view common-algo.c @ 994:5c5ade336926

Prefer stronger algorithms in algorithm negotiation. Prefer diffie-hellman-group14-sha1 (2048 bit) over diffie-hellman-group1-sha1 (1024 bit). Due to meet-in-the-middle attacks the effective key length of three key 3DES is 112 bits. AES is stronger and faster then 3DES. Prefer to delay the start of compression until after authentication has completed. This avoids exposing compression code to attacks from unauthenticated users. (github pull request #9)
author Fedor Brunner <fedor.brunner@azet.sk>
date Fri, 23 Jan 2015 23:00:25 +0800
parents 731f624af902
children 47643024fc90
line wrap: on
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/*
 * Dropbear SSH
 * 
 * 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 "algo.h"
#include "session.h"
#include "dbutil.h"
#include "kex.h"
#include "ltc_prng.h"
#include "ecc.h"

/* This file (algo.c) organises the ciphers which can be used, and is used to
 * decide which ciphers/hashes/compression/signing to use during key exchange*/

static int void_cipher(const unsigned char* in, unsigned char* out,
		unsigned long len, void* UNUSED(cipher_state)) {
	if (in != out) {
		memmove(out, in, len);
	}
	return CRYPT_OK;
}

static int void_start(int UNUSED(cipher), const unsigned char* UNUSED(IV), 
			const unsigned char* UNUSED(key), 
			int UNUSED(keylen), int UNUSED(num_rounds), void* UNUSED(cipher_state)) {
	return CRYPT_OK;
}

/* Mappings for ciphers, parameters are
   {&cipher_desc, keysize, blocksize} */

/* Remember to add new ciphers/hashes to regciphers/reghashes too */

#ifdef DROPBEAR_AES256
static const struct dropbear_cipher dropbear_aes256 = 
	{&aes_desc, 32, 16};
#endif
#ifdef DROPBEAR_AES128
static const struct dropbear_cipher dropbear_aes128 = 
	{&aes_desc, 16, 16};
#endif
#ifdef DROPBEAR_BLOWFISH
static const struct dropbear_cipher dropbear_blowfish = 
	{&blowfish_desc, 16, 8};
#endif
#ifdef DROPBEAR_TWOFISH256
static const struct dropbear_cipher dropbear_twofish256 = 
	{&twofish_desc, 32, 16};
#endif
#ifdef DROPBEAR_TWOFISH128
static const struct dropbear_cipher dropbear_twofish128 = 
	{&twofish_desc, 16, 16};
#endif
#ifdef DROPBEAR_3DES
static const struct dropbear_cipher dropbear_3des = 
	{&des3_desc, 24, 8};
#endif

/* used to indicate no encryption, as defined in rfc2410 */
const struct dropbear_cipher dropbear_nocipher =
	{NULL, 16, 8}; 

/* A few void* s are required to silence warnings
 * about the symmetric_CBC vs symmetric_CTR cipher_state pointer */
#ifdef DROPBEAR_ENABLE_CBC_MODE
const struct dropbear_cipher_mode dropbear_mode_cbc =
	{(void*)cbc_start, (void*)cbc_encrypt, (void*)cbc_decrypt};
#endif // DROPBEAR_ENABLE_CBC_MODE

const struct dropbear_cipher_mode dropbear_mode_none =
	{void_start, void_cipher, void_cipher};

#ifdef DROPBEAR_ENABLE_CTR_MODE
/* a wrapper to make ctr_start and cbc_start look the same */
static int dropbear_big_endian_ctr_start(int cipher, 
		const unsigned char *IV, 
		const unsigned char *key, int keylen, 
		int num_rounds, symmetric_CTR *ctr) {
	return ctr_start(cipher, IV, key, keylen, num_rounds, CTR_COUNTER_BIG_ENDIAN, ctr);
}
const struct dropbear_cipher_mode dropbear_mode_ctr =
	{(void*)dropbear_big_endian_ctr_start, (void*)ctr_encrypt, (void*)ctr_decrypt};
#endif // DROPBEAR_ENABLE_CTR_MODE

/* Mapping of ssh hashes to libtomcrypt hashes, including keysize etc.
   {&hash_desc, keysize, hashsize} */

#ifdef DROPBEAR_SHA1_HMAC
static const struct dropbear_hash dropbear_sha1 = 
	{&sha1_desc, 20, 20};
#endif
#ifdef DROPBEAR_SHA1_96_HMAC
static const struct dropbear_hash dropbear_sha1_96 = 
	{&sha1_desc, 20, 12};
#endif
#ifdef DROPBEAR_SHA2_256_HMAC
static const struct dropbear_hash dropbear_sha2_256 = 
	{&sha256_desc, 32, 32};
#endif
#ifdef DROPBEAR_SHA2_512_HMAC
static const struct dropbear_hash dropbear_sha2_512 =
	{&sha512_desc, 64, 64};
#endif
#ifdef DROPBEAR_MD5_HMAC
static const struct dropbear_hash dropbear_md5 = 
	{&md5_desc, 16, 16};
#endif

const struct dropbear_hash dropbear_nohash =
	{NULL, 16, 0}; /* used initially */
	

/* The following map ssh names to internal values.
 * The ordering here is important for the client - the first mode
 * that is also supported by the server will get used. */

algo_type sshciphers[] = {
#ifdef DROPBEAR_ENABLE_CTR_MODE
#ifdef DROPBEAR_AES128
	{"aes128-ctr", 0, &dropbear_aes128, 1, &dropbear_mode_ctr},
#endif
#ifdef DROPBEAR_AES256
	{"aes256-ctr", 0, &dropbear_aes256, 1, &dropbear_mode_ctr},
#endif
#endif /* DROPBEAR_ENABLE_CTR_MODE */

#ifdef DROPBEAR_ENABLE_CBC_MODE
#ifdef DROPBEAR_AES128
	{"aes128-cbc", 0, &dropbear_aes128, 1, &dropbear_mode_cbc},
#endif
#ifdef DROPBEAR_AES256
	{"aes256-cbc", 0, &dropbear_aes256, 1, &dropbear_mode_cbc},
#endif
#ifdef DROPBEAR_TWOFISH256
	{"twofish256-cbc", 0, &dropbear_twofish256, 1, &dropbear_mode_cbc},
	{"twofish-cbc", 0, &dropbear_twofish256, 1, &dropbear_mode_cbc},
#endif
#ifdef DROPBEAR_TWOFISH128
	{"twofish128-cbc", 0, &dropbear_twofish128, 1, &dropbear_mode_cbc},
#endif
#ifdef DROPBEAR_3DES
	{"3des-ctr", 0, &dropbear_3des, 1, &dropbear_mode_ctr},
#endif
#ifdef DROPBEAR_3DES
	{"3des-cbc", 0, &dropbear_3des, 1, &dropbear_mode_cbc},
#endif
#ifdef DROPBEAR_BLOWFISH
	{"blowfish-cbc", 0, &dropbear_blowfish, 1, &dropbear_mode_cbc},
#endif
#endif /* DROPBEAR_ENABLE_CBC_MODE */
#ifdef DROPBEAR_NONE_CIPHER
	{"none", 0, (void*)&dropbear_nocipher, 1, &dropbear_mode_none},
#endif
	{NULL, 0, NULL, 0, NULL}
};

algo_type sshhashes[] = {
#ifdef DROPBEAR_SHA2_256_HMAC
	{"hmac-sha2-256", 0, &dropbear_sha2_256, 1, NULL},
#endif
#ifdef DROPBEAR_SHA2_512_HMAC
	{"hmac-sha2-512", 0, &dropbear_sha2_512, 1, NULL},
#endif
#ifdef DROPBEAR_SHA1_96_HMAC
	{"hmac-sha1-96", 0, &dropbear_sha1_96, 1, NULL},
#endif
#ifdef DROPBEAR_SHA1_HMAC
	{"hmac-sha1", 0, &dropbear_sha1, 1, NULL},
#endif
#ifdef DROPBEAR_MD5_HMAC
	{"hmac-md5", 0, (void*)&dropbear_md5, 1, NULL},
#endif
#ifdef DROPBEAR_NONE_INTEGRITY
	{"none", 0, (void*)&dropbear_nohash, 1, NULL},
#endif
	{NULL, 0, NULL, 0, NULL}
};

#ifndef DISABLE_ZLIB
algo_type ssh_compress[] = {
	{"[email protected]", DROPBEAR_COMP_ZLIB_DELAY, NULL, 1, NULL},
	{"zlib", DROPBEAR_COMP_ZLIB, NULL, 1, NULL},
	{"none", DROPBEAR_COMP_NONE, NULL, 1, NULL},
	{NULL, 0, NULL, 0, NULL}
};
#endif

algo_type ssh_nocompress[] = {
	{"none", DROPBEAR_COMP_NONE, NULL, 1, NULL},
	{NULL, 0, NULL, 0, NULL}
};

algo_type sshhostkey[] = {
#ifdef DROPBEAR_ECDSA
#ifdef DROPBEAR_ECC_256
	{"ecdsa-sha2-nistp256", DROPBEAR_SIGNKEY_ECDSA_NISTP256, NULL, 1, NULL},
#endif
#ifdef DROPBEAR_ECC_384
	{"ecdsa-sha2-nistp384", DROPBEAR_SIGNKEY_ECDSA_NISTP384, NULL, 1, NULL},
#endif
#ifdef DROPBEAR_ECC_521
	{"ecdsa-sha2-nistp521", DROPBEAR_SIGNKEY_ECDSA_NISTP521, NULL, 1, NULL},
#endif
#endif
#ifdef DROPBEAR_RSA
	{"ssh-rsa", DROPBEAR_SIGNKEY_RSA, NULL, 1, NULL},
#endif
#ifdef DROPBEAR_DSS
	{"ssh-dss", DROPBEAR_SIGNKEY_DSS, NULL, 1, NULL},
#endif
	{NULL, 0, NULL, 0, NULL}
};

static const struct dropbear_kex kex_dh_group1 = {DROPBEAR_KEX_NORMAL_DH, dh_p_1, DH_P_1_LEN, NULL, &sha1_desc };
static const struct dropbear_kex kex_dh_group14 = {DROPBEAR_KEX_NORMAL_DH, dh_p_14, DH_P_14_LEN, NULL, &sha1_desc };

/* These can't be const since dropbear_ecc_fill_dp() fills out
 ecc_curve at runtime */
#ifdef DROPBEAR_ECDH
#ifdef DROPBEAR_ECC_256
static struct dropbear_kex kex_ecdh_nistp256 = {DROPBEAR_KEX_ECDH, NULL, 0, &ecc_curve_nistp256, &sha256_desc };
#endif
#ifdef DROPBEAR_ECC_384
static struct dropbear_kex kex_ecdh_nistp384 = {DROPBEAR_KEX_ECDH, NULL, 0, &ecc_curve_nistp384, &sha384_desc };
#endif
#ifdef DROPBEAR_ECC_521
static struct dropbear_kex kex_ecdh_nistp521 = {DROPBEAR_KEX_ECDH, NULL, 0, &ecc_curve_nistp521, &sha512_desc };
#endif
#endif /* DROPBEAR_ECDH */

#ifdef DROPBEAR_CURVE25519
/* Referred to directly */
static const struct dropbear_kex kex_curve25519 = {DROPBEAR_KEX_CURVE25519, NULL, 0, NULL, &sha256_desc };
#endif

algo_type sshkex[] = {
#ifdef DROPBEAR_CURVE25519
	{"[email protected]", 0, &kex_curve25519, 1, NULL},
#endif
#ifdef DROPBEAR_ECDH
#ifdef DROPBEAR_ECC_521
	{"ecdh-sha2-nistp521", 0, &kex_ecdh_nistp521, 1, NULL},
#endif
#ifdef DROPBEAR_ECC_384
	{"ecdh-sha2-nistp384", 0, &kex_ecdh_nistp384, 1, NULL},
#endif
#ifdef DROPBEAR_ECC_256
	{"ecdh-sha2-nistp256", 0, &kex_ecdh_nistp256, 1, NULL},
#endif
#endif
	{"diffie-hellman-group14-sha1", 0, &kex_dh_group14, 1, NULL},
	{"diffie-hellman-group1-sha1", 0, &kex_dh_group1, 1, NULL},
#ifdef USE_KEXGUESS2
	{KEXGUESS2_ALGO_NAME, KEXGUESS2_ALGO_ID, NULL, 1, NULL},
#endif
	{NULL, 0, NULL, 0, NULL}
};

/* algolen specifies the length of algo, algos is our local list to match
 * against.
 * Returns DROPBEAR_SUCCESS if we have a match for algo, DROPBEAR_FAILURE
 * otherwise */
int have_algo(char* algo, size_t algolen, algo_type algos[]) {

	int i;

	for (i = 0; algos[i].name != NULL; i++) {
		if (strlen(algos[i].name) == algolen
				&& (strncmp(algos[i].name, algo, algolen) == 0)) {
			return DROPBEAR_SUCCESS;
		}
	}

	return DROPBEAR_FAILURE;
}

/* Output a comma separated list of algorithms to a buffer */
void buf_put_algolist(buffer * buf, algo_type localalgos[]) {

	unsigned int i, len;
	unsigned int donefirst = 0;
	buffer *algolist = NULL;

	algolist = buf_new(200);
	for (i = 0; localalgos[i].name != NULL; i++) {
		if (localalgos[i].usable) {
			if (donefirst)
				buf_putbyte(algolist, ',');
			donefirst = 1;
			len = strlen(localalgos[i].name);
			buf_putbytes(algolist, localalgos[i].name, len);
		}
	}
	buf_putstring(buf, algolist->data, algolist->len);
	buf_free(algolist);
}

/* match the first algorithm in the comma-separated list in buf which is
 * also in localalgos[], or return NULL on failure.
 * (*goodguess) is set to 1 if the preferred client/server algos match,
 * 0 otherwise. This is used for checking if the kexalgo/hostkeyalgos are
 * guessed correctly */
algo_type * buf_match_algo(buffer* buf, algo_type localalgos[],
		enum kexguess2_used *kexguess2, int *goodguess)
{

	unsigned char * algolist = NULL;
	const unsigned char *remotenames[MAX_PROPOSED_ALGO], *localnames[MAX_PROPOSED_ALGO];
	unsigned int len;
	unsigned int remotecount, localcount, clicount, servcount, i, j;
	algo_type * ret = NULL;
	const unsigned char **clinames, **servnames;

	if (goodguess) {
		*goodguess = 0;
	}

	/* get the comma-separated list from the buffer ie "algo1,algo2,algo3" */
	algolist = buf_getstring(buf, &len);
	TRACE(("buf_match_algo: %s", algolist))
	if (len > MAX_PROPOSED_ALGO*(MAX_NAME_LEN+1)) {
		goto out;
	}

	/* remotenames will contain a list of the strings parsed out */
	/* We will have at least one string (even if it's just "") */
	remotenames[0] = algolist;
	remotecount = 1;
	for (i = 0; i < len; i++) {
		if (algolist[i] == '\0') {
			/* someone is trying something strange */
			goto out;
		}
		if (algolist[i] == ',') {
			algolist[i] = '\0';
			remotenames[remotecount] = &algolist[i+1];
			remotecount++;
		}
		if (remotecount >= MAX_PROPOSED_ALGO) {
			break;
		}
	}
	if (kexguess2 && *kexguess2 == KEXGUESS2_LOOK) {
		for (i = 0; i < remotecount; i++)
		{
			if (strcmp(remotenames[i], KEXGUESS2_ALGO_NAME) == 0) {
				*kexguess2 = KEXGUESS2_YES;
				break;
			}
		}
		if (*kexguess2 == KEXGUESS2_LOOK) {
			*kexguess2 = KEXGUESS2_NO;
		}
	}

	for (i = 0; localalgos[i].name != NULL; i++) {
		if (localalgos[i].usable) {
			localnames[i] = localalgos[i].name;
		} else {
			localnames[i] = NULL;
		}
	}
	localcount = i;

	if (IS_DROPBEAR_SERVER) {
		clinames = remotenames;
		clicount = remotecount;
		servnames = localnames;
		servcount = localcount;
	} else {
		clinames = localnames;
		clicount = localcount;
		servnames = remotenames;
		servcount = remotecount;
	}

	/* iterate and find the first match */
	for (i = 0; i < clicount; i++) {
		for (j = 0; j < servcount; j++) {
			if (!(servnames[j] && clinames[i])) {
				/* unusable algos are NULL */
				continue;
			}
			if (strcmp(servnames[j], clinames[i]) == 0) {
				/* set if it was a good guess */
				if (goodguess && kexguess2) {
					if (*kexguess2 == KEXGUESS2_YES) {
						if (i == 0) {
							*goodguess = 1;
						}

					} else {
						if (i == 0 && j == 0) {
							*goodguess = 1;
						}
					}
				}
				/* set the algo to return */
				if (IS_DROPBEAR_SERVER) {
					ret = &localalgos[j];
				} else {
					ret = &localalgos[i];
				}
				goto out;
			}
		}
	}

out:
	m_free(algolist);
	return ret;
}

#ifdef DROPBEAR_NONE_CIPHER

void
set_algo_usable(algo_type algos[], const char * algo_name, int usable)
{
	algo_type *a;
	for (a = algos; a->name != NULL; a++)
	{
		if (strcmp(a->name, algo_name) == 0)
		{
			a->usable = usable;
			return;
		}
	}
}

int
get_algo_usable(algo_type algos[], const char * algo_name)
{
	algo_type *a;
	for (a = algos; a->name != NULL; a++)
	{
		if (strcmp(a->name, algo_name) == 0)
		{
			return a->usable;
		}
	}
	return 0;
}

#endif /* DROPBEAR_NONE_CIPHER */

#ifdef ENABLE_USER_ALGO_LIST

char *
algolist_string(algo_type algos[])
{
	char *ret_list;
	buffer *b = buf_new(200);
	buf_put_algolist(b, algos);
	buf_setpos(b, b->len);
	buf_putbyte(b, '\0');
	buf_setpos(b, 4);
	ret_list = m_strdup(buf_getptr(b, b->len - b->pos));
	buf_free(b);
	return ret_list;
}

static algo_type*
check_algo(const char* algo_name, algo_type *algos)
{
	algo_type *a;
	for (a = algos; a->name != NULL; a++)
	{
		if (strcmp(a->name, algo_name) == 0)
		{
			return a;
		}
	}

	return NULL;
}

static void
try_add_algo(const char *algo_name, algo_type *algos, 
		const char *algo_desc, algo_type * new_algos, int *num_ret)
{
	algo_type *match_algo = check_algo(algo_name, algos);
	if (!match_algo)
	{
		dropbear_log(LOG_WARNING, "This Dropbear program does not support '%s' %s algorithm", algo_name, algo_desc);
		return;
	}

	new_algos[*num_ret] = *match_algo;
	(*num_ret)++;
}

/* Checks a user provided comma-separated algorithm list for available
 * options. Any that are not acceptable are removed in-place. Returns the
 * number of valid algorithms. */
int
check_user_algos(const char* user_algo_list, algo_type * algos, 
		const char *algo_desc)
{
	algo_type new_algos[MAX_PROPOSED_ALGO];
	/* this has two passes. first we sweep through the given list of
	 * algorithms and mark them as usable=2 in the algo_type[] array... */
	int num_ret = 0;
	char *work_list = m_strdup(user_algo_list);
	char *last_name = work_list;
	char *c;
	for (c = work_list; *c; c++)
	{
		if (*c == ',')
		{
			*c = '\0';
			try_add_algo(last_name, algos, algo_desc, new_algos, &num_ret);
			c++;
			last_name = c;
		}
	}
	try_add_algo(last_name, algos, algo_desc, new_algos, &num_ret);
	m_free(work_list);

	new_algos[num_ret].name = NULL;

	/* Copy one more as a blank delimiter */
	memcpy(algos, new_algos, sizeof(*new_algos) * (num_ret+1));
	return num_ret;
}
#endif /* ENABLE_USER_ALGO_LIST */