otp_mppe.c   [plain text]

/*
 * $Id$
 *
 *   This program is free software; you can redistribute it and/or modify
 *   it under the terms of the GNU General Public License as published by
 *   the Free Software Foundation; either version 2 of the License, or
 *   (at your option) any later version.
 *
 *   This program is distributed in the hope that it will be useful,
 *   but WITHOUT ANY WARRANTY; without even the implied warranty of
 *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *   GNU General Public License for more details.
 *
 *   You should have received a copy of the GNU General Public License
 *   along with this program; if not, write to the Free Software
 *   Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA
 *
 * Copyright 2001,2002  Google, Inc.
 * Copyright 2005,2006 TRI-D Systems, Inc.
 */

#include <freeradius-devel/ident.h>
RCSID("$Id$")

/* avoid inclusion of these FR headers which conflict w/ OpenSSL */
#define _FR_MD4_H
#define _FR_SHA1_H

#include <freeradius-devel/rad_assert.h>

#include "extern.h"
#include "otp.h"
#include "otp_mppe.h"

#include <openssl/des.h>
#include <openssl/md4.h>
#include <openssl/md5.h>
#include <openssl/sha.h>

#include <string.h>

/*
 * Add MPPE attributes to a request, if required.
 */
void
otp_mppe(REQUEST *request, otp_pwe_t pwe, const otp_option_t *opt,
         const char *passcode)
{
  VALUE_PAIR **avp = &request->reply->vps;
  VALUE_PAIR *cvp, *rvp, *vp;

  cvp = pairfind(request->packet->vps, pwattr[pwe - 1]);
  rvp = pairfind(request->packet->vps, pwattr[pwe]);

  switch (pwe) {
  case PWE_PAP:
  case PWE_CHAP:
    return;

  case PWE_MSCHAP:
    /* First, set some related attributes. */
    vp = pairmake("MS-MPPE-Encryption-Policy",
                  otp_mppe_policy[opt->mschap_mppe_policy], T_OP_EQ);
    rad_assert(vp != NULL);
    pairadd(avp, vp);
    vp = pairmake("MS-MPPE-Encryption-Types",
                  otp_mppe_types[opt->mschap_mppe_types], T_OP_EQ);
    rad_assert(vp != NULL);
    pairadd(avp, vp);

    /* If no MPPE, we're done. */
    if (!opt->mschap_mppe_policy)
      return;

    /*
     * Generate the MS-CHAP-MPPE-Keys attribute.  This is not specified
     * anywhere -- RFC 2548, par. 2.4.1 is the authority but it has
     * typos and omissions that make this unimplementable.  The
     * code here is based on experimental results provided by
     * Takahiro Wagatsuma <waga@sic.shibaura-it.ac.jp>.
     * We only support 128-bit keys derived from the NT hash; 40-bit
     * and 56-bit keys are derived from the LM hash, which besides
     * being deprecated, has severe security problems.
     */
    {
      size_t i, passcode_len;
      unsigned char password_unicode[2 * OTP_MAX_PASSCODE_LEN];
      unsigned char password_md[MD4_DIGEST_LENGTH];
      unsigned char mppe_keys[32];
      /*                    0x    ASCII(mppe_keys)      '\0' */
      char mppe_keys_string[2 + (2 * sizeof(mppe_keys)) + 1];

      /* Zero the LM-Key sub-field (and padding). */
      (void) memset(mppe_keys, 0, sizeof(mppe_keys));

      /*
       * The NT-Key sub-field is MD4(MD4(unicode(password))).
       * Start by hashing the unicode passcode.
       * This is broken because unicode chars are machine-ordered,
       * but the spec (RFC 2433) doesn't say how to prepare
       * the password for md4 (other than by example values).
       */
      passcode_len = strlen(passcode);
      for (i = 0; i < passcode_len; ++i) {
        /* Set the high order 8 bits to 0 (little-endian) */
        password_unicode[i * 2] = *passcode++;
        password_unicode[i * 2 + 1] = 0;
      }
      /* first md4 */
      (void) MD4(password_unicode, 2 * passcode_len, password_md);
      /* second md4 */
      (void) MD4(password_md, MD4_DIGEST_LENGTH, &mppe_keys[8]);

#if 0 /* encoding now handled in lib/radius.c:rad_pwencode() */
      {
        unsigned char md5_md[MD5_DIGEST_LENGTH];
        unsigned char encode_buf[AUTH_VECTOR_LEN + MAX_STRING_LEN];
        int secretlen;

        /* Now we must encode the key as User-Password is encoded. */
        secretlen = strlen(request->secret);
        (void) memcpy(encode_buf, request->secret, secretlen);
        (void) memcpy(encode_buf + secretlen, request->packet->vector,
                      AUTH_VECTOR_LEN);
        (void) MD5(encode_buf, secretlen + AUTH_VECTOR_LEN, md5_md);
        for (i = 0; i < 16; ++i)
          mppe_keys[i] ^= md5_md[i];
        (void) memcpy(encode_buf + secretlen, mppe_keys, MD5_DIGEST_LENGTH);
        (void) MD5(encode_buf, secretlen + MD5_DIGEST_LENGTH, md5_md);
        for (i = 0; i < 16; ++i)
          mppe_keys[i + 16] ^= md5_md[i];
      }
#endif /* 0 */

      /* Whew.  Now stringify it for pairmake(). */
      mppe_keys_string[0] = '0';
      mppe_keys_string[1] = 'x';
      for (i = 0; i < 32; ++i)
        (void) sprintf(&mppe_keys_string[i*2+2], "%02X", mppe_keys[i]);
      vp = pairmake("MS-CHAP-MPPE-Keys", mppe_keys_string, T_OP_EQ);
      rad_assert(vp != NULL);
      pairadd(avp, vp);
    } /* (doing mppe) */
  break; /* PWE_MSCHAP */

  case PWE_MSCHAP2:
  {
    size_t i;
    unsigned char password_md_md[MD4_DIGEST_LENGTH];

    /*
     * MS-CHAPv2 requires mutual authentication; we must prove
     * that we know the secret.  This is a bit circuitous: set
     * MD1 = SHA(MD4(MD4(unicode(password)))|NT_RESPONSE|MAGIC1),
     * MD2 = MSB8(SHA(PEER_CHALLENGE|MS_CHAP_CHALLENGE|USERNAME)),
     * and finally use SHA(MD1|MD2|MAGIC2) as the authenticator.
     * The authenticator is returned as the string "S=<auth>",
     * <auth> is the authenticator expressed as [uppercase] ASCII.
     * See RFC 2759.
     */
    {
      size_t passcode_len;
      unsigned char password_unicode[2 * OTP_MAX_PASSCODE_LEN];
      unsigned char password_md[MD4_DIGEST_LENGTH];

      SHA_CTX ctx;
      unsigned char md1[SHA_DIGEST_LENGTH];
      unsigned char md2[SHA_DIGEST_LENGTH];
      unsigned char auth_md[SHA_DIGEST_LENGTH];
      /*                  S=  (  ASCII(auth_md)   )  \0 */
      char auth_md_string[2 + (2 * sizeof(auth_md)) + 1];
      /*
       * ugh.  The ASCII authenticator (auth_md_string) is sent
       * along with a single (useless) binary byte (the ID).
       * So we must "stringify" it again (for pairmake()) since the
       * binary byte requires the attribute to be of type "octets".
       */
      /*                    0x  (ID) ( ASCII("S="ASCII(auth_md))) */
      char auth_octet_string[2 + 2 + (2 * sizeof(auth_md_string))];

      char *username = request->username->vp_strvalue;
      int username_len = request->username->length;

      /* "Magic server to client signing constant" */
      unsigned char magic1[39] =
        { 0x4D, 0x61, 0x67, 0x69, 0x63, 0x20, 0x73, 0x65, 0x72, 0x76,
          0x65, 0x72, 0x20, 0x74, 0x6F, 0x20, 0x63, 0x6C, 0x69, 0x65,
          0x6E, 0x74, 0x20, 0x73, 0x69, 0x67, 0x6E, 0x69, 0x6E, 0x67,
          0x20, 0x63, 0x6F, 0x6E, 0x73, 0x74, 0x61, 0x6E, 0x74 };
      /* "Pad to make it do more than one iteration" */
      unsigned char magic2[41] =
        { 0x50, 0x61, 0x64, 0x20, 0x74, 0x6F, 0x20, 0x6D, 0x61, 0x6B,
          0x65, 0x20, 0x69, 0x74, 0x20, 0x64, 0x6F, 0x20, 0x6D, 0x6F,
          0x72, 0x65, 0x20, 0x74, 0x68, 0x61, 0x6E, 0x20, 0x6F, 0x6E,
          0x65, 0x20, 0x69, 0x74, 0x65, 0x72, 0x61, 0x74, 0x69, 0x6F,
          0x6E };

      /*
       * Start by hashing the unicode passcode.
       * This is broken because unicode chars are machine-ordered,
       * but the spec (RFC 2759) doesn't say how to prepare
       * the password for md4 (other than by example values).
       */
      passcode_len = strlen(passcode);
      for (i = 0; i < passcode_len; ++i) {
        /* Set the high order 8 bits to 0 (little-endian) */
        password_unicode[i * 2] = *passcode++;
        password_unicode[i * 2 + 1] = 0;
      }
      /* first md4 */
      (void) MD4(password_unicode, 2 * passcode_len, password_md);
      /* second md4 */
      (void) MD4(password_md, MD4_DIGEST_LENGTH, password_md_md);

      /* MD1 */
      SHA1_Init(&ctx);
      SHA1_Update(&ctx, password_md_md, MD4_DIGEST_LENGTH);
      SHA1_Update(&ctx, rvp->vp_strvalue + 26, 24);
      SHA1_Update(&ctx, magic1, sizeof(magic1));
      SHA1_Final(md1, &ctx);

      /* MD2 */
      SHA1_Init(&ctx);
      SHA1_Update(&ctx, rvp->vp_strvalue + 2, 16);
      SHA1_Update(&ctx, cvp->vp_strvalue, 16);
      SHA1_Update(&ctx, username, username_len);
      SHA1_Final(md2, &ctx);

      /* The Authenticator */
      SHA1_Init(&ctx);
      SHA1_Update(&ctx, md1, SHA_DIGEST_LENGTH);
      SHA1_Update(&ctx, md2, 8);
      SHA1_Update(&ctx, magic2, sizeof(magic2));
      SHA1_Final(auth_md, &ctx);

      /* String conversion. */
      auth_md_string[0] = 'S';
      auth_md_string[1] = '=';
      for (i = 0; i < sizeof(auth_md); ++i)
        (void) sprintf(&auth_md_string[i * 2 + 2], "%02X", auth_md[i]);

      /* And then octet conversion.  Ugh! */
      auth_octet_string[0] = '0';
      auth_octet_string[1] = 'x';
      (void) sprintf(&auth_octet_string[2], "%02X", rvp->vp_strvalue[0]);
      for (i = 0; i < sizeof(auth_md_string) - 1; ++i)
        (void) sprintf(&auth_octet_string[i * 2 +4], "%02X", auth_md_string[i]);

      vp = pairmake("MS-CHAP2-Success", auth_octet_string, T_OP_EQ);
      rad_assert(vp != NULL);
      pairadd(avp, vp);
    } /* Generate mutual auth info. */

    /*
     * Now, set some MPPE related attributes.
     */
    vp = pairmake("MS-MPPE-Encryption-Policy",
                  otp_mppe_policy[opt->mschapv2_mppe_policy], T_OP_EQ);
    rad_assert(vp != NULL);
    pairadd(avp, vp);
    vp = pairmake("MS-MPPE-Encryption-Types",
                  otp_mppe_types[opt->mschapv2_mppe_types], T_OP_EQ);
    rad_assert(vp != NULL);
    pairadd(avp, vp);

    /* If no MPPE, we're done. */
    if (!opt->mschapv2_mppe_policy)
      return;

    /*
     * Generate the MPPE initial session key, per RFC 3079.
     * (Although, RFC 2548 leaves us guessing at how to generate this.)
     * For MS-CHAPv2 we support all key lengths (40-, 56- and 128-bit),
     * although MPPE via RADIUS supports only 40- and 128-bit keys.
     * This is a bit more complicated than MS-CHAP.  Start by generating
     * a "master session key"
     *    MSB16(SHA(NTPasswordHashHash|NT_RESPONSE|MAGIC1)), where
     * NTPasswordHashHash is MD4(MD4(unicode(password))), NT_RESPONSE
     * is from the MS-CHAP2-Response attribute, and MAGIC1 is a
     * constant from RFC 3079.  Then, we derive asymmetric send/receive
     * keys from the master session key.  The "master send key" is
     *     MSBx(SHA(MASTERKEY|SHSPAD1|MAGIC3|SHSPAD2)),
     * and the "master receive key" is
     *     MSBx(SHA(MASTERKEY|SHSPAD1|MAGIC2|SHSPAD2)), where
     * MASTERKEY is the "master session key" generated above, and the
     * other values are constants from RFC 3079.  MSBx is the x-most
     * significant bytes, where x is 5, 7, or 16 as appropriate for
     * the desired key length.  We always generate 16 byte (128-bit)
     * keys, the NAS is required to truncate as needed.
     */
    {
      /* These constants and key vars are named from RFC 3079. */
      /* "This is the MPPE Master Key" */
      unsigned char Magic1[27] =
        { 0x54, 0x68, 0x69, 0x73, 0x20, 0x69, 0x73, 0x20, 0x74,
          0x68, 0x65, 0x20, 0x4d, 0x50, 0x50, 0x45, 0x20, 0x4d,
          0x61, 0x73, 0x74, 0x65, 0x72, 0x20, 0x4b, 0x65, 0x79 };
      /* "On the client side, this is the send key; "
         "on the server side, it is the receive key." */
      unsigned char Magic2[84] =
        { 0x4f, 0x6e, 0x20, 0x74, 0x68, 0x65, 0x20, 0x63, 0x6c, 0x69,
          0x65, 0x6e, 0x74, 0x20, 0x73, 0x69, 0x64, 0x65, 0x2c, 0x20,
          0x74, 0x68, 0x69, 0x73, 0x20, 0x69, 0x73, 0x20, 0x74, 0x68,
          0x65, 0x20, 0x73, 0x65, 0x6e, 0x64, 0x20, 0x6b, 0x65, 0x79,
          0x3b, 0x20, 0x6f, 0x6e, 0x20, 0x74, 0x68, 0x65, 0x20, 0x73,
          0x65, 0x72, 0x76, 0x65, 0x72, 0x20, 0x73, 0x69, 0x64, 0x65,
          0x2c, 0x20, 0x69, 0x74, 0x20, 0x69, 0x73, 0x20, 0x74, 0x68,
          0x65, 0x20, 0x72, 0x65, 0x63, 0x65, 0x69, 0x76, 0x65, 0x20,
          0x6b, 0x65, 0x79, 0x2e };
      /* "On the client side, this is the receive key; "
         "on the server side, it is the send key." */
      unsigned char Magic3[84] =
        { 0x4f, 0x6e, 0x20, 0x74, 0x68, 0x65, 0x20, 0x63, 0x6c, 0x69,
          0x65, 0x6e, 0x74, 0x20, 0x73, 0x69, 0x64, 0x65, 0x2c, 0x20,
          0x74, 0x68, 0x69, 0x73, 0x20, 0x69, 0x73, 0x20, 0x74, 0x68,
          0x65, 0x20, 0x72, 0x65, 0x63, 0x65, 0x69, 0x76, 0x65, 0x20,
          0x6b, 0x65, 0x79, 0x3b, 0x20, 0x6f, 0x6e, 0x20, 0x74, 0x68,
          0x65, 0x20, 0x73, 0x65, 0x72, 0x76, 0x65, 0x72, 0x20, 0x73,
          0x69, 0x64, 0x65, 0x2c, 0x20, 0x69, 0x74, 0x20, 0x69, 0x73,
          0x20, 0x74, 0x68, 0x65, 0x20, 0x73, 0x65, 0x6e, 0x64, 0x20,
          0x6b, 0x65, 0x79, 0x2e };
      unsigned char SHSpad1[40] =
        { 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
          0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
          0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
          0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00 };
      unsigned char SHSpad2[40] =
        { 0xf2, 0xf2, 0xf2, 0xf2, 0xf2, 0xf2, 0xf2, 0xf2, 0xf2, 0xf2,
          0xf2, 0xf2, 0xf2, 0xf2, 0xf2, 0xf2, 0xf2, 0xf2, 0xf2, 0xf2,
          0xf2, 0xf2, 0xf2, 0xf2, 0xf2, 0xf2, 0xf2, 0xf2, 0xf2, 0xf2,
          0xf2, 0xf2, 0xf2, 0xf2, 0xf2, 0xf2, 0xf2, 0xf2, 0xf2, 0xf2 };
      unsigned char MasterKey[16];
      unsigned char MasterSendKey[16];
      unsigned char MasterReceiveKey[16];

      SHA_CTX ctx;
      unsigned char sha_md[SHA_DIGEST_LENGTH];
#if 0 /* salting/encoding now handled in lib/radius.c:tunnel_pwencode() */
      unsigned char md5_md[MD5_DIGEST_LENGTH];

      /*   From RFC 2548:           S                 R           A */
      unsigned char encode_buf[MAX_STRING_LEN + AUTH_VECTOR_LEN + 2];
      int secretlen;

      /* A useless value required by RFC 2548. */
      unsigned char salt[2];
      unsigned char mppe_key[32]; /* 1 + 16 + padding */
      /*                           0x   (   ASCII(salt)  ) */
      unsigned char mppe_key_string[2 + (2 * sizeof(salt)) +
      /*                            (   ASCII(mppe_key)  )  \0 */
                                    (2 * sizeof(mppe_key)) + 1];
#else /* 0 */
      /*                           0x   (   ASCII(mppe_key)   )  \0 */
      unsigned char mppe_key_string[2 + (2 * sizeof(MasterKey)) + 1];
#endif /* else !0 */

      /* Generate the master session key. */
      SHA1_Init(&ctx);
      SHA1_Update(&ctx, password_md_md, MD4_DIGEST_LENGTH);
      SHA1_Update(&ctx, rvp->vp_strvalue + 26, 24);
      SHA1_Update(&ctx, Magic1, sizeof(Magic1));
      SHA1_Final(sha_md, &ctx);
      (void) memcpy(MasterKey, sha_md, 16);

      /* Generate the master send key. */
      SHA1_Init(&ctx);
      SHA1_Update(&ctx, MasterKey, 16);
      SHA1_Update(&ctx, SHSpad1, 40);
      SHA1_Update(&ctx, Magic3, sizeof(Magic3));
      SHA1_Update(&ctx, SHSpad2, 40);
      SHA1_Final(sha_md, &ctx);
      (void) memcpy(MasterSendKey, sha_md, 16);

      /* Generate the master receive key. */
      SHA1_Init(&ctx);
      SHA1_Update(&ctx, MasterKey, 16);
      SHA1_Update(&ctx, SHSpad1, 40);
      SHA1_Update(&ctx, Magic2, sizeof(Magic3));
      SHA1_Update(&ctx, SHSpad2, 40);
      SHA1_Final(sha_md, &ctx);
      (void) memcpy(MasterReceiveKey, sha_md, 16);

      /*
       * Now, generate the MS-MPPE-Send-Key attribute.
       */
#if 0
      /* Setup the salt value. */
      salt[0] = 0x80;
      salt[1] = 0x01;

      /* Encode the key. */
      (void) memset(mppe_key, 0, sizeof(mppe_key));
      mppe_key[0] = 16; /* length */
      (void) memcpy(&mppe_key[1], MasterSendKey, 16);
      secretlen = strlen(request->secret);
      (void) memcpy(encode_buf, request->secret, secretlen);
      (void) memcpy(encode_buf + secretlen, request->packet->vector,
                    AUTH_VECTOR_LEN);
      (void) memcpy(encode_buf + secretlen + 16, salt, 2);
      (void) MD5(encode_buf, secretlen + AUTH_VECTOR_LEN + 2, md5_md);
      for (i = 0; i < 16; ++i)
        mppe_key[i] ^= md5_md[i];
      (void) memcpy(encode_buf + secretlen, mppe_key, 16);
      (void) MD5(encode_buf, secretlen + 16, md5_md);
      for (i = 0; i < 16; ++i)
        mppe_key[i + 16] ^= md5_md[i];

      /* Whew.  Now stringify it for pairmake(). */
      mppe_key_string[0] = '0';
      mppe_key_string[1] = 'x';
      (void) sprintf(&mppe_key_string[2], "%02X", salt[0]);
      (void) sprintf(&mppe_key_string[4], "%02X", salt[1]);
      for (i = 0; i < sizeof(mppe_key); ++i)
        (void) sprintf(&mppe_key_string[i*2+6], "%02X", mppe_key[i]);
#else /* 0 */
      mppe_key_string[0] = '0';
      mppe_key_string[1] = 'x';
      for (i = 0; i < sizeof(MasterSendKey); ++i)
        (void) sprintf(&mppe_key_string[i*2+2], "%02X", MasterSendKey[i]);
#endif /* else !0 */
      vp = pairmake("MS-MPPE-Send-Key", mppe_key_string, T_OP_EQ);
      rad_assert(vp != NULL);
      pairadd(avp, vp);

      /*
       * Generate the MS-MPPE-Recv-Key attribute.
       */
#if 0
      /* Setup the salt value. */
      salt[0] = 0x80;
      salt[1] = 0x02;

      /* Encode the key. */
      (void) memset(mppe_key, 0, sizeof(mppe_key));
      mppe_key[0] = 16; /* length */
      (void) memcpy(&mppe_key[1], MasterReceiveKey, 16);
      secretlen = strlen(request->secret);
      (void) memcpy(encode_buf, request->secret, secretlen);
      (void) memcpy(encode_buf + secretlen, request->packet->vector,
                    AUTH_VECTOR_LEN);
      (void) memcpy(encode_buf + secretlen + 16, salt, 2);
      (void) MD5(encode_buf, secretlen + AUTH_VECTOR_LEN + 2, md5_md);
      for (i = 0; i < 16; ++i)
        mppe_key[i] ^= md5_md[i];
      (void) memcpy(encode_buf + secretlen, mppe_key, 16);
      (void) MD5(encode_buf, secretlen + 16, md5_md);
      for (i = 0; i < 16; ++i)
        mppe_key[i + 16] ^= md5_md[i];

      /* Whew.  Now stringify it for pairmake(). */
      mppe_key_string[0] = '0';
      mppe_key_string[1] = 'x';
      (void) sprintf(&mppe_key_string[2], "%02X", salt[0]);
      (void) sprintf(&mppe_key_string[4], "%02X", salt[1]);
      for (i = 0; i < sizeof(mppe_key); ++i)
        (void) sprintf(&mppe_key_string[i*2+6], "%02X", mppe_key[i]);
#else /* 0 */
      mppe_key_string[0] = '0';
      mppe_key_string[1] = 'x';
      for (i = 0; i < sizeof(MasterReceiveKey); ++i)
        (void) sprintf(&mppe_key_string[i*2+2], "%02X", MasterReceiveKey[i]);
#endif /* else !0 */
      vp = pairmake("MS-MPPE-Recv-Key", mppe_key_string, T_OP_EQ);
      rad_assert(vp != NULL);
      pairadd(avp, vp);

    } /* (doing mppe) */
  } /* PWE_MSCHAP2 */
  break; /* PWE_MSCHAP2 */

  } /* switch (pwe) */

  return;
}