Secure Communications Over Insecure Channels
According to traditional conceptions of cryptographic
security, it is necessary to transmit 
a key, by secret means, before encrypted messages can
be sent securely.  This paper shows that it is 
possible to select a key over open communications channels
in such a fashion that communications security 
can be maintained.  A method is described which forces
any enemy to expend an amount of work which increases 
as the square of the work required of the two communicants
to select the key.  The method provides a 
logically new kind of protection against the passive
eaves dropper.  It suggests that further research 
on this topic will be highly rewarding, both
in a theoretical and a practical sense.
CACM April, 1978
Merkle, R.C.
