--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/common-kex.c	Thu Jan 11 03:14:55 2007 +0000
@@ -0,0 +1,722 @@
+/*
+ * Dropbear SSH
+ * 
+ * Copyright (c) 2002-2004 Matt Johnston
+ * Portions 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 "random.h"
+
+/* diffie-hellman-group1-sha1 value for p */
+static const unsigned char dh_p_val[] = {
+	0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xC9, 0x0F, 0xDA, 0xA2,
+    0x21, 0x68, 0xC2, 0x34, 0xC4, 0xC6, 0x62, 0x8B, 0x80, 0xDC, 0x1C, 0xD1,
+	0x29, 0x02, 0x4E, 0x08, 0x8A, 0x67, 0xCC, 0x74, 0x02, 0x0B, 0xBE, 0xA6,
+	0x3B, 0x13, 0x9B, 0x22, 0x51, 0x4A, 0x08, 0x79, 0x8E, 0x34, 0x04, 0xDD,
+	0xEF, 0x95, 0x19, 0xB3, 0xCD, 0x3A, 0x43, 0x1B, 0x30, 0x2B, 0x0A, 0x6D,
+	0xF2, 0x5F, 0x14, 0x37, 0x4F, 0xE1, 0x35, 0x6D, 0x6D, 0x51, 0xC2, 0x45,
+	0xE4, 0x85, 0xB5, 0x76, 0x62, 0x5E, 0x7E, 0xC6, 0xF4, 0x4C, 0x42, 0xE9,
+	0xA6, 0x37, 0xED, 0x6B, 0x0B, 0xFF, 0x5C, 0xB6, 0xF4, 0x06, 0xB7, 0xED,
+	0xEE, 0x38, 0x6B, 0xFB, 0x5A, 0x89, 0x9F, 0xA5, 0xAE, 0x9F, 0x24, 0x11,
+	0x7C, 0x4B, 0x1F, 0xE6, 0x49, 0x28, 0x66, 0x51, 0xEC, 0xE6, 0x53, 0x81,
+	0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF};
+#define DH_P_LEN sizeof(dh_p_val)
+
+static const int DH_G_VAL = 2;
+
+static void kexinitialise();
+void gen_new_keys();
+#ifndef DISABLE_ZLIB
+static void gen_new_zstreams();
+#endif
+static void read_kex_algos();
+/* helper function for gen_new_keys */
+static void hashkeys(unsigned char *out, int outlen, 
+		const hash_state * hs, unsigned const char X);
+
+
+/* Send our list of algorithms we can use */
+void send_msg_kexinit() {
+
+	CHECKCLEARTOWRITE();
+	buf_putbyte(ses.writepayload, SSH_MSG_KEXINIT);
+
+	/* cookie */
+	genrandom(buf_getwriteptr(ses.writepayload, 16), 16);
+	buf_incrwritepos(ses.writepayload, 16);
+
+	/* kex algos */
+	buf_put_algolist(ses.writepayload, sshkex);
+
+	/* server_host_key_algorithms */
+	buf_put_algolist(ses.writepayload, sshhostkey);
+
+	/* encryption_algorithms_client_to_server */
+	buf_put_algolist(ses.writepayload, sshciphers);
+
+	/* encryption_algorithms_server_to_client */
+	buf_put_algolist(ses.writepayload, sshciphers);
+
+	/* mac_algorithms_client_to_server */
+	buf_put_algolist(ses.writepayload, sshhashes);
+
+	/* mac_algorithms_server_to_client */
+	buf_put_algolist(ses.writepayload, sshhashes);
+
+	/* compression_algorithms_client_to_server */
+	buf_put_algolist(ses.writepayload, sshcompress);
+
+	/* compression_algorithms_server_to_client */
+	buf_put_algolist(ses.writepayload, sshcompress);
+
+	/* languages_client_to_server */
+	buf_putstring(ses.writepayload, "", 0);
+
+	/* languages_server_to_client */
+	buf_putstring(ses.writepayload, "", 0);
+
+	/* first_kex_packet_follows - unimplemented for now */
+	buf_putbyte(ses.writepayload, 0x00);
+
+	/* reserved unit32 */
+	buf_putint(ses.writepayload, 0);
+
+	/* set up transmitted kex packet buffer for hashing. 
+	 * This is freed after the end of the kex */
+	ses.transkexinit = buf_newcopy(ses.writepayload);
+
+	encrypt_packet();
+	ses.dataallowed = 0; /* don't send other packets during kex */
+
+	TRACE(("DATAALLOWED=0"))
+	TRACE(("-> KEXINIT"))
+	ses.kexstate.sentkexinit = 1;
+}
+
+/* *** NOTE regarding (send|recv)_msg_newkeys *** 
+ * Changed by mihnea from the original kex.c to set dataallowed after a 
+ * completed key exchange, no matter the order in which it was performed.
+ * This enables client mode without affecting server functionality.
+ */
+
+/* Bring new keys into use after a key exchange, and let the client know*/
+void send_msg_newkeys() {
+
+	TRACE(("enter send_msg_newkeys"))
+
+	/* generate the kexinit request */
+	CHECKCLEARTOWRITE();
+	buf_putbyte(ses.writepayload, SSH_MSG_NEWKEYS);
+	encrypt_packet();
+	
+
+	/* set up our state */
+	if (ses.kexstate.recvnewkeys) {
+		TRACE(("while RECVNEWKEYS=1"))
+		gen_new_keys();
+		kexinitialise(); /* we've finished with this kex */
+		TRACE((" -> DATAALLOWED=1"))
+		ses.dataallowed = 1; /* we can send other packets again now */
+		ses.kexstate.donefirstkex = 1;
+	} else {
+		ses.kexstate.sentnewkeys = 1;
+		TRACE(("SENTNEWKEYS=1"))
+	}
+
+	TRACE(("-> MSG_NEWKEYS"))
+	TRACE(("leave send_msg_newkeys"))
+}
+
+/* Bring the new keys into use after a key exchange */
+void recv_msg_newkeys() {
+
+	TRACE(("<- MSG_NEWKEYS"))
+	TRACE(("enter recv_msg_newkeys"))
+
+	/* simply check if we've sent SSH_MSG_NEWKEYS, and if so,
+	 * switch to the new keys */
+	if (ses.kexstate.sentnewkeys) {
+		TRACE(("while SENTNEWKEYS=1"))
+		gen_new_keys();
+		kexinitialise(); /* we've finished with this kex */
+	    TRACE((" -> DATAALLOWED=1"))
+	    ses.dataallowed = 1; /* we can send other packets again now */
+		ses.kexstate.donefirstkex = 1;
+	} else {
+		TRACE(("RECVNEWKEYS=1"))
+		ses.kexstate.recvnewkeys = 1;
+	}
+	
+	TRACE(("leave recv_msg_newkeys"))
+}
+
+
+/* Set up the kex for the first time */
+void kexfirstinitialise() {
+
+	ses.kexstate.donefirstkex = 0;
+	kexinitialise();
+}
+
+/* Reset the kex state, ready for a new negotiation */
+static void kexinitialise() {
+
+	struct timeval tv;
+
+	TRACE(("kexinitialise()"))
+
+	/* sent/recv'd MSG_KEXINIT */
+	ses.kexstate.sentkexinit = 0;
+	ses.kexstate.recvkexinit = 0;
+
+	/* sent/recv'd MSG_NEWKEYS */
+	ses.kexstate.recvnewkeys = 0;
+	ses.kexstate.sentnewkeys = 0;
+
+	/* first_packet_follows */
+	ses.kexstate.firstfollows = 0;
+
+	ses.kexstate.datatrans = 0;
+	ses.kexstate.datarecv = 0;
+
+	if (gettimeofday(&tv, 0) < 0) {
+		dropbear_exit("Error getting time");
+	}
+	ses.kexstate.lastkextime = tv.tv_sec;
+
+}
+
+/* Helper function for gen_new_keys, creates a hash. It makes a copy of the
+ * already initialised hash_state hs, which should already have processed
+ * the dh_K and hash, since these are common. X is the letter 'A', 'B' etc.
+ * out must have at least min(SHA1_HASH_SIZE, outlen) bytes allocated.
+ * The output will only be expanded once, since that is all that is required
+ * (for 3DES and SHA, with 24 and 20 bytes respectively). 
+ *
+ * See Section 5.2 of the IETF secsh Transport Draft for details */
+
+/* Duplicated verbatim from kex.c --mihnea */
+static void hashkeys(unsigned char *out, int outlen, 
+		const hash_state * hs, const unsigned char X) {
+
+	hash_state hs2;
+	unsigned char k2[SHA1_HASH_SIZE]; /* used to extending */
+
+	memcpy(&hs2, hs, sizeof(hash_state));
+	sha1_process(&hs2, &X, 1);
+	sha1_process(&hs2, ses.session_id, SHA1_HASH_SIZE);
+	sha1_done(&hs2, out);
+	if (SHA1_HASH_SIZE < outlen) {
+		/* need to extend */
+		memcpy(&hs2, hs, sizeof(hash_state));
+		sha1_process(&hs2, out, SHA1_HASH_SIZE);
+		sha1_done(&hs2, k2);
+		memcpy(&out[SHA1_HASH_SIZE], k2, outlen - SHA1_HASH_SIZE);
+	}
+}
+
+/* Generate the actual encryption/integrity keys, using the results of the
+ * key exchange, as specified in section 5.2 of the IETF secsh-transport
+ * draft. This occurs after the DH key-exchange.
+ *
+ * ses.newkeys is the new set of keys which are generated, these are only
+ * taken into use after both sides have sent a newkeys message */
+
+/* Originally from kex.c, generalized for cli/svr mode --mihnea */
+void gen_new_keys() {
+
+	unsigned char C2S_IV[MAX_IV_LEN];
+	unsigned char C2S_key[MAX_KEY_LEN];
+	unsigned char S2C_IV[MAX_IV_LEN];
+	unsigned char S2C_key[MAX_KEY_LEN];
+	/* unsigned char key[MAX_KEY_LEN]; */
+	unsigned char *trans_IV, *trans_key, *recv_IV, *recv_key;
+
+	hash_state hs;
+	unsigned int C2S_keysize, S2C_keysize;
+	char mactransletter, macrecvletter; /* Client or server specific */
+	int recv_cipher = 0, trans_cipher = 0;
+
+	TRACE(("enter gen_new_keys"))
+	/* the dh_K and hash are the start of all hashes, we make use of that */
+
+	sha1_init(&hs);
+	sha1_process_mp(&hs, ses.dh_K);
+	mp_clear(ses.dh_K);
+	m_free(ses.dh_K);
+	sha1_process(&hs, ses.hash, SHA1_HASH_SIZE);
+	m_burn(ses.hash, SHA1_HASH_SIZE);
+
+	if (IS_DROPBEAR_CLIENT) {
+	    trans_IV	= C2S_IV;
+	    recv_IV		= S2C_IV;
+	    trans_key	= C2S_key;
+	    recv_key	= S2C_key;
+	    C2S_keysize = ses.newkeys->trans_algo_crypt->keysize;
+	    S2C_keysize = ses.newkeys->recv_algo_crypt->keysize;
+		mactransletter = 'E';
+		macrecvletter = 'F';
+	} else {
+	    trans_IV	= S2C_IV;
+	    recv_IV		= C2S_IV;
+	    trans_key	= S2C_key;
+	    recv_key	= C2S_key;
+	    C2S_keysize = ses.newkeys->recv_algo_crypt->keysize;
+	    S2C_keysize = ses.newkeys->trans_algo_crypt->keysize;
+		mactransletter = 'F';
+		macrecvletter = 'E';
+	}
+
+	hashkeys(C2S_IV, SHA1_HASH_SIZE, &hs, 'A');
+	hashkeys(S2C_IV, SHA1_HASH_SIZE, &hs, 'B');
+	hashkeys(C2S_key, C2S_keysize, &hs, 'C');
+	hashkeys(S2C_key, S2C_keysize, &hs, 'D');
+
+	recv_cipher = find_cipher(ses.newkeys->recv_algo_crypt->cipherdesc->name);
+	if (recv_cipher < 0)
+	    dropbear_exit("crypto error");
+		
+	if (cbc_start(recv_cipher, recv_IV, recv_key, 
+			ses.newkeys->recv_algo_crypt->keysize, 0, 
+			&ses.newkeys->recv_symmetric_struct) != CRYPT_OK) {
+		dropbear_exit("crypto error");
+	}
+	trans_cipher = find_cipher(ses.newkeys->trans_algo_crypt->cipherdesc->name);
+	if (trans_cipher < 0)
+	    dropbear_exit("crypto error");
+		
+	if (cbc_start(trans_cipher, trans_IV, trans_key, 
+			ses.newkeys->trans_algo_crypt->keysize, 0, 
+			&ses.newkeys->trans_symmetric_struct) != CRYPT_OK) {
+		dropbear_exit("crypto error");
+	}
+	
+	/* MAC keys */
+	hashkeys(ses.newkeys->transmackey, 
+			ses.newkeys->trans_algo_mac->keysize, &hs, mactransletter);
+	hashkeys(ses.newkeys->recvmackey, 
+			ses.newkeys->recv_algo_mac->keysize, &hs, macrecvletter);
+
+#ifndef DISABLE_ZLIB
+	gen_new_zstreams();
+#endif
+	
+	/* Switch over to the new keys */
+	m_burn(ses.keys, sizeof(struct key_context));
+	m_free(ses.keys);
+	ses.keys = ses.newkeys;
+	ses.newkeys = NULL;
+
+	TRACE(("leave gen_new_keys"))
+}
+
+#ifndef DISABLE_ZLIB
+/* Set up new zlib compression streams, close the old ones. Only
+ * called from gen_new_keys() */
+static void gen_new_zstreams() {
+
+	/* create new zstreams */
+	if (ses.newkeys->recv_algo_comp == DROPBEAR_COMP_ZLIB) {
+		ses.newkeys->recv_zstream = (z_streamp)m_malloc(sizeof(z_stream));
+		ses.newkeys->recv_zstream->zalloc = Z_NULL;
+		ses.newkeys->recv_zstream->zfree = Z_NULL;
+		
+		if (inflateInit(ses.newkeys->recv_zstream) != Z_OK) {
+			dropbear_exit("zlib error");
+		}
+	} else {
+		ses.newkeys->recv_zstream = NULL;
+	}
+
+	if (ses.newkeys->trans_algo_comp == DROPBEAR_COMP_ZLIB) {
+		ses.newkeys->trans_zstream = (z_streamp)m_malloc(sizeof(z_stream));
+		ses.newkeys->trans_zstream->zalloc = Z_NULL;
+		ses.newkeys->trans_zstream->zfree = Z_NULL;
+	
+		if (deflateInit(ses.newkeys->trans_zstream, Z_DEFAULT_COMPRESSION) 
+				!= Z_OK) {
+			dropbear_exit("zlib error");
+		}
+	} else {
+		ses.newkeys->trans_zstream = NULL;
+	}
+	
+	/* clean up old keys */
+	if (ses.keys->recv_zstream != NULL) {
+		if (inflateEnd(ses.keys->recv_zstream) == Z_STREAM_ERROR) {
+			/* Z_DATA_ERROR is ok, just means that stream isn't ended */
+			dropbear_exit("crypto error");
+		}
+		m_free(ses.keys->recv_zstream);
+	}
+	if (ses.keys->trans_zstream != NULL) {
+		if (deflateEnd(ses.keys->trans_zstream) == Z_STREAM_ERROR) {
+			/* Z_DATA_ERROR is ok, just means that stream isn't ended */
+			dropbear_exit("crypto error");
+		}
+		m_free(ses.keys->trans_zstream);
+	}
+}
+#endif
+
+
+/* Executed upon receiving a kexinit message from the client to initiate
+ * key exchange. If we haven't already done so, we send the list of our
+ * preferred algorithms. The client's requested algorithms are processed,
+ * and we calculate the first portion of the key-exchange-hash for used
+ * later in the key exchange. No response is sent, as the client should
+ * initiate the diffie-hellman key exchange */
+
+/* Originally from kex.c, generalized for cli/svr mode --mihnea  */
+/* Belongs in common_kex.c where it should be moved after review */
+void recv_msg_kexinit() {
+	
+	unsigned int kexhashbuf_len = 0;
+	unsigned int remote_ident_len = 0;
+	unsigned int local_ident_len = 0;
+
+	TRACE(("<- KEXINIT"))
+	TRACE(("enter recv_msg_kexinit"))
+	
+	if (!ses.kexstate.sentkexinit) {
+		/* we need to send a kex packet */
+		send_msg_kexinit();
+		TRACE(("continue recv_msg_kexinit: sent kexinit"))
+	}
+
+	/* start the kex hash */
+	local_ident_len = strlen(LOCAL_IDENT);
+	remote_ident_len = strlen((char*)ses.remoteident);
+
+	kexhashbuf_len = local_ident_len + remote_ident_len
+		+ ses.transkexinit->len + ses.payload->len
+		+ KEXHASHBUF_MAX_INTS;
+
+	ses.kexhashbuf = buf_new(kexhashbuf_len);
+
+	if (IS_DROPBEAR_CLIENT) {
+
+		/* read the peer's choice of algos */
+		read_kex_algos();
+
+		/* V_C, the client's version string (CR and NL excluded) */
+	    buf_putstring(ses.kexhashbuf,
+			(unsigned char*)LOCAL_IDENT, local_ident_len);
+		/* V_S, the server's version string (CR and NL excluded) */
+	    buf_putstring(ses.kexhashbuf, ses.remoteident, remote_ident_len);
+
+		/* I_C, the payload of the client's SSH_MSG_KEXINIT */
+	    buf_putstring(ses.kexhashbuf,
+			ses.transkexinit->data, ses.transkexinit->len);
+		/* I_S, the payload of the server's SSH_MSG_KEXINIT */
+	    buf_setpos(ses.payload, 0);
+	    buf_putstring(ses.kexhashbuf, ses.payload->data, ses.payload->len);
+
+	} else {
+		/* SERVER */
+
+		/* read the peer's choice of algos */
+		read_kex_algos();
+		/* V_C, the client's version string (CR and NL excluded) */
+	    buf_putstring(ses.kexhashbuf, ses.remoteident, remote_ident_len);
+		/* V_S, the server's version string (CR and NL excluded) */
+	    buf_putstring(ses.kexhashbuf, 
+				(unsigned char*)LOCAL_IDENT, local_ident_len);
+
+		/* I_C, the payload of the client's SSH_MSG_KEXINIT */
+	    buf_setpos(ses.payload, 0);
+	    buf_putstring(ses.kexhashbuf, ses.payload->data, ses.payload->len);
+
+		/* I_S, the payload of the server's SSH_MSG_KEXINIT */
+	    buf_putstring(ses.kexhashbuf,
+			ses.transkexinit->data, ses.transkexinit->len);
+
+		ses.requirenext = SSH_MSG_KEXDH_INIT;
+	}
+
+	buf_free(ses.transkexinit);
+	ses.transkexinit = NULL;
+	/* the rest of ses.kexhashbuf will be done after DH exchange */
+
+	ses.kexstate.recvkexinit = 1;
+
+	TRACE(("leave recv_msg_kexinit"))
+}
+
+/* Initialises and generate one side of the diffie-hellman key exchange values.
+ * See the ietf-secsh-transport draft, section 6, for details */
+/* dh_pub and dh_priv MUST be already initialised */
+void gen_kexdh_vals(mp_int *dh_pub, mp_int *dh_priv) {
+
+	DEF_MP_INT(dh_p);
+	DEF_MP_INT(dh_q);
+	DEF_MP_INT(dh_g);
+
+	TRACE(("enter send_msg_kexdh_reply"))
+	
+	m_mp_init_multi(&dh_g, &dh_p, &dh_q, NULL);
+
+	/* read the prime and generator*/
+	bytes_to_mp(&dh_p, (unsigned char*)dh_p_val, DH_P_LEN);
+	
+	if (mp_set_int(&dh_g, DH_G_VAL) != MP_OKAY) {
+		dropbear_exit("Diffie-Hellman error");
+	}
+
+	/* calculate q = (p-1)/2 */
+	/* dh_priv is just a temp var here */
+	if (mp_sub_d(&dh_p, 1, dh_priv) != MP_OKAY) { 
+		dropbear_exit("Diffie-Hellman error");
+	}
+	if (mp_div_2(dh_priv, &dh_q) != MP_OKAY) {
+		dropbear_exit("Diffie-Hellman error");
+	}
+
+	/* Generate a private portion 0 < dh_priv < dh_q */
+	gen_random_mpint(&dh_q, dh_priv);
+
+	/* f = g^y mod p */
+	if (mp_exptmod(&dh_g, dh_priv, &dh_p, dh_pub) != MP_OKAY) {
+		dropbear_exit("Diffie-Hellman error");
+	}
+	mp_clear_multi(&dh_g, &dh_p, &dh_q, NULL);
+}
+
+/* This function is fairly common between client/server, with some substitution
+ * of dh_e/dh_f etc. Hence these arguments:
+ * dh_pub_us is 'e' for the client, 'f' for the server. dh_pub_them is 
+ * vice-versa. dh_priv is the x/y value corresponding to dh_pub_us */
+void kexdh_comb_key(mp_int *dh_pub_us, mp_int *dh_priv, mp_int *dh_pub_them,
+		sign_key *hostkey) {
+
+	mp_int dh_p;
+	mp_int *dh_e = NULL, *dh_f = NULL;
+	hash_state hs;
+
+	/* read the prime and generator*/
+	m_mp_init(&dh_p);
+	bytes_to_mp(&dh_p, dh_p_val, DH_P_LEN);
+
+	/* Check that dh_pub_them (dh_e or dh_f) is in the range [1, p-1] */
+	if (mp_cmp(dh_pub_them, &dh_p) != MP_LT 
+			|| mp_cmp_d(dh_pub_them, 0) != MP_GT) {
+		dropbear_exit("Diffie-Hellman error");
+	}
+	
+	/* K = e^y mod p = f^x mod p */
+	ses.dh_K = (mp_int*)m_malloc(sizeof(mp_int));
+	m_mp_init(ses.dh_K);
+	if (mp_exptmod(dh_pub_them, dh_priv, &dh_p, ses.dh_K) != MP_OKAY) {
+		dropbear_exit("Diffie-Hellman error");
+	}
+
+	/* clear no longer needed vars */
+	mp_clear_multi(&dh_p, NULL);
+
+	/* From here on, the code needs to work with the _same_ vars on each side,
+	 * not vice-versaing for client/server */
+	if (IS_DROPBEAR_CLIENT) {
+		dh_e = dh_pub_us;
+		dh_f = dh_pub_them;
+	} else {
+		dh_e = dh_pub_them;
+		dh_f = dh_pub_us;
+	} 
+
+	/* Create the remainder of the hash buffer, to generate the exchange hash */
+	/* K_S, the host key */
+	buf_put_pub_key(ses.kexhashbuf, 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_burn(ses.kexhashbuf);
+	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);
+	}
+}
+
+/* read the other side's algo list. buf_match_algo is a callback to match
+ * algos for the client or server. */
+static void read_kex_algos() {
+
+	/* for asymmetry */
+	algo_type * c2s_hash_algo = NULL;
+	algo_type * s2c_hash_algo = NULL;
+	algo_type * c2s_cipher_algo = NULL;
+	algo_type * s2c_cipher_algo = NULL;
+	algo_type * c2s_comp_algo = NULL;
+	algo_type * s2c_comp_algo = NULL;
+	/* the generic one */
+	algo_type * algo = NULL;
+
+	/* which algo couldn't match */
+	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 = ses.buf_match_algo(ses.payload, sshkex, &goodguess);
+	allgood &= goodguess;
+	if (algo == NULL) {
+		erralgo = "kex";
+		goto error;
+	}
+	TRACE(("kex algo %s", algo->name))
+	ses.newkeys->algo_kex = algo->val;
+
+	/* server_host_key_algorithms */
+	algo = ses.buf_match_algo(ses.payload, sshhostkey, &goodguess);
+	allgood &= goodguess;
+	if (algo == NULL) {
+		erralgo = "hostkey";
+		goto error;
+	}
+	TRACE(("hostkey algo %s", algo->name))
+	ses.newkeys->algo_hostkey = algo->val;
+
+	/* encryption_algorithms_client_to_server */
+	c2s_cipher_algo = ses.buf_match_algo(ses.payload, sshciphers, &goodguess);
+	if (c2s_cipher_algo == NULL) {
+		erralgo = "enc c->s";
+		goto error;
+	}
+	TRACE(("enc c2s is  %s", c2s_cipher_algo->name))
+
+	/* encryption_algorithms_server_to_client */
+	s2c_cipher_algo = ses.buf_match_algo(ses.payload, sshciphers, &goodguess);
+	if (s2c_cipher_algo == NULL) {
+		erralgo = "enc s->c";
+		goto error;
+	}
+	TRACE(("enc s2c is  %s", s2c_cipher_algo->name))
+
+	/* mac_algorithms_client_to_server */
+	c2s_hash_algo = ses.buf_match_algo(ses.payload, sshhashes, &goodguess);
+	if (c2s_hash_algo == NULL) {
+		erralgo = "mac c->s";
+		goto error;
+	}
+	TRACE(("hash c2s is  %s", c2s_hash_algo->name))
+
+	/* mac_algorithms_server_to_client */
+	s2c_hash_algo = ses.buf_match_algo(ses.payload, sshhashes, &goodguess);
+	if (s2c_hash_algo == NULL) {
+		erralgo = "mac s->c";
+		goto error;
+	}
+	TRACE(("hash s2c is  %s", s2c_hash_algo->name))
+
+	/* compression_algorithms_client_to_server */
+	c2s_comp_algo = ses.buf_match_algo(ses.payload, sshcompress, &goodguess);
+	if (c2s_comp_algo == NULL) {
+		erralgo = "comp c->s";
+		goto error;
+	}
+	TRACE(("hash c2s is  %s", c2s_comp_algo->name))
+
+	/* compression_algorithms_server_to_client */
+	s2c_comp_algo = ses.buf_match_algo(ses.payload, sshcompress, &goodguess);
+	if (s2c_comp_algo == NULL) {
+		erralgo = "comp s->c";
+		goto error;
+	}
+	TRACE(("hash s2c is  %s", s2c_comp_algo->name))
+
+	/* languages_client_to_server */
+	buf_eatstring(ses.payload);
+
+	/* languages_server_to_client */
+	buf_eatstring(ses.payload);
+
+	/* first_kex_packet_follows */
+	if (buf_getbool(ses.payload)) {
+		ses.kexstate.firstfollows = 1;
+		/* if the guess wasn't good, we ignore the packet sent */
+		if (!allgood) {
+			ses.ignorenext = 1;
+		}
+	}
+
+	/* Handle the asymmetry */
+	if (IS_DROPBEAR_CLIENT) {
+		ses.newkeys->recv_algo_crypt = 
+			(struct dropbear_cipher*)s2c_cipher_algo->data;
+		ses.newkeys->trans_algo_crypt = 
+			(struct dropbear_cipher*)c2s_cipher_algo->data;
+		ses.newkeys->recv_algo_mac = 
+			(struct dropbear_hash*)s2c_hash_algo->data;
+		ses.newkeys->trans_algo_mac = 
+			(struct dropbear_hash*)c2s_hash_algo->data;
+		ses.newkeys->recv_algo_comp = s2c_comp_algo->val;
+		ses.newkeys->trans_algo_comp = c2s_comp_algo->val;
+	} else {
+		/* SERVER */
+		ses.newkeys->recv_algo_crypt = 
+			(struct dropbear_cipher*)c2s_cipher_algo->data;
+		ses.newkeys->trans_algo_crypt = 
+			(struct dropbear_cipher*)s2c_cipher_algo->data;
+		ses.newkeys->recv_algo_mac = 
+			(struct dropbear_hash*)c2s_hash_algo->data;
+		ses.newkeys->trans_algo_mac = 
+			(struct dropbear_hash*)s2c_hash_algo->data;
+		ses.newkeys->recv_algo_comp = c2s_comp_algo->val;
+		ses.newkeys->trans_algo_comp = s2c_comp_algo->val;
+	}
+
+	/* reserved for future extensions */
+	buf_getint(ses.payload);
+	return;
+
+error:
+	dropbear_exit("no matching algo %s", erralgo);
+}