This book constitutes the thoroughly refereed post-conference proceedings of the workshop on Usable Security, USEC 2013, and the third Workshop on Applied Homomorphic Cryptography, WAHC 2013, held in conjunction with the 17th International Conference on Financial Cryptology and Data Security, FC 2013, in Okinawa, Japan. The 16 revised full papers presented were carefully selected from numerous submissions and cover all aspects of data security. The goal of the USEC workshop was to engage on all aspects of human factors and usability in the context of security. The goal of the WAHC workshop was to bring together professionals, researchers and practitioners in the area of computer security and applied cryptography with an interest in practical applications of homomorphic encryption, secure function evaluation, private information retrieval or searchable encryption to present, discuss, and share the latest findings in the field, and to exchange ideas that address real-world problems with practical solutions using homomorphic cryptography.