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Anti-rollback

Secure boot prevents unsigned firmware from running. Anti-rollback addresses a different problem: old firmware that is still correctly signed.

If an older signed image contains a serious vulnerability, secure boot alone may still allow it. Anti-rollback is the mechanism that refuses firmware below a configured floor.

Why it exists

The downgrade threat is simple:

  1. a device owner signs firmware version A
  2. version A later turns out to have a security bug
  3. version B fixes it
  4. an attacker with physical access flashes old signed version A

Anti-rollback closes that path when implemented and enabled correctly.

Irreversibility

On RP2350-class hardware, rollback state is normally backed by one-time-programmable state. That means:

  • floors go up, not down
  • rollback budget is finite
  • mistakes can orphan older images permanently

This is a production feature, not a day-one convenience setting.

Applicability

Use this page as the model. Do not assume the commands from another project apply directly to Pico FIDO or Pico OpenPGP.

For PicoKeys firmware, verify:

  • board family
  • secure boot status
  • available provisioning tool
  • image signing flow
  • documented rollback behavior

Operational rule

Raise a rollback floor only for a reason you can name:

  • a security fix blocks downgrade exploitation
  • old signed images should no longer be accepted
  • the team accepts the irreversible state change

Do not spend rollback budget on routine releases unless your process explicitly requires it.