When there are security updates, I review and install them as soon as possible and think about using automatic updates.
From time to time I want to boot from a clean boot CD and check if the system has been compromised.
For that reason, I want to check if any packages / binaries have been modified, check the bootloader, check for rootkits.
Let's suppose I booted from a clean boot CD and mounted the hdd filesystem.
How can I get list of all sha256 hash sums of all installed binaries and configuration files and check them against the versions from Debian repository?
I have looked into intrusion detection systems (debsums,) Afick, AIDE, FCheck, Integrit, Osiris, OSSEC, Samhain, Tripwire, but they all have in common, that they want to create a known-good database before auditing. This doesn't scale very well, because updates are pretty frequent, which render that known-good database less useful. Re-creating the known-good database after updating isn't very safe either - let's say apt-get had a bug and installed a malicious package, then the checksum of that malicious package would end up in the known-good database.
I think the real solution is checking against the distribution's package repository. How can I do that?
I've checked http://wiki.debian.org/SecureApt#How_to_manually_check_for_package.27s_integrity already, but instructions are incomplete.