Re: Re: XTS does not get the expected result for non-byte-aligned NIST vectors

On Thu, May 20, 2021 at 4:02 AM yu li <[email protected]> wrote:
>
> Thank you for your reply.
>
> All test vector in https://github.com/weidai11/cryptopp/blob/master/TestVectors/xts.txt.  are byte-aligned . I've tested these vectors locally, and they're all pass. But it doesn't have a non-byte-aligned vector like datalen=250bit in https://github.com/weidai11/cryptopp/blob/master/TestVectors/xts.txt.  We can found non-byte-aligned vector in https://csrc.nist.gov/Projects/Cryptographic-Algorithm-Validation-Program/CAVP-TESTING-BLOCK-CIPHER-MODES#XTS .  All byte-aligned vector in https://csrc.nist.gov/Projects/Cryptographic-Algorithm-Validation-Program/CAVP-TESTING-BLOCK-CIPHER-MODES#XTS can pass， but all non-byte-aligned vector are fail.

My bad Yu. I took alignment to mean type alignment. Sorry about that.

XTS mode in Crypto++ is byte oriented, not bit oriented. We could
possibly change that.

I'm looking at https://csrc.nist.gov/CSRC/media/Projects/Cryptographic-Algorithm-Validation-Program/documents/aes/XTSVS.pdf,
and it says (from p. 6):

An implementation may support a data unit length that is not a
multiple of 8 bits.  In this case, the plaintext (PT) and ciphertext
(CT) will be represented in the request, sample, and response files by
a bit string padded with zeros on the right to the next byte boundary,
in hexadecimal.  For example, suppose an implementation supports a 137
bit data unit.  The first 128-bit block consists of the first (i.e.,
leftmost) 128 bits.  If the second, nine-bit partial block is
011011011, then in the request and sample files it will be padded with
seven zeros on the right – 0110 1101 1000 0000 – and represented as
6d80 (hex).  Response files values should be formatted the same way.

The values seem non-sensical to me. Where did 137-bit data unit come
from? That's going to be a sector size in real life, so its going to
be 512, 2048, 4096, 64k, etc.

Jeff

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