U-Boot FIT Signature Verification

[takahiro.akashi at linaro.org]

On Wed, Sep 16, 2020 at 11:40:08AM +0000, Joakim Tjernlund wrote:
> On Wed, 2020-09-16 at 13:14 +0200, Heinrich Schuchardt wrote:
> > CAUTION: This email originated from outside of the organization. Do not click links or open attachments unless you recognize the sender and know the content is safe.
> > 
> > 
> > On 16.09.20 10:13, AKASHI Takahiro wrote:
> > > 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.
> > 
> > Yes, the problem starts with mkimage not writing the dates available in
> > the X509 certificate into the device tree.
> > 
> > The dates are accessible via the X509_get0_notBefore() and
> > X509_get0_notAfter() functions of the OpenSSL library.
> > 
> > 
> > Takahiro, could you, please, also look at the UEFI secure boot
> > implementation in U-Boot. EDK2 validates the dates via the embedded
> > OpenSSL library in
> > CryptoPkg/Library/OpensslLib/openssl/crypto/x509/x509_vfy.c, function
> > verify_chain(). We should not do less.
> 
> Does that mean that verified boot stops/fails when the date expires ?
> How do you guarantee that the device has the correct time ?

Good point. Reither had a similar comment.

For trusted timestamps, we need to support RFC3161 timestamp protocol
when signing an image.
During the image verification, the "signed" timestamp of the image will also
be verified with a certificate in "dbt" database.

Well, this is in UEFI world, not FIT signature verification.

(I have a prototype of timestamp revocation implementation as part of
UEFI secure boot on U-Boot, but never made it public yet.)

-Takahiro Akashi



>    Jocke