CS331 Quiz 2: Access Controls & Cryptography

State

Collection of the current values of all memory locations, all secondary storage, and

all registers and other components of the system.

Protection State

The subset of the state that deals with protection.

Access Control Matrix

Tool to describe the current protection state

Let _ be the set of possible protection states

P

Let _ be exactly those states in which the system is authorized to reside

Q

Whenever the system state is in _, the system is secure

Q

---

“___“ => the system is not secure

P - Q

Characterizing the states in Q ->

Security Policy

Preventing the system from entering a state in P – Q ->

Security Mechanism

Let _ be some restrictive set of states (actual states that security mechanism allows)

R

A security mechanism is precise if “_ = _”

R = Q

Access Control Matrix Model

• most precise model used to describe a protection state

• It characterizes the rights of each subject (active entity, such as a process) with respect

to every other entity.

The set of all protected entities (that is, entities that are relevant to the protection

state of the system) is called the set of _____.

- Example: processes and users

Objects (O)

The set of protection states of the system is represented by the triple: “(_,_ ,_ )”

(S, O, A)

Discretionary Access Control (DAC)

- If an individual user can set an access control mechanism to allow or deny access to an

object

- Also known as Identity-based access control

- Based on the identity

- The owner sets the rule

Mandatory Access Control (MAC)

- When a system mechanism controls access to an object and an individual user cannot

alter that access

- Also known as Rule-based access control

- Identity is irrelevant

Originator Controlled Access Control (OCAC)

- Bases access on the creator of an object

- The goal of this control is to allow the originator of the file (or of the information

it contains) to control the dissemination of the information

- The file owner cannot delegate access

Cryptosystem

a 5-tuple (E, D, M, K, C)

- M is the set of plaintexts

- K the set of keys

- C is the set of ciphertexts

- E: M × K → C is the set of enciphering functions

- D: C × K → M is the set of deciphering functions.

Classical Cryptosystem

- cryptosystems that use the same key for encipherment and decipherment.

- also called single-key or symmetric cryptosystems

Transposition Ciphers

__ rearranges the characters in the plaintext to form the ciphertext.

The letters are not changed.

Substitution Ciphers

__ changes characters in the plaintext to produce the ciphertext.

Public Key Cryptography

type of cryptography that distinguished

between encipherment and decipherment keys.

One of the keys would be publicly known; the other would be kept private by its owner

Public Key Cryptosystem Conditions:

• It must be computationally easy to encipher or decipher a message given the appropriate

key.

• It must be computationally infeasible to derive the private key from the public key.

• It must be computationally infeasible to determine the private key from a chosen

plaintext attack.

Interchange Key

__ a cryptographic key associated with a principal to a

communication

Session Key

__ is a cryptographic key associated with the communication itself. Generated for a single “_“ and is discarded when the “_“ ends.

Certificate

__ a token that binds an identity to a cryptographic key.

It binds

a. Public key

b. Identity of the Owner (name, organization, domain, etc.)

c. Validity period

d. CA’s signature

Certification authority (CA)

__ an entity that issues certificates

Authentication

ensures the public key actually belongs to the person/website it

claims

Trust Establishment

certificates are issued by trusted CAs that browsers/OS

already trust.

Prevents MitM Attacks

attacker cannot easily replace the key, since users can

verify authenticity using the CA’s signature.

Scalability

certificates allow Public keys to work securely on the Internet (HTTPS,

email signing, etc.)

Web Browser “___“ from the Certificate

requests the public key

Web Server “___“ the Certificate

validates.

Disadvantages of Public Key Cryptography

• mathematically intensive

• Man in the Middle Attack (attacker can substitute a fake public key during exchange)

• Storage and Management