SystemsSec 2018W Lecture 14

Audio

Lecture 14 audio.

Notes Student 1

► Many strategies are wrong: If there is one single bug in any major system we use, everything falls apart

► We can do better, but the way we do things now is not sustainable

→ Existence proof: Biology

1. Everything starts with a random process

2. How do biology systems protect itself again adversaries?

ANIMALS

• Animals face threats (ie. Falls of cliff, gets eaten)

• Threats from really small things (huge factor in mortality, ie. humans lifespan doubled because of disease control):

→ They see the animal as a resource, so why not use it?

→ Most important defence: Barrier defence

- Skin

→ But we can't keep everything out: Basic chemistry

- Stomach acid to react with what came into your body

- Digestive enzymes (enzyme: biological catalyst) breaks down proteins

• Analogies:

DNA = "Stored code"

→ Backbone = "Framework"

Proteins = "Running code"

T-cells = Has randomized detectors to find bad things. If binded to a regular cell, gets killed

→ Auto-immune disease

- T-cell recognizes some behaviour and reacts with it

- To prevent mistakes (ie. autoimmune disease)

○ Only battles when there is evidence cells are dying

VIRUSES

• Chunk of DNA/RNA (in between DNA/RNA and proteins) surrounded by proteins
• When comes in contact with cell, injects DNA into cell

- Overflow cell (cell running malicious code) until it explode, and continue to other cells

-Cells have vulnerabilities

□ Viruses targets fact that cells have semi-permeable membranes

- Defence

□ Cells have different membranes

IMMUNE SYSTEM

• Regular proteins will output certain peptide, immune system checks if its the right one

- Virus imitates the protein

• Red, hot: Immune system discovered dead cells and investigates
• Incompatible MHC: Organ rejects new organ

DIGESTIVE SYSTEM

• When your good bacteria turns bad, fecal transplant

The body is not an engineering system: Separation of concern is not there, they are all just cells.

Notes Student 2

Assignment now due March 5th Midterm postponed to March 7th

Using biology as an existence proof:

• The code inside you was generated by random code

In computer security, we are engaged in evolution

• The system's survival depends on evolution
• As adversary adapts, leads to new defenses

ANIMALS

Each animal has risks to survival: getting attacked, missing food

• There are also risks from really small things (which is a huge factor in mortality):
  • Think about why the human lifespan has doubled? Because we are getting infectious diseases under control
• The small thing sees the animal as home (animal = set of resources)
  • It's not necessarily malicious, it's a mobile place to live and eat

Animals need to have defences

• Barrier: skin → this is a physical layer
• Acid (stomach) → this is chemical, it'll just react with whatever comes into the body
• Digestive enzymes
  • Enzyme = biological catalyst, something that changes the rate of a reaction
  • Digestive enzymes = breaks down protein

You are made up of the following, and this is how it relates to computer science:

• DNA = stored code
  • Control code, and the patterns for the protein
  • Chain of 4-letters
• RNA
  • Carbohydrates
  • Protein = running code
• Made up of chains of 20 amino acids

Peptide = 6-10 amino acid chain

VIRUSES

What is a biological virus?

• A chunk of DNA or RNA surrounded by a coat of protein
• Gets into a cell and forms a virus
• The cell membrane should block this, but it has vulnerabilities
• One of the fundamental ways we are protected against this: cells are all a little different in what they allow and don't allow in (so not everyone would die from the same virus)

Immune system

• Made up of cells like the rest of your body
• When the virus has infected a cell, it runs malicious code inside the cell
• Problem: immune system needs a way of knowing what's going on inside a cell, but they can't puncture the cell
• Solution: the immune system looks at the cell's behaviour, puts the peptides on the outside of the cell
• Think in evolutionary terms, how would the virus try and get around this: make its proteins out of the same peptides as the one's you're trying to infect

Major Histocompatibility Complex (MHC)

• Found on the surfaces of cells, so immune system can recognize foreign substances
• In computer science terms: deals with the problem of recognizing malicious code
• This matters for things like organ transplant
• If you're getting a transplant from someone with incompatible MHC, you're immune system with attack the organ

How does this fit in with what we're talking about this term?

• Central problem of today's attacks: if I can find the vulnerability in one host, I can infect millions of others that are running the same thing

T-cells

• Not self-reactive
• Finds the bad small things
• Once the t-cells are release to circulate in the bloodstream, they are going to see patterns they haven't seen in testing
• How do you make sure these patterns do not cause an auto-immune disease?