On Thu, Jul 25, 2019 at 11:30:55PM -0400, Alvaro Herrera wrote:
> On 2019-Jul-25, Alvaro Herrera wrote:
> > On the other hand if the Key and IV are reused between messages then
> > the same plaintext will lead to the same ciphertext, so you can
> > potentially decrypt a message using a sufficiently large corpus of known
> > matching plaintext/ciphertext pairs, even without ever recovering the
> > key.
>
> Actually the attack being described presumes that you know *both the*
> *unencrypted data and the encrypted data* for a certain key/IV pair,
> and only then you can decrypt some other data. It doesn't follow that
> you can decrypt data just because somebody reused the IV for a second
> page ... I haven't seen any literature referenced that explains what
> this attack is.
I never addressed this exact comment. If someone can guess at some
known heap/index format markers at specific offsets in a page, they can
XOR that with the encrypted data to get the encryption bit stream. They
could then use that encrypted bit stream to XOR against another
encrypted page at the same offsets and with the same key/IV to see
unenrypted user data if it exists at the same page offsets. (The
all-zero empty space is a huge known format marker area.)
This is why CTR is so sensitive to reuse of the key/IV settings for
encrypting different data.
--
Bruce Momjian <bruce@momjian.us> http://momjian.us
EnterpriseDB http://enterprisedb.com
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