I wanted to share a project I’ve been working on. It’s called “sigsafe” and it is an electronic key tag that signs bitcoin transactions over a non-exploitable air gap. The device is probably too simple to be considered a hardware wallet; instead, it’s more like a paper wallet that can produce ECDSA signatures. The device has both high-security applications such as implementing a cold/hot wallet system where the cold wallet can only send coins to the hot wallet, and low-security applications such as a “tap and pay” tag for purchasing retail items at PoS terminals. Because the device uses the NFC standard, it is highly interoperable with existing phones, laptops, PoS terminals, and other RFID readers. In fact, when HTML5 browsers begin to support the Web NFC API, it should be possible to create webpages that request signatures from the sigsafe to complete an online payment or to login to a website using the bitID protocol and a single tap.
Here is a link to the white paper: http://sigsafe.ca/sigsafe.pdf
Abstract. A small electronic key tag for signing bitcoin transactions over a non-exploitable air gap is described. The tag communicates via a simple protocol with a NFC-enabled host, harvesting power directly from the NFC electromagnetic field and eliminating the need for a battery. After receiving a signature request from a host device, the tag checks the request against a set of rules and signs the transaction, provided none are violated. User-defined signing rules permit various levels of security from none (sign all requests), to locking the spend addresses, limiting the value of transactions, and requiring a password from the tag’s owner or cryptographic authentication from the host. Malware, hackers or thieves cannot feasibly extract the private keys even with physical access to the tag. A tag manufacturer could store a funded private key within each device sold, with a rule to produce only bitcoin-signed messages, as a proof-of-intent bond to earn customers’ trust.
Also posted on https://bitcointalk.org/index.php?topic=610453.0