view crypto_desc.c @ 1788:1fc0012b9c38

Fix handling of replies to global requests (#112) The current code assumes that all global requests want / need a reply. This isn't always true and the request itself indicates if it wants a reply or not. It causes a specific problem with [email protected] messages. These are sent by OpenSSH after authentication to inform the client of potential other host keys for the host. This can be used to add a new type of host key or to rotate host keys. The initial information message from the server is sent as a global request, but with want_reply set to false. This means that the server doesn't expect an answer to this message. Instead the client needs to send a prove request as a reply if it wants to receive proof of ownership for the host keys. The bug doesn't cause any current problems with due to how OpenSSH treats receiving the failure message. It instead treats it as a keepalive message and further ignores it. Arguably this is a protocol violation though of Dropbear and it is only accidental that it doesn't cause a problem with OpenSSH. The bug was found when adding host keys support to libssh, which is more strict protocol wise and treats the unexpected failure message an error, also see https://gitlab.com/libssh/libssh-mirror/-/merge_requests/145 for more information. The fix here is to honor the want_reply flag in the global request and to only send a reply if the other side expects a reply.
author Dirkjan Bussink <d.bussink@gmail.com>
date Thu, 10 Dec 2020 16:13:13 +0100
parents 34d9d3c022ce
children 13cb8cc1b0e4
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#include "includes.h"
#include "dbutil.h"
#include "crypto_desc.h"
#include "ltc_prng.h"
#include "ecc.h"
#include "dbrandom.h"

#if DROPBEAR_LTC_PRNG
	int dropbear_ltc_prng = -1;
#endif

/* Wrapper for libtommath */
static mp_err dropbear_rand_source(void* out, size_t size) {
	genrandom((unsigned char*)out, (unsigned int)size);
	return MP_OKAY;
}


/* Register the compiled in ciphers.
 * This should be run before using any of the ciphers/hashes */
void crypto_init() {

	const struct ltc_cipher_descriptor *regciphers[] = {
#if DROPBEAR_AES
		&aes_desc,
#endif
#if DROPBEAR_BLOWFISH
		&blowfish_desc,
#endif
#if DROPBEAR_TWOFISH
		&twofish_desc,
#endif
#if DROPBEAR_3DES
		&des3_desc,
#endif
		NULL
	};

	const struct ltc_hash_descriptor *reghashes[] = {
		/* we need sha1 for hostkey stuff regardless */
		&sha1_desc,
#if DROPBEAR_MD5_HMAC
		&md5_desc,
#endif
#if DROPBEAR_SHA256
		&sha256_desc,
#endif
#if DROPBEAR_SHA384
		&sha384_desc,
#endif
#if DROPBEAR_SHA512
		&sha512_desc,
#endif
		NULL
	};	
	int i;
	
	for (i = 0; regciphers[i] != NULL; i++) {
		if (register_cipher(regciphers[i]) == -1) {
			dropbear_exit("Error registering crypto");
		}
	}

	for (i = 0; reghashes[i] != NULL; i++) {
		if (register_hash(reghashes[i]) == -1) {
			dropbear_exit("Error registering crypto");
		}
	}

#if DROPBEAR_LTC_PRNG
	dropbear_ltc_prng = register_prng(&dropbear_prng_desc);
	if (dropbear_ltc_prng == -1) {
		dropbear_exit("Error registering crypto");
	}
#endif

	mp_rand_source(dropbear_rand_source);

#if DROPBEAR_ECC
	ltc_mp = ltm_desc;
	dropbear_ecc_fill_dp();
#endif
}