### Fall 2001, CSE 597E: Quiz 9 and solution - 28 Nov 2001

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1. [2 points] What is the definition of one-way function (only one answer, please)

1. A function f whose inverse does not exist
2. A function f such that f(x) can be computed in polynomial-time and a probabilistic polynomial-time algoritm that tries to compute the inverse may succeed only with negligible probability
3. A function f such that f(x) can be computed in polynomial-time and such that the inverse is negligible
4. A function which can be computed only in one direction

2. [3 points] Describe how hash functions are used to authenticate messages

3. [2 points] Given a photon, what does a point in the Poincare' sphere represent? (only one answer, please)

1. The speed of the photon wrt the three spacial coordinates
2. Various phisical properties of the photon (energy, wave length, etc.)
3. The posizion in space of the photon
4. The state of polarization of the photon

4. [3 points] Let B and B' be two conjugate bases. Then (chcek each sentence which is true)

1. B and B' are orthogonal (differ by 90 degrees)
2. A photon polarized wrt B and measured in B' revel no information
3. Given a photon in an arbitrary state, the probability that it behaves as B plus the probability that it behaves as B' is 1.

Please list all the questions you asked during the presentation