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get rid of nick's crazy voodoo dh checking.

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svn:r5518
This commit is contained in:
Roger Dingledine 2005-12-06 23:09:44 +00:00
parent 5c0338dca3
commit 485b2cb4dc
1 changed files with 8 additions and 40 deletions
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48
src/common/crypto.c
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@ -1436,60 +1436,28 @@ crypto_dh_get_public(crypto_dh_env_t *dh, char *pubkey, size_t pubkey_len)
}
/** Check for bad diffie-hellman public keys (g^x). Return 0 if the key is
* okay, or -1 if it's bad.
* okay (in the subgroup [2,p-2]), or -1 if it's bad.
* See http://www.cl.cam.ac.uk/ftp/users/rja14/psandqs.ps.gz for some tips.
*/
static int
tor_check_dh_key(BIGNUM *bn)
{
/* There are about 2^116 ways to have a 1024-bit key with <= 16 bits set,
* and similarly for <= 16 bits unset. This is negligible compared to the
* 2^1024 entry keyspace. */
#define MIN_DIFFERING_BITS 16
/* This covers another 2^25 keys, which is still negligible. */
#define MIN_DIST_FROM_EDGE (1<<24)
/* XXXX Note that this is basically voodoo. Really, we only care about 0,
* 1, and p-1. The "number of bits set" business is inherited from some
* dire warnings in the OpenSSH comments. Real Cryptographers assure us
* that these dire warnings are misplaced.
*
* Still, it can't hurt. -NM We will likely remove all the crud from this
* function in a future version, though. -RD
*/
int i, n_bits, n_set;
BIGNUM *x = NULL;
BIGNUM *x;
char *s;
tor_assert(bn);
x = BN_new();
tor_assert(x);
if (!dh_param_p)
init_dh_param();
if (bn->neg) {
warn(LD_CRYPTO, "Rejecting DH key < 0");
return -1;
}
if (BN_cmp(bn, dh_param_p)>=0) {
warn(LD_CRYPTO, "Rejecting DH key >= p");
return -1;
}
n_bits = BN_num_bits(bn);
n_set = 0;
for (i=0; i <= n_bits; ++i) {
if (BN_is_bit_set(bn, i))
++n_set;
}
if (n_set < MIN_DIFFERING_BITS || n_set >= n_bits-MIN_DIFFERING_BITS) {
warn(LD_CRYPTO, "Too few/many bits in DH key (%d)", n_set);
goto err;
}
BN_set_word(x, MIN_DIST_FROM_EDGE);
BN_set_word(x, 1);
if (BN_cmp(bn,x)<=0) {
warn(LD_CRYPTO, "DH key is too close to 0");
warn(LD_CRYPTO, "DH key must be at least 2.");
goto err;
}
BN_copy(x,dh_param_p);
BN_sub_word(x, MIN_DIST_FROM_EDGE);
BN_sub_word(x, 1);
if (BN_cmp(bn,x)>=0) {
warn(LD_CRYPTO, "DH key is too close to p");
warn(LD_CRYPTO, "DH key must be at most p-2.");
goto err;
}
BN_free(x);
@ -1497,7 +1465,7 @@ tor_check_dh_key(BIGNUM *bn)
err:
BN_free(x);
s = BN_bn2hex(bn);
warn(LD_CRYPTO, "Rejecting invalid DH key [%s]", s);
warn(LD_CRYPTO, "Rejecting insecure DH key [%s]", s);
OPENSSL_free(s);
return -1;
}