RSA

RSA is one of the most common modern cryptosystems, known for it's public and private key encryption. If you see public and private keys, there is a strong chance that it is an RSA problem, or at least RSA derived.

Read this: https://ctf101.org/cryptography/what-is-rsa/

Follow this writeup and submit your solution: https://quanyang.github.io/x-ctf-fact0r!z3-and-fact0r!z3_aga!n-crypto/

Some RSA problems will not be solved by default RSAtool runs. For those, you will often need an extension named Sage Math (which is not obvious as it not being there does not cause an obvious error). I keep a cloud server setup with a few crypto tools and Sage installed, and a ton of cores and virtual memory so that if I need to, I can turn it on, download the ciphers, brrrrrrrrrt and solve with zero effort. Definitely a CTF power move, and it is free as long as you remember to turn it off once you are done, because it costs about $1.20 a minute. If you forget to turn it off, you'll burn through your free credits instantly and then have an $1000 dollar bill at the end of the month.

High risk, high reward?