RE: Encrypted storage

[<Glenn_Everhart () bankone com>]

If your database is all encrypted, you have transformed an access control problem
for the original database into a key management problem. Specifically: what governs
who may get at plaintext and how secure is it?

If your database is one you (or just maybe you and some very few people you
REALLY REALLY trust) alone should access, encrypting the whole thing (or putting
it on a cryptodisk, equivalently) is a very sensible solution. Make sure you
have the key written out somewhere, preferably several times on different physical
containers, and locked up securely so you can recover if you forget the key. Then
go to it. If you are sharing access, everything depends on the key sharing
specifics. 

Encrypting all your stuff can be extremely high overhead. (My old cryptodisk code
for pdp11, on a pdp11/70, would either have the machine encrypting/decrypting or
letting it do useful other work: essentially it could not do both because the encrypt
or decrypt operations took ~100% of the CPU.) Only use it when you are sure that
the key management is handling your access control better than any other access
control scheme. Much of the time, it will not. It is good when the attack expected
is someone who might have system privs coming in and trying to take the data off
hours or from backups. IF the keys used are not kept online, you can make that
attacker's life difficult. 

Any time some mechanized process is going to decide when to decrypt encrypted data
for you, and can do so without being supplied extra information, an attacker can
analyze and duplicate what the machine process will do. Even if added information
is needed, if the system has not been designed carefully enough that information
might be revealed, allowing the crypto to be broken. Remember the stories about
FBI inserting key loggers on suspects' machines? 

It can be simpler to block users from access to "raw" disks or containers and build
a decent conventional access control system than trying to get key management
right. I advise using crypto for access control only sparingly, when you have
the time to really understand the key management issues.

Glenn Everhart


-----Original Message-----
From: Jeffrey Koniszewski [mailto:jkoniszewski () kronos com]
Sent: Wednesday, September 08, 2004 4:39 PM
To: webappsec () securityfocus com
Subject: Encrypted storage




I was wondering (because customers have asked me) whether anyone is configuring their database to store all information 
encrypted. Databases have this capability but the overhead can be so heavy that vendors don't recommend using it 
generically. Also, if most of the data is not sensitive it is a lot of work to protect small amounts of data. Is anyone 
aware of someone using this capability? Under what circumstances? What's the performance hit? What other gotchas? How 
about encrypted communication to the DB from the app server?


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