Mercurial > dropbear
view libtomcrypt/src/mac/xcbc/xcbc_init.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 | 6dba84798cd5 |
children |
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/* LibTomCrypt, modular cryptographic library -- Tom St Denis * * LibTomCrypt is a library that provides various cryptographic * algorithms in a highly modular and flexible manner. * * The library is free for all purposes without any express * guarantee it works. */ #include "tomcrypt.h" /** @file xcbc_init.c XCBC Support, start an XCBC state */ #ifdef LTC_XCBC /** Initialize XCBC-MAC state @param xcbc [out] XCBC state to initialize @param cipher Index of cipher to use @param key [in] Secret key @param keylen Length of secret key in octets Return CRYPT_OK on success */ int xcbc_init(xcbc_state *xcbc, int cipher, const unsigned char *key, unsigned long keylen) { int x, y, err; symmetric_key *skey; unsigned long k1; LTC_ARGCHK(xcbc != NULL); LTC_ARGCHK(key != NULL); /* schedule the key */ if ((err = cipher_is_valid(cipher)) != CRYPT_OK) { return err; } #ifdef LTC_FAST if (cipher_descriptor[cipher].block_length % sizeof(LTC_FAST_TYPE)) { return CRYPT_INVALID_ARG; } #endif skey = NULL; /* are we in pure XCBC mode with three keys? */ if (keylen & LTC_XCBC_PURE) { keylen &= ~LTC_XCBC_PURE; if (keylen < 2UL*cipher_descriptor[cipher].block_length) { return CRYPT_INVALID_ARG; } k1 = keylen - 2*cipher_descriptor[cipher].block_length; XMEMCPY(xcbc->K[0], key, k1); XMEMCPY(xcbc->K[1], key+k1, cipher_descriptor[cipher].block_length); XMEMCPY(xcbc->K[2], key+k1 + cipher_descriptor[cipher].block_length, cipher_descriptor[cipher].block_length); } else { /* use the key expansion */ k1 = cipher_descriptor[cipher].block_length; /* schedule the user key */ skey = XCALLOC(1, sizeof(*skey)); if (skey == NULL) { return CRYPT_MEM; } if ((err = cipher_descriptor[cipher].setup(key, keylen, 0, skey)) != CRYPT_OK) { goto done; } /* make the three keys */ for (y = 0; y < 3; y++) { for (x = 0; x < cipher_descriptor[cipher].block_length; x++) { xcbc->K[y][x] = y + 1; } cipher_descriptor[cipher].ecb_encrypt(xcbc->K[y], xcbc->K[y], skey); } } /* setup K1 */ err = cipher_descriptor[cipher].setup(xcbc->K[0], k1, 0, &xcbc->key); /* setup struct */ zeromem(xcbc->IV, cipher_descriptor[cipher].block_length); xcbc->blocksize = cipher_descriptor[cipher].block_length; xcbc->cipher = cipher; xcbc->buflen = 0; done: cipher_descriptor[cipher].done(skey); if (skey != NULL) { #ifdef LTC_CLEAN_STACK zeromem(skey, sizeof(*skey)); #endif XFREE(skey); } return err; } #endif /* ref: $Format:%D$ */ /* git commit: $Format:%H$ */ /* commit time: $Format:%ai$ */