如何创建加密字符串等串行密钥

below snippet which encrypt the string but encrypted string looks like random alphanumeric. but i want encrypted string like

5214-6548-4584-4568-abcd or ABCD-TEST-1F2D-FSDF

My snippet

$encrypted = base64_encode(mcrypt_encrypt(MCRYPT_RIJNDAEL_256, md5($key), $string, MCRYPT_MODE_CBC, md5(md5($key))));
var_dump($encrypted); // "ey7zu5zBqJB0rGtIn5UB1xG03efyCp+KSNR4/GAv14w="

the below snippet i took from source encryption

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