Open Stack

Bryan D. Payne wrote:
> If memory serves me right, XTS has some known issues (in particular
> data integrity issues and reply attacks).  I typically still prefer to
> use CBC as it is time tested and works nicely if you handle your IV's
> properly.

We understand that CBC has some watermarking issues for storage encryption use.  XTS is a NIST-approved cryptographic standard for this purpose.  http://csrc.nist.gov/publications/nistpubs/800-38E/nist-sp-800-38E.pdf.  You're right that this doesn't provide integrity checks, but the SP800-38E standard states "In the absence of authentication or access control, XTS-AES provides more protection than the other approved confidentiality-only modes against unauthorized manipulation of the encrypted data."  Also note that cryptsetup for dm-crypt uses XTS as the default mode now.  http://www.spinics.net/lists/dm-crypt/msg04885.html.   The normal usage of XTS would be in an encryption module that would reside directly with the hard drive platter that would be storing the encrypted data.  In our case, though we're sending the data over iSCSI to a remote drive, we believe this encryption mode can still support a reasonably secure solution, assuming that an enhanced key management server (forthcoming) will be implemented.  If the key is kept from compromise, the encrypted data cannot be easily manipulated or substituted in its encrypted form, and it would basically randomly corrupt data within that block.
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