Lecture 3 Flashcards
What is important for pseudo random generators value distribution?
They should generate a roughly even number of 0s and 1s.
What is the advantage of a statistical test against a pseudo random generator?
Its chance of predicting the key vs the chance of it successfully picking a random key. This will be 1 if the pseudo random generator is generating keys that seem random, or closer to 0 if not.
What is the non deterministic polynomial algorithm for solving keys? What does this mean for proving pseudo random generators?
We can simply guess the key, as such the secureness of a pseudo random generator cannot be proven.
How does a Merkle puzzle work?
the senders sends a large number of small encrypted texts with unknown(but short keys) the receiver brute forces one and then tells the sender publicly what the package number(contained inside with key) was, the key from inside is then used. The eavesdropper will know the number, but not the key.
What does semantic security involve?
An adversary gives two messages, you encode one and return it, if the adversary can guess which message is encoded better than half the time something is rong with our pseudo random generator.
How does Diffie-Hellman key exchange work?
Alice and Bob publicly agree on a large prime p(Several thousand bits), and a primitive root g modulo p.
Alice randomly chooses 2 <= a <= p - 2 and transmits ga(mod p).
Bob randomly chooses 2 <= b <= p - 2 and transmits gb(mod p).
Alice computes (gb)a and Bob computes (ga)b.
They hash this value to get the key.
This means Eve has ga, and gb, gab cannot be computed from just these.
What is the idea of public key encryption? How does this relate to trapdoor functions?
Uses a separate key for encryption and decryption. The encryption key is public, but the decryption key is only held at one end, this can be used to hide a secret stream cipher key.
A trapdoor function is a randomised algorithm that outputs a key pair, one is the public, and one is secret
