/*
 * file : auth.c
 * desc : des¾Ë°í¸®ÁòÀ» ÀÌ¿ëÇÏ¿© password¸¦ ÀÎÄÚµùÇÑ´Ù
 */
#include <stdio.h>
#include <unistd.h>
#include <string.h>

#include "auth.h"

int keyXORNumber = 0xe7;
int highBits[] = { 0xf0, 0xf0, 0xe0, 0xe0, 0xe0, 0xe0 };
int lowBits[] = { 0x00, 0x04, 0x08, 0x0c, 0x00, 0x04 };	

int encodeASC2NSC(char c) 
{
		int temp = c ^ keyXORNumber;
		int temp1 = (temp & 0xf0) >> 4;
		int temp2 = temp & 0x0f;
		int temp3 = (temp2 << 4);
		temp3 += temp1;
		return temp3;
}
	
int decodeNSC2ASC(char c) 
{
		int temp = c & 0xff;
		int temp1 = (temp & 0xf0) >> 4;
		int temp2 = temp & 0x0f;
		int temp3 = (temp2 << 4);
		temp3 += temp1;
		return temp3 ^ keyXORNumber;
}
	
int getFifthRepeated(int lastasc) 
{
	int ref = (lastasc - 0x20) / 0x10;
	int highBit = highBits[ref] - 0x40*(lastasc%4);
	int lowBit = lowBits[ref];
		
	return (highBit | lowBit);
}
	
int getLengthSum(int len) 
{
	return len ^ keyXORNumber;
}
	
char *encrypt(char *plain) 
{
	char encrypted[512];
	int i;
	char *ret;
	char tmp[4];

	if(plain != NULL && strlen(plain) > 0 && strlen(plain) <= 20) 
	{
		int encoded[24];
		int repeated[8];
		int last = encodeASC2NSC(plain[strlen(plain)-1]);

		repeated[0] = last / 4;
		repeated[1] = repeated[0]*2;
		repeated[2] = last;
		repeated[3] = repeated[2]*2;
		repeated[4] = getFifthRepeated(plain[strlen(plain)-1]);
		repeated[5] = repeated[4]*2;
		repeated[6] = last / 16;
		repeated[7] = repeated[6]*2 + 1; 
		
		memcpy(&encoded[2], &repeated[0], 8);
		memcpy(&encoded[10], &repeated[0], 8);
		memcpy(&encoded[18], &repeated[0], 6);
		
		encoded[0] = getLengthSum(strlen(plain));

		for(i = 0 ; i < strlen(plain) ; i++) 
		{
			encoded[i+1] = encodeASC2NSC(plain[i]);
		}
		
		for(i = 0 ; i < 24 ; i++)
		{
			if(encoded[i] == 0) encoded[i] = 1;
		}
		
		for(i = 0 ; i < 24; i++)
		{
			sprintf(tmp, "%02x", encoded[i]);
			sprintf(encrypted + i * 2, "%c%c", tmp[strlen(tmp)-2], tmp[strlen(tmp)-1]);
		}
	}

	ret = (char *)malloc(strlen(encrypted));
	strcpy(ret, encrypted);
	
	return ret;
}