RE: [EXT] Re: [RFC PATCH HBK: 0/8] HW BOUND KEY as TRUSTED KEY
From: Pankaj Gupta
Date: Wed Sep 07 2022 - 05:59:01 EST
> -----Original Message-----
> From: Jan Lübbe <jlu@xxxxxxxxxxxxxx>
> Sent: Wednesday, September 7, 2022 1:41 PM
> To: Pankaj Gupta <pankaj.gupta@xxxxxxx>; Jarkko Sakkinen
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> Subject: Re: [EXT] Re: [RFC PATCH HBK: 0/8] HW BOUND KEY as TRUSTED KEY
>
> Caution: EXT Email
>
> On Wed, 2022-09-07 at 07:22 +0000, Pankaj Gupta wrote:
> > Even if somehow the key is retrieved from the keyring, the retrieved
> > key would be an encrypted key.
> > This encrypted key can only be decrypted by Hardware, which generated it.
> >
> > Hence, the retrieved key is unusable outside of the hardware.
>
> NXP's CAAM unit (i.e. on i.MX6) supports several modes of sealed/encrypted
> keys.
> The (un)sealing process uses a key that is normally derived from a per-device
> key in eFUSES. One aspect of these modes is whether the plaintext key
> material is accessible to the kernel or not.
>
> Ahmad's patch set added support for a mode where the CAAM is used to
> seal plaintext known to the kernel to a "blob" (in CAAM terminology) on
> export to userspace and the reverse on import. This mode allows the kernel
> to use the plaintext for dm-crypt, to encrypt other keyrings and similar.
>
> The CAAM has another sealing mode, where it will not allow writing of the
> plaintext key to memory. Instead, it is kept in one of the CAAM-internal key
> registers. There, it can be used for cryptographic operations (i.e. AES). This
> way, the plaintext key is protected even from the kernel. The kernel could
> keep a copy of in sealed form, so it can reload the CAAM's key register when
> needed.
>
>
> Pankaj, is that the mode you intend to support with this series?
Yes, this is what is called as "black key", in CAAM terminology.
Black key is nothing but a HBK key.
This is what I am trying to achieve with this patch-set.
>
> Could you describe the high-level use-cases this would be need for,
> compared to the existing mode where plaintext keys are accessible to the
> kernel? In which cases would you use each mode?
>
High-level Use-case is to ensure runtime security.
By runtime security, I mean, key that is added to keyring after blob-decapsulation,
- if get stolen, then being plain key, security can be compromised.
- After this patch-set, if key get stolen, then being HBK(encrypted by H/W), will not be of any use without HW. Security is not compromised.
> Regards,
> Jan
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