Re: [meta-rauc] [RAUC] [Yocto] Rauc certificate expiration management advices

[Thorsten Scherer <tk-scherer@mailbox.org>]

Hello Adrien,

On Wed, Aug 14, 2019 at 03:56:07PM +0000, Adrien Martin wrote:
> Hello,
> 
> My name is Adrien Martin, embedded system engineer at STIMIO and I am facing an issue with rauc update security.
> Just to let you know, I don't have much experience with security concepts in general.
> 
> I am using Rauc (v0.4, quite old I admit) for an embedded linux system (imx6ul) with barebox bootloader, all images / bundles are generated via Yocto (Poky)
> 
> Following the documentation, you need to set :
> 
>   *   RAUC_KEY_FILE = "path/to/key.pem"     # What I call the private key
>   *   RAUC_CERT_FILE = "path/to/cert.pem" # What I call the certificate (public key)
> 
> As a result, when generating your image and bundle, you get :
> 
>   *   A linux image with /etc/rauc/cert.pem integrated to your rootfs
>   *   A signed bundle with the key.pem
> 
> My problem is what happens when the certificate is expired ?
> 
> My initial though was, I just have to generate a new cert.pem, based on the same private key.pem with a new valid lifetime period and set up this new cert in the yocto recipe.
> Then, I generate the bundle via Yocto and try to install it.
> 
> This doesn't work and gives me :
> # rauc info /var/volatile/original/msdi-bundle-msdi-imx6-1.raucb
> rauc-Message: Reading bundle: /var/volatile/original/msdi-bundle-msdi-imx6-1.raucb
> rauc-Message: Verifying bundle...
> signature verification failed: Verify error:self signed certificate
> 
> It looks like a bundle can only be use with the cert file set in the yocto recipe. This bundle will keep this cert file in /etc/rauc/ folder so all future bundle installations will need the exact same certificate.
> 
> Could you explain me what am I missing ? What method do you recommand to manage certificates expirations over time ?

I guess you're trying to replace the expired certificate in a "Single
Key" scenario, which is not possible [1].  The documentaion lists some
other variants, though I am not sure which one applies best to your
use-case (maybe install hooks??).

> 
> Thank you very much.
> 
> Best regards,
> 
> Adrien MARTIN
> Ingénieur Système Embarqué STIMIO
> adrien.martin@stimio.fr<mailto:adrien.martin@stimio.fr>
> 1 Avenue du Professeur Jean Rouxel, ZAC de la Fleuriaye, 44470 Carquefou
> www.stimio.fr<http://www.stimio.fr/>
> [stimio_logo]
> 
> _______________________________________________
> RAUC mailing list

Best regards,
Thorsten

[1] https://rauc.readthedocs.io/en/latest/advanced.html#single-key

--
Thorsten Scherer <tk-scherer@mailbox.org>

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