[RAUC] [Yocto] Rauc certificate expiration management advices

[Adrien Martin <adrien.martin@stimio.fr>]

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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 ?

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]


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