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BULL

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Latest release found by WalletScrutiny: 6.13.0 / 6.14.0

Developer
Bull Bitcoin (Android)
Satoshi Portal Inc (iPhone)
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Released
Android: 31st October 2023
iPhone: 29th September 2025
Source code
Public on github
Custody
Mixed: some features rely on third-party custody

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.

Passed all 7 tests

We answered the following questions in this order:

Is this product the original?

The answer is "yes".
If the answer were "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 were "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 were "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 were "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 were "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 were "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 were "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 were "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.
Does the product allow self-custody?

The answer is "yes".
If the answer were "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 were "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.

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 were "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 were "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 were "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 were "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.

Distribution

Google Play Zapstore Website

Build Verifications

If you have a binary for a version that doesn't appear on the list, you can dropselect the file here to register it so somebody can verify its reproducibility:

Drop binary file to verify

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Learn more

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.

Air Gapped: App works without internet

Air Gapped: App works without internet

Some apps mimic hardware wallets in that they don’t request permission to connect to the internet but instead they communicate through a companion app which has internet. That companion app might be on the same phone but with internet permission or it might be on a secondary phone such that the Air Gapped app can run on a phone that has no mobile or wifi internet configured at all.

Security: Splitting an app into a part that keeps the keys safe without access to leak them online and an app that has internet and all the rest can reduce the attack surface for the private keys. In theory this setup can be much more secure than the usual app that has both the private keys and internet access in one.

Why we list it for this wallet

Users can create PSBTs from watch-only wallets for offline signing.

Source: README

Legacy verification here

App Description from Google Play

Bull Bitcoin Mobile is a self-custodial Bitcoin and Liquid Network which offers non-custodial atomic swaps across Bitcoin, Lightning and Liquid.

General features

  • Non-custodial: private keys are generated on the device, and never leave the device.
  • Multiple wallets can be created. Users can switch easily from one wallet to the other on the wallet homepage.
  • Walets with BIP39 passphrases can be created.
  • Amounts can be viewed as Bitcoin or Sats.
  • Users can enable RBF for each transaction.
  • Users can send the full wallet balance (sweep a wallet).

Analysis

  1. We were given the 12-word phrase during the wallet creation stage

  2. The app has lightning, Bitcoin and liquid wallets.

Full SegWit Support

Full SegWit Support

SegWit which is short for “Segregated Witness” was an August 2017 upgrade to the Bitcoin protocol which came with new address types.

Full SegWit Support means that the wallet can both send to and receive to all SegWit address types, including bech32 starting with “bc1…”.

  • Receiving to SegWit addresses provides fee savings, as sending these funds is possible using less base-block space. In Bitcoin, transaction fees are proportional to the transaction size in bytes.
  • Receiving to bech32 addresses provides more fee savings than P2SH Segwit addresses.
  • Sending to SegWit addresses is sometimes required in order to use more modern tools that dropped support for legacy addresses, often because of another core property of SegWit transactions: They are not malleable, meaning that the transaction ID cannot be changed “in transit” (on unconfirmed transactions).

Why we list it for this wallet

Secure Bitcoin Wallet: this is a descriptor-based Bitcoin network wallet which uses bech32 segwit addresses.

Source: GitHub README

Lightning Network support

Lightning Network support

The lightning Network (LN) is a layer two protocol that promises instant, low fee micro payments. Some wallets do not support receiving transactions which disqualifies them for this feature.

Transactions on LN are

  • instant: It usually takes less than five seconds to finish a transaction.
  • cheap: Transactions usually cost a tiny percentage (0.1%) of the transferred amount and might also be free.
  • micro payments: The unit of account on the LN is micro Satoshis (mSat) or 0.00000000001 BTC.

LN is still in early development and several very feasible attacks are known that can cost users money or disrupt the network.

Why we list it for this wallet

Both these wallets are able to send and receive Lightning Network payments via the swap provider.

Source: GitHub README

Liquid Network Integration

Liquid Network Integration

The Liquid Network is a Bitcoin sidechain designed to enable faster and more private transactions, launched by Blockstream in 2018. It allows for the issuance of digital assets, including security tokens and stablecoins. Wallet integration with Liquid means users can send and receive Bitcoin and other assets issued on the Liquid Network. This feature assesses wallets that support both sending to and receiving from Liquid addresses. Learn more about Liquid.

  • Faster Transactions: Liquid provides faster and cheaper transactions compared to Bitcoin’s main chain, improving the user experience for certain use cases like transfer between exchanges that support Liquid.

  • Enhanced Privacy: Through Confidential Transactions, Liquid hides the amounts and types of assets being transferred, offering greater privacy for its users.

  • Asset Issuance: Users can issue and manage digital assets on the Liquid Network.

  • Bitcoin Custody: The Liquid Network is operated by a federation of members. “Liquid Bitcoins” are Liquid tokens representing actual Bitcoins in the custody of this federation. If the required quorum of the federation decides to use the bitcoins under their custody, they can. Therefore the user has to trust this federation.

  • Limited Adoption: As a specialized network, Liquid’s benefits are most pronounced in specific scenarios, and the ecosystem is smaller than Bitcoin’s main network, potentially limiting its utility for some users.

  • Fallback custody: Bitcoins held by the Liquid federation need to be rotated on a regular schedule. If the federation fails to do so, they can also be spent by Blockstream alone.

Why we list it for this wallet

Instant Payments Wallet: this is a descriptor-based Liquid network wallet which uses bech32 confidential segwit addresses.

Source: GitHub README

Hierarchically Deterministic

Hierarchically Deterministic

All accounts and keys are derived from one masterseed as defined in BIP 32, BIP 39, BIP 44, BIP 49, BIP 84 and BIP 86. While some wallets might use different definitions and not all support SegWit or Taproot, we only consider this feature as given if

  • the backup is a BIP 39 mnemonic
  • the funds are recoverable on a competitor’s product correctly implementing those standards
  • no address reuse
  • simple backup
  • no vendor lock-in

Why we list it for this wallet

Both wallets are created using the same mnemonic seed, so that a single backup is sufficient for both.

Source: GitHub README

Unlimited Accounts

Unlimited Accounts

The user can create or restore secondary BTC accounts

  • Accounting: Multiple accounts allow for easier separation of funds.
  • Privacy: Using an account with a positive balance at all time makes it relatively easy for blockchain analysis companies to determine the full history of the wallet. By using multiple accounts, emptying them at times, the user can retain some privacy.

Why we list it for this wallet

Multiple wallets can be created. Users can switch easily from one wallet to the other on the wallet homepage.

Source: GitHub README

Advanced UTXO Control

Advanced UTXO Control

The wallet offers advanced control over which Unspent Transaction Outputs (UTXOs) are spent. This goes beyond simple coin selection — it may include the ability to freeze or exclude specific UTXOs (e.g., dusting attacks or tainted coins), label UTXOs, or select inputs manually. The user does not necessarily need full visibility of all UTXOs, but has meaningful control over what gets spent.

  • Privacy: Prevent spending from UTXOs linked to unwanted transaction history, or avoid merging coins from different sources in one transaction.

  • Dust protection: Mark suspicious incoming transactions as “do not spend” to avoid revealing your wallet’s full UTXO set.

  • Fee optimization: Strategically select inputs to manage transaction size and fees.

Why we list it for this wallet

Coin selection: users can select which utxos will be spent for each transaction. The UTXOs will have the labels of the transactions that created them. When enabling coin selection, only the selected utxos will be used to create a transaction.

Source: GitHub README

Custom Node Connection

Custom Node Connection

The wallet can be configured to connect to a user-specified, independently operated Bitcoin node — such as Bitcoin Core, Electrum Server, or other compatible full node software — instead of the wallet provider’s default servers. The key requirement is that the node is clearly independent from the wallet vendor: a third-party node the user controls or trusts.

  • Privacy: Transaction queries go to your own node rather than a third-party server, so no provider learns your wallet addresses or balances.

  • Security: No risk of a provider lying about your balance or the state of the network.

  • Sovereignty: Full independence from wallet provider infrastructure.

  • Requires running and maintaining your own Bitcoin node.
  • More complex initial setup compared to using the provider’s default servers.

Why we list it for this wallet

Users can connect to their own electrum server.

Source: GitHub README

Free and Open Source (FOSS)

Free and Open Source (FOSS)

The wallet’s source code is published under a license approved by the Open Source Initiative (OSI) — such as MIT, GPL, Apache, or AGPL — allowing anyone to inspect, modify, and redistribute it. This is a prerequisite for independent security audits and reproducible builds. Licenses that are merely “source available” but not OSI-approved (e.g., those with Commons Clause restrictions, commercial use prohibitions, or other non-free terms) do NOT qualify. Reproducible builds are not sufficient alone.

  • Transparency: Anyone can verify what the code does — including whether it contains backdoors, bugs, or privacy-violating behavior.

  • Community auditing: More reviewers means vulnerabilities are more likely to be found and fixed.

  • Forkability: If the project is abandoned or goes rogue, the community can fork and continue it.

FOSS alone does not guarantee security. The released binary must also be reproducible from the public source to ensure users are actually running the code that was audited.

Why we list it for this wallet

MIT License Copyright (c) 2023 Satoshi Portal Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software

Source: GitHub README

NFC (Near Field Communication)

NFC (Near Field Communication)

The wallet supports Near Field Communication (NFC) for wireless interaction with hardware wallets, payment terminals, or signing cards. NFC enables tap-to-sign or tap-to-pay functionality over a very short range (typically a few centimeters) without cables or QR codes.

  • Convenience: Quick tap interaction — no cables to connect or QR codes to scan.
  • Hardware wallet compatibility: Some hardware signing cards communicate exclusively via NFC.
  • Requires NFC hardware on both devices.
  • Very short range limits usability compared to QR-based air-gapped setups.

Why we list it for this wallet

Users can import watch-only wallets via QR code, copy-pasting an Xpub/Ypub/Zpub, uploading a Coldcard file or via NFC (for Coldcard).

Source: GitHub README

An issue has been opened at https://github.com/SatoshiPortal/bullbitcoin-mobile/issues/326

Product page updated by Daniel Andrei R. Garcia

⚠️ Liquid Network Integration

Liquid Bitcoin is NOT Bitcoin. L-BTC is held by a federation of companies. If a quorum of federation members collude or are compelled, they can seize all L-BTC. If Blockstream alone fails to rotate keys on schedule, they gain unilateral control. Only use Liquid for amounts you'd trust to a corporate consortium.

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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.

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