-PPP Client Support for Microsoft's CHAP-80
-==========================================
+PPP Support for Microsoft's CHAP-80
+===================================
Eric Rosenquist rosenqui@strataware.com
(updated by Paul Mackerras)
(updated by Al Longyear)
(updated by Farrell Woods)
+(updated by Frank Cusack)
INTRODUCTION
the password were stored in cleartext.) The details of the Microsoft
extensions can be found in the document:
- <ftp://ftp.microsoft.com/developr/rfc/chapexts.txt>
+ <http://www.ietf.org/rfc/rfc2433.txt>
In short, MS-CHAP is identified as <auth chap 80> since the hex value
of 80 is used to designate Microsoft's scheme. Standard PPP CHAP uses
Windows NT Server systems are often configured to "Accept only
Microsoft Authentication" (this is intended to enhance security). Up
until now, that meant that you couldn't use this version of PPPD to
-connect to such a system. I've managed to get a client-only
-implementation of MS-CHAP working; it will authenticate itself to
-another system using MS-CHAP, but if you're using PPPD as a dial-in
-server, you won't be able to use MS-CHAP to authenticate the clients.
-This would not be a lot of extra work given that the framework is in
-place, but I didn't need it myself so I didn't implement it.
+connect to such a system.
BUILDING THE PPPD
CHAP, the MS-CHAP-specific problems you're likely to encounter are mostly
related to your Windows NT account and its settings. A Microsoft server
returns error codes in its CHAP response. The following are extracted from
-Microsoft's "chapexts.txt" file referenced above:
+RFC 2433:
646 ERROR_RESTRICTED_LOGON_HOURS
647 ERROR_ACCT_DISABLED
without getting any reply, try putting something in your chat script
to send the word CLIENT after the modem has connected.
-If everything compiles cleanly, but fails at authentication time, then
-it might be a case of the MD4 or DES code screwing up. The following
-small program can be used to test the MS-CHAP code to see if it
-produces a known response:
-
------------------
-#include <stdio.h>
-
-#include "pppd.h"
-#include "chap.h"
-#include "chap_ms.h"
-
-int main(argc, argv)
- int argc;
- char *argv[];
-{
- u_char challenge[8];
- int challengeInt[sizeof(challenge)];
- chap_state cstate;
- int i;
-
- if (argc != 3) {
- fprintf(stderr, "Usage: %s <16-hexchar challenge> <password>\n",
- argv[0]); exit(1);
- }
-
- sscanf(argv[1], "%2x%2x%2x%2x%2x%2x%2x%2x",
- challengeInt + 0, challengeInt + 1, challengeInt + 2,
- challengeInt + 3, challengeInt + 4, challengeInt + 5,
- challengeInt + 6, challengeInt + 7);
-
- for (i = 0; i < sizeof(challenge); i++)
- challenge[i] = (u_char)challengeInt[i];
-
- ChapMS(&cstate, challenge, sizeof(challenge), argv[2], strlen(argv[2]));
- printf("Response length is %d, response is:", cstate.resp_length);
-
- for (i = 0; i < cstate.resp_length; i++) {
- if (i % 8 == 0)
- putchar('\n');
- printf("%02X ", (unsigned int)cstate.response[i]);
- }
-
- putchar('\n');
-
- exit(0);
-}
--------------
-
-This needs to link against chap_ms.o, md4.o, and the DES library. When
-you run it with the command line:
-
- $ testchap 00000000000000000000000000000000 hello
-
-it should output the following:
-
- Response length is 49, response is:
- 00 00 00 00 00 00 00 00
- 00 00 00 00 00 00 00 00
- 00 00 00 00 00 00 00 00
- F4 D9 9D AF 82 64 DC 3C
- 53 F9 BC 92 14 B5 5D 9E
- 78 C4 21 48 9D B7 A8 B4
- 01
-
-if not, then either the DES library is not working, the MD4 code isn't
-working, or there are some problems with the port of the code in
-chap_ms.c.
-
-
STILL TO DO
A site using only MS-CHAP to authenticate has no need to store cleartext
could quite easily be lifted from chap_ms.c (you have to convert the
password to Unicode before hashing it). The chap_ms.c file would also have
to be changed to recognize a password hash (16 binary bytes == 32 ASCII hex
-characters) and skip the hashing stage.
-
-A server implementation would allow MS-CHAP to be used with Windows NT and
-Windows 95 clients for enhanced security. Some new command-line options
-would be required, as would code to generate the Challenge packet and
-verify the response. Most of the helper functions are in place, so this
-shouldn't be too hard for someone to add.
+characters) and skip the hashing stage. This would have no real security
+value as the hash is plaintext-equivalent.
projects / ppp.git / blobdiff