Weak bounded arithmetic, the Diffie-Hellman problem and Constable's Class K

The bounded arithmetic theory C/sub 2//sup 0/, which is closely related to the complexity class DLogTime-uniform TC/sup 0/, is extended by a function symbol and axioms for integer division, which is not known to be in DLogTime-uniform TC/sup 0/. About this extended theory C/sub 2//sup 0/[div], two main results are proved: (1). The Z/sub 1//sup b/-definable functions of C/sub 2//sup 0/[div] are exactly Constable's class K, a function algebra whose precise complexity-theoretic nature is yet to be determined. This also yields the new upper bound K/spl sube/uniform NC/sup 2/. (2). The /spl Delta//sub 1//sup b/-theorems C/sub 2//sup 0/[div] do not have Craig-interpolants of polynomial circuit size, unless the Diffie-Hellman key exchange protocol is insecure.