Hey! We at Xiomara would love to giveaway the flag to you. But, we can’t now, because someone just stole it from us and tried sending it to our rival, Jack. Our super strong web guy here came to the rescue and intercepted it on the way, but found that it was RSA encrypted! You are our crypto guy now. So, decrypt the message and as we promised, the flag is yours!

Jack’s public key

Let’s start with looking at the public key.

We see that public exponential is too low. If we call plain message as m and ciphertext as c, this is how c is generated.

We can write this equation as follows:

If the message is longer, we get larger k. However, if the message is short, we might brute force the value of k and decrypt the message.

Here is the code that brute forces k and decrypts the message.

Let’s run the script and get the flag.

Here is the flag xiomara{4y3_4y3_cryp70_6uy!}.