We consider a cryptographic scenario of two honest parties A and B facing an active eavesdropper E. They share no secret key initially but their final goal is to generate a shared information-theoretically secure key. We develop the special case represented in Maurer (1997) where a random binary string is broadcast by some center (like a satellite) over binary symmetric channels and received as X, Y, Z-strings with bit error probabilities /spl epsiv//sub A/, /spl epsiv//sub B/, /spl epsiv//sub E/ (/spl epsiv//sub A/