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DSS/HIPPA/SOX Unalterable Audit Logs?
analogrithems writes "Recently I was asked by one of the suits in my company to come up with a method to comply with the new PCI DSS policy that requires companies to have write once, read many logs. In short the requirement is for a secure method to make sure that once a log is written it can never be deleted or changed. So far I've only been able to find commercial and hardware-based solutions. I would prefer to use an open source solution. I know this policy is already part of HIPPA and soon to be part of SOX. It seems like there ought to be a way to do this with cryptography and checksums to ensure authenticity. Has anyone seen or developed such a solution? Or how have you made compliance?"
Optical media are great for write once, read many.
Cryptography, digital signatures, and checksums can only take you so far. They can detect tampering pretty easily. However, crypto can't prevent someone from deleting a file, although by checksumming or signing a whole bunch of files you could at least detect deletion of one of them. Ultimately, if you really want permanence, you need to write it out (as an above poster suggested) to some sort of write-once media. CD-Rs or DVD-Rs would obviously fit the bill here, although one can indeed delete a CD-R by simply throwing it out, of course.
:)
Another cheap write-only medium is paper; I suppose you could purchase a laser printer (or even a line printer), and have it spit out the logs as they occur. If you kept the printer in a locked transparent box, nobody but people with the keys would have access to the output.
You could burn the logs onto PROMs as well, that's pretty permanent
Anything on magnetic or flash media can be erased or tampered with somehow, unless the drive controller hardware itself prohibited overwriting existing data. Even then you're relying on someone not being able to replace the drive controller or take the drive apart and diddle the platters/flash chips directly (although I suppose a decent amount of epoxy could thwart this). Any software-based solution can be tampered with in theory. One hacker favorite (which may be a legend or not) is that people used to get root on other people's boxes and then replace their copy of PGP with an instrumented copy. Thus, even the encryption software became compromised.
For compliance, though, I'm not sure what kind of oversight you have to have. At the end of the day, somebody has to be trusted with these logs, and that person would almost assuredly have the power to destroy them, or at least portions of them.
At USENIX/EVT06 last year a team from the University of Iowa presented a cheap one-way data cable you could make with off-the-shelf parts from Radio Shack. Total cost is about $5 (for bulk, maybe $10 if you're buying single units) and it is provably, auditably, one-way. It was originally developed for electronic voting, to allow for counting computers to communicate with webservers that post election results. An attacker compromising the webserver cannot attack the counting computer, because there is literally no return path.
It works with very high reliability up to about 9600 baud.
You may be able to use this to your benefit. Have an isolated system air-gapped from the rest of the network which listens for log events on a one-way data cable. While you're no longer guaranteed to be safe (since if a logging PC is compromised, an attacker could send compromised data to the syslog PC and perhaps cause some sort of mayhem), but the lack of a return path makes interactive attacks infeasible.
ObDisclosure: I am a graduate student at UI and know the guy who invented the data cable, although I am not associated with the gadget.
I would dump it in GIT or the likes.... any change of it will be recorded ;)
Seriously, many version controlling systems already contain the data integrity and authenticity checks that you need
Some of the work I do may require something like this, so I'm considering implementing Guy Fawkes over syslog.
http://www.cl.cam.ac.uk/~rja14/Papers/fawkes.pdf
From the paper:
6.2 Tamper-evident audit trails
It is a well known problem that an intruder can often acquire root status by using well known operating system weaknesses, and then alter the audit and log information to remove the evidence of the intrusion. In order to prevent this, some Unix systems require that operations on log and audit data other than reads and appends be carried out from the system console. Others do not, and it could be of value to arrange alternative tamper-evidence mechanisms.
A first idea might be to simply sign and timestamp the audit trail at regular intervals, but this is not sufficient as a root intruder will be able to obtain the private signing key and retrospectively forge audit records. In addition, the intervals would have to be small (of the order of a second, or even less) and the computation of RSA or DSA signatures at this frequency could impose a noticeable system overhead.
In this application, the Guy Fawkes protocol appears well suited because of the low computational overhead (two hash function computations per signature) and the fact that all secrets are transient; this second's secret codeword is no use in forging a signature of a second ago.