Log in to the Wolfram User Portal with your Wolfram ID. Under the "My Products and Services" tab, you can find a list of all your registered products and their corresponding activation keys.
If you are a student or employee at a participating institution, you can often request a key through a dedicated Activation Key Request Form using your organizational email. mathematica 9 activation key generator
Enter the generated password into the dialog box on your offline machine to complete the setup. Risks of Unofficial Key Generators Log in to the Wolfram User Portal with your Wolfram ID