U-Boot FIT Signature Verification

[REITHER Robert - Contractor]

Hi there



I don't think it would make sense to check for expiration (even in case we would have full certificates like PKCS#7 verifiy)

At our point of the boot process we normally do not have access to a trusted time/date, so any check could be simply spoofed or even worse fails, because wall clock is not initialized properly.



I think even the EFI boot-process (or shim) does not check expiration date of their certificates!





What could make sense is a check for an expired certificate/key at signing time (including intermed certs), but not sure if this would be a too hard restriction (at least for developing/testing). I think a hint for the signer should be enough!



Regards

Robert



On Wed, Sep 16, 2020 at 01:19:03AM +0200, Heinrich Schuchardt wrote:

>

On 9/11/20 7:26 PM, Andrii Voloshyn wrote:

> > Hi there,

> >

> >     Does U-boot take into account certificate expiration date when verifying signed images in FIT? In other words, is date stored along with the public key in DTB file?

> >

> > Cheers,

> > Andy

> >

>

> Hello Philippe,

>

> looking at padding_pkcs_15_verify() in lib/rsa/rsa-verify.c I cannot

> find a comparison of the date on which an image was signed with the

> expiry date of the certificate. Shouldn't there be a check? Or did I

> simply look into the wrong function?



I think Simon is the right person to answer this question, but



as far as I know, we don't have any device tree property for the expiration date of a public key. See doc/uImage.FIT/signature.txt.



-Takahiro Akashi



> Best regards

>

> Heinrich