This app provides a iOS Safari extension, which implements the FIDO U2F protocol. The cryptographic keys used for authentication are generated and stored on the Secure Enclave Processor (SEP), requiring user interaction for signing operations. FIDO U2F is a cryptographic protocol for second factor authentication. In addition to registering a username and password with a website, you also register a "security key". This key may be a hardware device like a USB dongle, or a software application on your device. When authenticating with the website, you provide your username and password, and are then prompted to interact with your security key. At this point the key strongly authenticates you by digitally signing a challenge from the website. The signature is sent to the website, which can verify its authenticity and finish authenticating your session.