/*
 * Trivially encode strings to protect them from innocent eyes (i.e.,
 * inadvertent password compromises, like a network administrator
 * who's watching packets for legitimate reasons and accidentally sees
 * the password protocol go by).
 * 
 * This is NOT secure encryption.
 *
 * It would be tempting to encode the password according to username
 * and repository, so that the same password would encode to a
 * different string when used with different usernames and/or
 * repositories.  However, then users would not be able to cut and
 * paste passwords around.  They're not supposed to anyway, but we all
 * know they will, and there's no reason to make it harder for them if
 * we're not trying to provide real security anyway.
 */

/* Set this to test as a standalone program. */
/* #define DIAGNOSTIC */

#ifndef DIAGNOSTIC
#include "cvs.h"
#else /* ! DIAGNOSTIC */
/* cvs.h won't define this for us */
#define AUTH_CLIENT_SUPPORT
#define xmalloc malloc
/* Use "gcc -fwritable-strings". */
#include <stdio.h>
#include <stdio.h>
#include <string.h>
#endif /* ! DIAGNOSTIC */

#if defined(AUTH_CLIENT_SUPPORT) || defined(AUTH_SERVER_SUPPORT)

/* Map characters to each other randomly and symmetrically, A <--> B.
 *
 * We divide the ASCII character set into 3 domains: control chars (0
 * thru 31), printing chars (32 through 126), and "meta"-chars (127
 * through 255).  The control chars map _to_ themselves, the printing
 * chars map _among_ themselves, and the meta chars map _among_
 * themselves.  Why is this thus?
 *
 * No character in any of these domains maps to a character in another
 * domain, because I'm not sure what characters are valid in
 * passwords, or what tools people are likely to use to cut and paste
 * them.  It seems prudent not to introduce control or meta chars,
 * unless the user introduced them first.  And having the control
 * chars all map to themselves insures that newline and
 * carriage-return are safely handled.
 */

static unsigned char
shifts[] = {
    0,  1,  2,  3,  4,  5,  6,  7,  8,  9, 10, 11, 12, 13, 14, 15,
   16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31,
  114,120, 53, 79, 96,109, 72,108, 70, 64, 76, 67,116, 74, 68, 87,
  111, 52, 75,119, 49, 34, 82, 81, 95, 65,112, 86,118,110,122,105,
   41, 57, 83, 43, 46,102, 40, 89, 38,103, 45, 50, 42,123, 91, 35,
  125, 55, 54, 66,124,126, 59, 47, 92, 71,115, 78, 88,107,106, 56,
   36,121,117,104,101,100, 69, 73, 99, 63, 94, 93, 39, 37, 61, 48,
   58,113, 32, 90, 44, 98, 60, 51, 33, 97, 62, 77, 84, 80, 85,223,
  225,216,187,166,229,189,222,188,141,249,148,200,184,136,248,190,
  199,170,181,204,138,232,218,183,255,234,220,247,213,203,226,193,
  174,172,228,252,217,201,131,230,197,211,145,238,161,179,160,212,
  207,221,254,173,202,146,224,151,140,196,205,130,135,133,143,246,
  192,159,244,239,185,168,215,144,139,165,180,157,147,186,214,176,
  227,231,219,169,175,156,206,198,129,164,150,210,154,177,134,127,
  182,128,158,208,162,132,167,209,149,241,153,251,237,236,171,195,
  243,233,253,240,194,250,191,155,142,137,245,235,163,242,178,152 };


/* SCRAMBLE and DESCRAMBLE work like this:
 *
 * scramble(STR) returns SCRM, a scrambled copy of STR.  SCRM[0] is a
 * single letter indicating the scrambling method.  As of this
 * writing, the only valid method is 'A', but check the code for more
 * up-to-date information.  The copy will have been allocated with
 * xmalloc(). 
 *
 * descramble(SCRM) returns STR, again in its own xmalloc'd space.
 * descramble() uses SCRM[0] to determine which method of unscrambling
 * to use.  If it does not recognize the method, it dies with error.
 */

/* Return a xmalloc'd, scrambled version of STR. */
char *
scramble (char *str)
{
    int i;
    char *s;

    /* +2 to hold the 'A' prefix that indicates which version of
       scrambling this is (the first, obviously, since we only do one
       kind of scrambling so far), and then the '\0' of course.  */
    s = (char *) xmalloc (strlen (str) + 2);

    /* Scramble (TM) version prefix. */
    s[0] = 'A';
    strcpy (s + 1, str);

    for (i = 1; s[i]; i++)
	s[i] = shifts[(unsigned char)(s[i])];

    return s;
}

/* Decode the string in place. */
char *
descramble (char *str)
{
    char *s;
    int i;

    /* For now we can only handle one kind of scrambling.  In the future
       there may be other kinds, and this `if' will become a `switch'.  */
    if (str[0] != 'A')
#ifndef DIAGNOSTIC
	error (1, 0, "descramble: unknown scrambling method");
#else  /* DIAGNOSTIC */
    {
	fprintf (stderr, "descramble: unknown scrambling method\n", str);
	fflush (stderr);
	exit (EXIT_FAILURE);
    }
#endif  /* DIAGNOSTIC */

    /* Method `A' is symmetrical, so scramble again to decrypt. */
    s = scramble (str + 1);

    /* Shift the whole string one char to the left, pushing the unwanted
       'A' off the left end.  Safe, because s is null-terminated. */
    for (i = 0; s[i]; i++)
	s[i] = s[i + 1];

    return s;
}

#endif /* (AUTH_CLIENT_SUPPORT || AUTH_SERVER_SUPPORT) from top of file */

#ifdef DIAGNOSTIC
int
main( int argc, char **argv )
{
    int i;
    char *e, *m, biggie[256];

    char *cleartexts[5];
    cleartexts[0] = "first";
    cleartexts[1] = "the second";
    cleartexts[2] = "this is the third";
    cleartexts[3] = "$#% !!\\3";
    cleartexts[4] = biggie;

    /* Set up the most important test string: */
    /* Can't have a real ASCII zero in the string, because we want to
       use printf, so we substitute the character zero. */
    biggie[0] = '0';
    /* The rest of the string gets straight ascending ASCII. */
    for (i = 1; i < 256; i++)
	biggie[i] = i;

    /* Test all the strings. */
    for (i = 0; i < 5; i++)
    {
	printf ("clear%d: %s\n", i, cleartexts[i]);
	e = scramble (cleartexts[i]);
	printf ("scram%d: %s\n", i, e);
	m = descramble (e);
	free (e);
	printf ("clear%d: %s\n\n", i, m);
	free (m);
    }

    fflush (stdout);
    return 0;
}
#endif /* DIAGNOSTIC */

/*
 * ;;; The Emacs Lisp that did the dirty work ;;;
 * (progn
 * 
 *   ;; Helper func.
 *   (defun random-elt (lst)
 *     (let* ((len (length lst))
 *            (rnd (random len)))
 *       (nth rnd lst)))
 * 
 *   ;; A list of all characters under 127, each appearing once.
 *   (setq non-meta-chars
 *         (let ((i 0)
 *               (l nil))
 *           (while (< i 127)
 *             (setq l (cons i l) 
 *                   i (1+ i)))
 *           l))
 * 
 *   ;; A list of all characters 127 and above, each appearing once.
 *   (setq meta-chars
 *         (let ((i 127)
 *               (l nil))
 *           (while (< i 256)
 *             (setq l (cons i l) 
 *                   i (1+ i)))
 *           l))
 * 
 *   ;; A vector that will hold the chars in a random order.
 *   (setq scrambled-chars (make-vector 256 0))
 * 
 *   ;; These characters should map to themselves.
 *   (let ((i 0))
 *     (while (< i 32)
 *       (aset scrambled-chars i i)
 *       (setq non-meta-chars (delete i non-meta-chars) 
 *             i (1+ i))))
 *   
 *   ;; Assign random (but unique) values, within the non-meta chars. 
 *   (let ((i 32))
 *     (while (< i 127)
 *       (let ((ch (random-elt non-meta-chars)))
 *         (if (= 0 (aref scrambled-chars i))
 *             (progn
 *               (aset scrambled-chars i ch)
 *               (aset scrambled-chars ch i)
 *               (setq non-meta-chars (delete ch non-meta-chars)
 *                     non-meta-chars (delete i non-meta-chars))))
 *         (setq i (1+ i)))))
 * 
 *   ;; Assign random (but unique) values, within the non-meta chars. 
 *   (let ((i 127))
 *     (while (< i 256)
 *       (let ((ch (random-elt meta-chars)))
 *         (if (= 0 (aref scrambled-chars i))
 *             (progn
 *               (aset scrambled-chars i ch)
 *               (aset scrambled-chars ch i)
 *               (setq meta-chars (delete ch meta-chars)
 *                     meta-chars (delete i meta-chars))))
 *         (setq i (1+ i)))))
 * 
 *   ;; Now use the `scrambled-chars' vector to get your C array.
 *   )
 */
