This volume constitutes the refereed proceedings of the 11th IFIP WG 11.2 International Conference on Information Security Theory and Practices, WISTP 2017, held in Heraklion, Crete, Greece, in September 2017. The 8 revised full papers and 4 short papers presented were carefully reviewed and selected from 35 submissions. The papers are organized in the following topical sections: security in emerging systems; security of data; trusted execution; defenses and evaluation; and protocols and algorithms.