  In this paper we show that the existence of general indistinguishability
obfuscators conjectured in a few recent works implies, somewhat
counterintuitively, strong impossibility results for virtual black box
obfuscation. In particular, we show that indistinguishability obfuscation for
all circuits implies:
  * The impossibility of average-case virtual black box obfuscation with
auxiliary input for any circuit family with super-polynomial pseudo-entropy.
Such circuit families include all pseudo-random function families, and all
families of encryption algorithms and randomized digital signatures that
generate their required coin flips pseudo-randomly. Impossibility holds even
when the auxiliary input depends only on the public circuit family, and not the
specific circuit in the family being obfuscated.
  * The impossibility of average-case virtual black box obfuscation with a
universal simulator (with or without any auxiliary input) for any circuit
family with super-polynomial pseudo-entropy.
  These bounds significantly strengthen the impossibility results of Goldwasser
and Kalai (STOC 2005).
