Implement TOTP ("Google auth")

[slush0]

TPM can be easily turned into second-factor application like Google Auth:

• Server-provided secret is encrypted via CipherKeyValue and encrypted data stored in TPM
• New method in trezor-core will accept encrypted data and current timestamp (possible use of Roughtime?) and generate OTP to show on display.

That way Trezor works as common second factor (on services where superior U2F is not supported) and all OTP secrets are backed up in TPM, which solves common problem of losing server-provided secrets with losing mobile phone.

[nickels]

This would be an excellent addition!

[prusnak]

This depends on the firmware: https://github.com/trezor/trezor-core/issues/516

[zsoltsandor]

I second this.