On Fri, 2018-08-03 at 10:45 -0400, Mimi Zohar wrote: > On Fri, 2018-08-03 at 07:23 -0700, James Bottomley wrote: > > On Fri, 2018-08-03 at 07:58 -0400, Mimi Zohar wrote: > > > On Thu, 2018-08-02 at 17:14 +0100, David Howells wrote: > > > > Udit Agarwal <udit.agarwal@xxxxxxx> wrote: > > > > > > > > > +========== > > > > > +Secure Key > > > > > +========== > > > > > + > > > > > +Secure key is the new type added to kernel key ring service. > > > > > +Secure key is a symmetric type key of minimum length 32 > > > > > bytes > > > > > +and with maximum possible length to be 128 bytes. It is > > > > > produced > > > > > +in kernel using the CAAM crypto engine. Userspace can only > > > > > see > > > > > +the blob for the corresponding key. All the blobs are > > > > > displayed > > > > > +or loaded in hex ascii. > > > > > > > > To echo Mimi, this sounds suspiciously like it should have a > > > > generic interface, not one that's specifically tied to one > > > > piece of > > > > hardware - particularly if it's named with generic "secure". > > > > > > > > Can you convert this into a "symmetric" type and make the > > > > backend > > > > pluggable? > > > > > > TPM 1.2 didn't support symmetric keys. For this reason, the TPM > > > "unseals" the random number, used as a symmetric key, and returns > > > the > > > "unsealed" data to the kernel. > > > > > > Does anyone know if CAAM or TPM 2.0 have support for symmetric > > > keys? > > > > It depends what you mean by "support". The answer is technically > > yes, > > it's the TPM2_EncryptDecrypt primitive. However, the practical > > answer > > is that symmetric keys are mostly used for bulk operations and the > > TPM > > and its bus are way too slow to support that, so the only real, > > practical use case is to have the TPM govern the release conditions > > for > > symmetric keys which are later used by a fast bulk > > encryptor/decryptor > > based in software. > > > > > If they have symmetric key support, there would be no need for > > > the > > > symmetric key ever to leave the device in the clear. The device > > > would unseal/decrypt data, such as an encrypted key. > > > > > > The "symmetric" key type would be a generic interface for > > > different > > > devices. > > > > It's possible, but it would only work for a non-bulk use case; do > > we > > have one of those? > > "trusted" keys are currently being used to decrypt other keys (eg. > encrypted, ecryptfs, ...). Yes, but that's just double encryption: it serves no real security purpose because at the end of the chain, the symmetric key is released into kernel memory to use in software crypto. Unless you're using a high speed (and high cost) crypto accelerator with HSA, this will always be the case for bulk crypto. The other slight problem with this chain of crypto is that I can impose conditions on the key release from the TPM (well TPM2, since TPM1.2 has a very weak policy engine) but if we use intermediate steps, those conditions might not be preserved, so I think the ideal would be a trusted key being released directly to LUKS or ecryptfs because the TPM can then verify the policy at actual unseal time. I get that for the ecryptfs case you might want one key per file for sharding and sharing, and that's more like a bulk case because the TPM isn't going to keep up with the number of unseal operations required. James
