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[or-cvs] Backport: discard special bignum values
Update of /home/or/cvsroot/tor/src/common
In directory moria:/tmp/cvs-serv12269/src/common
Modified Files:
Tag: tor-0_1_0-patches
crypto.c
Log Message:
Backport: discard special bignum values
Index: crypto.c
===================================================================
RCS file: /home/or/cvsroot/tor/src/common/crypto.c,v
retrieving revision 1.137.2.2
retrieving revision 1.137.2.3
diff -u -d -r1.137.2.2 -r1.137.2.3
--- crypto.c 6 Jun 2005 21:33:41 -0000 1.137.2.2
+++ crypto.c 4 Aug 2005 23:15:05 -0000 1.137.2.3
@@ -107,6 +107,7 @@
EVP_PKEY *_crypto_pk_env_get_evp_pkey(crypto_pk_env_t *env, int private);
DH *_crypto_dh_env_get_dh(crypto_dh_env_t *dh);
+static int tor_check_bignum(BIGNUM *bn);
static int setup_openssl_threading(void);
/** Return the number of bytes added by padding method <b>padding</b>.
@@ -1223,12 +1224,16 @@
static BIGNUM *dh_param_p = NULL;
/** Shared G parameter for our DH key exchanges. */
static BIGNUM *dh_param_g = NULL;
+#define N_XX_GX 8
+static BIGNUM *dh_gx_xx[N_XX_GX];
/** Initialize dh_param_p and dh_param_g if they are not already
* set. */
static void init_dh_param(void) {
+ static int xx[] = { 0, 1, 2, -1, -2 };
BIGNUM *p, *g;
- int r;
+ BN_CTX *ctx;
+ int r, i;
if (dh_param_p && dh_param_g)
return;
@@ -1270,6 +1275,23 @@
tor_assert(r);
dh_param_p = p;
dh_param_g = g;
+
+ ctx = BN_CTX_new();
+ for (i=0; i<4; ++i) {
+ BIGNUM *x = BN_new(), *g_x = BN_new();
+ char *x_s, *g_x_s;
+ BN_copy(x, dh_param_p);
+ if (xx[i]<0) BN_sub_word(x,-xx[i]); else BN_set_word(x,xx[i]);
+ BN_mod_exp(g_x, dh_param_g, x, dh_param_p, ctx);
+ x_s = BN_bn2hex(x);
+ g_x_s = BN_bn2hex(g_x);
+ dh_gx_xx[i*2]=x;
+ dh_gx_xx[i*2+1]=g_x;
+ log_fn(LOG_DEBUG, "%d,%d <- %s, %s", i*2, i*2+1, x_s, g_x_s);
+ OPENSSL_free(x_s);
+ OPENSSL_free(g_x_s);
+ }
+ BN_CTX_free(ctx);
}
/** Allocate and return a new DH object for a key exchange.
@@ -1345,6 +1367,29 @@
return 0;
}
+/** DOCDOC later; 0 on ok, -1 on bad. */
+static int
+tor_check_bignum(BIGNUM *bn)
+{
+ int i;
+ tor_assert(bn);
+ if (!dh_param_p)
+ init_dh_param();
+ if (bn->neg) {
+ log_fn(LOG_WARN, "bn<0");
+ return -1;
+ }
+ for (i=0; i < N_XX_GX; ++i) {
+ if (!BN_cmp(bn, dh_gx_xx[i])) {
+ char *which = BN_bn2hex(dh_gx_xx[i]);
+ log_fn(LOG_WARN, "Tell Nick and Roger: bn #%d [%s]",i,which);
+ OPENSSL_free(which);
+ return -1;
+ }
+ }
+ return 0;
+}
+
#undef MIN
#define MIN(a,b) ((a)<(b)?(a):(b))
/** Given a DH key exchange object, and our peer's value of g^y (as a
@@ -1372,6 +1417,11 @@
if (!(pubkey_bn = BN_bin2bn((const unsigned char*)pubkey, pubkey_len, NULL)))
goto error;
+ if (tor_check_bignum(pubkey_bn)<0) {
+ /* Check for invalid public keys. */
+ log_fn(LOG_WARN,"Rejected invalid g^x");
+ goto error;
+ }
secret_tmp = tor_malloc(crypto_dh_get_bytes(dh)+1);
result = DH_compute_key((unsigned char*)secret_tmp, pubkey_bn, dh->dh);
if (result < 0) {