On Thu, Jul 25, 2019 at 09:11:18PM -0400, Sehrope Sarkuni wrote:
> On Thu, Jul 25, 2019 at 8:50 PM Bruce Momjian <bruce@momjian.us> wrote:
>
> On Thu, Jul 25, 2019 at 08:44:40PM -0400, Sehrope Sarkuni wrote:
> > You can still use CTR mode and include those to make the key + IV unique
> by
> > adding them to the derived key rather than the IV.
> >
> > The IV per-page would still be LSN + page-number (with the block number
> added
> > as it's evaluated across the page) and the relfilenode, heap/index,
> database,
> > and anything else to make it unique can be included in the HKDF to create
> the
> > per-file derived key.
>
> I thought if we didn't have to hash the stuff together we would be less
> likely to get collisions with the IV.
>
>
> IV creation not use any hashing and would never have collisions with the same
> key as it's LSN + page + block (concatenation).
>
> The derived keys would also not have collisions as the HKDF prevents that.
> Deriving two matching keys with different inputs has the same chance as
> randomly generating matching HMACs (effectively nil with something like
> HMAC-SHA-256).
>
> So there wouldn't be any reuse of the same key + IV. Even if two different
> files are encrypted with the same LSN + page the total operation (key + IV)
> would be different as they'd be using different derived keys.
Oh, mix the value into the derived key, not into the IV --- got it.
--
Bruce Momjian <bruce@momjian.us> http://momjian.us
EnterpriseDB http://enterprisedb.com
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