Notes for February 3, 1997

1.	Hello

a.	Homework grades will be mailed out tomorrow; take more care with your pro-
grams, as they often did not work as well as you thought.

2.	Puzzle of the day

a.	Key point: notice the size of the shell and of in.telnetd. If these are the same, the 
attacker left a back door to return through.

3.	ACLs

a.	Review description

b.	Show 2 UNIX implementations (DG/UX and UNICOS)

c.	Discuss revocation issue

4.	Operating systems as examples

a.	Fence registers

b.	Base & bounds registers

c.	Tagged architecture: tags indicate rights over each word. Ex: B6500 family, which 
also used them to type the words (data, pointers, control words like stack pointers) 
Also, can tag blocks of 128 words with one tag

d.	Go through how this works for paging, segmentation

5.	Capabilities

a.	File descriptors in UNIX

b.	Like an unforgeable ticket; can use crypto, or can use tags, or can use protected 
memory space  (the latter two more usual on a single system, the first on a net-
worked system)

c.	Show sample C-list

d.	Copy right