On Tue, Aug 10, 2021 at 11:46:49AM -0700, Eric Biggers wrote: > On Tue, Aug 10, 2021 at 09:06:36PM +0300, Jarkko Sakkinen wrote: > > > > > > > > I don't think this is right, or at least it does not follow the pattern > > > > in [*]. I.e. you should rather use trusted key to seal your fscrypt key. > > > > > > What's the benefit of the extra layer of indirection over just using a "trusted" > > > key directly? The use case for "encrypted" keys is not at all clear to me. > > > > Because it is more robust to be able to use small amount of trusted keys, > > which are not entirely software based. > > > > And since it's also a pattern on existing kernel features utilizing trusted > > keys, the pressure here to explain why break the pattern, should be on the > > side of the one who breaks it. > > This is a new feature, so it's on the person proposing the feature to explain > why it's useful. The purpose of "encrypted" keys is not at all clear, and the > documentation for them is heavily misleading. E.g.: > > "user space sees, stores, and loads only encrypted blobs" > (Not necessarily true, as I've explained previously.) > > "Encrypted keys do not depend on a trust source" ... "The main disadvantage > of encrypted keys is that if they are not rooted in a trusted key" > (Not necessarily true, and in fact it seems they're only useful when they > *do* depend on a trust source. At least that's the use case that is being > proposed here, IIUC.) > > I do see a possible use for the layer of indirection that "encrypted" keys are, > which is that it would reduce the overhead of having lots of keys be directly > encrypted by the TPM/TEE/CAAM. Is this the use case? If so, it needs to be > explained. If trusted keys are used directly, it's an introduction of a bottleneck. If they are used indirectly, you can still choose to have one trusted key per fscrypt key. Thus, it's obviously a bad idea to use them directly. /Jarkko
