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 > > -- Pengutronix e.K. | | Steuerwalder Str. 21 | http://www.pengutronix.de/ | 31137 Hildesheim, Germany | Phone: +49-5121-206917-0 | Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 |
