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scramble.c
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C/C++ Source or Header
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1996-09-28
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8KB
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247 lines
/*
* 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 legal 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 legal method is 'A', but check the code for more
* up-to-date information. The copy will have been allocated with
* malloc().
*
* descramble(SCRM) returns STR, again in its own malloc'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 malloc'd, scrambled version of STR. */
char *
scramble (str)
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);
s[0] = 'A'; /* Scramble (TM) version prefix. */
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 (str)
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 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.
* )
*/