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**[2 points]**What is the definition of one-way function (only one answer, please)- A function f whose inverse does not exist
- 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
- A function f such that f(x) can be computed in polynomial-time and such that the inverse is negligible
- A function which can be computed only in one direction

**[3 points]**Describe how hash functions are used to authenticate messages**[2 points]**Given a photon, what does a point in the Poincare' sphere represent? (only one answer, please)- The speed of the photon wrt the three spacial coordinates
- Various phisical properties of the photon (energy, wave length, etc.)
- The posizion in space of the photon
- The state of polarization of the photon

**[3 points]**Let B and B' be two conjugate bases. Then (chcek each sentence which is true)- B and B' are orthogonal (differ by 90 degrees)
- A photon polarized wrt B and measured in B' revel no information
- 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