Access control
Basic concepts

Access control
• What can you do after authentication? • ”The prevention of unauthorized use of a

resource, including the prevention of use of a resource in an unauthorized manner”
 (ITU-T Recommendation X.800)

AC concepts reference makes monitor request user or represented 
 subject by ”principal” process, method, 
 code…

Authorization decision

read, write, delete, create…

object file, memory, device, process, method, code… protected 
 entity

is granted access (or not)

active entity

Auth… what?
• Authentication: who made the request? • Authorization: is the subject authorized/ trusted to perform the operation?

• Basic: observe, alter – very abstract, good for modeling

Access operations

• Concretely: depend on context & implementation ‣ memory: read, write, execute

Examples, experience?

‣ files: … append, delete, change properties ‣ methods: … invoke, create, delegate…

Access control matrix
Matrix A subjects s in S bjorn amendra lila4711 rast1337

objects o in O assignment.txt read, write read read solution.txt read, write read grades.xls read, write read, write -

s has right r on o if r in A[s,o] (define rights needed for each operation)

rights R

Matrix implementation bjorn adriaan lila4711 rast1337 assignment.txt read, write read read solution.txt read, write read grades.xls read, write read, write -

Now consider 104 users, 107 files? Large, sparse matrix: impractical to implement (but useful as a model)

Capability Lists (CL) bjorn amendra lila4711 rast1337 assignment.txt read, write read read solution.txt read, write read grades.xls read, write read, write -

Row-wise: each subject s has {A[s,o], o in O} Must be unforgeable (cf tickets) and protected. May be passed to other subject (delegation).
Capability ≈ qualification, competence, capacity