MS SQL column encryption without certificate

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SQL

encryption

cryptography

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I am trying to encrypt one of my sensitive columns in a SQL Server table. I tried AES256 encryption with this script, and it works perfect. But I don't want to create Certificates, or Symmetric Keys on my SQL Server as it may be a security problem later. How can I encrypt the data with a single password or key in my query ? Another problem with this method is, I can use only a single master password for my encryption.

CREATE MASTER KEY ENCRYPTION
  BY PASSWORD = '$Passw0rd'
  GO

  CREATE CERTIFICATE AESEncryptTestCert
  WITH SUBJECT = 'AESEncrypt'
  GO

  CREATE SYMMETRIC KEY AESEncrypt
  WITH ALGORITHM = AES_256 ENCRYPTION
  BY CERTIFICATE AESEncryptTestCert;


 OPEN SYMMETRIC KEY AESEncrypt DECRYPTION
 BY CERTIFICATE AESEncryptTestCert
 SELECT ENCRYPTBYKEY(KEY_GUID('AESEncrypt'),'The text to be encrypted');