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simplesshd/dropbear/common-kex.c
Greg Alexander e9d95ce283 stock dropbear-2020.81 source tree
2020-12-28 16:40:37 -05:00

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/*
* 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 "dh_groups.h"
#include "ssh.h"
#include "packet.h"
#include "bignum.h"
#include "dbrandom.h"
#include "runopts.h"
#include "ecc.h"
#include "curve25519.h"
#include "crypto_desc.h"
static void kexinitialise(void);
static void gen_new_keys(void);
#ifndef DISABLE_ZLIB
static void gen_new_zstream_recv(void);
static void gen_new_zstream_trans(void);
#endif
static void read_kex_algos(void);
/* helper function for gen_new_keys */
static void hashkeys(unsigned char *out, unsigned int outlen,
const hash_state * hs, const unsigned 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, sigalgs);
/* 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, ses.compress_algos);
/* compression_algorithms_server_to_client */
buf_put_algolist(ses.writepayload, ses.compress_algos);
/* languages_client_to_server */
buf_putstring(ses.writepayload, "", 0);
/* languages_server_to_client */
buf_putstring(ses.writepayload, "", 0);
/* first_kex_packet_follows */
buf_putbyte(ses.writepayload, (ses.send_kex_first_guess != NULL));
/* 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 */
ses.kexstate.sentkexinit = 1;
ses.newkeys = (struct key_context*)m_malloc(sizeof(struct key_context));
if (ses.send_kex_first_guess) {
ses.newkeys->algo_kex = first_usable_algo(sshkex)->data;
ses.newkeys->algo_signature = first_usable_algo(sigalgs)->val;
ses.newkeys->algo_hostkey = signkey_type_from_signature(ses.newkeys->algo_signature);
ses.send_kex_first_guess();
}
TRACE(("DATAALLOWED=0"))
TRACE(("-> KEXINIT"))
}
static void switch_keys() {
TRACE2(("enter switch_keys"))
if (!(ses.kexstate.sentkexinit && ses.kexstate.recvkexinit)) {
dropbear_exit("Unexpected newkeys message");
}
if (!ses.keys) {
ses.keys = m_malloc(sizeof(*ses.newkeys));
}
if (ses.kexstate.recvnewkeys && ses.newkeys->recv.valid) {
TRACE(("switch_keys recv"))
#ifndef DISABLE_ZLIB
gen_new_zstream_recv();
#endif
ses.keys->recv = ses.newkeys->recv;
m_burn(&ses.newkeys->recv, sizeof(ses.newkeys->recv));
ses.newkeys->recv.valid = 0;
}
if (ses.kexstate.sentnewkeys && ses.newkeys->trans.valid) {
TRACE(("switch_keys trans"))
#ifndef DISABLE_ZLIB
gen_new_zstream_trans();
#endif
ses.keys->trans = ses.newkeys->trans;
m_burn(&ses.newkeys->trans, sizeof(ses.newkeys->trans));
ses.newkeys->trans.valid = 0;
}
if (ses.kexstate.sentnewkeys && ses.kexstate.recvnewkeys)
{
TRACE(("switch_keys done"))
ses.keys->algo_kex = ses.newkeys->algo_kex;
ses.keys->algo_hostkey = ses.newkeys->algo_hostkey;
ses.keys->algo_signature = ses.newkeys->algo_signature;
ses.keys->allow_compress = 0;
m_free(ses.newkeys);
ses.newkeys = NULL;
kexinitialise();
}
TRACE2(("leave switch_keys"))
}
/* 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 */
ses.kexstate.sentnewkeys = 1;
if (ses.kexstate.donefirstkex) {
ses.kexstate.donesecondkex = 1;
}
ses.kexstate.donefirstkex = 1;
ses.dataallowed = 1; /* we can send other packets again now */
gen_new_keys();
switch_keys();
TRACE(("leave send_msg_newkeys"))
}
/* Bring the new keys into use after a key exchange */
void recv_msg_newkeys() {
TRACE(("enter recv_msg_newkeys"))
ses.kexstate.recvnewkeys = 1;
switch_keys();
TRACE(("leave recv_msg_newkeys"))
}
/* Set up the kex for the first time */
void kexfirstinitialise() {
#ifdef DISABLE_ZLIB
ses.compress_algos = ssh_nocompress;
#else
switch (opts.compress_mode)
{
case DROPBEAR_COMPRESS_DELAYED:
ses.compress_algos = ssh_delaycompress;
break;
case DROPBEAR_COMPRESS_ON:
ses.compress_algos = ssh_compress;
break;
case DROPBEAR_COMPRESS_OFF:
ses.compress_algos = ssh_nocompress;
break;
}
#endif
kexinitialise();
}
/* Reset the kex state, ready for a new negotiation */
static void kexinitialise() {
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.them_firstfollows = 0;
ses.kexstate.datatrans = 0;
ses.kexstate.datarecv = 0;
ses.kexstate.our_first_follows_matches = 0;
ses.kexstate.lastkextime = monotonic_now();
}
/* 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.
*
* See Section 7.2 of rfc4253 (ssh transport) for details */
static void hashkeys(unsigned char *out, unsigned int outlen,
const hash_state * hs, const unsigned char X) {
const struct ltc_hash_descriptor *hash_desc = ses.newkeys->algo_kex->hash_desc;
hash_state hs2;
unsigned int offset;
unsigned char tmpout[MAX_HASH_SIZE];
memcpy(&hs2, hs, sizeof(hash_state));
hash_desc->process(&hs2, &X, 1);
hash_desc->process(&hs2, ses.session_id->data, ses.session_id->len);
hash_desc->done(&hs2, tmpout);
memcpy(out, tmpout, MIN(hash_desc->hashsize, outlen));
for (offset = hash_desc->hashsize;
offset < outlen;
offset += hash_desc->hashsize)
{
/* need to extend */
memcpy(&hs2, hs, sizeof(hash_state));
hash_desc->process(&hs2, out, offset);
hash_desc->done(&hs2, tmpout);
memcpy(&out[offset], tmpout, MIN(outlen - offset, hash_desc->hashsize));
}
m_burn(&hs2, sizeof(hash_state));
}
/* Generate the actual encryption/integrity keys, using the results of the
* key exchange, as specified in section 7.2 of the transport rfc 4253.
* 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 */
static 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;
const struct ltc_hash_descriptor *hash_desc = ses.newkeys->algo_kex->hash_desc;
char mactransletter, macrecvletter; /* Client or server specific */
TRACE(("enter gen_new_keys"))
/* the dh_K and hash are the start of all hashes, we make use of that */
hash_desc->init(&hs);
hash_process_mp(hash_desc, &hs, ses.dh_K);
mp_clear(ses.dh_K);
m_free(ses.dh_K);
hash_desc->process(&hs, ses.hash->data, ses.hash->len);
buf_burn(ses.hash);
buf_free(ses.hash);
ses.hash = NULL;
if (IS_DROPBEAR_CLIENT) {
trans_IV = C2S_IV;
recv_IV = S2C_IV;
trans_key = C2S_key;
recv_key = S2C_key;
mactransletter = 'E';
macrecvletter = 'F';
} else {
trans_IV = S2C_IV;
recv_IV = C2S_IV;
trans_key = S2C_key;
recv_key = C2S_key;
mactransletter = 'F';
macrecvletter = 'E';
}
hashkeys(C2S_IV, sizeof(C2S_IV), &hs, 'A');
hashkeys(S2C_IV, sizeof(S2C_IV), &hs, 'B');
hashkeys(C2S_key, sizeof(C2S_key), &hs, 'C');
hashkeys(S2C_key, sizeof(S2C_key), &hs, 'D');
if (ses.newkeys->recv.algo_crypt->cipherdesc != NULL) {
int recv_cipher = -1;
if (ses.newkeys->recv.algo_crypt->cipherdesc->name != NULL) {
recv_cipher = find_cipher(ses.newkeys->recv.algo_crypt->cipherdesc->name);
if (recv_cipher < 0) {
dropbear_exit("Crypto error");
}
}
if (ses.newkeys->recv.crypt_mode->start(recv_cipher,
recv_IV, recv_key,
ses.newkeys->recv.algo_crypt->keysize, 0,
&ses.newkeys->recv.cipher_state) != CRYPT_OK) {
dropbear_exit("Crypto error");
}
}
if (ses.newkeys->trans.algo_crypt->cipherdesc != NULL) {
int trans_cipher = -1;
if (ses.newkeys->trans.algo_crypt->cipherdesc->name != NULL) {
trans_cipher = find_cipher(ses.newkeys->trans.algo_crypt->cipherdesc->name);
if (trans_cipher < 0) {
dropbear_exit("Crypto error");
}
}
if (ses.newkeys->trans.crypt_mode->start(trans_cipher,
trans_IV, trans_key,
ses.newkeys->trans.algo_crypt->keysize, 0,
&ses.newkeys->trans.cipher_state) != CRYPT_OK) {
dropbear_exit("Crypto error");
}
}
if (ses.newkeys->trans.algo_mac->hash_desc != NULL) {
hashkeys(ses.newkeys->trans.mackey,
ses.newkeys->trans.algo_mac->keysize, &hs, mactransletter);
ses.newkeys->trans.hash_index = find_hash(ses.newkeys->trans.algo_mac->hash_desc->name);
}
if (ses.newkeys->recv.algo_mac->hash_desc != NULL) {
hashkeys(ses.newkeys->recv.mackey,
ses.newkeys->recv.algo_mac->keysize, &hs, macrecvletter);
ses.newkeys->recv.hash_index = find_hash(ses.newkeys->recv.algo_mac->hash_desc->name);
}
/* Ready to switch over */
ses.newkeys->trans.valid = 1;
ses.newkeys->recv.valid = 1;
m_burn(C2S_IV, sizeof(C2S_IV));
m_burn(C2S_key, sizeof(C2S_key));
m_burn(S2C_IV, sizeof(S2C_IV));
m_burn(S2C_key, sizeof(S2C_key));
m_burn(&hs, sizeof(hash_state));
TRACE(("leave gen_new_keys"))
}
#ifndef DISABLE_ZLIB
int is_compress_trans() {
return ses.keys->trans.algo_comp == DROPBEAR_COMP_ZLIB
|| (ses.authstate.authdone
&& ses.keys->trans.algo_comp == DROPBEAR_COMP_ZLIB_DELAY);
}
int is_compress_recv() {
return ses.keys->recv.algo_comp == DROPBEAR_COMP_ZLIB
|| (ses.authstate.authdone
&& ses.keys->recv.algo_comp == DROPBEAR_COMP_ZLIB_DELAY);
}
static void* dropbear_zalloc(void* UNUSED(opaque), uInt items, uInt size) {
return m_calloc(items, size);
}
static void dropbear_zfree(void* UNUSED(opaque), void* ptr) {
m_free(ptr);
}
/* Set up new zlib compression streams, close the old ones. Only
* called from gen_new_keys() */
static void gen_new_zstream_recv() {
/* create new zstreams */
if (ses.newkeys->recv.algo_comp == DROPBEAR_COMP_ZLIB
|| ses.newkeys->recv.algo_comp == DROPBEAR_COMP_ZLIB_DELAY) {
ses.newkeys->recv.zstream = (z_streamp)m_malloc(sizeof(z_stream));
ses.newkeys->recv.zstream->zalloc = dropbear_zalloc;
ses.newkeys->recv.zstream->zfree = dropbear_zfree;
if (inflateInit(ses.newkeys->recv.zstream) != Z_OK) {
dropbear_exit("zlib error");
}
} else {
ses.newkeys->recv.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);
}
}
static void gen_new_zstream_trans() {
if (ses.newkeys->trans.algo_comp == DROPBEAR_COMP_ZLIB
|| ses.newkeys->trans.algo_comp == DROPBEAR_COMP_ZLIB_DELAY) {
ses.newkeys->trans.zstream = (z_streamp)m_malloc(sizeof(z_stream));
ses.newkeys->trans.zstream->zalloc = dropbear_zalloc;
ses.newkeys->trans.zstream->zfree = dropbear_zfree;
if (deflateInit2(ses.newkeys->trans.zstream, Z_DEFAULT_COMPRESSION,
Z_DEFLATED, DROPBEAR_ZLIB_WINDOW_BITS,
DROPBEAR_ZLIB_MEM_LEVEL, Z_DEFAULT_STRATEGY)
!= Z_OK) {
dropbear_exit("zlib error");
}
} else {
ses.newkeys->trans.zstream = NULL;
}
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 /* DISABLE_ZLIB */
/* 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 */
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"))
}
/* "Once a party has sent a SSH_MSG_KEXINIT message ...
further SSH_MSG_KEXINIT messages MUST NOT be sent" */
if (ses.kexstate.recvkexinit) {
dropbear_exit("Unexpected KEXINIT");
}
/* start the kex hash */
local_ident_len = strlen(LOCAL_IDENT);
remote_ident_len = strlen(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, 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,
(const char*)ses.transkexinit->data, ses.transkexinit->len);
/* I_S, the payload of the server's SSH_MSG_KEXINIT */
buf_setpos(ses.payload, ses.payload_beginning);
buf_putstring(ses.kexhashbuf,
(const char*)buf_getptr(ses.payload, ses.payload->len-ses.payload->pos),
ses.payload->len-ses.payload->pos);
ses.requirenext = SSH_MSG_KEXDH_REPLY;
} 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, LOCAL_IDENT, local_ident_len);
/* I_C, the payload of the client's SSH_MSG_KEXINIT */
buf_setpos(ses.payload, ses.payload_beginning);
buf_putstring(ses.kexhashbuf,
(const char*)buf_getptr(ses.payload, ses.payload->len-ses.payload->pos),
ses.payload->len-ses.payload->pos);
/* I_S, the payload of the server's SSH_MSG_KEXINIT */
buf_putstring(ses.kexhashbuf,
(const char*)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"))
}
#if DROPBEAR_NORMAL_DH
static void load_dh_p(mp_int * dh_p)
{
bytes_to_mp(dh_p, ses.newkeys->algo_kex->dh_p_bytes,
ses.newkeys->algo_kex->dh_p_len);
}
/* Initialises and generate one side of the diffie-hellman key exchange values.
* See the transport rfc 4253 section 8 for details */
/* dh_pub and dh_priv MUST be already initialised */
struct kex_dh_param *gen_kexdh_param() {
struct kex_dh_param *param = NULL;
DEF_MP_INT(dh_p);
DEF_MP_INT(dh_q);
DEF_MP_INT(dh_g);
TRACE(("enter gen_kexdh_vals"))
param = m_malloc(sizeof(*param));
m_mp_init_multi(&param->pub, &param->priv, &dh_g, &dh_p, &dh_q, NULL);
/* read the prime and generator*/
load_dh_p(&dh_p);
mp_set_ul(&dh_g, DH_G_VAL);
/* calculate q = (p-1)/2 */
/* dh_priv is just a temp var here */
if (mp_sub_d(&dh_p, 1, &param->priv) != MP_OKAY) {
dropbear_exit("Diffie-Hellman error");
}
if (mp_div_2(&param->priv, &dh_q) != MP_OKAY) {
dropbear_exit("Diffie-Hellman error");
}
/* Generate a private portion 0 < dh_priv < dh_q */
gen_random_mpint(&dh_q, &param->priv);
/* f = g^y mod p */
if (mp_exptmod(&dh_g, &param->priv, &dh_p, &param->pub) != MP_OKAY) {
dropbear_exit("Diffie-Hellman error");
}
mp_clear_multi(&dh_g, &dh_p, &dh_q, NULL);
return param;
}
void free_kexdh_param(struct kex_dh_param *param)
{
mp_clear_multi(&param->pub, &param->priv, NULL);
m_free(param);
}
/* 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(struct kex_dh_param *param, mp_int *dh_pub_them,
sign_key *hostkey) {
DEF_MP_INT(dh_p);
DEF_MP_INT(dh_p_min1);
mp_int *dh_e = NULL, *dh_f = NULL;
m_mp_init_multi(&dh_p, &dh_p_min1, NULL);
load_dh_p(&dh_p);
if (mp_sub_d(&dh_p, 1, &dh_p_min1) != MP_OKAY) {
dropbear_exit("Diffie-Hellman error");
}
/* Check that dh_pub_them (dh_e or dh_f) is in the range [2, p-2] */
if (mp_cmp(dh_pub_them, &dh_p_min1) != MP_LT
|| mp_cmp_d(dh_pub_them, 1) != MP_GT) {
dropbear_exit("Diffie-Hellman error");
}
/* K = e^y mod p = f^x mod p */
m_mp_alloc_init_multi(&ses.dh_K, NULL);
if (mp_exptmod(dh_pub_them, &param->priv, &dh_p, ses.dh_K) != MP_OKAY) {
dropbear_exit("Diffie-Hellman error");
}
/* clear no longer needed vars */
mp_clear_multi(&dh_p, &dh_p_min1, 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 = &param->pub;
dh_f = dh_pub_them;
} else {
dh_e = dh_pub_them;
dh_f = &param->pub;
}
/* 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 */
finish_kexhashbuf();
}
#endif
#if DROPBEAR_ECDH
struct kex_ecdh_param *gen_kexecdh_param() {
struct kex_ecdh_param *param = m_malloc(sizeof(*param));
if (ecc_make_key_ex(NULL, dropbear_ltc_prng,
&param->key, ses.newkeys->algo_kex->ecc_curve->dp) != CRYPT_OK) {
dropbear_exit("ECC error");
}
return param;
}
void free_kexecdh_param(struct kex_ecdh_param *param) {
ecc_free(&param->key);
m_free(param);
}
void kexecdh_comb_key(struct kex_ecdh_param *param, buffer *pub_them,
sign_key *hostkey) {
const struct dropbear_kex *algo_kex = ses.newkeys->algo_kex;
/* public keys from client and server */
ecc_key *Q_C, *Q_S, *Q_them;
Q_them = buf_get_ecc_raw_pubkey(pub_them, algo_kex->ecc_curve);
if (Q_them == NULL) {
dropbear_exit("ECC error");
}
ses.dh_K = dropbear_ecc_shared_secret(Q_them, &param->key);
/* Create the remainder of the hash buffer, to generate the exchange hash
See RFC5656 section 4 page 7 */
if (IS_DROPBEAR_CLIENT) {
Q_C = &param->key;
Q_S = Q_them;
} else {
Q_C = Q_them;
Q_S = &param->key;
}
/* K_S, the host key */
buf_put_pub_key(ses.kexhashbuf, hostkey, ses.newkeys->algo_hostkey);
/* Q_C, client's ephemeral public key octet string */
buf_put_ecc_raw_pubkey_string(ses.kexhashbuf, Q_C);
/* Q_S, server's ephemeral public key octet string */
buf_put_ecc_raw_pubkey_string(ses.kexhashbuf, Q_S);
/* K, the shared secret */
buf_putmpint(ses.kexhashbuf, ses.dh_K);
ecc_free(Q_them);
m_free(Q_them);
/* calculate the hash H to sign */
finish_kexhashbuf();
}
#endif /* DROPBEAR_ECDH */
#if DROPBEAR_CURVE25519
struct kex_curve25519_param *gen_kexcurve25519_param() {
/* Per http://cr.yp.to/ecdh.html */
struct kex_curve25519_param *param = m_malloc(sizeof(*param));
const unsigned char basepoint[32] = {9};
genrandom(param->priv, CURVE25519_LEN);
dropbear_curve25519_scalarmult(param->pub, param->priv, basepoint);
return param;
}
void free_kexcurve25519_param(struct kex_curve25519_param *param) {
m_burn(param->priv, CURVE25519_LEN);
m_free(param);
}
void kexcurve25519_comb_key(const struct kex_curve25519_param *param, const buffer *buf_pub_them,
sign_key *hostkey) {
unsigned char out[CURVE25519_LEN];
const unsigned char* Q_C = NULL;
const unsigned char* Q_S = NULL;
char zeroes[CURVE25519_LEN] = {0};
if (buf_pub_them->len != CURVE25519_LEN)
{
dropbear_exit("Bad curve25519");
}
dropbear_curve25519_scalarmult(out, param->priv, buf_pub_them->data);
if (constant_time_memcmp(zeroes, out, CURVE25519_LEN) == 0) {
dropbear_exit("Bad curve25519");
}
m_mp_alloc_init_multi(&ses.dh_K, NULL);
bytes_to_mp(ses.dh_K, out, CURVE25519_LEN);
m_burn(out, sizeof(out));
/* Create the remainder of the hash buffer, to generate the exchange hash.
See RFC5656 section 4 page 7 */
if (IS_DROPBEAR_CLIENT) {
Q_C = param->pub;
Q_S = buf_pub_them->data;
} else {
Q_S = param->pub;
Q_C = buf_pub_them->data;
}
/* K_S, the host key */
buf_put_pub_key(ses.kexhashbuf, hostkey, ses.newkeys->algo_hostkey);
/* Q_C, client's ephemeral public key octet string */
buf_putstring(ses.kexhashbuf, (const char*)Q_C, CURVE25519_LEN);
/* Q_S, server's ephemeral public key octet string */
buf_putstring(ses.kexhashbuf, (const char*)Q_S, CURVE25519_LEN);
/* K, the shared secret */
buf_putmpint(ses.kexhashbuf, ses.dh_K);
/* calculate the hash H to sign */
finish_kexhashbuf();
}
#endif /* DROPBEAR_CURVE25519 */
void finish_kexhashbuf(void) {
hash_state hs;
const struct ltc_hash_descriptor *hash_desc = ses.newkeys->algo_kex->hash_desc;
hash_desc->init(&hs);
buf_setpos(ses.kexhashbuf, 0);
hash_desc->process(&hs, buf_getptr(ses.kexhashbuf, ses.kexhashbuf->len),
ses.kexhashbuf->len);
ses.hash = buf_new(hash_desc->hashsize);
hash_desc->done(&hs, buf_getwriteptr(ses.hash, hash_desc->hashsize));
buf_setlen(ses.hash, hash_desc->hashsize);
#if defined(DEBUG_KEXHASH) && DEBUG_TRACE
if (!debug_trace) {
printhex("kexhashbuf", ses.kexhashbuf->data, ses.kexhashbuf->len);
printhex("kexhash", ses.hash->data, ses.hash->len);
}
#endif
buf_burn(ses.kexhashbuf);
buf_free(ses.kexhashbuf);
m_burn(&hs, sizeof(hash_state));
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 = buf_newcopy(ses.hash);
}
}
/* 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 */
int kexguess2 = 0;
buf_incrpos(ses.payload, 16); /* start after the cookie */
memset(ses.newkeys, 0x0, sizeof(*ses.newkeys));
/* kex_algorithms */
#if DROPBEAR_KEXGUESS2
if (buf_has_algo(ses.payload, KEXGUESS2_ALGO_NAME) == DROPBEAR_SUCCESS) {
kexguess2 = 1;
}
#endif
#if DROPBEAR_EXT_INFO
/* Determine if SSH_MSG_EXT_INFO messages should be sent.
Should be done for the first key exchange. Only required on server side
for server-sig-algs */
if (IS_DROPBEAR_SERVER) {
if (!ses.kexstate.donefirstkex) {
if (buf_has_algo(ses.payload, SSH_EXT_INFO_C) == DROPBEAR_SUCCESS) {
ses.allow_ext_info = 1;
}
}
}
#endif
algo = buf_match_algo(ses.payload, sshkex, kexguess2, &goodguess);
allgood &= goodguess;
if (algo == NULL || algo->data == NULL) {
/* kexguess2, ext-info-c, ext-info-s should not match negotiation */
erralgo = "kex";
goto error;
}
TRACE(("kexguess2 %d", kexguess2))
TRACE(("kex algo %s", algo->name))
ses.newkeys->algo_kex = algo->data;
/* server_host_key_algorithms */
algo = buf_match_algo(ses.payload, sigalgs, kexguess2, &goodguess);
allgood &= goodguess;
if (algo == NULL) {
erralgo = "hostkey";
goto error;
}
TRACE(("signature algo %s", algo->name))
ses.newkeys->algo_signature = algo->val;
ses.newkeys->algo_hostkey = signkey_type_from_signature(ses.newkeys->algo_signature);
/* encryption_algorithms_client_to_server */
c2s_cipher_algo = buf_match_algo(ses.payload, sshciphers, 0, NULL);
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 = buf_match_algo(ses.payload, sshciphers, 0, NULL);
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 = buf_match_algo(ses.payload, sshhashes, 0, NULL);
#if DROPBEAR_AEAD_MODE
if (((struct dropbear_cipher_mode*)c2s_cipher_algo->mode)->aead_crypt != NULL) {
c2s_hash_algo = NULL;
} else
#endif
if (c2s_hash_algo == NULL) {
erralgo = "mac c->s";
goto error;
}
TRACE(("hash c2s is %s", c2s_hash_algo ? c2s_hash_algo->name : "<implicit>"))
/* mac_algorithms_server_to_client */
s2c_hash_algo = buf_match_algo(ses.payload, sshhashes, 0, NULL);
#if DROPBEAR_AEAD_MODE
if (((struct dropbear_cipher_mode*)s2c_cipher_algo->mode)->aead_crypt != NULL) {
s2c_hash_algo = NULL;
} else
#endif
if (s2c_hash_algo == NULL) {
erralgo = "mac s->c";
goto error;
}
TRACE(("hash s2c is %s", s2c_hash_algo ? s2c_hash_algo->name : "<implicit>"))
/* compression_algorithms_client_to_server */
c2s_comp_algo = buf_match_algo(ses.payload, ses.compress_algos, 0, NULL);
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 = buf_match_algo(ses.payload, ses.compress_algos, 0, NULL);
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);
/* their first_kex_packet_follows */
if (buf_getbool(ses.payload)) {
TRACE(("them kex firstfollows. allgood %d", allgood))
ses.kexstate.them_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.crypt_mode =
(struct dropbear_cipher_mode*)s2c_cipher_algo->mode;
ses.newkeys->trans.crypt_mode =
(struct dropbear_cipher_mode*)c2s_cipher_algo->mode;
ses.newkeys->recv.algo_mac =
#if DROPBEAR_AEAD_MODE
s2c_hash_algo == NULL ? ses.newkeys->recv.crypt_mode->aead_mac :
#endif
(struct dropbear_hash*)s2c_hash_algo->data;
ses.newkeys->trans.algo_mac =
#if DROPBEAR_AEAD_MODE
c2s_hash_algo == NULL ? ses.newkeys->trans.crypt_mode->aead_mac :
#endif
(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.crypt_mode =
(struct dropbear_cipher_mode*)c2s_cipher_algo->mode;
ses.newkeys->trans.crypt_mode =
(struct dropbear_cipher_mode*)s2c_cipher_algo->mode;
ses.newkeys->recv.algo_mac =
#if DROPBEAR_AEAD_MODE
c2s_hash_algo == NULL ? ses.newkeys->recv.crypt_mode->aead_mac :
#endif
(struct dropbear_hash*)c2s_hash_algo->data;
ses.newkeys->trans.algo_mac =
#if DROPBEAR_AEAD_MODE
s2c_hash_algo == NULL ? ses.newkeys->trans.crypt_mode->aead_mac :
#endif
(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;
}
#if DROPBEAR_FUZZ
if (fuzz.fuzzing) {
fuzz_kex_fakealgos();
}
#endif
/* reserved for future extensions */
buf_getint(ses.payload);
if (ses.send_kex_first_guess && allgood) {
TRACE(("our_first_follows_matches 1"))
ses.kexstate.our_first_follows_matches = 1;
}
return;
error:
dropbear_exit("No matching algo %s", erralgo);
}
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