  The HTTPS protocol has enforced a higher level of robustness to several
attacks; however, it is not easy to set up the required certificates on
intranets, nor is it effective in the case the server confidentiality is not
reliable, as in the case of cloud services, or it could be compromised. A
simple method is proposed to encrypt the data on the client side, using Web
Assembly. It never transfers data to the server as clear text. Searching fields
in the server is made possible by an encoding scheme that ensures a stable
prefix correspondence between ciphertext and plaintext. The method has been
developed for a semantic medical database, and allows accessing personal data
using an additional password while maintaining non-sensitive information in
clear form. Web Assembly has been chosen to guarantee the fast and efficient
execution of encrypting/decrypting operations and because of its characteristic
of producing modules that are very robust against reverse engineering. The code
is available at https://github.com/mfalda/client-encdec.
