Re: security of re-encryption

[Philippe Cerfon <philcerf@gmail.com>]

Hey Michael.

Thanks for your reply! :-)

> Consider just that the first several bytes of the HTTP
> request portion of a HTTPS transaction are not just guessable, but
> can
> pretty much be considered to be _known_ since they are essentially
> dictated by the HTTP standard.

I had thought about that, too, but imagined that the following might
make a difference:
- With HTTP, only the first few bytes are the same (more or less)
unless one transmits large files or so (but then again, wouldn't TLS
renegotiations hapen after a while)? With LUKS one migh have many TB
of ciphertext (before and after). So I wondered whether that could
make a difference.
- With TLS, doesn't one typically have some ephemeral key, and even if
that was compromised only that particular session (or part thereof)
would be compromised. For cryptsetup the key is "static", so the
effect would be much bigger.

Of course I didn't want to imply, that I'd knew of any such attack.
I'm not an expert, so I merely asked whether something is known and
whether re-recryption is recommended from a security point of view!

So I guess it is. Thanks for your help.

Sincerely,
Philippe