view common-algo.c @ 1902:4a6725ac957c

Revert "Don't include sk keys at all in KEX list" This reverts git commit f972813ecdc7bb981d25b5a63638bd158f1c8e72. The sk algorithms need to remain in the sigalgs list so that they are included in the server-sig-algs ext-info message sent by the server. RFC8308 for server-sig-algs requires that all algorithms are listed (though OpenSSH client 8.4p1 tested doesn't require that)
author Matt Johnston <matt@ucc.asn.au>
date Thu, 24 Mar 2022 13:42:08 +0800
parents 6cb6e81ca765
children 13cb8cc1b0e4
line wrap: on
line source
/*
 * 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 "dh_groups.h"
#include "ltc_prng.h"
#include "ecc.h"
#include "gcm.h"
#include "chachapoly.h"
#include "ssh.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 */

#if DROPBEAR_AES256
static const struct dropbear_cipher dropbear_aes256 = 
	{&aes_desc, 32, 16};
#endif
#if DROPBEAR_AES128
static const struct dropbear_cipher dropbear_aes128 = 
	{&aes_desc, 16, 16};
#endif
#if DROPBEAR_TWOFISH256
static const struct dropbear_cipher dropbear_twofish256 = 
	{&twofish_desc, 32, 16};
#endif
#if DROPBEAR_TWOFISH128
static const struct dropbear_cipher dropbear_twofish128 = 
	{&twofish_desc, 16, 16};
#endif
#if 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 */
#if DROPBEAR_ENABLE_CBC_MODE
const struct dropbear_cipher_mode dropbear_mode_cbc =
	{(void*)cbc_start, (void*)cbc_encrypt, (void*)cbc_decrypt, NULL, NULL, NULL};
#endif /* DROPBEAR_ENABLE_CBC_MODE */

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

#if 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, NULL, NULL, NULL};
#endif /* DROPBEAR_ENABLE_CTR_MODE */

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

#if DROPBEAR_SHA1_HMAC
static const struct dropbear_hash dropbear_sha1 = 
	{&sha1_desc, 20, 20};
#endif
#if DROPBEAR_SHA1_96_HMAC
static const struct dropbear_hash dropbear_sha1_96 = 
	{&sha1_desc, 20, 12};
#endif
#if DROPBEAR_SHA2_256_HMAC
static const struct dropbear_hash dropbear_sha2_256 = 
	{&sha256_desc, 32, 32};
#endif
#if DROPBEAR_SHA2_512_HMAC
static const struct dropbear_hash dropbear_sha2_512 =
	{&sha512_desc, 64, 64};
#endif
#if 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[] = {
#if DROPBEAR_CHACHA20POLY1305
	{"[email protected]", 0, &dropbear_chachapoly, 1, &dropbear_mode_chachapoly},
#endif

#if DROPBEAR_ENABLE_GCM_MODE
#if DROPBEAR_AES128
	{"[email protected]", 0, &dropbear_aes128, 1, &dropbear_mode_gcm},
#endif
#if DROPBEAR_AES256
	{"[email protected]", 0, &dropbear_aes256, 1, &dropbear_mode_gcm},
#endif
#endif /* DROPBEAR_ENABLE_GCM_MODE */

#if DROPBEAR_ENABLE_CTR_MODE
#if DROPBEAR_AES128
	{"aes128-ctr", 0, &dropbear_aes128, 1, &dropbear_mode_ctr},
#endif
#if DROPBEAR_AES256
	{"aes256-ctr", 0, &dropbear_aes256, 1, &dropbear_mode_ctr},
#endif
#if DROPBEAR_TWOFISH_CTR
/* twofish ctr is conditional as it hasn't been tested for interoperability, see options.h */
#if DROPBEAR_TWOFISH256
	{"twofish256-ctr", 0, &dropbear_twofish256, 1, &dropbear_mode_ctr},
#endif
#if DROPBEAR_TWOFISH128
	{"twofish128-ctr", 0, &dropbear_twofish128, 1, &dropbear_mode_ctr},
#endif
#endif /* DROPBEAR_TWOFISH_CTR */
#endif /* DROPBEAR_ENABLE_CTR_MODE */

#if DROPBEAR_ENABLE_CBC_MODE
#if DROPBEAR_AES128
	{"aes128-cbc", 0, &dropbear_aes128, 1, &dropbear_mode_cbc},
#endif
#if DROPBEAR_AES256
	{"aes256-cbc", 0, &dropbear_aes256, 1, &dropbear_mode_cbc},
#endif
#if DROPBEAR_TWOFISH256
	{"twofish256-cbc", 0, &dropbear_twofish256, 1, &dropbear_mode_cbc},
	{"twofish-cbc", 0, &dropbear_twofish256, 1, &dropbear_mode_cbc},
#endif
#if DROPBEAR_TWOFISH128
	{"twofish128-cbc", 0, &dropbear_twofish128, 1, &dropbear_mode_cbc},
#endif
#endif /* DROPBEAR_ENABLE_CBC_MODE */

#if DROPBEAR_3DES
#if DROPBEAR_ENABLE_CTR_MODE
	{"3des-ctr", 0, &dropbear_3des, 1, &dropbear_mode_ctr},
#endif
#if DROPBEAR_ENABLE_CBC_MODE
	{"3des-cbc", 0, &dropbear_3des, 1, &dropbear_mode_cbc},
#endif
#endif /* DROPBEAR_3DES */

#if DROPBEAR_ENABLE_CBC_MODE
#endif /* DROPBEAR_ENABLE_CBC_MODE */
	{NULL, 0, NULL, 0, NULL}
};

algo_type sshhashes[] = {
#if DROPBEAR_SHA1_96_HMAC
	{"hmac-sha1-96", 0, &dropbear_sha1_96, 1, NULL},
#endif
#if DROPBEAR_SHA1_HMAC
	{"hmac-sha1", 0, &dropbear_sha1, 1, NULL},
#endif
#if DROPBEAR_SHA2_256_HMAC
	{"hmac-sha2-256", 0, &dropbear_sha2_256, 1, NULL},
#endif
#if DROPBEAR_SHA2_512_HMAC
	{"hmac-sha2-512", 0, &dropbear_sha2_512, 1, NULL},
#endif
#if DROPBEAR_MD5_HMAC
	{"hmac-md5", 0, (void*)&dropbear_md5, 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}
};

algo_type ssh_delaycompress[] = {
	{"[email protected]", DROPBEAR_COMP_ZLIB_DELAY, 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 sigalgs[] = {
#if DROPBEAR_ED25519
	{"ssh-ed25519", DROPBEAR_SIGNATURE_ED25519, NULL, 1, NULL},
#if DROPBEAR_SK_ED25519
	{"[email protected]", DROPBEAR_SIGNATURE_SK_ED25519, NULL, 1, NULL},
#endif
#endif
#if DROPBEAR_ECDSA
#if DROPBEAR_ECC_256
	{"ecdsa-sha2-nistp256", DROPBEAR_SIGNATURE_ECDSA_NISTP256, NULL, 1, NULL},
#endif
#if DROPBEAR_ECC_384
	{"ecdsa-sha2-nistp384", DROPBEAR_SIGNATURE_ECDSA_NISTP384, NULL, 1, NULL},
#endif
#if DROPBEAR_ECC_521
	{"ecdsa-sha2-nistp521", DROPBEAR_SIGNATURE_ECDSA_NISTP521, NULL, 1, NULL},
#endif
#if DROPBEAR_SK_ECDSA
	{"[email protected]", DROPBEAR_SIGNATURE_SK_ECDSA_NISTP256, NULL, 1, NULL},
#endif
#endif
#if DROPBEAR_RSA
#if DROPBEAR_RSA_SHA256
	{"rsa-sha2-256", DROPBEAR_SIGNATURE_RSA_SHA256, NULL, 1, NULL},
#endif
#if DROPBEAR_RSA_SHA1
	{"ssh-rsa", DROPBEAR_SIGNATURE_RSA_SHA1, NULL, 1, NULL},
#endif
#endif
#if DROPBEAR_DSS
	{"ssh-dss", DROPBEAR_SIGNATURE_DSS, NULL, 1, NULL},
#endif
	{NULL, 0, NULL, 0, NULL}
};

#if DROPBEAR_DH_GROUP1
static const struct dropbear_kex kex_dh_group1 = {DROPBEAR_KEX_NORMAL_DH, dh_p_1, DH_P_1_LEN, NULL, &sha1_desc };
#endif
#if DROPBEAR_DH_GROUP14_SHA1
static const struct dropbear_kex kex_dh_group14_sha1 = {DROPBEAR_KEX_NORMAL_DH, dh_p_14, DH_P_14_LEN, NULL, &sha1_desc };
#endif
#if DROPBEAR_DH_GROUP14_SHA256
static const struct dropbear_kex kex_dh_group14_sha256 = {DROPBEAR_KEX_NORMAL_DH, dh_p_14, DH_P_14_LEN, NULL, &sha256_desc };
#endif
#if DROPBEAR_DH_GROUP16
static const struct dropbear_kex kex_dh_group16_sha512 = {DROPBEAR_KEX_NORMAL_DH, dh_p_16, DH_P_16_LEN, NULL, &sha512_desc };
#endif

#if DROPBEAR_ECDH
#if DROPBEAR_ECC_256
static const struct dropbear_kex kex_ecdh_nistp256 = {DROPBEAR_KEX_ECDH, NULL, 0, &ecc_curve_nistp256, &sha256_desc };
#endif
#if DROPBEAR_ECC_384
static const struct dropbear_kex kex_ecdh_nistp384 = {DROPBEAR_KEX_ECDH, NULL, 0, &ecc_curve_nistp384, &sha384_desc };
#endif
#if DROPBEAR_ECC_521
static const struct dropbear_kex kex_ecdh_nistp521 = {DROPBEAR_KEX_ECDH, NULL, 0, &ecc_curve_nistp521, &sha512_desc };
#endif
#endif /* DROPBEAR_ECDH */

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

/* data == NULL for non-kex algorithm identifiers */
algo_type sshkex[] = {
#if DROPBEAR_CURVE25519
	{"curve25519-sha256", 0, &kex_curve25519, 1, NULL},
	{"[email protected]", 0, &kex_curve25519, 1, NULL},
#endif
#if DROPBEAR_ECDH
#if DROPBEAR_ECC_521
	{"ecdh-sha2-nistp521", 0, &kex_ecdh_nistp521, 1, NULL},
#endif
#if DROPBEAR_ECC_384
	{"ecdh-sha2-nistp384", 0, &kex_ecdh_nistp384, 1, NULL},
#endif
#if DROPBEAR_ECC_256
	{"ecdh-sha2-nistp256", 0, &kex_ecdh_nistp256, 1, NULL},
#endif
#endif
#if DROPBEAR_DH_GROUP14_SHA256
	{"diffie-hellman-group14-sha256", 0, &kex_dh_group14_sha256, 1, NULL},
#endif
#if DROPBEAR_DH_GROUP14_SHA1
	{"diffie-hellman-group14-sha1", 0, &kex_dh_group14_sha1, 1, NULL},
#endif
#if DROPBEAR_DH_GROUP1
	{"diffie-hellman-group1-sha1", 0, &kex_dh_group1, 1, NULL},
#endif
#if DROPBEAR_DH_GROUP16
	{"diffie-hellman-group16-sha512", 0, &kex_dh_group16_sha512, 1, NULL},
#endif
#if DROPBEAR_KEXGUESS2
	{KEXGUESS2_ALGO_NAME, 0, NULL, 1, NULL},
#endif
#if DROPBEAR_EXT_INFO
#if DROPBEAR_CLIENT
	/* Set unusable by svr_algos_initialise() */
	{SSH_EXT_INFO_C, 0, NULL, 1, NULL},
#endif
#endif
	{NULL, 0, NULL, 0, NULL}
};

/* Output a comma separated list of algorithms to a buffer */
void buf_put_algolist_all(buffer * buf, const algo_type localalgos[], int useall) {
	unsigned int i, len;
	unsigned int donefirst = 0;
	unsigned int startpos;

	startpos = buf->pos;
	/* Placeholder for length */
	buf_putint(buf, 0); 
	for (i = 0; localalgos[i].name != NULL; i++) {
		if (localalgos[i].usable || useall) {
			if (donefirst) {
				buf_putbyte(buf, ',');
			}
			donefirst = 1;
			len = strlen(localalgos[i].name);
			buf_putbytes(buf, (const unsigned char *) localalgos[i].name, len);
		}
	}
	/* Fill out the length */
	len = buf->pos - startpos - 4;
	buf_setpos(buf, startpos);
	buf_putint(buf, len);
	TRACE(("algolist add %d '%.*s'", len, len, buf_getptr(buf, len)))
	buf_incrwritepos(buf, len);
}

void buf_put_algolist(buffer * buf, const algo_type localalgos[]) {
	buf_put_algolist_all(buf, localalgos, 0);
}

/* returns a list of pointers into algolist, of null-terminated names.
   ret_list should be passed in with space for *ret_count elements,
   on return *ret_count has the number of names filled.
   algolist is modified. */
static void get_algolist(char* algolist, unsigned int algolist_len,
				const char* *ret_list, unsigned int *ret_count) {
	unsigned int max_count = *ret_count;
	unsigned int i;

	if (*ret_count == 0) {
		return;
	}
	if (algolist_len > MAX_PROPOSED_ALGO*(MAX_NAME_LEN+1)) {
		*ret_count = 0;
	}

	/* ret_list will contain a list of the strings parsed out.
	   We will have at least one string (even if it's just "") */
	ret_list[0] = algolist;
	*ret_count = 1;
	for (i = 0; i < algolist_len; i++) {
		if (algolist[i] == '\0') {
			/* someone is trying something strange */
			*ret_count = 0;
			return;
		}

		if (algolist[i] == ',') {
			if (*ret_count >= max_count) {
				dropbear_exit("Too many remote algorithms");
				*ret_count = 0;
				return;
			}
			algolist[i] = '\0';
			ret_list[*ret_count] = &algolist[i+1];
			(*ret_count)++;
		}
	}
}

/* Return DROPBEAR_SUCCESS if the namelist contains algo,
DROPBEAR_FAILURE otherwise. buf position is not incremented. */
int buf_has_algo(buffer *buf, const char *algo) {
	unsigned char* algolist = NULL;
	unsigned int orig_pos = buf->pos;
	unsigned int len, remotecount, i;
	const char *remotenames[MAX_PROPOSED_ALGO];
	int ret = DROPBEAR_FAILURE;

	algolist = buf_getstring(buf, &len);
	remotecount = MAX_PROPOSED_ALGO;
	get_algolist(algolist, len, remotenames, &remotecount);
	for (i = 0; i < remotecount; i++)
	{
		if (strcmp(remotenames[i], algo) == 0) {
			ret = DROPBEAR_SUCCESS;
			break;
		}
	}
	if (algolist) {
		m_free(algolist);
	}
	buf_setpos(buf, orig_pos);
	return ret;
}

algo_type * first_usable_algo(algo_type algos[]) {
	int i;
	for (i = 0; algos[i].name != NULL; i++) {
		if (algos[i].usable) {
			return &algos[i];
		}
	}
	return NULL;
}

/* 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[],
		int kexguess2, int *goodguess) {
	char * algolist = NULL;
	const 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 char **clinames, **servnames;

	if (goodguess) {
		*goodguess = 0;
	}

	/* get the comma-separated list from the buffer ie "algo1,algo2,algo3" */
	algolist = buf_getstring(buf, &len);
	DEBUG3(("buf_match_algo: %s", algolist))
	remotecount = MAX_PROPOSED_ALGO;
	get_algolist(algolist, len, remotenames, &remotecount);

	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 != NULL) {
					if (kexguess2) {
						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;
}

#if DROPBEAR_USER_ALGO_LIST

char *
algolist_string(const 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((const char *) 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;
}

/* 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+1];
	char *work_list = m_strdup(user_algo_list);
	char *start = work_list;
	char *c;
	int n;
	/* So we can iterate and look for null terminator */
	memset(new_algos, 0x0, sizeof(new_algos));
	for (c = work_list, n = 0; ; c++)
	{
		char oc = *c;
		if (n >= MAX_PROPOSED_ALGO) {
			dropbear_exit("Too many algorithms '%s'", user_algo_list);
		}
		if (*c == ',' || *c == '\0') {
			algo_type *match_algo = NULL;
			*c = '\0';
			match_algo = check_algo(start, algos);
			if (match_algo) {
				if (check_algo(start, new_algos)) {
					TRACE(("Skip repeated algorithm '%s'", start))
				} else {
					new_algos[n] = *match_algo;
					n++;
				}
			} else {
				dropbear_log(LOG_WARNING, "This Dropbear program does not support '%s' %s algorithm", start, algo_desc);
			}
			c++;
			start = c;
		}
		if (oc == '\0') {
			break;
		}
	}
	m_free(work_list);
	/* n+1 to include a null terminator */
	memcpy(algos, new_algos, sizeof(*new_algos) * (n+1));
	return n;
}
#endif /* DROPBEAR_USER_ALGO_LIST */