[Cryptography] Security on TRIM for full-disk encrypted SSDs

[RB]

On Thu, Apr 21, 2016 at 3:19 PM, Peter Fairbrother <peter at m-o-o-t.org> wrote:
> You think that an attacker knowing how much data you send doesn't affect
> confidentiality?
>
> hmmm, how many files on t'internet are 2798954788 bytes long?

You're right - that matters, but only for specific threat models,
particularly those involving transmission of illicit material.
Returning to the problem at hand - that of allowing one's opponent to
know one's net drive allocation by enabling TRIM under encryption -
the answer remains "it may matter".  If you're storing a known
quantity of illicit material in a way that could be separated from the
rest of the noise on your system, then yes - enabling TRIM is probably
dangerous.

For the rest of us that simply wish to prevent data loss or
modification in the event of a lost or stolen system or drive and lack
illicit material?  TRIM can be a great disk-longevity option that does
not affect our threat model.

You have to know what you're defending and what you're defending it
against.  Because they have customers with varying threat models, FDE
developers have historically tended toward the conservative extreme
and are just now offering exceptions to that.  For the average user,
however, the performance and operational load of that extreme may
outweigh actual concerns.