The encryption is a technology that transforms former data, and prevents the meaning being understood.
However, being possible to return it in not understanding the meaning because it is meaningless is assumption.
It is called a decryption to return it to former data, and calls former data a plaintext.

The encryption is intended because data is not naturally stolen by the third party.
Therefore, code strength is valued unlike other algorithms as for above all.
As for the algorithm deciphered easily no matter how it is high-speed, the usage is limited.

For instance, if CAESAR (Caesar) is moved by one character, it becomes DBFTBS.
If this is moved to the direction oppositely by one character, former CAESAR can be derived.

The following program applies this to a general binary file.

[   Directions   ]
CodeCaesar (input file name, output file name, and password);
- The password is made a numerical value within the range of 0-255.
- If the password is made the number of minuses, it is possible to decode.

 void CodeCaesar(char finame[],char foname[],int key)  
{

	FILE *fi,*fo;  
	int value;  

	fi = fopen(finame,"rb");  
	if (fi == NULL) return;  fo = fopen(foname,"wb");  
	if (fo == NULL) return;  
	
	while ((value = getc(fi)) != EOF) { 
		putc(value + key,fo); 
	}
	
	fclose(fi);  
	fclose(fo);

}

The Caesar code is easily deciphered because it is simple.
Then, use the exclusive-OR to make it to cramped a little more.

[   Exclusive-OR   ]
When the same number is input by calculating the binary number, the output becomes 0.

The following program applies this to a general binary file.

[   Directions   ]
CodeExor (input file name, output file name, and password);
- The password is made a numerical value within the range of 0-255.
- It is possible to decode by the same password.

 void CodeExor(char finame[],char foname[],int key)  
{

	FILE *fi,*fo;  
	int value;  

	fi = fopen(finame,"rb");  
	if (fi == NULL) return;  fo = fopen(foname,"wb");  
	if (fo == NULL) return;  
	
	while ((value = getc(fi)) != EOF) { 
		putc(value ^ key,fo); 
	}
	
	fclose(fi);  
	fclose(fo);

}

The decipherment is easy because there are only 256 kinds of passwords in a current encryption.
Then, a longer password should be able to be used.

The idea is simple. Only have to use two or more numerical values repeatedly.
The following program applies this to a general binary file.

[   Directions   ]
CodeExor (input file name, output file name, and password character string);
- The password can specify the character string of arbitrary length.
- It is possible to decode by the same password.

 void CodeExorLong(char finame[],char foname[],char key[])  
{

	FILE *fi,*fo;  
	int value,i = 0;  

	fi = fopen(finame,"rb");  
	if (fi == NULL) return;  fo = fopen(foname,"wb");  
	if (fo == NULL) return;  
	
	while ((value = getc(fi)) != EOF) { 
		putc(value ^ key[i],fo); 
		i++;  
		if (key[i] == '\0') i = 0;  
	}
	
	fclose(fi);  
	fclose(fo);

}

Because the same deal keeps being returned in the quasi-random number if an initial value is the same
Whenever an initial value is set from the password, the same calculation result is obtained.

[ Algorithm of   random numbers   ]
If the compiler is different, the random numbers algorithm of a standard library is also different.
Therefore, the numerical result is different in a different compiler.
It is necessary to make the algorithm of random numbers for myself to prevent this.

[   Directions   ]
CodeExorRandom (input file name, output file name, and password character string);
- The password can specify the character string of arbitrary length.
- It is possible to decode by the same password.

 int GetRandom(int min,int max)  
{
	return min + (int)(rand()*(max-min+1.0)/(1.0+RAND_MAX));  
}

void CodeExorRandom(char finame[],char foname[],char key[])  
{

	FILE *fi,*fo;  
	int value,early = 0,i;  

	fi = fopen(finame,"rb");  
	if (fi == NULL) return;  fo = fopen(foname,"wb");  
	if (fo == NULL) return;  
	
	for (i = 0;key[i] != '\0';i++) { 
		early += key[i]; 
	}
	
	srand(early);  
	
	i = 0;  
	while ((value = getc(fi)) != EOF) { 
		putc(value ^ GetRandom(0,255),fo); 
		i++;  
		if (key[i] == '\0') i = 0;  
	}
	
	fclose(fi);  
	fclose(fo);

}

[ Practical use degree of   this encryption   ]
If both of the encryption shown here become the natures by the simple expedient, it is possible to decipher it.
However, the amount operation can be high-speed, and easily make the program.
If it is extent built into the save data of the self-made game, it is very practicable.

The save data might be able to be remodeled easily even in a game on the market though it is a bytalk.
Especially, the nymph system game : the system save data Only bury it with 0xFF.
There is what comes for both CG and the recollection to be shown easily a lot, too.
The company is encrypted like the programmer and this, etc.