Encryption brings data into a state that cannot be interpreted by anyone who does not have access to the decryption key, password, or certificates. Though encryption does not restrict the access to the data, it ensures that if data loss happens, then in that case data is useless to the person who does not have access to the decryption key/password/certificates. Though when you use encryption, there should be a maintenance strategy for passwords, keys, and certificates.
To meet the demands of regulatory compliance and corporate data security standards, SQL Server allows you to enable encryption at column/cell level or on the database level. You can even use file level encryption provided by Windows for database files.
Though there are several ways/levels to implement encryption in SQL Server, I am going to focus on Transparent Data Encryption (TDE) in this article, which was introduced in SQL Server 2008 and available in later releases. For more information click here.