--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/svr-kex.c	Tue Jun 01 02:46:09 2004 +0000
@@ -0,0 +1,274 @@
+/*
+ * Dropbear - a SSH2 server
+ * 
+ * Copyright (c) 2002,2003 Matt Johnston
+ * 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 "random.h"
+
+
+static void send_msg_kexdh_reply(mp_int *dh_e);
+
+/* 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() {
+
+	mp_int dh_e;
+
+	TRACE(("enter recv_msg_kexdh_init"));
+	if (!ses.kexstate.recvkexinit) {
+		dropbear_exit("Premature kexdh_init message received");
+	}
+
+	m_mp_init(&dh_e);
+	buf_getmpint(ses.payload, &dh_e);
+
+	send_msg_kexdh_reply(&dh_e);
+
+	mp_clear(&dh_e);
+
+	send_msg_newkeys();
+	ses.expecting = SSH_MSG_NEWKEYS;
+	TRACE(("leave recv_msg_kexdh_init"));
+}
+	
+/* 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 ietf-secsh-transport draft, section 6, for details */
+static void send_msg_kexdh_reply(mp_int *dh_e) {
+
+	mp_int dh_p, dh_q, dh_g, dh_y, dh_f;
+	unsigned char randbuf[DH_P_LEN];
+	int dh_q_len;
+	hash_state hs;
+
+	TRACE(("enter send_msg_kexdh_reply"));
+	
+	m_mp_init_multi(&dh_g, &dh_p, &dh_q, &dh_y, &dh_f, NULL);
+
+	/* read the prime and generator*/
+	if (mp_read_unsigned_bin(&dh_p, (unsigned char*)dh_p_val, DH_P_LEN)
+			!= MP_OKAY) {
+		dropbear_exit("Diffie-Hellman error");
+	}
+	
+	if (mp_set_int(&dh_g, DH_G_VAL) != MP_OKAY) {
+		dropbear_exit("Diffie-Hellman error");
+	}
+
+	/* calculate q = (p-1)/2 */
+	if (mp_sub_d(&dh_p, 1, &dh_y) != MP_OKAY) { /*dh_y is just a temp var here*/
+		dropbear_exit("Diffie-Hellman error");
+	}
+	if (mp_div_2(&dh_y, &dh_q) != MP_OKAY) {
+		dropbear_exit("Diffie-Hellman error");
+	}
+
+	dh_q_len = mp_unsigned_bin_size(&dh_q);
+
+	/* calculate our random value dh_y */
+	do {
+		assert((unsigned int)dh_q_len <= sizeof(randbuf));
+		genrandom(randbuf, dh_q_len);
+		if (mp_read_unsigned_bin(&dh_y, randbuf, dh_q_len) != MP_OKAY) {
+			dropbear_exit("Diffie-Hellman error");
+		}
+	} while (mp_cmp(&dh_y, &dh_q) == MP_GT || mp_cmp_d(&dh_y, 0) != MP_GT);
+
+	/* f = g^y mod p */
+	if (mp_exptmod(&dh_g, &dh_y, &dh_p, &dh_f) != MP_OKAY) {
+		dropbear_exit("Diffie-Hellman error");
+	}
+	mp_clear(&dh_g);
+
+	/* K = e^y mod p */
+	ses.dh_K = (mp_int*)m_malloc(sizeof(mp_int));
+	m_mp_init(ses.dh_K);
+	if (mp_exptmod(dh_e, &dh_y, &dh_p, ses.dh_K) != MP_OKAY) {
+		dropbear_exit("Diffie-Hellman error");
+	}
+
+	/* clear no longer needed vars */
+	mp_clear_multi(&dh_y, &dh_p, &dh_q, NULL);
+
+	/* Create the remainder of the hash buffer, to generate the exchange hash */
+	/* K_S, the host key */
+	buf_put_pub_key(ses.kexhashbuf, ses.opts->hostkey, 
+			ses.newkeys->algo_hostkey);
+	/* e, exchange value sent by the client */
+	buf_putmpint(ses.kexhashbuf, dh_e);
+	/* f, exchange value sent by the server */
+	buf_putmpint(ses.kexhashbuf, &dh_f);
+	/* K, the shared secret */
+	buf_putmpint(ses.kexhashbuf, ses.dh_K);
+
+	/* calculate the hash H to sign */
+	sha1_init(&hs);
+	buf_setpos(ses.kexhashbuf, 0);
+	sha1_process(&hs, buf_getptr(ses.kexhashbuf, ses.kexhashbuf->len),
+			ses.kexhashbuf->len);
+	sha1_done(&hs, ses.hash);
+	buf_free(ses.kexhashbuf);
+	ses.kexhashbuf = NULL;
+	
+	/* first time around, we set the session_id to H */
+	if (ses.session_id == NULL) {
+		/* create the session_id, this never needs freeing */
+		ses.session_id = (unsigned char*)m_malloc(SHA1_HASH_SIZE);
+		memcpy(ses.session_id, ses.hash, SHA1_HASH_SIZE);
+	}
+	
+	/* we can start creating the kexdh_reply packet */
+	CHECKCLEARTOWRITE();
+	buf_putbyte(ses.writepayload, SSH_MSG_KEXDH_REPLY);
+	buf_put_pub_key(ses.writepayload, ses.opts->hostkey,
+			ses.newkeys->algo_hostkey);
+
+	/* put f */
+	buf_putmpint(ses.writepayload, &dh_f);
+	mp_clear(&dh_f);
+
+	/* calc the signature */
+	buf_put_sign(ses.writepayload, ses.opts->hostkey, 
+			ses.newkeys->algo_hostkey, ses.hash, SHA1_HASH_SIZE);
+
+	/* the SSH_MSG_KEXDH_REPLY is done */
+	encrypt_packet();
+
+	TRACE(("leave send_msg_kexdh_reply"));
+}
+
+/* read the client's choice of algorithms */
+void svr_read_kex() {
+
+	algo_type * algo;
+	char * erralgo = NULL;
+
+	int goodguess = 0;
+	int allgood = 1; /* we AND this with each goodguess and see if its still
+						true after */
+
+	buf_incrpos(ses.payload, 16); /* start after the cookie */
+
+	ses.newkeys = (struct key_context*)m_malloc(sizeof(struct key_context));
+
+	/* kex_algorithms */
+	algo = svr_buf_match_algo(ses.payload, sshkex, &goodguess);
+	allgood &= goodguess;
+	if (algo == NULL) {
+		erralgo = "kex";
+		goto error;
+	}
+	ses.newkeys->algo_kex = algo->val;
+
+	/* server_host_key_algorithms */
+	algo = svr_buf_match_algo(ses.payload, sshhostkey, &goodguess);
+	allgood &= goodguess;
+	if (algo == NULL) {
+		erralgo = "hostkey";
+		goto error;
+	}
+	ses.newkeys->algo_hostkey = algo->val;
+
+	/* encryption_algorithms_client_to_server */
+	algo = svr_buf_match_algo(ses.payload, sshciphers, &goodguess);
+	if (algo == NULL) {
+		erralgo = "enc c->s";
+		goto error;
+	}
+	ses.newkeys->recv_algo_crypt = (struct dropbear_cipher*)algo->data;
+
+	/* encryption_algorithms_server_to_client */
+	algo = svr_buf_match_algo(ses.payload, sshciphers, &goodguess);
+	if (algo == NULL) {
+		erralgo = "enc s->c";
+		goto error;
+	}
+	ses.newkeys->trans_algo_crypt = (struct dropbear_cipher*)algo->data;
+
+	/* mac_algorithms_client_to_server */
+	algo = svr_buf_match_algo(ses.payload, sshhashes, &goodguess);
+	if (algo == NULL) {
+		erralgo = "mac c->s";
+		goto error;
+	}
+	ses.newkeys->recv_algo_mac = (struct dropbear_hash*)algo->data;
+
+	/* mac_algorithms_server_to_client */
+	algo = svr_buf_match_algo(ses.payload, sshhashes, &goodguess);
+	if (algo == NULL) {
+		erralgo = "mac s->c";
+		goto error;
+	}
+	ses.newkeys->trans_algo_mac = (struct dropbear_hash*)algo->data;
+
+	/* compression_algorithms_client_to_server */
+	algo = svr_buf_match_algo(ses.payload, sshcompress, &goodguess);
+	if (algo == NULL) {
+		erralgo = "comp c->s";
+		goto error;
+	}
+	ses.newkeys->recv_algo_comp = algo->val;
+
+	/* compression_algorithms_server_to_client */
+	algo = svr_buf_match_algo(ses.payload, sshcompress, &goodguess);
+	if (algo == NULL) {
+		erralgo = "comp s->c";
+		goto error;
+	}
+	ses.newkeys->trans_algo_comp = algo->val;
+
+	/* languages_client_to_server */
+	buf_eatstring(ses.payload);
+
+	/* languages_server_to_client */
+	buf_eatstring(ses.payload);
+
+	/* first_kex_packet_follows */
+	if (buf_getbyte(ses.payload)) {
+		ses.kexstate.firstfollows = 1;
+		/* if the guess wasn't good, we ignore the packet sent */
+		if (!allgood) {
+			ses.ignorenext = 1;
+		}
+	}
+
+	/* reserved for future extensions */
+	buf_getint(ses.payload);
+	return;
+
+error:
+	dropbear_exit("no matching algo %s", erralgo);
+}