Commit f14743a9 authored by Nick Mathewson's avatar Nick Mathewson 🦞
Browse files

Note that much of check_dh_key is voodoo; make x in DH be only 320 bits for DH... 

Note that much of check_dh_key is voodoo; make x in DH be only 320 bits for DH speed improvement: this wants auditing. [We have blessing from Ian on this.]  (Note that DH in SSL is not yet affected.)


svn:r5359
parent a3c53e0a

src/common/crypto.c

+24 −0
Original line number Diff line number Diff line
@@ -1390,6 +1390,8 @@ crypto_dh_new(void) 
  return NULL;

}



#define DH_PRIVATE_KEY_BITS 320



/** Return the length of the DH key in <b>dh</b>, in bytes.

 */

int
@@ -1405,7 +1407,22 @@ crypto_dh_get_bytes(crypto_dh_env_t *dh) 
int

crypto_dh_generate_public(crypto_dh_env_t *dh)

{

  int pk_bits = BN_num_bits(dh->dh->p);

  if (pk_bits > DH_PRIVATE_KEY_BITS)

    pk_bits = DH_PRIVATE_KEY_BITS;

 again:

  if (!dh->dh->priv_key) {

    dh->dh->priv_key = BN_new();

    if (!dh->dh->priv_key) {

      err(LD_MM, "Unable to allocate BN.");

      return -1;

    }

  }

  /* We generate the key ourselves so that we can get a 2-3x speedup by using

   * a 320-bit x instead of a 1024-bit x. */

  if (!BN_rand(dh->dh->priv_key, pk_bits, 0, 0)) {

    crypto_log_errors(LOG_WARN, "Generating DH private key");

  }

  if (!DH_generate_key(dh->dh)) {

    crypto_log_errors(LOG_WARN, "generating DH key");

    return -1;
@@ -1462,6 +1479,13 @@ tor_check_dh_key(BIGNUM *bn) 
#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, 2, and -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.

   */

  int i, n_bits, n_set;

  BIGNUM *x = NULL;

  char *s;