The challenge was called Revolutional Secure Angou. A zip file (revolutional-secure-angou-de97106aa248a41a40fdd001fc5f7b4b4f28a39eb6bcabf8401b108b7a8961c5) was given to us. Inside we could find three file: an
RSA public key
publickey.pem (PEM formatted), the encrypted flag
flag.encrypted and the Ruby script called generator.rb used to
generate both the public key and the ciphertext. Our goal is obvious: decrypt
the file flag.encrypted .