The Magento Encryption Key is generated during the Magento Installation. It is used for the encryption and the security storage of the sensitive data in the script's database.
The Magento Encryption Key is kept in the app/etc/local.xml file. You can open it through File Manager tool in your cPanel or FTP for example. In this file, you can look for the following code:
The ENCRYPTION_KEY string is replaced by the actual encryption key.