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    SubjectRe: [PATCH v2] fscrypt: support trusted keys
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    On 17.08.21 15:55, Mimi Zohar wrote:
    > On Tue, 2021-08-17 at 15:04 +0200, Ahmad Fatoum wrote:
    >> Hi,
    >>
    >> On 12.08.21 02:54, Mimi Zohar wrote:
    >>> On Wed, 2021-08-11 at 10:16 -0700, Eric Biggers wrote:
    >>>
    >>>> Neither of you actually answered my question, which is whether the support for
    >>>> trusted keys in dm-crypt is a mistake. I think you're saying that it is? That
    >>>> would imply that fscrypt shouldn't support trusted keys, but rather encrypted
    >>>> keys -- which conflicts with Ahmad's patch which is adding support for trusted
    >>>> keys. Note that your reasoning for this is not documented at all in the
    >>>> trusted-encrypted keys documentation; it needs to be (email threads don't really
    >>>> matter), otherwise how would anyone know when/how to use this feature?
    >>>
    >>> True, but all of the trusted-encrypted key examples in the
    >>> documentation are "encrypted" type keys, encrypted/decrypted based on a
    >>> "trusted" type key. There are no examples of using the "trusted" key
    >>> type directly. Before claiming that adding "trusted" key support in
    >>> dm-crypt was a mistake, we should ask Ahmad why he felt dm-crypt needed
    >>> to directly support "trusted" type keys.
    >>
    >> I wanted to persist the dm-crypt key as a sealed blob. With encrypted keys,
    >> I would have to persist and unseal two blobs (load trusted key blob, load
    >> encrypted key blob rooted to trusted key) with no extra benefit.
    >>
    >> I thus added direct support for trusted keys. Jarkko even commented on the
    >> thread, but didn't voice objection to the approach (or agreement for that
    >> matter), so I assumed the approach is fine.
    >>
    >> I can see the utility of using a single trusted key for TPMs, but for CAAM,
    >> I see none and having an encrypted key for every trusted key just makes
    >> it more cumbersome.
    >>
    >> In v1 here, I added encrypted key support as well, but dropped it for v2,
    >> because I am not in a position to justify its use. Now that you and Eric
    >> discussed it, should I send v3 with support for both encrypted and trusted
    >> keys like with dm-crypt or how should we proceed?
    >
    > With some applications, the indirection is important. It allows the
    > "encrypted" key type to be updated/re-encypted based on a new "trusted"
    > key, without affecting the on disk encrypted key usage.

    Those applications were already able to use the encrypted key support
    in dm-crypt. For those where re-encryption/PCR-sealing isn't required,
    direct trusted key support offers a simpler way to integrate.

    > As much as I expected, directly using "trusted" keys is a result of the
    > new trusted key sources.

    More users = more use cases. You make it sound like a negative
    thing.

    > I have no opinion as to whether this is/isn't a valid usecase.

    So you'd be fine with merging trusted key support as is and leave encrypted
    key support to someone who has a valid use case and wants to argue
    in its favor?

    Cheers,
    Ahmad

    >
    > thanks,
    >
    > Mimi
    >
    >


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