Guerrero    o Add hodlTestnet to the igno
2019-04-02 11:27 -0400 Igor Guerrero    o Bump version
2019-03-15 11:18 -0400 Igor Guerrero    M─┤ Merge pull request #41 from
[main] 475dc72f34fe410f567482a13fc0bd9784d2f2e8 - commit 3 of 2119   0%
+        versionCode 10
+        versionName "3.3.2"
         multiDexEnabled true

we find 2 commits labled “Bump version” that both set the version name to “3.3.2”.

By the way, the wallet did not see an update since a long time. Those changes are from April 2019.

Anyway, the two “3.3.2” branches get merged on April 22nd, the day of the Google Play release. We’ll try that one: 394f23041b. We will raise the bar in the future and refuse to search for commits like that though. Have a tag or we can’t verify the build.

Anyway … we’ll try the same we tried with BRD:

$ git checkout 394f23041b
$ git submodule update --init --recursive
$ docker run -v $PWD:/mnt -it beevelop/cordova bash
root@7d56c86f8fae:/# cd /mnt/
root@7d56c86f8fae:/mnt# yes | $ANDROID_HOME/tools/bin/sdkmanager "platforms;android-28"
root@7d56c86f8fae:/mnt# /opt/android/tools/bin/sdkmanager ndk-bundle
root@7d56c86f8fae:/mnt# ./gradlew :app:assemble

So lets compare it with the version from the Play Store:

$ apktool d -o fromBuild app/build/outputs/apk/hodl/release/app-hodl-release-unsigned.apk
$ apktool d -o fromPlay ./appFromPlay.apk
$ diff --brief --recursive fromBuild fromPlay
Files fromBuild/AndroidManifest.xml and fromPlay/AndroidManifest.xml differ
Files fromBuild/apktool.yml and fromPlay/apktool.yml differ
Files fromBuild/lib/arm64-v8a/libcore-lib.so and fromPlay/lib/arm64-v8a/libcore-lib.so differ
Files fromBuild/lib/armeabi-v7a/libcore-lib.so and fromPlay/lib/armeabi-v7a/libcore-lib.so differ
Files fromBuild/lib/x86/libcore-lib.so and fromPlay/lib/x86/libcore-lib.so differ
Files fromBuild/lib/x86_64/libcore-lib.so and fromPlay/lib/x86_64/libcore-lib.so differ
Files fromBuild/original/AndroidManifest.xml and fromPlay/original/AndroidManifest.xml differ
Only in fromPlay/original/META-INF: CERT.RSA
Only in fromPlay/original/META-INF: CERT.SF
Files fromBuild/original/META-INF/MANIFEST.MF and fromPlay/original/META-INF/MANIFEST.MF differ
Files fromBuild/smali/co/hodlwallet/BuildConfig.smali and fromPlay/smali/co/hodlwallet/BuildConfig.smali differ
Files fromBuild/smali/co/hodlwallet/presenter/activities/camera/CameraActivity.smali and fromPlay/smali/co/hodlwallet/presenter/activities/camera/CameraActivity.smali differ
Files fromBuild/smali/co/hodlwallet/presenter/activities/settings/NodesActivity$1.smali and fromPlay/smali/co/hodlwallet/presenter/activities/settings/NodesActivity$1.smali differ
Files fromBuild/smali/co/hodlwallet/tools/animation/BRAnimator.smali and fromPlay/smali/co/hodlwallet/tools/animation/BRAnimator.smali differ
Files fromBuild/smali/co/hodlwallet/tools/manager/BRApiManager.smali and fromPlay/smali/co/hodlwallet/tools/manager/BRApiManager.smali differ
Files fromBuild/smali/co/hodlwallet/tools/manager/BREventManager.smali and fromPlay/smali/co/hodlwallet/tools/manager/BREventManager.smali differ
Files fromBuild/smali/co/hodlwallet/tools/manager/SyncManager$SyncProgressTask.smali and fromPlay/smali/co/hodlwallet/tools/manager/SyncManager$SyncProgressTask.smali differ
Files fromBuild/smali/co/hodlwallet/tools/qrcode/QRCodeReaderView$DecodeFrameTask.smali and fromPlay/smali/co/hodlwallet/tools/qrcode/QRCodeReaderView$DecodeFrameTask.smali differ
Files fromBuild/smali/co/hodlwallet/tools/qrcode/QRUtils.smali and fromPlay/smali/co/hodlwallet/tools/qrcode/QRUtils.smali differ
Files fromBuild/smali/co/hodlwallet/tools/security/BRKeyStore.smali and fromPlay/smali/co/hodlwallet/tools/security/BRKeyStore.smali differ
Files fromBuild/smali/co/hodlwallet/tools/security/BRSender$1.smali and fromPlay/smali/co/hodlwallet/tools/security/BRSender$1.smali differ
Files fromBuild/smali/co/hodlwallet/tools/security/PostAuth$7.smali and fromPlay/smali/co/hodlwallet/tools/security/PostAuth$7.smali differ
Files fromBuild/smali/co/hodlwallet/tools/security/PostAuth.smali and fromPlay/smali/co/hodlwallet/tools/security/PostAuth.smali differ
Files fromBuild/smali/co/hodlwallet/tools/security/RootHelper.smali and fromPlay/smali/co/hodlwallet/tools/security/RootHelper.smali differ
Files fromBuild/smali/co/hodlwallet/tools/sqlite/CurrencyDataSource.smali and fromPlay/smali/co/hodlwallet/tools/sqlite/CurrencyDataSource.smali differ
Files fromBuild/smali/co/hodlwallet/tools/sqlite/MerkleBlockDataSource.smali and fromPlay/smali/co/hodlwallet/tools/sqlite/MerkleBlockDataSource.smali differ
Files fromBuild/smali/co/hodlwallet/tools/sqlite/PeerDataSource.smali and fromPlay/smali/co/hodlwallet/tools/sqlite/PeerDataSource.smali differ
Files fromBuild/smali/co/hodlwallet/tools/sqlite/TransactionDataSource.smali and fromPlay/smali/co/hodlwallet/tools/sqlite/TransactionDataSource.smali differ
Files fromBuild/smali/co/hodlwallet/tools/threads/PaymentProtocolPostPaymentTask.smali and fromPlay/smali/co/hodlwallet/tools/threads/PaymentProtocolPostPaymentTask.smali differ
Files fromBuild/smali/co/hodlwallet/tools/threads/PaymentProtocolTask.smali and fromPlay/smali/co/hodlwallet/tools/threads/PaymentProtocolTask.smali differ
Files fromBuild/smali/co/hodlwallet/tools/util/Bip39Reader.smali and fromPlay/smali/co/hodlwallet/tools/util/Bip39Reader.smali differ
Files fromBuild/smali/co/hodlwallet/tools/util/BRCompressor.smali and fromPlay/smali/co/hodlwallet/tools/util/BRCompressor.smali differ
Files fromBuild/smali/co/hodlwallet/tools/util/BytesUtil.smali and fromPlay/smali/co/hodlwallet/tools/util/BytesUtil.smali differ
Files fromBuild/smali/co/hodlwallet/wallet/BRWalletManager.smali and fromPlay/smali/co/hodlwallet/wallet/BRWalletManager.smali differ
Files fromBuild/smali/co/platform/APIClient.smali and fromPlay/smali/co/platform/APIClient.smali differ
Files fromBuild/smali/co/platform/kvstore/RemoteKVStore.smali and fromPlay/smali/co/platform/kvstore/RemoteKVStore.smali differ
Files fromBuild/smali/co/platform/kvstore/ReplicatedKVStore.smali and fromPlay/smali/co/platform/kvstore/ReplicatedKVStore.smali differ
Files fromBuild/smali/co/platform/middlewares/APIProxy.smali and fromPlay/smali/co/platform/middlewares/APIProxy.smali differ
Files fromBuild/smali/co/platform/middlewares/HTTPFileMiddleware.smali and fromPlay/smali/co/platform/middlewares/HTTPFileMiddleware.smali differ
Files fromBuild/smali/co/platform/middlewares/plugins/CameraPlugin$2.smali and fromPlay/smali/co/platform/middlewares/plugins/CameraPlugin$2.smali differ
Files fromBuild/smali/co/platform/middlewares/plugins/CameraPlugin.smali and fromPlay/smali/co/platform/middlewares/plugins/CameraPlugin.smali differ
Files fromBuild/smali/co/platform/middlewares/plugins/WalletPlugin$1.smali and fromPlay/smali/co/platform/middlewares/plugins/WalletPlugin$1.smali differ
Files fromBuild/smali/co/platform/tools/BRBitId$2.smali and fromPlay/smali/co/platform/tools/BRBitId$2.smali differ
Files fromBuild/smali/co/platform/tools/BRBitId.smali and fromPlay/smali/co/platform/tools/BRBitId.smali differ

Using diffoscope which also takes a deeper look at binaries we find:

├── AndroidManifest.xml (decoded)
│ ├── AndroidManifest.xml
│ │ @@ -1,9 +1,9 @@
│ │  <?xml version="1.0" encoding="utf-8"?>
│ │ -<manifest android:versionCode="10" android:versionName="3.3.2" package="co.hodlwallet" platformBuildVersionCode="10" platformBuildVersionName="3.3.2" xmlns:android="http://schemas.android.com/apk/res/android">
│ │ +<manifest android:versionCode="11" android:versionName="3.3.2" package="co.hodlwallet" platformBuildVersionCode="11" platformBuildVersionName="3.3.2" xmlns:android="http://schemas.android.com/apk/res/android">

that the version differs, which tells us with certainty that the version in Google Play is not in GitHub:

We tried the last revision before the versionName was set to 3.3.3 which uses the versionCode 10. Google rejects updates with equal versionCodes, so this is kind of understandable and happened to all of us release managers but not committing a new revision and not tagging stuff is at least sloppy and as we hope will soon be unacceptable.

Which is a grave issue with verification though, are the differences in lib/x86/libcore-lib.so. Those are 50MB in the diffoscope decompiled form and beyond human review.

That is not good enough.

Our verdict for now: not verifiable.

Verdict Explained

Not verifiable: The provided Source Code could not be verified to match the app released on Google Play.

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.