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SatoChipApplet

Open source javacard applet implementing a Bitcoin hardware wallet with full BIP32 support.

Demonstration

demonstrationon youtube

Introduction

SatoChip stands for Secure Anonymous Trustless and Open Chip. It is a javacard applet that can be used as a secure hardware wallet running for example on a Yubikey Neo. The SatoChip has full BIP32 supports.

Using SatoChip, an initial BIP32 seed is imported in the javacard and private keys are derived as requested by an external application. Private keys are never exported outside of the secure chip. To improve performances, the result of key derivation is cached in secure memory for future requests so that a specific derivation path is only computed once.

The Satochip also supports the import of regular (non-BIP32 keys) such as vanity keys. Here again, private keys cannot be exported outside of the secure chip. Up to 16 regular keys can be imported on the chip. In any case, the private keys can be used to sign transactions and Bitcoin messages, if sufficient credentials are provided.

Access to private keys (creation, derivation and signature) is enforced through the use of PIN code.

The Satochip wallet is currently in Beta, use with caution! In this phase, it is strongly recommended to use the software on the Bitcoin testnet only. This software is provided 'as-is', without any express or implied warranty. In no event will the authors be held liable for any damages arising from the use of this software.

Advantages:

  • Code is free and open source (no NDA required!)
  • Code easy to read and maintain (java card is a subset of java)
  • Multiple form factor could be supported in addition to Yubikey (e.g sim cards)
  • Plug and play
  • Smartcards have a long experience in dealing with security and physical security in particular
  • Can be easily used or extended for other crypto-currencies
  • A test package is run during build to ensure that critical functionalities are implemented correctly

Also, if used with a Yubikey:

  • Yubikey has minimal size and is practically indestructible
  • The Yubico company is not going anywhere anytime soon!
  • Many promising functionalities: NFC, Yubikey OTP, U2F, ...
  • Possibility to use the HMAC-SHA1 challenge-response of the Yubikey as second factor for additional security against malwares

Disadvantages:

  • This is still experimental code, use with caution!
  • Building the applet is a bit tricky
  • The software implementation of HMAC-SHA512 could have an potential impact on the physical security against side-channel attacks (for attackers with physical access to the chip).

Supported hardware

To support Bitcoin signatures, the javacard must support ALG_ECDSA_SHA_256, which in practice requires a javacard compliant with the JavaCard 3.0.1 specification. Note that this is a necessary but not sufficient condition since javacards typically implements only a subset of the specification. A detailed list of javacard and their supported features is available here.

An interesting guide to consult before shopping can be found here

tested and working

Yubikey Neo

Important remark: the Yubikeys currently sold by Yubico are configured for production only and it is not possible to load the applet on these dongles (see this link for more details). Only the development Yubikeys (with serial number below 3,000,000) are suitable for our use!

NXP JCOP J2D081

Available for purchase here (minimum quantity order: 5 pieces)

Swissbit PS-100u VE card Secure micro SD memory card

More info here (Note however that Swissbit does not sell its product directly to end users but only to business partners)

J3D081 JCOP v2.4.2 R2

Available here

Buidl

You can build the javacard CAP files or use the last version built.

To generate the CAP file from the sources, you can use the Eclipse IDE with the ant-javacard Ant task (see the instruction on the ant-javacard github repository).

Install

Once you have a CAP file, you have to download it on the chip card. You can use GlobalPlatformPro to do this:

  • Download the latest release from https://github.com/martinpaljak/GlobalPlatformPro/releases
  • (Put the CAP file in the same folder as the GPJ jar file for convenience)
  • To list the applets loaded on a smartcard: gp.exe -l
  • To load the SatoChip applet: gp.exe -install .\SatoChip-2.2.2.cap
  • To delete the SatoChip applet: gp.exe -uninstall .\SatoChip-2.2.2.cap

A more detailed tutorial is available on the GlobalPlatformPro repository.

Use

To use the applet, you have to connect your client application to the smartcard and send command APDU. These commands will be processed by the smartcard who will then send a response APDU. The Electrum-Satochip is a version of electrum that was slightly modified to integrate the Satochip hardware wallet.

Deprecated (use older releases for this)

SatoChipClient is a small java library that allows to easily interface the SatoChip applet to your application through a simple set of API. An example of application is the BitcoinWallet java application, that uses SatoChipClient through another Bitcoin library called BitcoinCore.

Credits

License

This application is distributed under the GNU Affero General Public License version 3.

Some parts of the code may be licensed under a different (MIT-like) license. Contact me if you feel that some license combination is inappropriate.

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Open source javacard applet implementing a Bitcoin hardware wallet with full BIP32 support

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