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diff --git a/mdk-stage1/ppp/README.MSCHAP80 b/mdk-stage1/ppp/README.MSCHAP80 new file mode 100644 index 000000000..d3ed291b7 --- /dev/null +++ b/mdk-stage1/ppp/README.MSCHAP80 @@ -0,0 +1,284 @@ +PPP Client Support for Microsoft's CHAP-80 +========================================== + +Eric Rosenquist rosenqui@strataware.com +(updated by Paul Mackerras) +(updated by Al Longyear) +(updated by Farrell Woods) + +INTRODUCTION + +Microsoft has introduced an extension to the Challenge/Handshake +Authentication Protocol (CHAP) which avoids storing cleartext +passwords on a server. (Unfortunately, this is not as secure as it +sounds, because the encrypted password stored on a server can be used +by a bogus client to gain access to the server just as easily as if +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> + +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 +a value of 5. If you enable PPP debugging with the "debug" option and +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>] + ^^^^^^^^^^^^ + +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 may need to get Eric Young's libdes library in +order to use my MS-CHAP extensions. A lot of UNIX systems already +have DES encryption available via the crypt(3), encrypt(3) and +setkey(3) interfaces. Some may (such as that on Digital UNIX) +provide only the encryption mechanism and will not perform +decryption. This is okay. We only need to encrypt to perform +MS-CHAP authentication. + +If you have encrypt/setkey available, then hopefully you need only +define these two things in your Makefile: -DUSE_CRYPT and -DCHAPMS. +Skip the paragraphs below about obtaining and building libdes. Do +the "make clean" and "make" as described below. Linux users +should not need to modify their Makefiles. Instead, +just do "make CHAPMS=1 USE_CRYPT=1". + +If you don't have encrypt and setkey, you will need Eric Young's +libdes library. 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. + + +CONFIGURATION + +If you've never used PPPD with CHAP before, read the man page (type +"man pppd") and read the description in there. Basically, you need to +edit the "chap-secrets" file typically named /etc/ppp/chap-secrets. +This should contain the following two lines for each system with which +you use CHAP (with no leading blanks): + + RemoteHost Account Secret + Account RemoteHost Secret + +Note that you need both lines and that item 1 and 2 are swapped in the +second line. I'm not sure why you need it twice, but it works and I didn't +have time to look into it further. The "RemoteHost" is a somewhat +arbitrary name for the remote Windows NT system you're dialing. It doesn't +have to match the NT system's name, but it *does* have to match what you +use with the "remotename" parameter. The "Account" is the Windows NT +account name you have been told to use when dialing, and the "Secret" is +the password for that account. For example, if your service provider calls +their machine "DialupNT" and tells you your account and password are +"customer47" and "foobar", add the following to your chap-secrets file: + + DialupNT customer47 foobar + customer47 DialupNT foobar + +The only other thing you need to do for MS-CHAP (compared to normal CHAP) +is to always use the "remotename" option, either on the command line or in +your "options" file (see the pppd man page for details). In the case of +the above example, you would need to use the following command line: + + pppd name customer47 remotename DialupNT <other options> + +or add: + + name customer47 + remotename DialupNT + +to your PPPD "options" file. + +The "remotename" option is required for MS-CHAP since Microsoft PPP servers +don't send their system name in the CHAP challenge packet. + + +E=691 (AUTHENTICATION_FAILURE) ERRORS WHEN YOU HAVE THE VALID SECRET (PASSWORD) + +If your RAS server is not the domain controller and is not a 'stand-alone' +server then it must make a query to the domain controller for your domain. + +You need to specify the domain name with the user name when you attempt to +use this type of a configuration. The domain name is specified with the +local name in the chap-secrets file and with the option for the 'name' +parameter. + +For example, the previous example would become: + + DialupNT domain\\customer47 foobar + domain\\customer47 DialupNT foobar + +and + + pppd name 'domain\\customer47' remotename DialupNT <other options> + +or add: + + name domain\\customer47 + remotename DialupNT + +when the Windows NT domain name is simply called 'domain'. + + +TROUBLESHOOTING + +Assuming that everything else has been configured correctly for PPP and +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: + + 646 ERROR_RESTRICTED_LOGON_HOURS + 647 ERROR_ACCT_DISABLED + 648 ERROR_PASSWD_EXPIRED + 649 ERROR_NO_DIALIN_PERMISSION + 691 ERROR_AUTHENTICATION_FAILURE + 709 ERROR_CHANGING_PASSWORD + +You'll see these in your pppd log as a line similar to: + + Remote message: E=649 R=0 + +The "E=" is the error number from the table above, and the "R=" flag +indicates whether the error is transient and the client should retry. If +you consistently get error 691, then either you're using the wrong account +name/password, or the DES library or MD4 hashing (in md4.c) aren't working +properly. Verify your account name and password (use a Windows NT or +Windows 95 system to dial-in if you have one available). If that checks +out, test the DES library with the "destest" program included with the DES +library. If DES checks out, the md4.c routines are probably failing +(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. + +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. + +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 +passwords in the "chap-secrets" file. A utility that spits out the ASCII +hex MD4 hash of a given password would be nice, and would allow that hash +to be used in chap-secrets in place of the password. The code to do this +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. |