Covert communication allows us to transmit messages in such a way that it isnot possible to detect that the communication is occurring. This providesprotection in situations where knowledge that people are talking to each othermay be incriminating to them. In this work, we study how covert communicationcan be used for a different purpose: secret key expansion. First, we show thatany message transmitted in a secure covert protocol is also secret andtherefore unknown to an adversary. We then propose a protocol that uses covertcommunication where the amount of key consumed in the protocol is smaller thanthe transmitted key, thus leading to secure secret key expansion. We deriveprecise conditions showing that secret key expansion from covert communicationis possible when there are sufficiently low levels of noise for a givensecurity level. We conclude by examining how secret key expansion from covertcommunication can be performed in a computational security model.
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