Introductory materials

• What is CTF? An introduction to security Capture The Flag competitions
• How To Learn Hacking With CTFs
• CTF 101

Platforms for beginners:

• picoGym – easy challenges from previous picoCTFs
• Ethical hacking for beginners by Hacking-lab

Popular CTF Platforms:

• TryHackMe
• HackTheBox
• CyptoHack
• VulnHub
• OverTheWire

Platform with CTF announcements and published solutions:

CTFtime

Recommended Links:

• Web
  • TryHackMe – Basic pentesting
  • TryHackMe – Owasp Top 10
  • TryHackMe – Vulnversity
  • Web challenges writeups
• Reverse engineering
  • TryHackMe – Intro to x86-64
  • TryHackMe – CC: Ghidra
  • TryHackMe – Reversing ELF
  • Reverse engineering challenges writeups
• Cryptography
  • TryHackMe – Cryptography for dummies
  • TryHackMe – Encryption 101 
  • Crypto challenges writeups 
• Forensics
  • Steganography
    • TryHackMe – CC: Steganography
    • Steganography challenges writeups
  • PCAP analysis
    • TryHackMe – Wireshark: The Basics
    • PCAP challenges writeups
• Binary exploitation – PWN
  • TryHackMe – Pwn 101
  • Nightmare
  • PWN college
  • Binary Exploitation challenges writeups