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HODL Wallet : Bitcoin Wallet

Google Play
Latest Release: 3.3.5 18th May 2020

Our wallet review process

We examine wallets starting at the code level and continue all the way up to the finished app that lives on your device. Provided below is an outline of each of these steps along with security tips for you and general test results.

Developer

Hodl Wallet INC

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Custody

Self-custodial: The user holds the keys

But This product was removed from the platform.

As part of our Methodology, we ask: Is the product self-custodial?

The answer is "yes". The user has control of their own keys.
Read more

Source code

Public on github

Released

24th September 2018

Application build

We could not verify that the provided code matches the binary!
See the last Issue we created.

See test result
Tested 7th May 2024

Distribution

Google Play
3.6/5 stars via 124 ratings

Platform notes

On the Google Play Store, there are many apps that have Bitcoin in their name or description but don’t allow the user to use Bitcoin or they don’t look like Bitcoin wallets but turn out to be. We run our tests and document our findings.

Passed 9 of 10 tests

We answered the following questions in this order:
We stopped asking questions after we encountered a failed answer.

Do many people use this product?

The answer is "yes".
If the answer was "no", we would mark it as "Few users" and the following would apply:

The answer is "no". We marked it as "Few users".

We did not ask this question because we failed at a previous question.
If the answer was "no", we would mark it as "Few users" and the following would apply:

We focus on products that have the biggest impact if things go wrong and this one probably doesn’t have many users according to data publicly available.

Is this product the original?

The answer is "yes".
If the answer was "no", we would mark it as "Fake" and the following would apply:

The answer is "no". We marked it as "Fake".

We did not ask this question because we failed at a previous question.
If the answer was "no", we would mark it as "Fake" and the following would apply:

The bigger wallets often get imitated by scammers that abuse the reputation of the product by imitating its name, logo or both.

Imitating a competitor is a huge red flag and we urge you to not put any money into this product!

The product 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 product 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.
Is it a wallet?

The answer is "yes".
If the answer was "no", we would mark it as "Not a wallet" and the following would apply:

The answer is "no". We marked it as "Not a wallet".

We did not ask this question because we failed at a previous question.
If the answer was "no", we would mark it as "Not a wallet" and the following would apply:

If it’s called “wallet” but is actually only a portfolio tracker, we don’t look any deeper, assuming it is not meant to control funds. What has no funds, can’t lose your coins. It might still leak your financial history!

If you can buy Bitcoins with this app but only into another wallet, it’s not a wallet itself.

Is it for bitcoins?

The answer is "yes".
If the answer was "no", we would mark it as "A wallet but not for Bitcoin" and the following would apply:

The answer is "no". We marked it as "A wallet but not for Bitcoin".

We did not ask this question because we failed at a previous question.
If the answer was "no", we would mark it as "A wallet but not for Bitcoin" and the following would apply:

At this point we only look into wallets that at least also support BTC.

Can it send and receive bitcoins?

The answer is "yes".
If the answer was "no", we would mark it as "Can't send or receive bitcoins" and the following would apply:

The answer is "no". We marked it as "Can't send or receive bitcoins".

We did not ask this question because we failed at a previous question.
If the answer was "no", we would mark it as "Can't send or receive bitcoins" and the following would apply:

If it is for holding BTC but you can’t actually send or receive them with this product then it doesn’t function like a wallet for BTC but you might still be using it to hold your bitcoins with the intention to convert back to fiat when you “cash out”.

All products in this category are custodial and thus funds are at the mercy of the provider.

The product 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 product 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.
Is the product self-custodial?

The answer is "yes".
If the answer was "no", we would mark it as "Custodial: The provider holds the keys" and the following would apply:

The answer is "no". We marked it as "Custodial: The provider holds the keys".

We did not ask this question because we failed at a previous question.
If the answer was "no", we would mark it as "Custodial: The provider holds the keys" and the following would apply:

A custodial service is a service where the funds are held by a third party like the provider. The custodial service can at any point steal all the funds of all the users at their discretion. Our investigations stop there.

Some services might claim their setup is super secure, that they don’t actually have access to the funds, or that the access is shared between multiple parties. For our evaluation of it being a wallet, these details are irrelevant. They might be a trustworthy Bitcoin bank and they might be a better fit for certain users than being your own bank but our investigation still stops there as we are only interested in wallets.

Products that claim to be non-custodial but feature custodial accounts without very clearly marking those as custodial are also considered “custodial” as a whole to avoid misguiding users that follow our assessment.

This verdict means that the provider might or might not publish source code and maybe it is even possible to reproduce the build from the source code but as it is custodial, the provider already has control over the funds, so it is not a wallet where you would be in exclusive control of your funds.

We have to acknowledge that a huge majority of Bitcoiners are currently using custodial Bitcoin banks. If you do, please:

  • Do your own research if the provider is trust-worthy!
  • Check if you know at least enough about them so you can sue them when you have to!
  • Check if the provider is under a jurisdiction that will allow them to release your funds when you need them?
  • Check if the provider is taking security measures proportional to the amount of funds secured? If they have a million users and don’t use cold storage, that hot wallet is a million times more valuable for hackers to attack. A million times more effort will be taken by hackers to infiltrate their security systems.
The product 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 product 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.
Is the source code publicly available?

The answer is "yes".
If the answer was "no", we would mark it as "No source for current release found" and the following would apply:

The answer is "no". We marked it as "No source for current release found".

We did not ask this question because we failed at a previous question.
If the answer was "no", we would mark it as "No source for current release found" and the following would apply:

A wallet that claims to not give the provider the means to steal the users’ funds might actually be lying. In the spirit of “Don’t trust - verify!” you don’t want to take the provider at his word, but trust that people hunting for fame and bug bounties could actually find flaws and back-doors in the wallet so the provider doesn’t dare to put these in.

Back-doors and flaws are frequently found in closed source products but some remain hidden for years. And even in open source security software there might be catastrophic flaws undiscovered for years.

An evil wallet provider would certainly prefer not to publish the code, as hiding it makes audits orders of magnitude harder.

For your security, you thus want the code to be available for review.

If the wallet provider doesn’t share up to date code, our analysis stops there as the wallet could steal your funds at any time, and there is no protection except the provider’s word.

“Up to date” strictly means that any instance of the product being updated without the source code being updated counts as closed source. This puts the burden on the provider to always first release the source code before releasing the product’s update. This paragraph is a clarification to our rules following a little poll.

We are not concerned about the license as long as it allows us to perform our analysis. For a security audit, it is not necessary that the provider allows others to use their code for a competing wallet. You should still prefer actual open source licenses as a competing wallet won’t use the code without giving it careful scrutiny.

The product 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 product 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.
Is the decompiled binary legible?

The answer is "yes".
If the answer was "no", we would mark it as "Obfuscated" and the following would apply:

The answer is "no". We marked it as "Obfuscated".

We did not ask this question because we failed at a previous question.
If the answer was "no", we would mark it as "Obfuscated" and the following would apply:

When compiling source code to binary, usually a lot of meta information is retained. A variable storing a masterseed would usually still be called masterseed, so an auditor could inspect what happens to the masterseed. Does it get sent to some server? But obfuscation would rename it for example to _t12, making it harder to find what the product is doing with the masterseed.

In benign cases, code symbols are replaced by short strings to make the binary smaller but for the sake of transparency this should not be done for non-reproducible Bitcoin wallets. (Reproducible wallets could obfuscate the binary for size improvements as the reproducibility would assure the link between code and binary.)

Especially in the public source cases, obfuscation is a red flag. If the code is public, why obfuscate it?

As obfuscation is such a red flag when looking for transparency, we do also sometimes inspect the binaries of closed source apps.

As looking for code obfuscation is a more involved task, we do not inspect many apps but if we see other red flags, we might test this to then put the product into this red-flag category.

The product 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 product 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.
Can the product be built from the source provided?

The answer is "yes".
If the answer was "no", we would mark it as "Failed to build from source provided!" and the following would apply:

The answer is "no". We marked it as "Failed to build from source provided!".

We did not ask this question because we failed at a previous question.
If the answer was "no", we would mark it as "Failed to build from source provided!" and the following would apply:

Published code doesn’t help much if the app fails to compile.

We try to compile the published source code using the published build instructions into a binary. If that fails, we might try to work around issues but if we consistently fail to build the app, we give it this verdict and open an issue in the issue tracker of the provider to hopefully verify their app later.

The product 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 product 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.
Does the published binary match the published source code?

The answer is "yes".
If the answer was "no", we would mark it as "Not reproducible from source provided" and the following would apply:

The answer is "no". We marked it as "Not reproducible from source provided".

We did not ask this question because we failed at a previous question.
If the answer was "no", we would mark it as "Not reproducible from source provided" and the following would apply:

Published code doesn’t help much if it is not what the published binary was built from. That is why we try to reproduce the binary. We

  1. obtain the binary from the provider
  2. compile the published source code using the published build instructions into a binary
  3. compare the two binaries
  4. 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 binary we can create and the binary we can find for download 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 binary 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 product 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 product 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.
HODL Wallet : Bitcoin Wallet  App Store

Application build test result

App and Company History

We didn’t dig further as to why the dates don’t line up. Our guess is it has something to do with paperwork and filings that do not coincide with the press releases. But ultimately, BitStop became the surviving monolithic entity - hence, the reason for the redirection of the domains.

Why does Coin Cloud have so many apps?

Bad versioning. We took a look at the history of the url “coin.cloud/app” and found that the app was different.

For June 2021 the linked apps were:

For March 2023 the linked apps were:

Main Review dated 2022-05-09

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

BRD Bitcoin Wallet Bitcoin BTC      ? 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
v2
$ 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 Bitcoin Wallet Bitcoin BTC :

$ 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
...
BUILD SUCCESSFUL in 4m 7s

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.

Tests performed by Leo Wandersleb, Daniel Andrei R. Garcia

Do your own research

In addition to reading our analysis, it is important to do your own checks. Before transferring any bitcoin to your wallet, look up reviews for the wallet you want to use. They should be easy to find. If they aren't, that itself is a reason to be extra careful.