  Oblivious transfer is a primitive of paramount importance in cryptography or,
more precisely, two- and multi-party computation due to its universality.
Unfortunately, oblivious transfer cannot be achieved in an unconditionally
secure way for both parties from scratch. Therefore, it is a natural question
what information-theoretic primitives or computational assumptions oblivious
transfer can be based on.
  The results in our thesis are threefold. First, we present a protocol that
implements oblivious transfer from a weakened oblivious transfer called
universal oblivious transfer, where one of the two players may get additional
information. Our reduction is about twice as efficient as previous results.
  Weak oblivious transfer is an even weaker form of oblivious transfer, where
both players may obtain additional information about the other player's input,
and where the output can contain errors. We give a new, weaker definition of
weak oblivious transfer, as well as new reductions with a more detailed
analysis.
  Finally, we carry over our results to the computational setting and show how
a weak oblivious transfer that is sometimes incorrect and only mildly secure
against computationally bounded adversaries can be strengthened.
