1. Difficult. The El-Gamel system was the most confusing, just because it's new to me right now. After reading the section a couple times it is beginning to make sense. The security comes from Eve not being able to find $a$ when $\beta = \alpha^a \pmod{p}$, for given $(\alpha, \beta, p)$. The security hole when the same value of $k$ is used twice makes sense.
2. Interesting: I liked the section 9.4 on birthday attacks on signatures, that it's possible to find repeats in the hashes by possibly making many insignificant changes in the document. I also liked the way to foil this plan, by changing the document slightly. Anyways.
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