On Aug 22, 2018, at 12:35 PM, Alan Somers <asom...@freebsd.org> wrote:
> Only encrypting L0 blocks also leaks a lot of information. That means that,
> if encryption is set to anything but "off", watermarking attacks will still
> be possible based on the size and sparsity of a file. Because I believe that
> with any encryption mode, ZFS turns continuous runs of zeros into holes. And
> I don't see anything in zio_crypt.c that addresses that.
I’m not sure about that. However, with compression=off,
dd if=/dev/zero of=bigfile bs=1m count=1024
results in a file that is 1565148 blocks (of 128k bytes), which supports your
statement.
With compression=on, it creates a 1 block file.
Sean.
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