Encrypt a function in PE and decrypt in memory- C++

I want to keep an important function encrypted in the exe and while running the program, decrypt it at run time from memory. After execution of the function, I will encrypt it back in the memory (so that memory dump can't be analyzed).

I am able to decrypt and encrypt it in memory successfully. But I am not sure, keeping a function as encrypted in an exe is possible or not. If possible, how can I do it? I am trying to find the function offset and encrypt the function body. Keeping a function body encrypted will corrupt the exe? Please help me with suggestions. Below given is the memory encryption/decryption code:

<pre>void TestFunction()
{
	MessageBoxA(0, "This will be encrypted", "Test", 0);
}
void stubFunction()
{

}

static bool XORMemory(DWORD pStartAddr, int nLength)
{
	if (!pStartAddr || nLength <= 0)
		return false;

	unsigned char* p = (unsigned char*)(pStartAddr);
	p = p + 4;
	for (int i = 0; i < nLength; i++)
	{
		*p++ ^= 0x5A;
	}

	return true;
}