new PE section

#include <stdio.h>
#include <windows.h>

DWORD align(DWORD size, DWORD align, DWORD addr){
    if (!(size % align))
        return addr + size;
    return addr + (size / align + 1) * align;
}

bool AddSection(char *filepath, char *sectionName, DWORD sizeOfSection){
    HANDLE file = CreateFile(filepath, GENERIC_READ | GENERIC_WRITE, 0, NULL, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, NULL);
    if (file == INVALID_HANDLE_VALUE)
        return false;
    DWORD fileSize = GetFileSize(file, NULL);
    //so we know how much buffer to allocate
    BYTE *pByte = new BYTE[fileSize];
    DWORD dw;
    //lets read the entire file,so we can use the PE information
    ReadFile(file, pByte, fileSize, &dw, NULL);

    PIMAGE_DOS_HEADER dos = (PIMAGE_DOS_HEADER)pByte;
    if (dos->e_magic != IMAGE_DOS_SIGNATURE)
        return false; //invalid PE
    PIMAGE_FILE_HEADER FH = (PIMAGE_FILE_HEADER)(pByte + dos->e_lfanew + sizeof(DWORD));
    PIMAGE_OPTIONAL_HEADER OH = (PIMAGE_OPTIONAL_HEADER)(pByte + dos->e_lfanew + sizeof(DWORD)+sizeof(IMAGE_FILE_HEADER));
    PIMAGE_SECTION_HEADER SH = (PIMAGE_SECTION_HEADER)(pByte + dos->e_lfanew + sizeof(IMAGE_NT_HEADERS));

    ZeroMemory(&SH[FH->NumberOfSections], sizeof(IMAGE_SECTION_HEADER));
    CopyMemory(&SH[FH->NumberOfSections].Name, sectionName, 8);
    //We use 8 bytes for section name,cause it is the maximum allowed section name size

    //lets insert all the required information about our new PE section
    SH[FH->NumberOfSections].Misc.VirtualSize = align(sizeOfSection, OH->SectionAlignment, 0);
    SH[FH->NumberOfSections].VirtualAddress = align(SH[FH->NumberOfSections - 1].Misc.VirtualSize, OH->SectionAlignment, SH[FH->NumberOfSections - 1].VirtualAddress);
    SH[FH->NumberOfSections].SizeOfRawData = align(sizeOfSection, OH->FileAlignment, 0);
    SH[FH->NumberOfSections].PointerToRawData = align(SH[FH->NumberOfSections - 1].SizeOfRawData, OH->FileAlignment, SH[FH->NumberOfSections - 1].PointerToRawData);
    SH[FH->NumberOfSections].Characteristics = 0xE00000E0;
    /*
        0xE00000E0 = IMAGE_SCN_MEM_WRITE |
                     IMAGE_SCN_CNT_CODE  |
                     IMAGE_SCN_CNT_UNINITIALIZED_DATA  |
                     IMAGE_SCN_MEM_EXECUTE |
                     IMAGE_SCN_CNT_INITIALIZED_DATA |
                     IMAGE_SCN_MEM_READ
    */
    SetFilePointer(file, SH[FH->NumberOfSections].PointerToRawData + SH[FH->NumberOfSections].SizeOfRawData, NULL, FILE_BEGIN);
    //end the file right here,on the last section + it's own size
    SetEndOfFile(file);
    //now lets change the size of the image,to correspond to our modifications
    //by adding a new section,the image size is bigger now
    OH->SizeOfImage = SH[FH->NumberOfSections].VirtualAddress + SH[FH->NumberOfSections].Misc.VirtualSize;
    //and we added a new section,so we change the NOS too
    FH->NumberOfSections += 1;
    SetFilePointer(file, 0, NULL, FILE_BEGIN);
    //and finaly,we add all the modifications to the file
    WriteFile(file, pByte, fileSize, &dw, NULL);
    CloseHandle(file);
    return true;
}

bool AddCode(char *filepath){
    HANDLE file = CreateFile(filepath, GENERIC_READ | GENERIC_WRITE, 0, NULL, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, NULL);
    if (file == INVALID_HANDLE_VALUE)
        return false;
    DWORD filesize = GetFileSize(file, NULL);
    BYTE *pByte = new BYTE[filesize];
    DWORD dw;
    ReadFile(file, pByte, filesize, &dw, NULL);
    PIMAGE_DOS_HEADER dos = (PIMAGE_DOS_HEADER)pByte;
    PIMAGE_NT_HEADERS nt = (PIMAGE_NT_HEADERS)(pByte + dos->e_lfanew);

    //since we added a new section,it must be the last section added,cause of the code inside
    //AddSection function,thus we must get to the last section to insert our secret data :)
    PIMAGE_SECTION_HEADER first = IMAGE_FIRST_SECTION(nt);
    PIMAGE_SECTION_HEADER last = first + (nt->FileHeader.NumberOfSections - 1);

    SetFilePointer(file, last->PointerToRawData, NULL, FILE_BEGIN);
    char *str = "ATHENIAN WAS HERE";
    WriteFile(file, str, strlen(str), &dw, 0);
    CloseHandle(file);
    return TRUE;
}

void main()
{
    if (AddSection("C:\\Users\\M\\Desktop\\Athena.exe", ".ATH", 400)){
        printf("Section added!\n");
        //Lets insert data into the last section
        if (AddCode("C:\\Users\\M\\Desktop\\Athena.exe")){
            printf("Code written!\n");
        }
        else
            printf("Error writting code!\n");
    }
    else
        printf("Error adding section!\n");
}