philip@axis.UUCP (02/15/87)
Crypt - Decrypt Program
~~~~~~~~~~~~~~~~~~~~~~~
This program is based upon the German WW2 enigma machine.
This worked as follows:
The machine contained several (3 or 4, depending upon the service) rotors,
with contacts on each face. Each rotor had a different mapping (ie wiring)
scheme between the contacts.
Each contact on the input side of rotor 1 was connected to input keys
(letters and numbers). Pressing the key marked 'A' would pass an electric
current into the corresponding contact on the input rotor, this current would
exit on some other contact on the output side, depending upon the internal
wiring.
After each key press, the input rotor would turn one position (thus, pressing
'A' again, would result in a current flowing out of a different output
contact.
After completing one revolution, rotor number two would move one position.
The key to this depended upon the order of the rotors, and their starting
positions.
To decode, simply reverse the current flow, ie, connect the keyboard to the
output, and replace the input by a series of lamps corresponding to the
keys.
This program simulates one of these machines, with several refinements:
1) Each rotor has 256 positions
2) The key is not the ordering and starting positions of the rotors,
since new and different rotors are created for each input key.
3) The movement of the rotors is not a simple as described above.
It is basically that, but with rotors selected on a random basis,
they are advanced a random number of positions.
The result is (I believe - not being a Cryptologist), somewhat more
secure than the original machines, and certainly more secure than the
original UNIX crypt - which has a single rotor, with a reciprocal
mapping - ie if an input of 'A' maps to an output of 'Z', then in the
same rotor position, a 'Z' must map to an 'A'.
if anyone finds a method of breaking this crypt program, I would be glad
to hear about it.
Philip Peake (philip@axis.uucp)
NOTES:
The program must have two links, one called crypt, and the other
called decrypt. Passing a crypted document through crypt again,
even with the same key, will not decrypt it.
===============================================================================
#include <stdio.h>
#define ROTORSIZ 256
#define MASK 0377
#define EMPTY 07777
#define X_SIZE 4099
char *strrchr();
unsigned r1[ROTORSIZ];
unsigned r2[ROTORSIZ];
unsigned r3[ROTORSIZ];
unsigned char x[X_SIZE];
init(password, decrypt)
char *password;
int decrypt;
{
register int index;
register int i;
int pipe_fd[2];
unsigned random;
long seed = 123L;
char buf[13];
strncpy(buf, password, 8);
while (*password) *password++ = '\0';
buf[8] = buf[0];
buf[9] = buf[1];
pipe(pipe_fd);
if (fork() == 0)
{
close(0);
close(1);
dup(pipe_fd[0]);
dup(pipe_fd[1]);
execl("/usr/lib/makekey", "-", 0);
execl("/lib/makekey", "-", 0);
exit(1);
}
write(pipe_fd[1], buf, 10);
wait((int *) NULL);
if (read(pipe_fd[0], buf, 13) != 13)
{
fprintf(stderr, "crypt: cannot generate key\n");
exit(1);
}
for (i = 0 ; i < ROTORSIZ; i++) r1[i] = r2[i] = r3[i] = EMPTY;
for (i = 2; i < 13; i++) seed = seed * buf[i] + i;
i = 0;
while (i < ROTORSIZ)
{
seed = (long)(5L * seed + (long)i);
random = (unsigned)(seed % 65521L);
index = (int)(random & MASK);
if (r1[index] == EMPTY)
r1[index] = i++;
else
continue;
}
i = 0;
while (i < ROTORSIZ)
{
seed = (long)(5L * seed + (long)i);
random = (unsigned)(seed % 65521L);
index = (int)(random & MASK);
if (r2[index] == EMPTY)
r2[index] = i++;
else
continue;
}
i = 0;
while (i < ROTORSIZ)
{
seed = (long)(5L * seed + (long)i);
random = (unsigned)(seed % 65521L);
index = (int)(random & MASK);
if (r3[index] == EMPTY)
r3[index] = i++;
else
continue;
}
for (i = 0; i < X_SIZE; i++)
{
seed = (long)(5L * seed + (long)i);
random = (unsigned)(seed % 65521L);
x[i] = random & 03;
}
if (decrypt)
{
invert(r1);
invert(r2);
invert(r3);
}
}
invert(r)
unsigned r[ROTORSIZ];
{
unsigned t[ROTORSIZ];
register int i;
for (i = 0; i < ROTORSIZ; i++) t[i] = r[i];
for (i = 0; i < ROTORSIZ; i++) r[t[i]] = i;
}
crypt()
{
register int ch;
register int i = 0;
register unsigned ofs1 = 0;
register unsigned ofs2 = 0;
register unsigned ofs3 = 0;
while ((ch = getchar()) != EOF)
{
putchar(r3[r2[r1[ch+ofs1&MASK]+ofs2&MASK]+ofs3&MASK]);
switch (x[i]){
case 00:
ofs1 = ++ofs1 & MASK;
break;
case 01:
ofs2 = ++ofs2 & MASK;
break;
case 02:
ofs3 = ++ofs3 & MASK;
break;
}
if (ofs1 == 0) ofs2 = ++ofs2 & MASK;
if (ofs2 == 0) ofs3 = ++ofs3 & MASK;
if (++i == X_SIZE) i = 0;
}
}
decrypt()
{
register int ch;
register int i = 0;
register unsigned ofs1 = 0;
register unsigned ofs2 = 0;
register unsigned ofs3 = 0;
while ((ch = getchar()) != EOF)
{
putchar(r1[r2[r3[ch]-ofs3&MASK]-ofs2&MASK]-ofs1&MASK);
switch (x[i]){
case 00:
ofs1 = ++ofs1 & MASK;
break;
case 01:
ofs2 = ++ofs2 & MASK;
break;
case 02:
ofs3 = ++ofs3 & MASK;
break;
}
if (ofs1 == 0) ofs2 = ++ofs2 & MASK;
if (ofs2 == 0) ofs3 = ++ofs3 & MASK;
if (++i == X_SIZE) i = 0;
}
}
main(argc, argv)
int argc;
char *argv[];
{
int flag;
char *p;
p = strrchr(argv[0], '/');
if (p == NULL) p = argv[0];
else ++p;
if (strcmp(p, "crypt") == 0) flag = 0;
else flag = 1;
if (argc != 2)
init(getpass("Enter key: "), flag);
else
init(argv[1], flag);
if (flag) decrypt();
else crypt();
}