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anti-rollback counter

A number burned into eFuse that only goes up; images older than it won't boot.

An anti-rollback counter stores a minimum security version in eFuse; the bootloader refuses images whose secure_version is lower, and the counter is raised when a newer image is marked valid.

Examples

  • When 1.5.0 with secure_version 2 is marked valid, the eFuse counter rises from 1 to 2, and the signed 1.4.0 with secure_version 1 will no longer boot.

  • Because the eFuse field has only a few bits, secure_version is raised only for releases that fix a security hole, not for every release.

See also

downgrade attack eFuse update manifest
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