CS338 Computer Security
Wednesday, 30 October 2024

+ Test corrections back
- nice job!
- a few comments
    - 2(e) What computational fact makes RSA secure?
        good: "factoring is slow"
        better: start with public key (n,e), it's hard to get d
    - 4(c) What is a port, and what is its purpose
        good: "identifies a service on a computer/server"
        not good: "usually is a well-known number, only sometimes
            is a random number"
        better, part 1: "a port identifies a process on a computer
            that is either waiting for connection requests or
            involved in a connection"
        better, part 2: there are "well-known" ports associated with
            common services

            cat /etc/services
            less /etc/services
        
        better, part 3: when a client makes a TCP connection, the
            client gets a port, and it is randomly assigned
    - 5(a) What does a cryptographic hash function do?
        [look it up on wikipedia]
        right: H(D) is the same every time for a given D
        wrong kinda: the data D can't be found given H(D)
        right kinda: it is computationally very hard to find D from H(D)

        wrong: the hash value H(D) is unique to D
        because:
            - the domain of a hash function H is infinite (i.e., you can
                feed any number of bytes into H)
            - the size of H(D) is a fixed number of bytes
                (e.g., SHA-256 digest is always 256 bits / 32 bytes long)
            - i.e., the range H is finite, so
            - some/maybe all H(D)'s could come from an infinite number of potential Ds

    - 9(c,d) - validating a certificate
        - Alice connects to Somebody (she hopes it's Bob)
        - Somebody sends her a certificate that says:
            "bob.com" || P_B || Sig_CA
        - Alice "validates" or "verifies" the certificate
            - checks the expiration date
            - checks that the identity "bob.com" is who Alice wants to talk to
            - ...
            - Is the Sig_CA legit for the combo "bob.com" || P_B?
                E(P_CA, Sig_CA) ==? H("bob.com" || P_B)
              If yes, then CA says "the real bob.com goes with this P_B"
                                    "the real bob.com has S_B"
        - The certificate is public, so Mal/Eve could have sent Bob's cert to Alice
        - Is Somebody Bob?
            alternatively: Is Somebody in control of S_B
          Send a random challenge X, force Somebody to sign it. Sig good? Yay,
            we will accept that Somebody is Bob

+ Homework questions
- ??
- WTH is going on with that bash command?

+ Project ideas?

+ SQL injection
- RDBMS, like postgresql
- SQL
- bad web programming
- ...