VivoKey
The VivoKey is an NFC-only device designed to cover the bulk of use cases of the YubiKey while also having space for general user-supplied applications such as transit pass emulation via the Fidesmo platform. It is Paralyne-C coated and on a flexible PCB intended for implantation and is currently in human trials.
For people who are not as into scalpels, it would of course be possible to insert such a device into a watch band or bracelet.
Advantages
- 100% of application code is public and auditable
- Applications can be updated
- Very unlikely to be lost
Disadvantages
- Hardware design and JavaCard OS not available for public auditing.
- Does not support physical touch allowing a remote attacker unlimited uses
- Entropy source is controlled entirely by NXP
