/*

 * Dropbear - a SSH2 server

 * 

 * Copyright (c) 2002,2003 Matt Johnston

 * Copyright (c) 2004 by Mihnea Stoenescu

 * All rights reserved.

 * 

 * Permission is hereby granted, free of charge, to any person obtaining a copy

 * of this software and associated documentation files (the "Software"), to deal

 * in the Software without restriction, including without limitation the rights

 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell

 * copies of the Software, and to permit persons to whom the Software is

 * furnished to do so, subject to the following conditions:

 * 

 * The above copyright notice and this permission notice shall be included in

 * all copies or substantial portions of the Software.

 * 

 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR

 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,

 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE

 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER

 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,

 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE

 * SOFTWARE. */

#include "includes.h"

#include "dbutil.h"

#include "algo.h"

#include "buffer.h"

#include "session.h"

#include "kex.h"

#include "ssh.h"

#include "packet.h"

#include "bignum.h"

#include "dbrandom.h"

#include "runopts.h"

#include "ecc.h"

#include "gensignkey.h"

static void send_msg_kexdh_reply(mp_int *dh_e, buffer *ecdh_qs);

#if DROPBEAR_EXT_INFO

static void send_msg_ext_info(void);

#endif

/* Handle a diffie-hellman key exchange initialisation. This involves

 * calculating a session key reply value, and corresponding hash. These

 * are carried out by send_msg_kexdh_reply(). recv_msg_kexdh_init() calls

 * that function, then brings the new keys into use */

void recv_msg_kexdh_init() {

  DEF_MP_INT(dh_e);

  buffer *ecdh_qs = NULL;

  TRACE(("enter recv_msg_kexdh_init"))

  if (!ses.kexstate.recvkexinit) {

    dropbear_exit("Premature kexdh_init message received");

  }

  switch (ses.newkeys->algo_kex->mode) {

#if DROPBEAR_NORMAL_DH

    case DROPBEAR_KEX_NORMAL_DH:

      m_mp_init(&dh_e);

      if (buf_getmpint(ses.payload, &dh_e) != DROPBEAR_SUCCESS) {

        dropbear_exit("Bad kex value");

      }

      break;

#endif

#if DROPBEAR_ECDH

    case DROPBEAR_KEX_ECDH:

#endif

#if DROPBEAR_CURVE25519

    case DROPBEAR_KEX_CURVE25519:

#endif

#if DROPBEAR_ECDH || DROPBEAR_CURVE25519

      ecdh_qs = buf_getstringbuf(ses.payload);

      break;

#endif

  }

  if (ses.payload->pos != ses.payload->len) {

    dropbear_exit("Bad kex value");

  }

  send_msg_kexdh_reply(&dh_e, ecdh_qs);

  mp_clear(&dh_e);

  if (ecdh_qs) {

    buf_free(ecdh_qs);

    ecdh_qs = NULL;

  }

  send_msg_newkeys();

#if DROPBEAR_EXT_INFO

  /* Only send it following the first newkeys */

  if (!ses.kexstate.donesecondkex && ses.allow_ext_info) {

    send_msg_ext_info();

  }

#endif

  ses.requirenext = SSH_MSG_NEWKEYS;

  TRACE(("leave recv_msg_kexdh_init"))

}

#if DROPBEAR_DELAY_HOSTKEY

static void svr_ensure_hostkey() {

  const char* fn = NULL;

  char *expand_fn = NULL;

  enum signkey_type type = ses.newkeys->algo_hostkey;

  void **hostkey = signkey_key_ptr(svr_opts.hostkey, type);

  int ret = DROPBEAR_FAILURE;

  if (hostkey && *hostkey) {

    return;

  }

  switch (type)

  {

#if DROPBEAR_RSA

    case DROPBEAR_SIGNKEY_RSA:

      fn = RSA_PRIV_FILENAME;

      break;

#endif

#if DROPBEAR_DSS

    case DROPBEAR_SIGNKEY_DSS:

      fn = DSS_PRIV_FILENAME;

      break;

#endif

#if DROPBEAR_ECDSA

    case DROPBEAR_SIGNKEY_ECDSA_NISTP256:

    case DROPBEAR_SIGNKEY_ECDSA_NISTP384:

    case DROPBEAR_SIGNKEY_ECDSA_NISTP521:

      fn = ECDSA_PRIV_FILENAME;

      break;

#endif

#if DROPBEAR_ED25519

    case DROPBEAR_SIGNKEY_ED25519:

      fn = ED25519_PRIV_FILENAME;

      break;

#endif

    default:

      dropbear_assert(0);

  }

  expand_fn = expand_homedir_path(fn);

  ret = readhostkey(expand_fn, svr_opts.hostkey, &type);

  if (ret == DROPBEAR_SUCCESS) {

    goto out;

  }

  if (signkey_generate(type, 0, expand_fn, 1) == DROPBEAR_FAILURE) {

    goto out;

  }

  /* Read what we just generated (or another process raced us) */

  ret = readhostkey(expand_fn, svr_opts.hostkey, &type);

  if (ret == DROPBEAR_SUCCESS) {

    char *fp = NULL;

    unsigned int len;

    buffer *key_buf = buf_new(MAX_PUBKEY_SIZE);

    buf_put_pub_key(key_buf, svr_opts.hostkey, type);

    buf_setpos(key_buf, 4);

    len = key_buf->len - key_buf->pos;

    fp = sign_key_fingerprint(buf_getptr(key_buf, len), len);

    dropbear_log(LOG_INFO, "Generated hostkey %s, fingerprint is %s",

      expand_fn, fp);

    m_free(fp);

    buf_free(key_buf);

  }

out:

  if (ret == DROPBEAR_FAILURE) {

    dropbear_exit("Couldn't read or generate hostkey %s", expand_fn);

  }

    m_free(expand_fn);

}

#endif

/* Generate our side of the diffie-hellman key exchange value (dh_f), and

 * calculate the session key using the diffie-hellman algorithm. Following

 * that, the session hash is calculated, and signed with RSA or DSS. The

 * result is sent to the client. 

 *

 * See the transport RFC4253 section 8 for details

 * or RFC5656 section 4 for elliptic curve variant. */

static void send_msg_kexdh_reply(mp_int *dh_e, buffer *ecdh_qs) {

  TRACE(("enter send_msg_kexdh_reply"))

  /* we can start creating the kexdh_reply packet */

  CHECKCLEARTOWRITE();

#if DROPBEAR_DELAY_HOSTKEY

  if (svr_opts.delay_hostkey)

  {

    svr_ensure_hostkey();

  }

#endif

#if DROPBEAR_FUZZ

  if (fuzz.fuzzing && fuzz.skip_kexmaths) {

    fuzz_fake_send_kexdh_reply();

    return;

  }

#endif

  buf_putbyte(ses.writepayload, SSH_MSG_KEXDH_REPLY);

  buf_put_pub_key(ses.writepayload, svr_opts.hostkey,

      ses.newkeys->algo_hostkey);

  switch (ses.newkeys->algo_kex->mode) {

#if DROPBEAR_NORMAL_DH

    case DROPBEAR_KEX_NORMAL_DH:

      {

      struct kex_dh_param * dh_param = gen_kexdh_param();

      kexdh_comb_key(dh_param, dh_e, svr_opts.hostkey);

      /* put f */

      buf_putmpint(ses.writepayload, &dh_param->pub);

      free_kexdh_param(dh_param);

      }

      break;

#endif

#if DROPBEAR_ECDH

    case DROPBEAR_KEX_ECDH:

      {

      struct kex_ecdh_param *ecdh_param = gen_kexecdh_param();

      kexecdh_comb_key(ecdh_param, ecdh_qs, svr_opts.hostkey);

      buf_put_ecc_raw_pubkey_string(ses.writepayload, &ecdh_param->key);

      free_kexecdh_param(ecdh_param);

      }

      break;

#endif

#if DROPBEAR_CURVE25519

    case DROPBEAR_KEX_CURVE25519:

      {

      struct kex_curve25519_param *param = gen_kexcurve25519_param();

      kexcurve25519_comb_key(param, ecdh_qs, svr_opts.hostkey);

      buf_putstring(ses.writepayload, param->pub, CURVE25519_LEN);

      free_kexcurve25519_param(param);

      }

      break;

#endif

  }

  /* calc the signature */

  buf_put_sign(ses.writepayload, svr_opts.hostkey, 

      ses.newkeys->algo_signature, ses.hash);

  /* the SSH_MSG_KEXDH_REPLY is done */

  encrypt_packet();

  TRACE(("leave send_msg_kexdh_reply"))

}

#if DROPBEAR_EXT_INFO

/* Only used for server-sig-algs on the server side */

static void send_msg_ext_info(void) {

  TRACE(("enter send_msg_ext_info"))

  buf_putbyte(ses.writepayload, SSH_MSG_EXT_INFO);

  /* nr-extensions */

  buf_putint(ses.writepayload, 1);

  buf_putstring(ses.writepayload, SSH_SERVER_SIG_ALGS, strlen(SSH_SERVER_SIG_ALGS));

  buf_put_algolist_all(ses.writepayload, sigalgs, 1);

  encrypt_packet();

  TRACE(("leave send_msg_ext_info"))

}

#endif