## With Safari, you learn the way you learn best. Get unlimited access to videos, live online training, learning paths, books, tutorials, and more.

No credit card required

# Chapter 19. Returning to “Coin Flipping Over Telephone”

The first cryptographic protocol of this book, “Coin Flipping Over Telephone” (Prot 1.1), is specified using a “magic function” f. Let us recap two properties of this function (Property 1.1):

1. For every integer x, it is easy to compute f(x) from x while given any value f(x) it is impossible to find any information about a pre-image x, e.g., whether x is an odd or even number.

2. It impossible to find a pair of integers (x, y) satisfying x ≠ y and f(x) = f(y).

So far, this “magic function” remains magic. No supporting evidence for the two uses of the word “impossible” has been provided, let alone the provision of a concrete realization of the function (and hence of Prot 1.1).

In fact, in ...

## With Safari, you learn the way you learn best. Get unlimited access to videos, live online training, learning paths, books, interactive tutorials, and more.

No credit card required