Abstract. We show that some problems in information security can be solved with-
out using one-way functions. The latter are usually regarded as a central concept of
cryptography, but the very existence of one-way functions depends on di±cult con-
jectures in complexity theory, most notably on the notorious P 6= NP" conjecture.
This is why cryptographic primitives that do not employ one-way functions are often
called unconditionally secure".
In this paper, we suggest protocols for secure computation of the sum, product,
and some other functions of two or more elements of an arbitrary constructible ring,
without using any one-way functions. A new input that we o®er here is that, in
contrast with other proposals, we conceal intermediate results" of a computation.
For example, when we compute the sum of k numbers, only the ¯nal result is known
to the parties; partial sums are not known to anybody. Other applications of our
method include voting/rating over insecure channels and a rather elegant and e±cient
solution of the wo millionaires problem".
Then, while it is fairly obvious that a secure (bit) commitment between two parties
is impossible without a one-way function, we show that it is possible if the number
of parties is at least 3. We also show how our unconditionally secure (bit) commit-
ment scheme for 3 parties can be used to arrange an unconditionally secure (bit)
commitment between just two parties if they use a dummy" (e.g., a computer) as
the third party. We explain how our concept of a dummy" is di®erent from a well-
known concept of a rusted third party". Based on a similar idea, we also o®er an
unconditionally secure k-n oblivious transfer protocol between two parties who use a
dummy".
We also suggest a protocol, without using a one-way function, for the so-called
mental poker", i.e., a fair card dealing (and playing) over distance.
Finally, we propose a secret sharing scheme where an advantage over Shamir's
and other known secret sharing schemes is that nobody, including the dealer, ends
up knowing the shares (of the secret) owned by any particular player.
It should be mentioned that computational cost of our protocols is negligible to
the point that all of them can be executed without a computer.