/*
* Function to find the multiplicative inverse of a given poly
* @param: a valid poly
* @output: multiplicative inverse of poly if it has one and print out the processes to stdout
*/
void inverse(uint8_t inv_poly[])
{
//Construct lookup_table to find multiplicative inverse of a byte
struct lookup_table mytable = construct_table();
uint8_t temp[5]; //initialize temp to be x^4 + 1 or {01}{00}{00}{00}{01}, but ignore the coefficient of x^4
uint8_t quo[4];
uint8_t aux[4];
uint8_t temp_aux[4];
uint8_t rem[4];
//initialize reminder, quotient and aux
for(int k=0; k < 4; k++)
{
quo[k] = 0x00;
aux[k] = 0x00;
rem[k] = 0x00;
temp[k] = 0x00;
temp_aux[k] = 0x00;
}
//set the last byte of temp to be {01} since we have x^4 + 1
temp[3] = 0x01;
//print first round
printOutput_inverse(1, temp, quo, temp_aux);
//Set rem to be poly
memcpy(rem, inv_poly, 4);
//set last byte of aux to be {01} since now x=1 for second round
aux[3] = 0x01;
//print second round
printOutput_inverse(2, rem, quo, aux);
/*
* Now go through the last 4 rounds to complete our multiplicative inverse process.
* We could end sooner if the poly has no inverse (rem = 00) or we arrive at rem = const sooner than 4 rounds
*/
int isInverse = 1;
for(int k = 3; k < 7; k++)
{
struct long_division result;
if(k == 3) //take special care for first division since the dividend has 4th degree (x^4 + 1)
{
result = divide(temp, rem, mytable, 1);
}
else
{
result = divide(temp, rem, mytable, 0);
}
/*
* Compute aux
*/
struct modprod_result quo_aux = modprod(result.quo, aux, 0);
//aux holder to later update the previous aux
uint8_t aux_holder[4];
memcpy(aux_holder, aux, 4);
//Perform XOR with previous aux
for(int i = 0; i < 4; i++)
{
aux[i] = quo_aux.modprod_poly[i] ^ temp_aux[i];
}
//Update previous aux
memcpy(temp_aux, aux_holder, 4);
//print output
printOutput_inverse(k, result.rem, result.quo, aux);
/*
* Perform check on rem to see if we can stop early for the following cases:
* Case 1: rem = {00}{00}{00}{00} - stop the loop and report that the input poly does not have multiplicative inverse
* Case 2: rem = {00}{00}{00}{01} - rem is a constant with reminder = 01 signaling that we are done
*/
if(result.rem[0] == 0x00 && result.rem[1] == 0x00 && result.rem[2] == 0x00)
{
if(result.rem[3] == 0x00)
{
isInverse = 0;
break;
}
else if(result.rem[3] == 0x01)
{
break;
}
}
/*
* Update temp and rem for next round
* now temp = rem and rem = result.rem
*/
memcpy(temp, rem, 4);
memcpy(rem, result.rem, 4);
}
//print last statement for inverse process
if(!isInverse)
{
fprintf(stdout, "{%02x}{%02x}{%02x}{%02x} does not have a multiplicative inverse\n", inv_poly[0], inv_poly[1], inv_poly[2], inv_poly[3]);
}
else
{
fprintf(stdout, "Multiplicative inverse of {%02x}{%02x}{%02x}{%02x} is {%02x}{%02x}{%02x}{%02x}\n", inv_poly[0], inv_poly[1], inv_poly[2], inv_poly[3], aux[0], aux[1], aux[2], aux[3]);
}
}
// Main method of HW6, mostly taking user input and running the correct prog
int main(int argc, char *argv[]) {
// Look for correct command line arguments
if(argc <= 1) {
usage();
return 0;
} else {
if(strcmp(argv[1], "tablecheck") == 0) {
// Tablecheck prog should be run
FILE* tablefile = NULL;
for(int i=2; i<argc; i++) {
if(strncmp(argv[i], "-t=", 3) == 0) {
tablefile = fopen(argv[i]+3, "r");
if(tablefile == NULL) {
fprintf(stderr, "ERROR: invalid file '%s' for reading.\n", argv[i]+3);
return 0;
}
}
}
if(tablefile) {
tablecheck(tablefile);
fclose(tablefile);
} else {
usage("tablecheck");
}
}
else if(strcmp(argv[1], "modprod") == 0) {
// Modprod prog should be run
char *poly1 = NULL;
char *poly2 = NULL;
for(int i=2; i<argc; i++) {
if(strncmp(argv[i], "-p1=", 4) == 0) {
poly1 = argv[i]+4;
}
else if(strncmp(argv[i], "-p2=", 4) == 0) {
poly2 = argv[i]+4;
}
}
if(poly1 && poly2) {
modprod(poly1, poly2);
} else {
usage("modprod");
}
}
else if(strcmp(argv[1], "keyexpand") == 0) {
// Keyexpand prog should be run
char *key = NULL;
FILE* tablefile = NULL;
for(int i=2; i<argc; i++) {
if(strncmp(argv[i], "-k=", 3) == 0) {
key = argv[i]+3;
}
else if(strncmp(argv[i], "-t=", 3) == 0) {
tablefile = fopen(argv[i]+3, "r");
if(tablefile == NULL) {
fprintf(stderr, "ERROR: invalid file '%s' for reading.\n", argv[i]+3);
return 0;
}
}
}
if(key && tablefile) {
keyexpand(key, tablefile);
fclose(tablefile);
} else {
usage("keyexpand");
}
}
else if(strcmp(argv[1], "encrypt") == 0) {
// Encrypt prog should be run
char *key = NULL;
FILE* tablefile = NULL;
for(int i=2; i<argc; i++) {
if(strncmp(argv[i], "-k=", 3) == 0) {
key = argv[i]+3;
}
else if(strncmp(argv[i], "-t=", 3) == 0) {
tablefile = fopen(argv[i]+3, "r");
if(tablefile == NULL) {
fprintf(stderr, "ERROR: invalid file '%s' for reading.\n", argv[i]+3);
return 0;
}
}
}
if(key && tablefile) {
if(argv[argc-1][0] != '-') {
// Take input from file
FILE* fin = NULL;
fin = fopen(argv[argc-1], "r");
if(fin == NULL) {
fprintf(stderr, "ERROR: invalid file '%s' for reading.\n", argv[argc-1]);
return 0;
}
encrypt(key, tablefile, fin);
fclose(fin);
} else {
// Take input from cmd line
encrypt(key, tablefile, stdin);
}
fclose(tablefile);
} else {
usage("encrypt");
}
}
else if(strcmp(argv[1], "decrypt") == 0) {
// Decrypt prog should be run
char *key = NULL;
FILE* tablefile = NULL;
for(int i=2; i<argc; i++) {
if(strncmp(argv[i], "-k=", 3) == 0) {
key = argv[i]+3;
}
else if(strncmp(argv[i], "-t=", 3) == 0) {
tablefile = fopen(argv[i]+3, "r");
if(tablefile == NULL) {
fprintf(stderr, "ERROR: invalid file '%s' for reading.\n", argv[i]+3);
return 0;
}
}
}
if(key && tablefile) {
if(argv[argc-1][0] != '-') {
// Take input from file
FILE* fin = NULL;
fin = fopen(argv[argc-1], "r");
if(fin == NULL) {
fprintf(stderr, "ERROR: invalid file '%s' for reading.\n", argv[argc-1]);
return 0;
}
decrypt(key, tablefile, fin);
fclose(fin);
} else {
// Take input from cmd line
decrypt(key, tablefile, stdin);
}
fclose(tablefile);
} else {
usage("decrypt");
}
}
else if(strcmp(argv[1], "inverse") == 0) {
// Inverse prog should be run
char *poly = NULL;
for(int i=2; i<argc; i++) {
if(strncmp(argv[i], "-p=", 3) == 0) {
poly = argv[i]+3;
}
}
if(poly) {
inverse(poly);
} else {
usage("inverse");
}
}
else {
// Failed input
usage();
}
}
return 0;
}