This volume constitutes the refereed proceedings of two workshops: the Second International Workshop on Modern Cryptography and Security Engineering (MoCrySEn 2013) and the Third International Workshop on Security and Cognitive Informatics for Homeland Defense (SeCIHD 2013) held within the framework of the IFIP 8.4, 8.9, TC 5 International Cross-Domain Conference, CD-ARES 2013, in Regensburg, Germany, in September 2013. The 16 revised papers presented at MoCrySEn 2013 were carefully reviewed and selected from 30 submissions. They deal with symmetric-key cryptography, public-key cryptography,...