Mercurial > dropbear
view libtomcrypt/src/mac/xcbc/xcbc_done.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_done.c XCBC Support, terminate the state */ #ifdef LTC_XCBC /** Terminate the XCBC-MAC state @param xcbc XCBC state to terminate @param out [out] Destination for the MAC tag @param outlen [in/out] Destination size and final tag size Return CRYPT_OK on success */ int xcbc_done(xcbc_state *xcbc, unsigned char *out, unsigned long *outlen) { int err, x; LTC_ARGCHK(xcbc != NULL); LTC_ARGCHK(out != NULL); /* check structure */ if ((err = cipher_is_valid(xcbc->cipher)) != CRYPT_OK) { return err; } if ((xcbc->blocksize > cipher_descriptor[xcbc->cipher].block_length) || (xcbc->blocksize < 0) || (xcbc->buflen > xcbc->blocksize) || (xcbc->buflen < 0)) { return CRYPT_INVALID_ARG; } /* which key do we use? */ if (xcbc->buflen == xcbc->blocksize) { /* k2 */ for (x = 0; x < xcbc->blocksize; x++) { xcbc->IV[x] ^= xcbc->K[1][x]; } } else { xcbc->IV[xcbc->buflen] ^= 0x80; /* k3 */ for (x = 0; x < xcbc->blocksize; x++) { xcbc->IV[x] ^= xcbc->K[2][x]; } } /* encrypt */ cipher_descriptor[xcbc->cipher].ecb_encrypt(xcbc->IV, xcbc->IV, &xcbc->key); cipher_descriptor[xcbc->cipher].done(&xcbc->key); /* extract tag */ for (x = 0; x < xcbc->blocksize && (unsigned long)x < *outlen; x++) { out[x] = xcbc->IV[x]; } *outlen = x; #ifdef LTC_CLEAN_STACK zeromem(xcbc, sizeof(*xcbc)); #endif return CRYPT_OK; } #endif /* ref: $Format:%D$ */ /* git commit: $Format:%H$ */ /* commit time: $Format:%ai$ */