On Wed, Jun 20, 2018 at 06:19:40PM -0400, Joe Conway wrote:
> On 06/20/2018 05:12 PM, Bruce Momjian wrote:
> > On Mon, Jun 18, 2018 at 11:06:20AM -0400, Joe Conway wrote:
> >>> At the same time, having to have a bunch of independently-decipherable
> >>> short field values is not real secure either, especially if they're known
> >>> to all be encrypted with the same key. But what you know or can guess
> >>> about the plaintext in such cases would be target-specific, rather than
> >>> an attack that could be built once and used against any PG database.
> >>
> >> Again is dependent on the specific solution for encryption. In some
> >> cases you might do something like generate a single use random key,
> >> encrypt the payload with that, encrypt the single use key with the
> >> "global" key, append the two results and store.
> >
> > Even if they are encrypted with the same key, they use different
> > initialization vectors that are stored inside the encrypted payload, so
> > you really can't identify much except the length, as Robert stated.
>
> The more you encrypt with a single key, the more fuel you give to the
> person trying to solve for the key with cryptanalysis.
>
> By encrypting only essentially random data (the single use keys,
> generated with cryptographically strong random number generator) with
> the "master key", and then encrypting the actual payloads (which are
> presumably more predictable than the strong random single use keys), you
> minimize the probability of someone cracking your master key and you
> also minimize the damage caused by someone cracking one of the single
> use keys.
Yeah, I have a slide about that too, and the previous and next slide:
http://momjian.us/main/writings/crypto_hw_use.pdf#page=90
The more different keys you use the encrypt data, the more places you
have to store it.
--
Bruce Momjian <bruce@momjian.us> http://momjian.us
EnterpriseDB http://enterprisedb.com
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