/*
 * Captain Midnight decoder badge simulator (first version)
 *
 * Don't forget to 18 20 13 3 8  26 14 24 20  14 23 1 16 17 13 3 5
 *
 * mab@crypto.com - 11/17/2000
 *
 * Usage: badge {E|D} key
 *   where E is encrypt mode and D is decrypt mode
 *   and key is a number from 1-26 representing the number
 *   setting for the letter "A" on the dial.
 *   Encryption mode expects ascii on stdin; decryption mode
 *   expects one ciphertext number or nonnumeric char  per line.
 */
 
#include <stdio.h>
#include <ctype.h>

static char ROTOR[]="AXNQEGMKFWZHIOBLTDSRCJVUPY";

main(argc, argv)
     int argc;
     char **argv;
{
	char mode;
	int c;
	int key;
	char linein[1024];
	int i;
	
	if (argc != 3) {
		fprintf(stderr,"usage: badge e/d key\n");
		exit (1);
	}
	mode = *(argv[1]);
	key = atoi(argv[2]);
	if (isupper(mode))
		mode=tolower(mode);
	if (((mode!='e') && (mode!='d')) || (key < 1) || (key > 26)) {
		fprintf(stderr,"Usage: badge e/d key\n");
		exit (1);
	}
	--key;
	if (mode=='e')
		while ((c=getchar()) != EOF) {
			if (isalpha(c)) {
				if (islower(c))
					c=toupper(c);
				printf("%d\n",badge_encrypt(key,c));
			} else
				if (c=='\n')
					printf("\n");
				else
					if (isdigit(c) || (c == '\\'))
						printf("\\%c\n",c);
					else
						printf("%c\n",c);
		}
	else
		while (fgets(linein,sizeof(linein),stdin) != NULL) {
			i=atoi(linein);
			if ((i>0) && (i<27))
				printf("%c",badge_decrypt(key,i));
			else
				if (linein[0] == '\\')
					printf("%c",linein[1]);
				else
					printf("%c",linein[0]);
		}
}


badge_encrypt(key,c)
    int key;
    int c;
{
	return ((rotorpos(c) + key)%26 + 1);
}

badge_decrypt(key,i)
    int key;
    int i;
{
	return ROTOR[abs((i-1) + (26-key)) % 26];
}


rotorpos(c)
    int c;
{
	int i;
	
        for (i=0; i<26; i++)
	       if (ROTOR[i]==c)
		       return i;
        return -1;
}