# Introduction to Security
> *All satisfied with their seats? O.K. No talking, no smoking, no
> knitting, no newspaper reading, no sleeping, and for God's sake take
> notes.* —Vladimir Nabokov
**November 2, 1988:** Robert Tappan Morris, Jr. released the "great
worm." (His dad, Bob Morris, was chief scientist at NSA's National
Computer Security Center.) This was the first worm; the first malware to
get media attention; and the first conviction under the Computer Fraud
and Abuse Act. Morris was 23 years old, and a first year grad student at
Cornell. (He released the worm from MIT, though.) He later claimed the
worm's purpose was to measure size of Internet, but the immediate effect
was denial of service (DoS). The Internet "came apart" as hosts were
overloaded by invisible processes. System admins had to disconnect from
the network to isolate their systems from infection. The US GAO later
estimated the cost of recovery was somewhere in $100k to $10m. Morris
was tried in US District Court. His sentence: 3 years probation, 400
hours community service, and a $13k fine. In 1999, he received a PhD
from Harvard. And now he's a professor at MIT.
**June 1, 2012:** The *New York Times* reports that the US and Israel
created Stuxnet, the first (publicly known) cyberweapon. Its provenance
was initially unknown. The weapon first infects Windows systems, then
subsequently infects an industrial control device, causing it to vary
the frequency of its motor and do physical harm. But, the weapon hides
that frequency change from the device's monitoring system, so that the
harm won't be noticed until it's too late. The purpose of the weapon
seemed to be destruction of centrifuges in Iranian uranium enrichment
**Today,** security is
- *hard:* we don't (fully) know how to accomplish it,
- *interesting:* involves lots of cool ideas, and
- *important:* society depends on computers, hence their security.
That's what makes this such a fun field of study.
### Defining security
A computer system is *secure* when it
- does what it should
- and nothing more.
A *security policy* stipulates what should and should not be done.
Policies can be long English documents, mathematical axioms, etc. But
almost everyone agrees that security policies are formulated in terms of
three basic *aspects* of security: confidentiality, integrity,
Protection of assets from unauthorized disclosure. Assets could be
information, or resources. Disclosure must be to someone; that might
be a person, a program, another computer system, etc. To generalize
those entities, define a *principal* to be any entity that can take
actions. So, confidentiality is about which principals are allowed
to learn what. *Secrecy* is synonymous with confidentiality.
- keep contents of file from being read. (Access control.)
- keep value of variable secret. That's harder, needs compiler/runtime
support. (Information flow.)
- keep behavior of system secret. Even harder: suppose
system load goes up when system is processing secret
information. Anyone on system can observe load. (Covert
- keep information about an individual secret. Hard these
days with lots of databases. Can be linked against one another,
new information extracted. Gender, DOB, ZIP uniquely identify
about 99% of people in Cambridge, MA. (Database privacy.)
*Privacy* is the confidentiality of identifying information about
individuals, which could be people, organizations, etc. Sometimes
privacy is construed as legal right. Don't say "keep information
private" unless you really mean that the information is about an
individual and is identifying. (**All your vocabulary are belong to
Protection of assets from unauthorized modification. I.e., what
changes are allowed to system and its environment. Changes can
include initial sources, hence provenance. The environment can
- output is correct according to a mathematical
- no exceptions are thrown.
- resource consumption is bounded.
- only certain principals are allowed to write a file.
- data are not corrupted or tainted by downloaded programs.
Protections of assets from loss of use. Denial of service (DoS)
attacks typically cause violations of availability properties.
- system must accept inputs periodically (OS doesn't
- produce output by specified time (program terminates)
- process requests fairly (order received, priority, etc.)
For each of the following attacks, what is a policy that the
attack violates? What aspect of security does that policy address?
1. Gina forges Roger's signature on a deed.
2. Rhonda registers the domain name cupress.com and refuses to let
Cornell’s publication house, Cornell University Press, use that
domain name unless Cornell buys the domain name from her.
3. Jonah obtains Peter’s credit card number and has the bank cancel
the card and replace it with another card bearing a different