I want to create a program, which can encrypt and decrypt a complete file with an individual password. Is there any way to manage this in Qt and/or C++ and how?
I've never used it myself, but I've heard great things about QCA. It's cross platfrom, uses a Qt-style API and Qt datatypes.
www.cryptopp.com is a very complete C++ library with implementations of most algorithms.
The actual program (select file, read, obtain key, encrypt etc) should be piece of cake.