TLDR
   - Figure out this is LCS35 Time Capsule Crypto-Puzzle.
   - Try to factor n. Succeed.
   - Apply Euler’s theorem and solve the puzzle to get the flag.
Read complete writeup: [https://sectt.github.io/writeups/CryptoCTF19/crypto_timecapsule/README](https://sectt.github.io/writeups/CryptoCTF19/crypto_timecapsule/README)