Security is a complex topic, here we will try to make things easier to decipher, and understand. This page will go from zero to tin foil hat.
Understanding the concept of nesting is essential when drawing up your security plan. Disable all unnecessary services, uninstall all unnecessary software, disable all unnecessary kernel options, set useflags to -useflag to cut cruft down in sources, pass data through other servers performing specific functions like firewalling, or caching that will obfuscate the source of data. Data integrity requires off site backups so floods, power outages, wars, etc do not compromise your datas existence. Encrypt your drives so if they are physically taken your data is safe. Sign messages with gpg, use ssh instead of telnet, create ssl certificates. Monitor logs for malicious activity. If possible the last layer of security should be once all systems are broken and compromised, do not have anything of value or important going on with the system. separating computing tasks in the network over several computers helps to this end. corporations have email servers, web servers, routers, so on so forth.
If someone can take your system, your going to have a bad day. anchor your system to permanent structures, such as rack mounting. have security cameras, and locked doors.
- install sudo, make a wheel fake root user with an arbitrary name, and disable the root account with 'passwd -e -l'. Use
sudo -ito access root, or even setup terminals to run sudo -i when they start, add the fake root user to the root group. Attackers now have to guess the fake root user name also, not just the password.
- install a syslog
- install nftables
- install sshguard and have it watch logs for multiple failed login attempts, and block attackers.
apparmor, tomoyo, and selinux are mandatory access control systems.
sys-auth/pambase has use flags for making private temporary directories on a per user basis.
Random Number Generation
Random numbers are used for generating ssl keys, gpg keys, ssh keys etc. Predictable numbers, even slightly predictable compromise security. Do not use via or intel hwrngs as /dev/random entropy sources.
Password cracking systems rely upon you not watching logs, and easily guessable passwords. Use lower case, upper case, numbers, and symbols. 8 positions long takes less than a day to crack, where 16 takes thousands of years, 24 is probably impossible to break in a life time on a single computer.
The major thing to watch out for is that crackers don't use 1 computer, they use 100 concurrently hammering the attack surface in concert with each other.
To block pings until reboot:
root # echo 1 >/proc/sys/net/ipv4/icmp_echo_ignore_all
To permanently block pings:
root # echo "net.ipv4.icmp_echo_ignore_all = 1" >> /etc/sysctl.conf
Absolutely never use WEP or WPS. Disable them, they're compromised. Make a WPA or WPA2 key that is not a word or easily guessable. 1337 speak is also counting as whole words.