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🔍 Last analysed 19th May 2022 . Bad Interface
7th December 2019

The design of the device does not allow to verify what is being signed!

As part of our Methodology, we ask:

Can the user verify and approve transactions on the device?

If the answer is "no", we mark it as "Bad Interface".

These are devices that might generate secure private key material, outside the reach of the provider but that do not have the means to let the user verify transactions on the device itself. This verdict includes screen-less smart cards or USB-dongles.

The wallet lacks either an output device such as a screen, an input device such as touch or physical buttons or both. In consequence, crucial elements of approving transactions is being delegated to other hardware such as a general purpose PC or phone which defeats the purpose of a hardware wallet.

Another consquence of a missing screen is that the user is faced with the dilemma of either not making a backup or having to pass the backup through an insecure device for display or storage.

The software of the device might be perfect but this device cannot be recommended due to this fundamental flaw.

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.

Help spread awareness for build reproducibility

Please help us spread the word discussing build reproducibility with KoinKeep  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.

If you find something we should include, you can create an issue or edit this analysis yourself and create a merge request for your changes.

The Analysis 

Product Description

A list of KoinKeep’s features.

Public Key Cryptography

  • 32 byte secp256k1 keys are used exclusively.
  • All keys are stored in as few places as possible. Keys on the hardware device never go to the phone and vice versa.


  • Any number of KoinKeep hardware wallets can be combined into a multi-sig arrangement.
  • When using multiple devices, two-thirds of the collection are required to unlock funds.

Local Transaction Signing

  • Transaction payloads are transferred between devices, signed and passed back.
  • Transactions are taken to hardware wallets individually, so they never need to be in the same location.

On-chain Two-factor Authentication (2FA)

  • KoinKeeps use a unique bitcoin script format that allows for on-chain 2FA
  • The key for this 2FA is stored in the user’s phone and is never transferred to the device.
  • This key is required but not sufficient to unlock funds.

The unique input script format is: [Signature] OP_CHECKSIGVERIFY [Signature] [Signature] OP_2 [Public Key] [Public Key] [Public Key] OP_3 OP_CHECK


  • Nothing sensitive is ever sent over Bluetooth (ie. no keys).
  • All communication over Bluetooth is encrypted AES_CBC anyway.
  • All encryption keys are 32 bytes.
  • Initial setup performs diffie key exchange. After which the device will only ever recognize that single key forever.
  • Nonces are used to prevent replay attacks.

Encrypted Storage

  • All device storage is encrypted.
  • Encryption is done with AES_CBC.
  • The encryption key is 32 bytes.
  • The encryption key is never stored in permanent memory.
  • The encryption key is instead stored on the user’s phone and given to the device during signing.
  • Learn more about KoinKeep’s storage encryption strategy
  • Direct-access SPV Bitcoin Wallet
  • KoinKeep’s phone application connects directly to the Bitcoin network as an SPV (Simple Payment Verification) wallet.
  • Bloom filters are used in a privacy-increasing fashion.
  • When a bloom filter is updated all currently connected nodes are disconnected. New nodes receive the updated bloom filter. This prevents nodes from being able to ‘diff’ the bloom filters and reduce your privacy.

Whitelist Nodes

  • You can specify nodes to always connect to.
  • You can specify nodes to only connect to by marking them as “master nodes.” This is helpful if you run your own node to further increase your privacy.

Built in Block Explorer

  • Using online block explorers decreases privacy, because their servers can track you.
  • KoinKeep’s phone app has a built-in basic block explorer, which shows all transactions relevant to your wallet.

KoinKeep has a companion app in the Apple Store.


The website is no longer online. Its twitter account’s last post was made in December 21, 2020. It is highly likely the device is no longer for sale. Apart from that, it has no display interface. It claims to mitigate the “trusted screen problem” through this:

Gatekeeper is available on GitHub:

GateKeeper is a tool for verifying withdrawal transactions and more. It will verify that your Bitcoin wallet is not lying or stealing from you.

GateKeeper should be used:

  • After a withdrawal transaction is created.
  • Before a transaction is published.
  • To ensure the transaction is not published, make your withdrawal transaction in an offline environment.

The basic idea is that the user instead of using an online companion app to interface with his hardware wallet, the user uses yet another offline device to read and interpret the tx before it reaches an internet-connected device which indeed can solve the security issue of all our Bad Interface! devices but at a huge cost:


  1. Create unsigned transaction on companion app on internet connected machine
  2. Verify details on hardware wallet
  3. Approve - Signed transaction gets sent back to companion app
  4. Companion app broadcasts


  1. Create unsigned transaction on companion app on internet connected machine
  2. Blindly approve - Signed transaction gets sent to third device?
  3. Third device displays details. If those are ok, transfer the signed transaction to companion app
  4. Companion app broadcasts

So here it is not clear if that third device sits between companion app and hardware wallet. If that is the case - the unsigned transaction is passed through the third device to the hardware wallet - the user is susceptible to that third device being compromised and showing X while getting signed and broadcast Y. If it does not see the transaction prior to HW signing it, the information flow gets even more complicated but the chances of a compromised “GateKeeper” doing harm vanish.

All in all GateKeeper is a neat idea but doesn’t save this product from a negative verdict regarding the lack of a display.