Smart card wallet

This pages gathers resources for the implementation of a Bitcoin wallet on a smart card.

Rationale

• Computers and smartphones are target for malware. The software on a smart card can be protected.
• Smart cards do not need a battery, nor internet connection, they are robust.
• Adoption: people are already used to paying with smart cards.

Desired features

• no blockchain, no node; the card contains only private keys, and an algorithm to sign a transaction
• the smart card should have its own keyboard (for pin code protection) and display (to show the transaction amount)

(<- Alternative to this is the card returning, to the terminal screen, the debit amount multiplied by a number only the card holder knows which cycles from 1 to 100 to 1 incrementing by 1 each transfer - the card is locked 10 minutes if a second amount is send before a pin is typed.)

• The card holder will know pin, puk, private key and address only from when he programmed it or ordered his smart card.
• the card should implement a deterministic wallet, so that funds can be recovered if the card is lost.

Usage scenario

• the reading device may belong to a merchant at a point of sale; it cannot be trusted with private keys.
• the reading device is connected to a full bitcoin node; it can be trusted for getting and sending blockchain information.
• the reading device sends to the card the current balance of its bitcoin addresses. This information can be cached in the card.
• the reading device sends a bitcoin receiving address and transaction amount to the card.
• the amount is displayed by the card ; the user confirms the transaction with his pin code.
• the smart card creates a signed transaction and sends it to the reading device
• the transaction is checked and broadcast by the bitcoin node.

Implementation steps

1. write a bitcoin daemon that can talk to a lightweight wallet

• this has been done already, see for example bitcoinjs: https://github.com/bitcoinjs/bitcoinjs-lib
• See also this pull request: importexporttx can be used to broadcast the transaction
• https://bitcointalk.org/index.php?topic=28278.msg383312#msg383312

2. write a lightweight wallet

• wallet without blockchain, in order to test the daemon
• this lightweight wallet will be later implemented on the card
• use it to define the communication protocol between card and reading device.

update: this is done, see Electrum

3. implement wallet on a simple smart card

• http://www.opensc-project.org/opensc openSC : tools and libraries for smart cards.
• amadousarr.free.fr/crypto/ECDSAJAVACARD.pdf : A Software Implementation of ECDSA on a Java Smart Card
• http://www.acs.com.hk : cards, readers, development kits; no display, pincode needs to be typed on the reading device
• http://www.basiccard.com/index.html?overview.htm : Smart Card (ZC7.5) which contains RSA/EC and DES/AES coprocessors. Used in an implementation of the OpenPGP Card 2.0 standard (http://g10code.com/p-card.html)

4. implement wallet on a smart card with display and pincode

list of vendors:

• http://www.nidsecurity.com/products/solution-enterprise.html (smart cards with LCD displays)
• http://www.avesodisplays.com/ (smard cards with flexible displays)

references

• https://bitcointalk.org/index.php?topic=7539.0 Bitcoin smartcard Point of Sale terminal
• https://bitcointalk.org/index.php?topic=20933.0 Bitcoin and Smart Cards