Security+ concept drills: control types, ports, and choosing the right cryptography

Control categories and types

Controls are grouped by category (technical, managerial, operational, physical) and by type or function (preventive, deterrent, detective, corrective, compensating, directive). Many questions ask you to classify a control, and some controls fit more than one function, such as a camera that both deters and detects.

control             | category    | function
firewall rule       | technical   | preventive
security camera     | physical    | detective, deterrent
backup restore      | technical   | corrective
acceptable use policy | managerial | directive
guard at entrance   | operational | preventive, deterrent

Ports worth knowing cold

Know the common ports and their secure alternatives: Telnet 23 versus SSH 22, HTTP 80 versus HTTPS 443, LDAP 389 versus LDAPS 636, FTP 20 and 21 versus SFTP over SSH 22 or FTPS, SMTP 25 and submission 587, DNS 53, RDP 3389, SMB 445, and SNMP 161 with SNMPv3 for authentication and encryption.

• Insecure to secure: 23 to 22, 80 to 443, 389 to 636
• File transfer: FTP 21 versus SFTP 22
• Mail: 25 relay, 587 submission, 993 IMAPS
• Management: 3389 RDP, 161 SNMP (use v3)

Lab: verify ports in your own lab

Scan your own lab hosts to see real services on these ports, then connect to one insecure and one secure service and compare what a packet capture shows. Seeing a Telnet password in cleartext next to an encrypted SSH session makes the port pairs stick far better than a list.

nmap -sV -p 22,23,80,443,389,636,445,3389 10.10.10.0/24
sudo tcpdump -i eth0 -A port 23 -c 40     # credentials visible in Telnet
sudo tcpdump -i eth0 -A port 22 -c 40     # encrypted after key exchange

Choosing the right primitive

Confidentiality of bulk data uses symmetric encryption such as AES. Key exchange and digital signatures use asymmetric algorithms. Integrity without a key uses hashing such as SHA-256; integrity with a shared key uses an HMAC. Password storage uses slow, salted algorithms such as bcrypt or Argon2. Questions usually describe a requirement and ask for the matching tool.