1. 
   Challenge-Response
   A security procedure in which one communicator requests authentication of another communicator, and the latter replies with a pre-established appropriate reply.
   Found op http://www.encyclo.co.uk/visitor-contributions.php
   
   
2. 
   Challenge-Response
   (In topic `Security`) Challenge/Response is an authentication process that verifies an identity by requiring correct authentication information to be provided in response to a challenge.
   Found op http://www.it-architects.co.uk/a_-_z_glossary_index/Security_Glossary_/secu
   
   

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