# Master Key

A master key is a cryptographic asymmetric key (RSA) used to encrypt, sign and validate license files. The public part of the master key is stored inside the protected assembly and is automatically used to validate loaded license files whilst the private part of the master key is used to encrypt and sign those files.

In addition the master key defines a "slot" where information like evaluation periods, expiration dates, numbers of uses, etc. are stored. If you change the master key a different slot would be used. If you protect different assemblies with different master keys, they would each use their own slots. For example, if you want multiple assemblies to share the same number of uses, you would need to protect them with the same master key.

When you create license files for your protected software, you must use the same master key that you used to produce the .NET Reactor protected output.

This master key is generated when you create your project, which must be saved to preserve the original key. Never hand out the Master Key to anybody!