I recently purchased Windows 8.1 Professional and now I don't need my retail copy of Windows 8 Professional Upgrade since I only have one PC. About 4 months ago I threw away the retail box and manual that came with my Windows 8 because I didn't think that I would ever resell it and I hated the designed of the retail packaging and so I kept the discs and key in a CD binder. Since I don't have the retail packaging/manual anymore I don't have the Certificate of Authenticity. According to US law, would it be illegal for me to resell my used copy of Windows 8 Professional Upgrade retail version without the certificate of authenticity?