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Polymorphic algorithms make it difficult for such software to recognize the offending code because it constantly mutates. Malicious programmers have sought to protect their encrypted code from this virus-scanning strategy by rewriting the unencrypted decryption engine (and the resulting encrypted payload) each time the virus or worm is propagated.
The C++ examples in this section demonstrate the principle of using composition and interfaces to achieve code reuse and polymorphism. Due to the C++ language not having a dedicated keyword to declare interfaces, the following C++ example uses inheritance from a pure abstract base class.
A polymorphic engine (sometimes called mutation engine or mutating engine) is a software component that uses polymorphic code to alter the payload while preserving the same functionality. Polymorphic engines are used almost exclusively in malware , with the purpose of being harder for antivirus software to detect.
Templates in C++ provide a sophisticated mechanism for writing generic, polymorphic code (i.e. parametric polymorphism). In particular, through the curiously recurring template pattern, it is possible to implement a form of static polymorphism that closely mimics the syntax for overriding virtual functions.
Self-modifying code is also sometimes used by programs that do not want to reveal their presence, such as computer viruses and some shellcodes. Viruses and shellcodes that use self-modifying code mostly do this in combination with polymorphic code. Modifying a piece of running code is also used in certain attacks, such as buffer overflows.
Polymorphism can be distinguished by when the implementation is selected: statically (at compile time) or dynamically (at run time, typically via a virtual function). This is known respectively as static dispatch and dynamic dispatch, and the corresponding forms of polymorphism are accordingly called static polymorphism and dynamic polymorphism.
The curiously recurring template pattern (CRTP) is an idiom, originally in C++, in which a class X derives from a class template instantiation using X itself as a template argument. [1] More generally it is known as F-bound polymorphism, and it is a form of F-bounded quantification.
The code makes a polymorphic call on {SURFACE}.draw indirectly by way of the `drawing_agent', which is the first call (dispatch) of the double-dispatch pattern. It passes an indirect and polymorphic agent (`drawing_data_agent'), allowing our visitor code to only know about two things: