On Thu, Sep 26, 2013 at 02:06:21PM +0200, Pavel Machek wrote: > > For the symmetric key solution, I will try HMAC (Hash Message > > Authentication Code). It's already used in networking, hope the > > performance is not too bad to a big image. > > Kernel already supports crc32 of the hibernation image, you may want > to take a look how that is done. > > Maybe you want to replace crc32 with cryptographics hash (sha1?) and > then use only hash for more crypto? That way speed of whatever crypto > you do should not be an issue. Well, yes, one could skip the CRC when the signing is enabled to gain a little speedup. > Actually... > > Is not it as simple as storing hash of hibernation image into NVRAM > and then verifying the hash matches the value in NVRAM on next > startup? No encryption needed. First, there is no encryption going on. Only doing a HMAC (digest (hash) using a key) of the image. Second, since NVRAM is accessible through efivarsfs, storing the hash in NVRAM wouldn't prevent an attacker from modifying the hash to match a modified image. There is a reason why the key for the HMAC is stored in the NVRAM in a BootServices variable that isn't accessible from the OS and is write-protected on hardware level from the OS. > And that may even be useful for non-secure-boot people, as it ensures > you boot right image after resume, boot it just once, etc... The HMAC approach isn't much more complicated, and it gives you all these benefits even with secure boot disabled. -- Vojtech Pavlik Director SUSE Labs -- To unsubscribe from this list: send the line "unsubscribe linux-efi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
