reversing php dencryption function using openssl_encrypt

hello all,

i’m solving a ctf challenge and i have this function that decrypts the cipher
i want to build a function that encrypts plain text using
vmUeu7D9bzE5JmNE as a key

example output:

//$EncString = encryptString("aaaaaaaaaaaaaaaaaaaaa", "vmUeu7D9bzE5JmNE");

decryption function :

function decryptString($ciphertext, $password)
    $ciphertext = base64_decode($ciphertext);
    if (!hash_equals(hash_hmac('sha256', substr($ciphertext, 48) . substr($ciphertext, 0, 16) , hash('sha256', $password, true) , true) , substr($ciphertext, 16, 32))) 
        return null;
    return openssl_decrypt(substr($ciphertext, 48) , "AES-256-CBC", hash('sha256', $password, true) , OPENSSL_RAW_DATA, substr($ciphertext, 0, 16));

i want to reverse the decryption function , i tried but i couldn’t

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Author: Mo Salah