The below example specifies the use of encryption, Essentially you are using the connection string from the SQL SQL server to be encrypted.
<connectionStrings>
<add name="MyConnection" connectionString="Data Source=tcp:sql1001.smarterasp.net;Initial Catalog=DB_XXX_db1;User ID=DB1_user;Password=*****; encrypt=true;TrustServerCertificate=True" providerName="System.Data.SqlClient"/>
</connectionStrings>