We are asked to find the version of a key-value store hosted on keystore.hkn.

We first look for open ports using nmap:

$ nmap -p- keystore.hkn
Starting Nmap 7.92 ( https://nmap.org ) at 2023-03-20 10:30 EDT
Nmap scan report for keystore.hkn (77.184.238.37)
Host is up (0.00025s latency).
Not shown: 65534 closed tcp posts (conn-refused)
PORT     STATE SERVICE
6379/tcp open  redis

Nmap done: 1 IP address (1 host up) scanned in 3.20 seconds
Sh

We can see that redis is running on port 6379, lets scan the version on that port:

$ nmap -p6379 -sV keystore.hkn
Starting Nmap 7.92 ( https://nmap.org ) at 2023-03-20 10:30 EDT
Nmap scan report for keystore.hkn (77.184.238.37)
Host is up (0.00031s latency).

PORT     STATE SERVICE VERSION
6379/tcp open  redis   Redis key-value store 7.0.8
Sh

The key-value store version is Redis key-value store 7.0.8 so the flag is DDC{Redis key-value store 7.0.8}