Merge pull request #4 from EternalLearner42/master

Updated with some basic references

README.md

@@ -168,24 +168,28 @@ If you want to support another repository containing **hardening** recipes, plea
 
 #### :information_source: Introduction
 
-The primary goal of many possible attacks is to stop them where possible, and failing that slow them down so that hopefully someone will notice the attacker tearing apart a system in someone's office.
+The primary goal of physical security is to stop physical attacks whenever possible, and, failing that, to slow them down so that hopefully someone will notice the presence of the attacker in a restricted area, preventing any tampering with the system. [Weak physical security often invalidates any other security measure](https://www.lynda.com/Linux-tutorials/Physical-security-concepts/728406/750240-4.html), and thus should be prioritized. 
 
 #### :eight_pointed_black_star: Secure rooms
 
-For secure rooms make sure that the walls go beyond the false ceiling, and below the raised floor, large vents should also be covered with bars if possible.
+For secure rooms make sure that the walls go beyond the false ceiling, and below the raised floor ([source](https://books.google.pt/books?id=XD68NYRPD9oC&pg=PA158&lpg=PA158&dq=physical+security+computer+systems+false+ceiling&source=bl&ots=1wzz6IsBfw&sig=ACfU3U0IPb8NrSiQaQoZFfnu4eMbRgYngQ&hl=en&sa=X&redir_esc=y#v=onepage&q=physical%20security%20computer%20systems%20false%20ceiling&f=false)), large vents should also be [covered with bars](https://books.google.pt/books?id=6yTGIaHLNsAC&pg=PA160&lpg=PA160&dq=covering+vents+with+bars+physical+security&source=bl&ots=2k-196Kwwk&sig=ACfU3U0KsfGhDk06A6qUHIXt88xEi8FZ6w&hl=en&sa=X&redir_esc=y#v=onepage&q=covering%20vents%20with%20bars%20physical%20security&f=false) if possible.
 
 #### :eight_pointed_black_star: Monitoring
 
-Monitoring the room with CCTV or wired cameras. It's great way to provide security for your server room or data center. As well as providing video footage of events which may occur - door open events, motion detection or any other sensor event, they also act as a visual deterrent to would be criminals.
+Monitoring the room with CCTV or wired cameras is a great way to provide security for your server room or data center. As well as providing video footage of events which may occur - door open events, motion detection or any other sensor event, they also act as a visual deterrent to would be criminals.
 
 Solution for remotely monitoring the temperature ensue proactively notify you when the temperature goes above or below pre-defined thresholds, potentially allowing you to take corrective measures before encountering costly downtime.
 
+[Source](https://www.enviromon.net/monitoring-physical-security-server-room/)
+
 #### :eight_pointed_black_star: Air conditioning
 
 Computer equipment generates heat, and is sensitive to heat, humidity, and dust, but also the need for very high resilience and failover requirements. Maintaining a stable temperature and humidity within tight tolerances is critical to IT system reliability.
 
 Air conditioning designs for most computer or server rooms will vary depending on various design considerations, but they are generally one of two types: "up-flow" and "down-flow" configurations.
 
+[Source](https://www.enviromon.net/how-to-monitor-server-room-temperature/)
+
 #### :eight_pointed_black_star: Fire protection
 
 The fire protection system's main goal should be to detect and alert of fire in the early stages, then bring fire under control without disrupting the flow of business and without threatening the personnel in the facility. Server room fire suppression technology has been around for as long as there have been server rooms.
@@ -194,16 +198,22 @@ There are a series of things you need in a fire suppression system:
 
 - an emergency power off function
 - gas-based suppression system
-- water detection sensors in/on the floor
+- fire detection sensors
+
+[Source](https://www.controlfiresystems.com/news/what-type-of-suppression-system-works-best-for-computer-room-fires/)
 
 #### :eight_pointed_black_star: Locked racks
 
 All systems should be securely fastened to something with a cable system, or locked in an equipment cage if possible. Case locks should be used when possible to slow attackers down.
 
+[Source](https://securitytoday.com/blogs/reaction/2018/02/Securing-the-Physical-Safety-of-Data-with-Rack-Level-Access-Control.aspx)
+
 #### :eight_pointed_black_star: Console security
 
 With physical access to most machines you can simply reboot the system and ask it nicely to launch into single user mode, or tell it to use `/bin/sh` for init.
 
+[Source](https://www.tldp.org/HOWTO/Security-HOWTO/physical-security.html)
+
 #### :eight_pointed_black_star: BIOS protection
 
 In the program itself to edit the BIOS settings:
@@ -224,6 +234,8 @@ Because the methods for setting a BIOS password vary between computer manufactur
 
   > For this reason, it is good practice to lock the computer case if possible. However, consult the manual for the computer or motherboard before attempting to disconnect the CMOS battery.
   
+[Source](https://csrc.nist.gov/csrc/media/publications/sp/800-147b/final/documents/draft-sp800-147b_july2012.pdf)
+
 #### :ballot_box_with_check: Summary checklist
 
 | <b>Item</b> | <b>True</b> | <b>False</b> |
@@ -265,6 +277,8 @@ Before this you should to answer the following questions:
   * during boot process
   * mixed above or manually
   
+[Source](https://uchicago.service-now.com/it?id=kb_article&kb=KB06000398)
+
 #### :eight_pointed_black_star: Encrypt root filesystem
 
 Unlocked during boot, using passphrases or USB stick with keyfiles.
@@ -290,6 +304,8 @@ Before this you should to answer the following questions:
 
 The following recipe should be made after installing the system (however, these steps are included in this section to avoid mixing issues).
 
+[Source](https://security.stackexchange.com/questions/166075/encrypting-the-boot-partition-in-a-linux-system-can-protect-from-an-evil-maid-a)
+
 ###### Create copy of your /boot
 
 ```bash