Mercurial > dropbear
view gcm.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 | 5b701bf529aa |
children |
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/* * Dropbear SSH * * Copyright (c) 2002,2003 Matt Johnston * Copyright (c) 2020 by Vladislav Grishenko * 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 "dbutil.h" #include "gcm.h" #if DROPBEAR_ENABLE_GCM_MODE #define GHASH_LEN 16 static const struct dropbear_hash dropbear_ghash = {NULL, 0, GHASH_LEN}; static int dropbear_gcm_start(int cipher, const unsigned char *IV, const unsigned char *key, int keylen, int UNUSED(num_rounds), dropbear_gcm_state *state) { int err; TRACE2(("enter dropbear_gcm_start")) if ((err = gcm_init(&state->gcm, cipher, key, keylen)) != CRYPT_OK) { return err; } memcpy(state->iv, IV, GCM_NONCE_LEN); TRACE2(("leave dropbear_gcm_start")) return CRYPT_OK; } static int dropbear_gcm_crypt(unsigned int UNUSED(seq), const unsigned char *in, unsigned char *out, unsigned long len, unsigned long taglen, dropbear_gcm_state *state, int direction) { unsigned char *iv, tag[GHASH_LEN]; int i, err; TRACE2(("enter dropbear_gcm_crypt")) if (len < 4 || taglen != GHASH_LEN) { return CRYPT_ERROR; } gcm_reset(&state->gcm); if ((err = gcm_add_iv(&state->gcm, state->iv, GCM_NONCE_LEN)) != CRYPT_OK) { return err; } if ((err = gcm_add_aad(&state->gcm, in, 4)) != CRYPT_OK) { return err; } if ((err = gcm_process(&state->gcm, (unsigned char *) in + 4, len - 4, out + 4, direction)) != CRYPT_OK) { return err; } if (direction == LTC_ENCRYPT) { gcm_done(&state->gcm, out + len, &taglen); } else { gcm_done(&state->gcm, tag, &taglen); if (constant_time_memcmp(in + len, tag, taglen) != 0) { return CRYPT_ERROR; } } /* increment invocation counter */ iv = state->iv + GCM_IVFIX_LEN; for (i = GCM_IVCTR_LEN - 1; i >= 0 && ++iv[i] == 0; i--); TRACE2(("leave dropbear_gcm_crypt")) return CRYPT_OK; } static int dropbear_gcm_getlength(unsigned int UNUSED(seq), const unsigned char *in, unsigned int *outlen, unsigned long len, dropbear_gcm_state* UNUSED(state)) { TRACE2(("enter dropbear_gcm_getlength")) if (len < 4) { return CRYPT_ERROR; } LOAD32H(*outlen, in); TRACE2(("leave dropbear_gcm_getlength")) return CRYPT_OK; } const struct dropbear_cipher_mode dropbear_mode_gcm = {(void *)dropbear_gcm_start, NULL, NULL, (void *)dropbear_gcm_crypt, (void *)dropbear_gcm_getlength, &dropbear_ghash}; #endif /* DROPBEAR_ENABLE_GCM_MODE */