Mercurial > dropbear
view libtomcrypt/src/mac/hmac/hmac_file.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 | e9dba7abd939 |
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 hmac_file.c HMAC support, process a file, Tom St Denis/Dobes Vandermeer */ #ifdef LTC_HMAC /** HMAC a file @param hash The index of the hash you wish to use @param fname The name of the file you wish to HMAC @param key The secret key @param keylen The length of the secret key @param out [out] The HMAC authentication tag @param outlen [in/out] The max size and resulting size of the authentication tag @return CRYPT_OK if successful, CRYPT_NOP if file support has been disabled */ int hmac_file(int hash, const char *fname, const unsigned char *key, unsigned long keylen, unsigned char *out, unsigned long *outlen) { #ifdef LTC_NO_FILE LTC_UNUSED_PARAM(hash); LTC_UNUSED_PARAM(fname); LTC_UNUSED_PARAM(key); LTC_UNUSED_PARAM(keylen); LTC_UNUSED_PARAM(out); LTC_UNUSED_PARAM(outlen); return CRYPT_NOP; #else hmac_state hmac; FILE *in; unsigned char *buf; size_t x; int err; LTC_ARGCHK(fname != NULL); LTC_ARGCHK(key != NULL); LTC_ARGCHK(out != NULL); LTC_ARGCHK(outlen != NULL); if ((buf = XMALLOC(LTC_FILE_READ_BUFSIZE)) == NULL) { return CRYPT_MEM; } if ((err = hash_is_valid(hash)) != CRYPT_OK) { goto LBL_ERR; } if ((err = hmac_init(&hmac, hash, key, keylen)) != CRYPT_OK) { goto LBL_ERR; } in = fopen(fname, "rb"); if (in == NULL) { err = CRYPT_FILE_NOTFOUND; goto LBL_ERR; } do { x = fread(buf, 1, LTC_FILE_READ_BUFSIZE, in); if ((err = hmac_process(&hmac, buf, (unsigned long)x)) != CRYPT_OK) { fclose(in); /* we don't trap this error since we're already returning an error! */ goto LBL_CLEANBUF; } } while (x == LTC_FILE_READ_BUFSIZE); if (fclose(in) != 0) { err = CRYPT_ERROR; goto LBL_CLEANBUF; } err = hmac_done(&hmac, out, outlen); LBL_CLEANBUF: zeromem(buf, LTC_FILE_READ_BUFSIZE); LBL_ERR: #ifdef LTC_CLEAN_STACK zeromem(&hmac, sizeof(hmac_state)); #endif XFREE(buf); return err; #endif } #endif /* ref: $Format:%D$ */ /* git commit: $Format:%H$ */ /* commit time: $Format:%ai$ */