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.
Joe
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