EYCC 2025 — Crypto Challenges#

First Challenge: Veiled Secret#

This challenge was about decrypting a secret message:

1
MKywL3gznaqhM2ghqzuxnzMvq-TulsD==TOR13

I noticed the TOR13 at the end, which points to starting with ROT13.

So, I copied the secret message to my go-to decoder, Dcode, and checked the output:

Now we’re left with Base64 encoded text, so I decoded it in the same website and got the flag:

Second Challenge: Golden Spiral#

We were given a file named goldenSpiral. It was not executable, so I made it executable:

1
chmod +x goldenSpiral

Then I tried executing it:

1
./goldenSpiral

But it threw an error:

1
bash: ./goldenSpiral: cannot execute: required file not found

I checked the file type:

1
file goldenSpiral

It revealed that it was an ELF executable requiring this interpreter:

1
/nix/store/lmn7lwydprqibdkghw7wgcn21yhllz13-glibc-2.40–66/lib/ld-linux-x86–64.so.2

After running the file with the required interpreter, an encrypted flag was returned:

1
fzef{7i0fGcobhxzwr4j}

The challenge mentioned a sequence that “grows almost exponentially,” suggesting the Fibonacci sequence. Since the encrypted flag seemed alphabetically shifted, I used this Fibonacci Cipher Decoder and started from 1 (because e comes right before f in the alphabet).

And we got the flag!

Third Challenge: Silent Keys#

This challenge was an RSA decryption challenge.

We were given:

1
n = 148304669693572711157725718049458731328582148078019
2
e = 65537
3
c = 35618364216358867907731764651946346081071748936005

The hint said:

n is the product of two primes; one of them is the integer part of pi multiplied by 10^5

This challenge can be solved in two ways:

1. Directly inputting the values in Dcode to get the flag:

2. Or factorizing n using factordb to get p and q:

Then calculating d from p, q, e:

Finally, decrypt the ciphertext c to reveal the flag:

And that’s all! Don’t forget to check my other write-ups for the Web, Forensics, and OSINT challenges!