Lecture 11: 16th October 2019

Question 1

What is x.509?

Answer 1

A standard for the format of public key certificates used in many Internet protocols

Question 2

How can we implement private comms on the Internet?

Answer 2

We need to make protocols that ensure the source and destination IP addresses and ports and the message body of packets are unreadable

Question 3

Where can secure comms be implemented in the 5-layer model?

Answer 3

any point

Question 4

How does security impact network load?

Answer 4

Increases load by ~80-90% due to greater number of packets

Question 5

What is a MAC?

Answer 5

MAC = message authentication code = A short piece of data attached to messages to authenticate them generated from a keyed hash function using the message data and a symmetric key known to the sender and receiver.

Question 6

What are MACs aka?

Answer 6

MIC and tag

Question 7

What are session keys?

Answer 7

Single-use randomly generated symmetric keys used for encrypting communications between two hosts over the course of one connection. They limit the legibility of the messages to only themselves during that session.

Question 8

What is SSL?

Answer 8

SSL = Secure Sockets Layer = A protocol that enables encrypted communications over a network (the Internet). SSL is at the transport layer, sitting on top of TCP, and provides an application interface for secure and encrypted communications

Question 9

Where is SSL on the layered model?

Answer 9

the transport layer

Question 10

How does SSL work?

Answer 10

SSL has normal process of handshake/data exchange/close but also includes choosing the cipher suite and keys in the handshake so that from then all communications are encrypted and secure

Question 11

What is SSL’s flow of control?

Answer 11

TCP handshake:

• A to B : syn (synchronise)
• B to A : syn OK
• A to B : syn OK ack

then comms

TCP FIN:
- A to B: Fin
- B to A: Fin Ack
(or other way around)

Handshake and fin are unencrypted. Cipher suite choosing and key exchange in “comms” section above, but immediately after handshake

Question 12

What is a nonce?

Answer 12

“number only once”: random number used to identify a communications exchange and establish secure communications; ~ a session key

Question 13

How are nonces involved with SSL handshakes?

Answer 13

Server sends a nonce back to client with certificate and cipher suite choice

Question 14

How are ciphers agreed in SSL handshakes?

Answer 14

Client tells server which algorithms it supports; server chooses an algorithm from the list and sends choice

Question 15

What are some vulnerabilities in HTTPS?

Answer 15

Heartbleed in the past; incorrect usage leads to vulnerabilities; anyone can get CAs; breaches in any CA affects them all and all of them can make a certificate for any site

Question 16

What is the difference between HTTPS, SSL, TLS, and STARTTLS?

Answer 16

HTTPS = an extension of HTTP implementing secure communication over a computer network that is widely used on the Internet. In HTTPS, the communication protocol is encrypted using TLS or, formerly, its predecessor, SSL

SSL = Secure Sockets Layer = A protocol that enables encrypted communications over a network (the Internet). SSL is at the transport layer, sitting on top of TCP, and provides an application interface for secure and encrypted communications

TLS = A cryptographic protocol implementing secure, encrypted communications over a network. It is at the transport and session layer and is on top of TCP, again providing an application interface for secure and encrypted communications

STARTTLS = An extension to SMTP facilitates secure and encrypted communications between SMTP clients and servers. Tries to use TLS and falls back to SSL.

Question 17

What is the weakest-link problem with CAs?

Answer 17

The fact that any CA can issue a certificate for any site, a breach in 1 affects all their certificates and all other CAs

Question 18

Why do cookies present a security vulnerability?

Answer 18

Set-cookie allows inspection and alteration of a user’s cookie data by a server

Question 19

Why do forms on websites present security vulnerabilities?

Answer 19

You can pass scripts to servers in input elements to make them execute. GET requests include parameters in the URL in plaintext, POST requests need a max length, and PHP is susceptible to SQL injections and needs filter sanitising

Question 20

What is filter sanitising?

Answer 20

Removing certain characters to stop inputs being executable script statements

Question 21

What are SQL injection attacks?

Answer 21

Using web page inputs to insert SQL statements into a server to execute and perform some malicious actions

Question 22

How can you use forms to execute JS code?

Answer 22

Put escaped JS code into form inputs to possibly get processed and executed

Question 23

What is cross-site scripting?

Answer 23

Cross-site scripting (XSS) is when attackers inject client-side scripts into trusted web pages viewed by other users.

Question 24

How can HTML source code allow footprinting?

Answer 24

Looking at artefacts such as comments, TODOs, etc. might give you clues as to the architecture of the site that may allow you to design a viable attack.

Question 25

What is session hijacking?

Answer 25

The exploitation of a valid computer session - session key - to gain the ability to authenticate themselves as a different user connected to a server in a session.

Question 26

What is HTTP response splitting?

Answer 26

When an attacker alters the HTTP responses given by a server to include false endings within their header so the actual response body is ignored, instead returning a payload determined by the attacker. This allows the attacker to include an abrtirary number of headers in a response or even send multiple.

Question 27

What is cache poisoning?

Answer 27

When a malformed HTTP response, generated by an attacker, is served to multiple users from a web cache until the cache entry from that response is destroyed.

Question 28

What are the 5 steps in assessing a web service?

Answer 28

1. Identify the web service running – look at HTTP head or use WebServerFP or hmap type tools
2. Identify subsystems and enabled components (extensions, verified and unverified components) such as ASP.NET, Frontpage, PHP,
   OpenSSL, IIS ISAPI extensions.
3. Investigate known vulnerabilities in web services – MITRE, CVE, metasploit tools etc for lists or tools such as N-Stealth, nkito (Linux)
4. Identify poorly constructed or protected sensitive data – poor HTTP authentication, URL query strings
5. Assess CGI, ASP etc scripts – look for parm manipulation, filter evasion, patch regularly. Some assessment tools are available such as Achilles, Exodus, WebSleuth.

Question 29

What are some issues with email services?

Answer 29

Emails have suffered from trojans, vurises, hoaxes and of course spam.

Encryption can be done through PGP (Pretty Good Privacy) or S/MIME (Secure/Mutipurpose Internet Mail Extensions) which was designed to support Internet email. Both are used for Outook, Eudora etc and allow end-to-end security.

Question 30

How do the transit problems with Internet traffic apply to email?

Answer 30

1. interception - some organisations protect email up to the edge of the network, and some may copy all emails (legal or government companies) as email are evidence or legal documents
2. monitoring - some organisations monitor email for business patterns or for information disclosure. Some companies state they have the right to access email at any time.
3. anonymisation - some companies (Yahoo, Hotmail) offer free email addresses which can be treated as once use disposable emails.
4. remailers - these are 3rd party mailers who forward email onto a designated recipient. The third party keeps detailed records to allow forwarding in both directions to recipient and sender. Essentially this is not anonymity but pseudonimity. However, a TOR like setup can allow a series of co-operating servers to hide sender details under asymmetric encryption.
5. spoofing- the SMTP protocol does not check for legitimacy or accuracy. (See https://tools.ietf.org/html/rfc821 or rfc7435)

Question 31

What is STARTTLS?

Answer 31

An extension to SMTP facilitates secure and encrypted communications between SMTP clients and servers. Tries to use TLS and falls back to SSL.

Question 32

How does STARTTLS work?

Answer 32

STARTTLS encrypts a session after it is established. After an SMTP session is initiated an email server lists the services or features it supports. If encryption is not available then the unencrypted transfer of data will occur. it tries to with TLS at first then falls back to SSL.

Question 33

What is STARTTLS stripping?

Answer 33

This attack takes advantage of the fail-open design of STARTTLS, that is, the SMTP servers using cleartext if the STARTTLS handshake fails. Like many security mechanisms, STARTTLS is designed to “fail open” rather than “fail closed,” meaning that when certain errors happen, servers will simply send e-mail in unencrypted form rather than failing to send the message at all. Network actors can exploit this design by sending certain types of packets that trigger a fail-open error.

Question 34

What are some remaining issues with security on the web despite the use of encryption and certificates?

Answer 34

Privacy from looking at headers even if encrypted; easy to get SSL certificate; exploits and vulnerabilities in site backends; exploits (injections) from web browsers; exploits from URL parameters, etc

Question 35

What are X.509 certificates composed of?

Answer 35

unique ID; subject; signature algorithm used; signature; issuer; valid from; valid until; key-usage (how to use public key); public key; thumbprint algorithm; thumbprint.

Question 36

What are some security issues associated with databases?

Answer 36

1. Access Control: restriction levels of read, write (update). Delete must be at admin level.
2. Authentication: Pre phase of authentication needed for access.
3. Physical DB integrity: power failures, disc failure etc should not affect the data.
4. Logical DB integrity: The structure of the DB is preserved after data modification (no loss of fields, keys etc).
5. Auditability: for forensic or legal reasons as well as reconstruction.
6. Two phase update: designed to prevent problems during update (long intent phase and then commit phase when commit flag is set)