CS 120/ E-177: Introduction to Cryptography
Salil Vadhan and Alon Rosen Dec. 18, 2006
Lecture Notes 22:
Conclusions
1 What to take away
How to think about cryptographic problems
precisely
.
•
Command of basic cryptographic notions encryption, one-way functions, pseudorandom
generators, MACs, etc.
•
Dening security
Adversary's goal
Probability
of success
Adversary's computational resources
Adversary's access to system and the communication model
Conservative approach
•
Constructions
Build complex cryptographic objects from simpler objects/assumptions.
Justify via
reductions.
Always analyze wrt success probability.
Stated asymptotically, but can be analyzed concretely
•
Some Q's to ask yourself when encountering a new cryptographic protocol:
What are we trying to achieve?
What are the building blocks? And what are reasonable assumptions about them?
Do the assumptions about the building blocks provably imply security of the protocol? If
not, are the building blocks at least being used in a way intuitively appropriate to their
properties?
•
Assumptions we have used
complexity assumptions (stronger than
P6=NP
, e.g. one-way functions)
adversary's computational resources
one protocol running over single communication line, with passive or active adversary in
between
public keys readily available
secret keys truly secret, generating using perfect random bits
party = algorithm = black box mapping inputs to outputs
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