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. As much as I expected, directly using "trusted" keys is a result of the new trusted key sources. I have no opinion as to whether this is/isn't a valid usecase. thanks, Mimi
