Bitkey - Bitcoin Wallet
App StoreOur 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.
Released
13th March 2024
Custody
Self-custodial: The user holds the keys
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
Application build
If you have a binary for a version that doesn't appear on the list, you can drop the file here to register it so somebody can verify its reproducibility:
Passed all 7 tests
We answered the following questions in this order:
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 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.
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.
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.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 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.
Application build test result
(Analysis from Android review)
Disclaimer: The WalletScrutiny project is sponsored by Spiral, a subsidiary of Block.
Analysis
This is the companion app to the 
Bitkey
. It requires an NFC-capable phone, otherwise the app would not be installed.
Verified Builds
Version 2025.1.1 (1)
We endeavored to follow the instructions in the README to build the app.
However, we noticed some recurring problems.
Git version not found.
2.446 Package git is not available, but is referred to by another package.
2.446 This may mean that the package is missing, has been obsoleted, or
2.446 is only available from another source
2.446 However the following packages replace it:
2.446 git-svn
2.446
2.451 E: Version '1:2.34.1-1ubuntu1.12' for 'git' was not found
This was remedied by replacing this line in the Dockerfile, to a git version that is not pinned.
RUN apt update && apt upgrade -y
RUN apt install -y git
Next, we then had problems with the segment of the script that looks for aapt2. Although we followed the instructions in the ‘prep stage’, this did not work until we installed build-tools-34.0.0 and exported aapt2 to the correct path.
Version 2025.1.1 (1) Build Results
Comparing builds:
+ '[' 2 -ne 2 ']'
+ which diff
+ which /home/dannybuntu/Android/Sdk/build-tools/34.0.0/aapt2
+ lhs_comparable=verify-apk/from-device/comparable
+ lhs_apks=verify-apk/from-device/normalized-names
+ rhs_comparable=verify-apk/locally-built/comparable
+ rhs_apks=verify-apk/locally-built/normalized-names
++ find verify-apk/from-device/normalized-names -maxdepth 1 -mindepth 1 -type f -exec basename '{}' ';'
+ lhs_apk_files='base.apk
en.apk
xxhdpi.apk
arm64_v8a.apk'
++ find verify-apk/locally-built/normalized-names -maxdepth 1 -mindepth 1 -type f -exec basename '{}' ';'
+ rhs_apk_files='base.apk
en.apk
xxhdpi.apk
arm64_v8a.apk'
+++ echo 'base.apk
en.apk
xxhdpi.apk
arm64_v8a.apk'
++ sort -u /dev/fd/63 /dev/fd/62
+++ echo 'base.apk
en.apk
xxhdpi.apk
arm64_v8a.apk'
+ all_apk_files='arm64_v8a.apk
base.apk
en.apk
xxhdpi.apk'
++ diff -x resources.arsc -r verify-apk/from-device/comparable verify-apk/locally-built/comparable
+ differences='Binary files verify-apk/from-device/comparable/base/classes2.dex and verify-apk/locally-built/comparable/base/classes2.dex differ
Binary files verify-apk/from-device/comparable/base/classes.dex and verify-apk/locally-built/comparable/base/classes.dex differ'
+ diff_exit_status=1
+ diff_result=1
+ declare -a aapt_differences
+ for apk_file in $all_apk_files
+ '[' '!' -f verify-apk/from-device/normalized-names/arm64_v8a.apk ']'
+ '[' '!' -f verify-apk/locally-built/normalized-names/arm64_v8a.apk ']'
+ unzip -l verify-apk/from-device/normalized-names/arm64_v8a.apk resources.arsc
Archive: verify-apk/from-device/normalized-names/arm64_v8a.apk
Length Date Time Name
--------- ---------- ----- ----
--------- -------
0 0 files
+ lhs_contains_resources_exit_code=11
+ unzip -l verify-apk/locally-built/normalized-names/arm64_v8a.apk resources.arsc
Archive: verify-apk/locally-built/normalized-names/arm64_v8a.apk
Length Date Time Name
--------- ---------- ----- ----
--------- -------
0 0 files
+ rhs_contains_resources_exit_code=11
+ '[' 11 -ne 0 ']'
+ '[' 11 -eq 0 ']'
+ '[' 11 -eq 0 ']'
+ echo 'Skipping aapt2 diff of arm64_v8a.apk as it doesn'\''t contain resources.arsc file'
Skipping aapt2 diff of arm64_v8a.apk as it doesn't contain resources.arsc file
+ for apk_file in $all_apk_files
+ '[' '!' -f verify-apk/from-device/normalized-names/base.apk ']'
+ '[' '!' -f verify-apk/locally-built/normalized-names/base.apk ']'
+ unzip -l verify-apk/from-device/normalized-names/base.apk resources.arsc
Archive: verify-apk/from-device/normalized-names/base.apk
Length Date Time Name
--------- ---------- ----- ----
124232 1981-01-01 01:01 resources.arsc
--------- -------
124232 1 file
+ lhs_contains_resources_exit_code=0
+ unzip -l verify-apk/locally-built/normalized-names/base.apk resources.arsc
Archive: verify-apk/locally-built/normalized-names/base.apk
Length Date Time Name
--------- ---------- ----- ----
124232 1981-01-01 01:01 resources.arsc
--------- -------
124232 1 file
+ rhs_contains_resources_exit_code=0
+ '[' 0 -ne 0 ']'
+ '[' 0 -ne 0 ']'
++ /home/dannybuntu/Android/Sdk/build-tools/34.0.0/aapt2 diff verify-apk/from-device/normalized-names/base.apk verify-apk/locally-built/normalized-names/base.apk
+ aapt_difference=
+ aapt_diff_exit_status=0
+ '[' '' '!=' '' ']'
+ diff_result=1
+ for apk_file in $all_apk_files
+ '[' '!' -f verify-apk/from-device/normalized-names/en.apk ']'
+ '[' '!' -f verify-apk/locally-built/normalized-names/en.apk ']'
+ unzip -l verify-apk/from-device/normalized-names/en.apk resources.arsc
Archive: verify-apk/from-device/normalized-names/en.apk
Length Date Time Name
--------- ---------- ----- ----
48692 1981-01-01 01:01 resources.arsc
--------- -------
48692 1 file
+ lhs_contains_resources_exit_code=0
+ unzip -l verify-apk/locally-built/normalized-names/en.apk resources.arsc
Archive: verify-apk/locally-built/normalized-names/en.apk
Length Date Time Name
--------- ---------- ----- ----
48692 1981-01-01 01:01 resources.arsc
--------- -------
48692 1 file
+ rhs_contains_resources_exit_code=0
+ '[' 0 -ne 0 ']'
+ '[' 0 -ne 0 ']'
++ /home/dannybuntu/Android/Sdk/build-tools/34.0.0/aapt2 diff verify-apk/from-device/normalized-names/en.apk verify-apk/locally-built/normalized-names/en.apk
+ aapt_difference=
+ aapt_diff_exit_status=0
+ '[' '' '!=' '' ']'
+ diff_result=1
+ for apk_file in $all_apk_files
+ '[' '!' -f verify-apk/from-device/normalized-names/xxhdpi.apk ']'
+ '[' '!' -f verify-apk/locally-built/normalized-names/xxhdpi.apk ']'
+ unzip -l verify-apk/from-device/normalized-names/xxhdpi.apk resources.arsc
Archive: verify-apk/from-device/normalized-names/xxhdpi.apk
Length Date Time Name
--------- ---------- ----- ----
9852 1981-01-01 01:01 resources.arsc
--------- -------
9852 1 file
+ lhs_contains_resources_exit_code=0
+ unzip -l verify-apk/locally-built/normalized-names/xxhdpi.apk resources.arsc
Archive: verify-apk/locally-built/normalized-names/xxhdpi.apk
Length Date Time Name
--------- ---------- ----- ----
9852 1981-01-01 01:01 resources.arsc
--------- -------
9852 1 file
+ rhs_contains_resources_exit_code=0
+ '[' 0 -ne 0 ']'
+ '[' 0 -ne 0 ']'
++ /home/dannybuntu/Android/Sdk/build-tools/34.0.0/aapt2 diff verify-apk/from-device/normalized-names/xxhdpi.apk verify-apk/locally-built/normalized-names/xxhdpi.apk
+ aapt_difference=
+ aapt_diff_exit_status=0
+ '[' '' '!=' '' ']'
+ diff_result=1
+ '[' 1 -eq 0 ']'
+ printf 'The builds are NOT identical!\n\n'
The builds are NOT identical!
+ printf 'Found differences:\n\n'
Found differences:
+ echo 'Binary files verify-apk/from-device/comparable/base/classes2.dex and verify-apk/locally-built/comparable/base/classes2.dex differ
Binary files verify-apk/from-device/comparable/base/classes.dex and verify-apk/locally-built/comparable/base/classes.dex differ'
Binary files verify-apk/from-device/comparable/base/classes2.dex and verify-apk/locally-built/comparable/base/classes2.dex differ
Binary files verify-apk/from-device/comparable/base/classes.dex and verify-apk/locally-built/comparable/base/classes.dex differ
+ echo
+ exit 1
Asciicast
Diffoscope Results
Analysis
diffo-arm64.apk - reproducible
- When comparing the arm64_v8a.apk files, we observe the following:
- Signing-related diffs: (stamp-cert-sha256, BNDLTOOL.SF, BNDLTOOL.RSA, MANIFEST.MF)
-
The expected 1 to 2 line difference in AndroidManifest.xml:
<meta-data·android:name="com.android.vending.derived.apk.id"·android:value="3"/> </application>
diffo-base.apk - non-reproducible
- In base.apk, we note:
-
We note the minor diff in AndroidManifest.xml:
android:requiredSplitTypes="base__abi,base__density"·android:splitTypes=""· - We observe
stamp-cert-sha256:·'8' - The most significant diffs we observed in base.apk include those in classes.dex and classes2.dex
- Checksum Differences
- The checksum field in classes.dex and classes2.dex files are different.
- This suggests that the contents of the DEX files are not identical.
- Signature Differences
- The signature field is also different, which is expected since the checksum differs.
- The signature is a cryptographic hash of the file’s contents, so any change in the code or structure will alter it.
- File Size Differences
- The file_size of classes.dex in both builds has slight variations (e.g., 9819452 bytes vs. 9819444 bytes).
-
We take a deeper look into the diffs in classes2.dex with:
$ unzip -j base.apk classes2.dex -d play-classes2.dex/ $ unzip -j base.apk classes2.dex -d built-classes2.dex/ $ dexdump -d play-classes2.dex/classes2.dex > play_classes2.txt $ dexdump -d built-classes2.dex/classes2.dex > built_classes2.txt $ diffoscope --html diffo-classes2.dex.html built_classes2.txt ../../from-device/normalized-names/play_classes2.txtWe come up with the diffoscope results in diffo-classes2.dex.html
- We also note some differences in splits0.xml:
<entry·key="he"·split="config.he"/><entry·key="in"·split="config.in"/>in from-device but in locally-built, it is<entry·key="id"·split="config.id"/>
- Checksum Differences
-
diffo-en.apk - reproducible
- In en.apk, we note:
- We note signing-related differences, including stamp-cert-sha256
-
We note the minor diff in AndroidManifest.xml, present in from-device but not in locally-built:
<meta-data·android:name="com.android.vending.derived.apk.id"·android:value="3"/> ··</application>
-
Using a different approach with
apktool, we note that no differences are observed between the from-device and locally-built en.apk.$ apktool d en.apk -o en_decoded I: Using Apktool 2.7.0-dirty on en.apk I: Loading resource table... I: Decoding AndroidManifest.xml with resources... I: Loading resource table from file: /home/dannybuntu/.local/share/apktool/framework/1.apk I: Regular manifest package... I: Decoding file-resources... I: Decoding values */* XMLs... I: Copying assets and libs... I: Copying unknown files... I: Copying original files... dannybuntu@MS-7978:~/work/builds/world.bitkey.app/2025.1.1/bitkey/verify-apk/locally-built/normalized-names$ cd ../../from-device/normalized-names/ dannybuntu@MS-7978:~/work/builds/world.bitkey.app/2025.1.1/bitkey/verify-apk/from-device/normalized-names$ apktool d en.apk -o en_decoded I: Using Apktool 2.7.0-dirty on en.apk I: Loading resource table... I: Decoding AndroidManifest.xml with resources... I: Loading resource table from file: /home/dannybuntu/.local/share/apktool/framework/1.apk I: Regular manifest package... I: Decoding file-resources... I: Decoding values */* XMLs... I: Copying assets and libs... I: Copying unknown files... I: Copying original files... dannybuntu@MS-7978:~/work/builds/world.bitkey.app/2025.1.1/bitkey/verify-apk/from-device/normalized-names$ cd ../.. dannybuntu@MS-7978:~/work/builds/world.bitkey.app/2025.1.1/bitkey/verify-apk$ diff -r from-device/normalized-names/en_decoded/res locally-built/normalized-names/en_decoded/res dannybuntu@MS-7978:~/work/builds/world.bitkey.app/2025.1.1/bitkey/verify-apk$
diffo-xxhdpi.apk - reproducible
- In xxhdpi.apk, we note:
-
In AndroidManifest.xml, we see the expected diff:
<meta-data·android:name="com.android.vending.derived.apk.id"·android:value="3"/> ··</application> - We also observe the expected ‘stamp-cert-sha256’ difference.
-
Resources.arsc:
000012d0:·676c·6500·0202·1000·4802·0000·0800·0400··gle.....H....... 000012d0:·676c·6500·0202·1000·4802·0000·0800·0000··gle.....H.......
-
-
Using another method with
apktool, we note that no differences are observed between the from-device and locally-built xxhdpi.apk not seen by using diffoscope.dannybuntu@MS-7978:~/work/builds/world.bitkey.app/2025.1.1/bitkey/verify-apk$ apktool d from-device/normalized-names/xxhdpi.apk -o from-device/normalized-names/xxhdpi_decoded I: Using Apktool 2.7.0-dirty on xxhdpi.apk I: Loading resource table... I: Decoding AndroidManifest.xml with resources... I: Loading resource table from file: /home/dannybuntu/.local/share/apktool/framework/1.apk I: Regular manifest package... I: Decoding file-resources... I: Decoding values */* XMLs... I: Copying assets and libs... I: Copying unknown files... I: Copying original files... dannybuntu@MS-7978:~/work/builds/world.bitkey.app/2025.1.1/bitkey/verify-apk$ apktool d locally-built/normalized-names/xxhdpi.apk -o locally-built/normalized-names/xxhdpi_decoded I: Using Apktool 2.7.0-dirty on xxhdpi.apk I: Loading resource table... I: Decoding AndroidManifest.xml with resources... I: Loading resource table from file: /home/dannybuntu/.local/share/apktool/framework/1.apk I: Regular manifest package... I: Decoding file-resources... I: Decoding values */* XMLs... I: Copying assets and libs... I: Copying unknown files... I: Copying original files... dannybuntu@MS-7978:~/work/builds/world.bitkey.app/2025.1.1/bitkey/verify-apk$ diff -r from-device/normalized-names/xxhdpi_decoded/ locally-built/normalized-names/xxhdpi_decoded/ diff -r from-device/normalized-names/xxhdpi_decoded/AndroidManifest.xml locally-built/normalized-names/xxhdpi_decoded/AndroidManifest.xml 1,4c1,2 < <?xml version="1.0" encoding="utf-8" standalone="no"?><manifest xmlns:android="http://schemas.android.com/apk/res/android" android:splitTypes="base__density" package="world.bitkey.app" split="config.xxhdpi"> < <application android:extractNativeLibs="false" android:hasCode="false"> < <meta-data android:name="com.android.vending.derived.apk.id" android:value="3"/> < </application> --- > <?xml version="1.0" encoding="utf-8" standalone="no"?><manifest xmlns:android="http://schemas.android.com/apk/res/android" package="world.bitkey.app" split="config.xxhdpi"> > <application android:extractNativeLibs="false" android:hasCode="false"/> diff -r from-device/normalized-names/xxhdpi_decoded/apktool.yml locally-built/normalized-names/xxhdpi_decoded/apktool.yml 14,15c14 < unknownFiles: < stamp-cert-sha256: '8' --- > unknownFiles: {} Binary files from-device/normalized-names/xxhdpi_decoded/original/AndroidManifest.xml and locally-built/normalized-names/xxhdpi_decoded/original/AndroidManifest.xml differ Only in from-device/normalized-names/xxhdpi_decoded/original: META-INF Only in from-device/normalized-names/xxhdpi_decoded/original: stamp-cert-sha256 Only in from-device/normalized-names/xxhdpi_decoded/: unknown dannybuntu@MS-7978:~/work/builds/world.bitkey.app/2025.1.1/bitkey/verify-apk$ diff -r from-device/normalized-names/xxhdpi_decoded/res locally-built/normalized-names/xxhdpi_decoded/res dannybuntu@MS-7978:~/work/builds/world.bitkey.app/2025.1.1/bitkey/verify-apk$
Conclusion
- We combined two approaches to verify the build:
- The approach based on bitkey’s own script
- The approach based on
apktoolanddiffoscope - We observe that bitkey’s script’s output indicated the main difference between classes.dex and classes2.dex.
- Expected diffs are found in AndroidManifest.xml, stamp-cert-sha256, and resources.arsc.
- 3 of the split apks have minor diffs that qualify each to be reproducible: xxhdpi.apk, en.apk, and arm64_v8a.apk.
- However, the diffs in base.apk, which is the main apk, are more significant and thus not reproducible.
In summation, both the bitkey approach and ours come to an agreement that version 2025.1.1 is not verifiable
Standard procedure states that an issue must be filed with the provider in the relevant repository. However, Bitkey’s repository has its ‘Issues’ tab hidden, and thus we cannot post it there.
We are posting the issue in our own repository instead.
Tests performed by 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.
<img src="https://walletscrutiny.com/images/social/iphone/world.bitkey.app.png">
