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Challenges

These are some of the free sites to practice different skills. Mostly infosec and programming:

Cryptography

• https://cryptopals.com/
• https://cryptohack.org/
• https://github.com/fancy-cryptography/fancy-cryptography

Exploitation

• http://exploit.education/
• https://github.com/shellphish/how2heap
• https://pwn.college/
• https://guyinatuxedo.github.io/

CTFs and pentest

• https://overthewire.org/
• https://ctftime.org
• https://www.vulnhub.com
• https://tryhackme.com

Reverse Engineering

• https://0xinfection.github.io/reversing/
• https://crackmes.one/
• https://microcorruption.com/