j3d1/tinc
1
0
Fork 0
Code Issues 1 Pull requests Releases Wiki Activity

Added explaination of our key exchange using RSA encryption.

Browse source
This commit is contained in:
Guus Sliepen 2001-03-02 11:25:56 +00:00
parent 125c497881
commit d2a54597e0
1 changed files with 19 additions and 4 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

23
src/protocol.c
View file

@ -17,7 +17,7 @@
along with this program; if not, write to the Free Software
Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
$Id: protocol.c,v 1.28.4.83 2001/02/27 16:37:28 guus Exp $
$Id: protocol.c,v 1.28.4.84 2001/03/02 11:25:56 guus Exp $
*/
#include "config.h"
@ -521,7 +521,17 @@ cp
RAND_bytes(cl->cipher_outkey, len);
cl->cipher_outkey[0] &= 0x0F; /* Make sure that the random data is smaller than the modulus of the RSA key */
/* The message we send must be smaller than the modulus of the RSA key.
By definition, for a key of k bits, the following formula holds:
2^(k-1) <= modulus < 2^(k)
Where ^ means "to the power of", not "xor".
This means that to be sure, we must choose our message < 2^(k-1).
This can be done by setting the most significant bit to zero.
*/
cl->cipher_outkey[0] &= 0x7F;
if(debug_lvl >= DEBUG_SCARY_THINGS)
{
@ -530,9 +540,14 @@ cp
syslog(LOG_DEBUG, _("Generated random meta key (unencrypted): %s"), buffer);
}
/* Encrypt the random data */
/* Encrypt the random data
if(RSA_public_encrypt(len, cl->cipher_outkey, buffer, cl->rsa_key, RSA_NO_PADDING) != len) /* NO_PADDING because the message size equals the RSA key size and it is totally random */
We do not use one of the PKCS padding schemes here.
This is allowed, because we encrypt a totally random string
with a length equal to that of the modulus of the RSA key.
*/
if(RSA_public_encrypt(len, cl->cipher_outkey, buffer, cl->rsa_key, RSA_NO_PADDING) != len)
{
syslog(LOG_ERR, _("Error during encryption of meta key for %s (%s)"), cl->name, cl->hostname);
free(buffer);