view crypto_desc.c @ 1790:42745af83b7d

Introduce extra delay before closing unauthenticated sessions To make it harder for attackers, introduce a delay to keep an unauthenticated session open a bit longer, thus blocking a connection slot until after the delay. Without this, while there is a limit on the amount of attempts an attacker can make at the same time (MAX_UNAUTH_PER_IP), the time taken by dropbear to handle one attempt is still short and thus for each of the allowed parallel attempts many attempts can be chained one after the other. The attempt rate is then: "MAX_UNAUTH_PER_IP / <process time of one attempt>". With the delay, this rate becomes: "MAX_UNAUTH_PER_IP / UNAUTH_CLOSE_DELAY".
author Thomas De Schampheleire <thomas.de_schampheleire@nokia.com>
date Wed, 15 Feb 2017 13:53:04 +0100
parents 34d9d3c022ce
children 13cb8cc1b0e4
line wrap: on
line source

#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
}