Mercurial > dropbear
view libtomcrypt/src/pk/dh/dh_import.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" #ifdef LTC_MDH /** Import a DH key from a binary packet @param in The packet to read @param inlen The length of the input packet @param key [out] Where to import the key to @return CRYPT_OK if successful, on error all allocated memory is freed automatically */ int dh_import(const unsigned char *in, unsigned long inlen, dh_key *key) { unsigned char flags[1]; int err; unsigned long version; LTC_ARGCHK(in != NULL); LTC_ARGCHK(key != NULL); /* init */ if ((err = mp_init_multi(&key->x, &key->y, &key->base, &key->prime, NULL)) != CRYPT_OK) { return err; } /* find out what type of key it is */ err = der_decode_sequence_multi(in, inlen, LTC_ASN1_SHORT_INTEGER, 1UL, &version, LTC_ASN1_BIT_STRING, 1UL, &flags, LTC_ASN1_EOL, 0UL, NULL); if (err != CRYPT_OK && err != CRYPT_INPUT_TOO_LONG) { goto error; } if (version == 0) { if (flags[0] == 1) { key->type = PK_PRIVATE; if ((err = der_decode_sequence_multi(in, inlen, LTC_ASN1_SHORT_INTEGER, 1UL, &version, LTC_ASN1_BIT_STRING, 1UL, flags, LTC_ASN1_INTEGER, 1UL, key->prime, LTC_ASN1_INTEGER, 1UL, key->base, LTC_ASN1_INTEGER, 1UL, key->x, LTC_ASN1_EOL, 0UL, NULL)) != CRYPT_OK) { goto error; } /* compute public key: y = (base ^ x) mod prime */ if ((err = mp_exptmod(key->base, key->x, key->prime, key->y)) != CRYPT_OK) { goto error; } } else if (flags[0] == 0) { key->type = PK_PUBLIC; if ((err = der_decode_sequence_multi(in, inlen, LTC_ASN1_SHORT_INTEGER, 1UL, &version, LTC_ASN1_BIT_STRING, 1UL, flags, LTC_ASN1_INTEGER, 1UL, key->prime, LTC_ASN1_INTEGER, 1UL, key->base, LTC_ASN1_INTEGER, 1UL, key->y, LTC_ASN1_EOL, 0UL, NULL)) != CRYPT_OK) { goto error; } } else { err = CRYPT_INVALID_PACKET; goto error; } } else { err = CRYPT_INVALID_PACKET; goto error; } /* check public key */ if ((err = dh_check_pubkey(key)) != CRYPT_OK) { goto error; } return CRYPT_OK; error: dh_free(key); return err; } #endif /* LTC_MDH */ /* ref: $Format:%D$ */ /* git commit: $Format:%H$ */ /* commit time: $Format:%ai$ */