NCSC-TG-017: A Guide to Understanding Identification and Authentication in Trusted Systems, September 1991. (Light Blue Book)
You can download it from the following link: https://packetstormsecurity.com/files/download/14007/NCSC-TG-017.txt
Source: https://packetstormsecurity.com/files/14007/NCSC-TG-017.txt.html