Cryptag - Encrypted, taggable, searchable cloud storage

CrypTag is an idea, a spec, an API, and a piece of software that makes it easy to build a zero-knowledge system, which means that the server holding user data doesn't know what it is (since it's encrypted).

It is meant as a primitive to be used to build more sophisticated systems that would rather not re-implement the pieces necessary to build a zero-knowledge system, but several useful command line applications have been built with it so far, namely cput (for encrypting/saving files), cget (for fetching/decrypting files), and cpass (CryptPass, a password manager).