Greg Low provides an explanation:
The Service Master Key (SMK) is one of the most misunderstood security components in SQL Server.
It is frequently described as:
- The root of all encryption
- The key that protects everything
- Something you must back up constantly
Those statements are not entirely wrong – but they are incomplete, and in some cases actively misleading.
It’s important to understand what the Service Master Key actually does, when it matters, when it doesn’t, and why many operational decisions around it are based on myth rather than mechanics.
Read on to learn more about what the key is, what exactly it protects, and some practical guidance around managing it.