Usenet 1994 January/usenetsourcesnewsgroupsinfomagicjanuary1994.iso/sources/net/crypt

Internet Message Format | 1987-02-18 | 8KB

From [e-mail] Sun Feb 15 14:33:00 1987
Path: beno!seismo!mcvax!inria!axis!philip
From: [e-mail]
Newsgroups: net.sources
Subject: A crypt program
Keywords: A public domain crypt program
Message-ID: <[e-mail]>
Date: 15 Feb 87 19:33:00 GMT
Organization: Axis Digital, Paris
Lines: 262
Posted: Sun Feb 15 19:33:00 1987


            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    ([e-mail])

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();
}


From [e-mail] Wed Feb 18 06:17:24 1987
Path: beno!seismo!mcvax!inria!axis!philip
From: [e-mail]
Newsgroups: net.sources
Subject: Crypt program - mods.
Keywords: makekey replacement code
Message-ID: <[e-mail]>
Date: 18 Feb 87 11:17:24 GMT
Organization: Axis Digital, Paris
Lines: 73
Posted: Wed Feb 18 11:17:24 1987

In the crypt program I recently posted, there was a call made to a
small program "/usr/lib/makekey". Apparently this does not exist on all
*IX* machines.

I really dont see why - it is a 4 or 5 line program which reads a
password on its stdin, and prints the encrypted result on its stdout,
using exactly the same routines as passwd does.

Rather than re-write the program, I have made some mods to the crypt source
to make the calls directly.

Since the library routine is called 'crypt', the routine within my program
has to change its name, 'encrypt' is also used in the library, so the
final name change is to 'encode'.

The following is a diff of the changes required (actually, the source becomes
smaller and simpler .... )

============================================================================

19a20
>     char        *crypt();
22d22
<     int        pipe_fd[2];
25c25,27
<     char        buf[13];
---
>     char        buf[14];
>     char        key[9];
>     char        salt[3];
27,30c29,32
<     strncpy(buf, password, 8);
<     while (*password) *password++ = '\0';
<     buf[8] = buf[0];
<     buf[9] = buf[1];
---
>     strncpy(key, password, 8);
>     salt[0] = key[0];
>     salt[1] = key[1];
>     salt[2] = '\0';
32c34
<     pipe(pipe_fd);
---
>     strncpy(buf, crypt(key, salt), 13);
34,53d35
<     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);
<     }
<
119c101
< crypt()
---
> encode()
202c184
<     else      crypt();
---
>     else      encode();