i need help with task 7 in this lab

https://seedsecuritylabs.org/Labs_16.04/Crypto/Crypto_Encryption/

there is a txt called word i have to read from it to find the key

8 Task 7: Programming using the Crypto Library

This task is mainly designed for students in Computer Science/Engineering or related fields, where pro- gramming is required. Students should check with their professors to see whether this task is required for their courses or not.

In this task, you are given a plaintext and a ciphertext, and your job is to find the key that is used for the encryption. You do know the following facts:

The aes-128-cbc cipher is used for the encryption.

The key used to encrypt this plaintext is an English word shorter than 16 characters; the word can be found from a typical English dictionary. Since the word has less than 16 characters (i.e. 128 bits), pound signs (#: hexadecimal value is 0x23) are appended to the end of the word to form a key of 128 bits.

Your goal is to write a program to find out the encryption key. You can download a English word list from the Internet. We have also linked one on the web page of this lab. The plaintext, ciphertext, and IV are listed in the following:

Plaintext (total 21 characters): This is a top secret.

Ciphertext (in hex format): 764aa26b55a4da654df6b19e4bce00f4 ed05e09346fb0e762583cb7da2ac93a2

SEED Labs Secret-Key Encryption Lab 7

IV (in hex format): aabbccddeeff00998877665544332211

You need to pay attention to the following issues:

If you choose to store the plaintext message in a file, and feed the file to your program, you need to check whether the file length is 21. If you type the message in a text editor, you need to be aware that some editors may add a special character to the end of the file.

The easiest way to store the message in a file is to use the following command (the -n flag tells echo not to add a trailing newline):

$ echo -n "This is a top secret." > file

In this task, you are supposed to write your own program to invoke the crypto library. No credit will be given if you simply use the openssl commands to do this task. Sample code can be found from the following URL:

https://www.openssl.org/docs/man1.0.2/crypto/EVP_EncryptInit.html

When you compile your code using gcc, do not forget to include the -lcrypto flag, because your code needs the crypto library. See the following example:

$ gcc -o myenc myenc.c -lcrypto

helpful website

https://www.vsaytech.com/others/crypto-lab-secret-key-encryption-part-2/

if you scroll down you can find helpful way