Recently, a secure key exchange technique was developed, in which both communicators (Alice and Bob) randomly select between two known resistors. By measuring the resulting thermal noise on a shared wire, they can each determine the resistor chosen by their counterpart, while the eavesdropper (Eve) cannot determine this. By repeating this transaction, they can create a common secure key, one bit a time. Although theoretically elegant, this approach is difficult to realize in practice. In this

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... practice. In this paper, we present a practical realization of a secure key exchange technique, intended for use over the Ethernet. Our approach is inspired by the above scheme with significant differences. In our approach, Alice and Bob utilize programmable resistors and exchange their resistance values securely. Our technique has been implemented in a hardware FPGA based platform, and was found to be able to exchange 4 secure bits per transaction over a 100ft CAT5 cable.