It’s a write-up about the challenge : Ringzer0CTF - File Recovery
Challenge 49 - File recovery
1. Challenge
The crypto challenge is a folder :
- flag.enc
- private.pem
2. Solution
We have one cripted file and one private key. The file private.pem contained the RSA private key :
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-----BEGIN RSA PRIVATE KEY-----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-----END RSA PRIVATE KEY-----
This is why, we used openssl to decrypt the cripted file : flag.enc with this private key.
openssl rsautl -decrypt -inkey private.pem -in flag.enc -out flag.txt
In the new file flag.txt we discovered the solution : FLAG-vOAM5ZcReMNzJqOfxLauakHx