encryption.c

#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#define debug 0

char word[100000];
int ch_count=0;

unsigned char get_bit(unsigned char value, unsigned char shift)
{
        switch (shift)
        {
        case 0:
                return value & 0x1;
        case 1:
                return (value & 0x2) > 1;
        case 2:
                return (value & 0x4) > 2;
        case 3:
                return (value & 0x8) > 3;
        case 4:
                return (value & 0x10) > 4;
        case 5:
                return (value & 0x20) > 5;
        case 6:
                return (value & 0x40) > 6;
        case 7:
                return (value & 0x80) > 7;
        }
}

unsigned char set_bit(unsigned char value, unsigned char set, unsigned char shift)
{
        if (debug) printf("set_bit %d %d %d\n", value, set, shift);
        if (set == 1)
        {
                switch (shift)
                {
                case 0:
                        return value | 0x1;
                case 1:
                        return value | 0x2;
                case 2:
                        return value | 0x4;
                case 3:
                        return value | 0x8;
                case 4:
                        return value | 0x10;;
                case 5:
                        return value | 0x20;
                case 6:
                        return value | 0x40;
                case 7:
                        return value | 0x80;

                }
        }

        if (set == 0)
        {
                switch (shift)
                {
                case 0:
                        return value & ~0x1;
                case 1:
                        return value & ~0x2;
                case 2:
                        return value & ~0x4;
                case 3:
                        return value & ~0x8;
                case 4:
                        return value & ~0x10;
                case 5:
                        return value & ~0x20;
                case 6:
                        return value & ~0x40;
                case 7:
                        return value & ~0x80;
                }
        }
}

void bit_change(unsigned char* value, unsigned char bit_1, unsigned char bit_2)
{
        unsigned char tmp_bit_1, tmp_bit_2, tmp_value;
        tmp_value = *value;
        tmp_bit_1 = get_bit(tmp_value, bit_1);
        if (debug) printf("tmp_bit_1 %d\n", tmp_bit_1);
        tmp_bit_2 = get_bit(tmp_value, bit_2);
        if (debug)printf("tmp_bit_2 %d\n", tmp_bit_2);
        if (debug)printf("tmp_value %d\n", tmp_value);
        tmp_value = set_bit(tmp_value, tmp_bit_1, bit_2);
        //tmp_value=tmp_value&~0x4;
        if (debug)printf("1.tmp_value %d %x %d\n", tmp_value, tmp_bit_1, bit_2);
        tmp_value = set_bit(tmp_value, tmp_bit_2, bit_1);
        //tmp_value=tmp_value|0x1;
        if (debug)printf("2.tmp_value %d %x %d\n", tmp_value, 0x1, bit_1);
        if (debug)printf("tmp_value %d\n", tmp_value);
        *value = tmp_value;
}

void en_readfile(char *filename)
{
        FILE* ptr;
    char ch;
        printf("!=>%s\n", filename);
    ptr = fopen(filename, "r");
    if (NULL == ptr) {
        printf("file can't be opened \n");
        }

    //printf("content of this file are \n");

    // Printing what is written in file
    // character by character using loop.
    while (ch != EOF){
        ch_count=ch_count+1;
        //printf("%c",ch);
        ch = fgetc(ptr);
        printf("%d\n", ch);
        }
    //printf("%d\n",ch_count);
    fclose(ptr);
    ptr = fopen(filename, "r");
    for(int i=0;i<ch_count-1;i++){
        word[i]=fgetc(ptr);
        //printf("%c",word[i]);
        }
    // Closing the file
    fclose(ptr);
}
void can_read_readfile(char *filename)
{

        FILE* ptr;
    char ch;
        printf("!=>%s\n", filename);
    ptr = fopen(filename, "r");
    if (NULL == ptr) {
        printf("file can't be opened \n");
        }

    //printf("content of this file are \n");

    // Printing what is written in file
    // character by character using loop.
    while (ch != EOF){
        ch_count=ch_count+1;
        printf("%d\n",ch);
        ch = fgetc(ptr);
        //printf("%d\n", ch);
        }
//    printf("%d\n",ch_count);
    fclose(ptr);
    ptr = fopen(filename, "r");
    for(int i=0;i<ch_count-1;i++){
        word[i]=fgetc(ptr);
        //printf("%c",word[i]);
        }
    // Closing the file
    fclose(ptr);
}
struct EXCHANGE_BIT
{
        unsigned char bit_1;
        unsigned char bit_2;
}_EXCHANGE_BIT;

int main(int argc, char *argv[])
{

        FILE* en;
        int in_put=atoi(argv[1]);
        //char fliename=atoi(argv[2]);
        printf("==>%s\n", argv[2]);
        struct EXCHANGE_BIT exchange_bit1[2];
        struct EXCHANGE_BIT exchange_bit2[2];
        struct EXCHANGE_BIT exchange_bit3[2];
        struct EXCHANGE_BIT exchange_bit4[2];
        exchange_bit1[0].bit_1 = 4;
        exchange_bit1[0].bit_2 = 2;
        exchange_bit1[1].bit_1 = 2;
        exchange_bit1[1].bit_2 = 4;

        exchange_bit2[0].bit_1 = 0;
        exchange_bit2[0].bit_2 = 3;
        exchange_bit2[1].bit_1 = 3;
        exchange_bit2[1].bit_2 = 0;

        exchange_bit3[0].bit_1 = 1;
        exchange_bit3[0].bit_2 = 6;
        exchange_bit3[1].bit_1 = 6;
        exchange_bit3[1].bit_2 = 1;

        exchange_bit4[0].bit_1 = 5;
        exchange_bit4[0].bit_2 = 7;
        exchange_bit4[1].bit_1 = 7;
        exchange_bit4[1].bit_2 = 5;
        //printf("%x\n",word[0]);
        if (in_put==0){
                can_read_readfile(argv[2]);
                en = fopen(argv[3], "w");

                for(int j0=0;j0<ch_count-1;j0++){
                        //printf("1.%d %x\n",j0, word[j0]);
                        bit_change(&word[j0], exchange_bit1[0].bit_1, exchange_bit1[0].bit_2);
                        bit_change(&word[j0], exchange_bit2[0].bit_1, exchange_bit2[0].bit_2);
                        bit_change(&word[j0], exchange_bit3[0].bit_1, exchange_bit3[0].bit_2);
                        bit_change(&word[j0], exchange_bit4[0].bit_1, exchange_bit4[0].bit_2);
                        //printf("2.%d %x\n",j0, word[j0]);
                        fputc(word[j0],en);
                        }
                fclose(en);

        }



        else if (in_put==1){
                en_readfile(argv[2]);
                en = fopen(argv[3], "w");

                for(int j1=0;j1<ch_count-1;j1++){
                        //printf("3.%d %x\n",j1, word[j1]);
                        bit_change(&word[j1], exchange_bit1[1].bit_1, exchange_bit1[1].bit_2);
                        bit_change(&word[j1], exchange_bit2[1].bit_1, exchange_bit2[1].bit_2);
                        bit_change(&word[j1], exchange_bit3[1].bit_1, exchange_bit3[1].bit_2);
                        bit_change(&word[j1], exchange_bit4[1].bit_1, exchange_bit4[1].bit_2);
                        fputc(word[j1],en);
                        //printf("4.%d %x\n",j1, word[j1]);

                }
                fclose(en);

        }
}