The plaintext you obtained from the last question is used as a symmetric key to encrypt a secret message. The message is encrypted by openssl enc using aes$-256-$cbc cipher, nosalt, with the hex string of iv being $5$a$04$ec$902686$fb$05$a$6$b$7$a$338$b$6$e$07760.$

The example command for encryption is $($with the key replaced by $******)$ :

openssl enc $-$aes$-256-$cbc $-$nosalt $-$e $-$in secret.txt $-$out secret.txt$.$enc $-$K $\text{'}*********\text{'}-$iv $\text{'}5$a$04$ec$902686$fb$05$a$6$b$7$a$338$b$6$e$07760\text{'}$

secret.txt$.$enc is attached. Decrypt the secret, and find the message.

$($When you decrypt the secret, you will receive a warning from openssl: "hex string is too short, padding with zero bytes to length". This is because the length of the private key we use is less than $256-$bit. In such cases, openssl pads private key with zeros. Please use stronger keys in real life.$)$