Mathematics, cryptography, and the real world

Among the many reactions to Neil Koblitz’ article on modern cryptography in the Notices of the AMS the most interesting reply I’ve read is this one by Steven Bellovin:

Mathematicians have known since Euclid that axioms are important.
Security, though, is math embedded in the real world, and that
matters. Put another way, Euclidean geometry is completely valid as a
pure mathematical system. But that doesn’t mean it applies in a
relativistic universe. Sure, we live far from any space-warping
masses, so we can pretend that the angles in our triangles add up to
180 degrees. In the security world, though, the attacker will toss a
black hole at us to warp the space around our provably-secure
triangular encryptor. Was that proof of security flawed? Ask Riemann
or Lobachevsky.