• Kyle Rankin's avatar
    Use the Librem Key as a TPM work-alike in the absence of a TPM · 778ea80e
    Kyle Rankin authored and Matt Devillier's avatar Matt Devillier committed
    On machines without a TPM, we'd still like some way for the BIOS to
    attest that it has not been modified. With a Librem Key, we can have the
    BIOS use its own ROM measurement converted to a SHA256sum and truncated
    so it fits within an HOTP secret. Like with a TPM, a malicious BIOS with
    access to the correct measurements can send pre-known good measurements
    to the Librem Key.
    This approach provides one big drawback in that we have to truncate the
    SHA256sum to 20 characters so that it fits within the limitations of
    HOTP secrets. This means the possibility of collisions is much higher
    but again, an attacker could also capture and spoof an existing ROM's
    measurements if they have prior access to it, either with this approach
    or with a TPM.
    Signed-off-by: Kyle Rankin's avatarKyle Rankin <kyle.rankin@puri.sm>