-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
see something like the following in your logs, the remote server is
requesting MS-CHAP:
- rcvd [LCP ConfReq id=0x2 <asyncmap 0x0> <auth chap 80> <magic 0x46a3>]
- ^^^^^^^^^^^^
+ rcvd [LCP ConfReq id=0x2 <asyncmap 0x0> <auth MS> <magic 0x46a3>]
+ ^^^^^^^
-The standard pppd implementation will indicate its lack of support for
-MS-CHAP by NAKing it:
-
- sent [LCP ConfNak id=0x2 <auth chap 05>]
-
-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.
-
-
-BUILDING THE PPPD
-
-MS-CHAP uses a combination of MD4 hashing and DES encryption for
-authentication. You'll need to get Eric Young's libdes library in
-order to use my MS-CHAP extensions. You can find it in:
-
-ftp://ftp.funet.fi/pub/crypt/mirrors/ftp.psy.uq.oz.au/DES/libdes-3.06.tar.gz
-
-Australian residents can get libdes from Eric Young's site:
-
-ftp://ftp.psy.uq.oz.au/pub/Crypto/DES/libdes-3.06.tar.gz
-
-It is also available on many other sites (ask Archie).
-
-I used libdes-3.06, but hopefully anything newer than that will work
-also. Get the library, build and test it on your system, and install
-it somewhere (typically /usr/local/lib and /usr/local/include).
-
-You should now be ready to (re)compile the PPPD. Go to the pppd
-subdirectory and make sure the Makefile contains "-DCHAPMS" in the
-CFLAGS or COMPILE_FLAGS macro, and that the LIBS macro (or LDADD for
-BSD systems) contains "-ldes". Depending on your system and where the
-DES library was installed, you may also need to alter the include and
-library paths used by your compiler.
-
-Do a "make clean" and then a "make" to rebuild pppd. Assuming all
-goes well, install the new pppd and move on to the CONFIGURATION
-section.
+MS-CHAP is enabled by default under Linux in pppd/Makefile.linux by
+the line "CHAPMS=y".
CONFIGURATION
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
(system byte ordering may be a problem) or my code is screwing up. I've
only got access to a Linux system, so you're on your own for anything else.
-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[0];
-{
- 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.
-
+Another thing that might cause problems is that some RAS servers won't
+respond at all to LCP config requests without seeing the word "CLIENT"
+from the other end. If you see pppd sending out LCP config requests
+without getting any reply, try putting something in your chat script
+to send the word CLIENT after the modem has connected.
STILL TO DO
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