Mercurial > dropbear
view libtomcrypt/src/pk/katja/katja_exptmod.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 katja_exptmod.c Katja PKCS-style exptmod, Tom St Denis */ #ifdef LTC_MKAT /** Compute an RSA modular exponentiation @param in The input data to send into RSA @param inlen The length of the input (octets) @param out [out] The destination @param outlen [in/out] The max size and resulting size of the output @param which Which exponent to use, e.g. PK_PRIVATE or PK_PUBLIC @param key The RSA key to use @return CRYPT_OK if successful */ int katja_exptmod(const unsigned char *in, unsigned long inlen, unsigned char *out, unsigned long *outlen, int which, katja_key *key) { void *tmp, *tmpa, *tmpb; unsigned long x; int err; LTC_ARGCHK(in != NULL); LTC_ARGCHK(out != NULL); LTC_ARGCHK(outlen != NULL); LTC_ARGCHK(key != NULL); /* is the key of the right type for the operation? */ if (which == PK_PRIVATE && (key->type != PK_PRIVATE)) { return CRYPT_PK_NOT_PRIVATE; } /* must be a private or public operation */ if (which != PK_PRIVATE && which != PK_PUBLIC) { return CRYPT_PK_INVALID_TYPE; } /* init and copy into tmp */ if ((err = mp_init_multi(&tmp, &tmpa, &tmpb, NULL)) != CRYPT_OK) { return err; } if ((err = mp_read_unsigned_bin(tmp, (unsigned char *)in, (int)inlen)) != CRYPT_OK) { goto error; } /* sanity check on the input */ if (mp_cmp(key->N, tmp) == LTC_MP_LT) { err = CRYPT_PK_INVALID_SIZE; goto done; } /* are we using the private exponent and is the key optimized? */ if (which == PK_PRIVATE) { /* tmpa = tmp^dP mod p */ if ((err = mp_exptmod(tmp, key->dP, key->p, tmpa)) != CRYPT_OK) { goto error; } /* tmpb = tmp^dQ mod q */ if ((err = mp_exptmod(tmp, key->dQ, key->q, tmpb)) != CRYPT_OK) { goto error; } /* tmp = (tmpa - tmpb) * qInv (mod p) */ if ((err = mp_sub(tmpa, tmpb, tmp)) != CRYPT_OK) { goto error; } if ((err = mp_mulmod(tmp, key->qP, key->p, tmp)) != CRYPT_OK) { goto error; } /* tmp = tmpb + q * tmp */ if ((err = mp_mul(tmp, key->q, tmp)) != CRYPT_OK) { goto error; } if ((err = mp_add(tmp, tmpb, tmp)) != CRYPT_OK) { goto error; } } else { /* exptmod it */ if ((err = mp_exptmod(tmp, key->N, key->N, tmp)) != CRYPT_OK) { goto error; } } /* read it back */ x = (unsigned long)mp_unsigned_bin_size(key->N); if (x > *outlen) { *outlen = x; err = CRYPT_BUFFER_OVERFLOW; goto done; } /* this should never happen ... */ if (mp_unsigned_bin_size(tmp) > mp_unsigned_bin_size(key->N)) { err = CRYPT_ERROR; goto done; } *outlen = x; /* convert it */ zeromem(out, x); if ((err = mp_to_unsigned_bin(tmp, out+(x-mp_unsigned_bin_size(tmp)))) != CRYPT_OK) { goto error; } /* clean up and return */ err = CRYPT_OK; goto done; error: done: mp_clear_multi(tmp, tmpa, tmpb, NULL); return err; } #endif /* ref: $Format:%D$ */ /* git commit: $Format:%H$ */ /* commit time: $Format:%ai$ */