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, ...). Mimi
