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Discard special bignum values.

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svn:r4706
This commit is contained in:
Nick Mathewson 2005-08-04 23:14:42 +00:00
parent 9198c55c4b
commit 7a9eb49f5f
1 changed files with 51 additions and 1 deletions
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52
src/common/crypto.c
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@ -108,6 +108,7 @@ RSA *_crypto_pk_env_get_rsa(crypto_pk_env_t *env);
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>.
@ -1257,12 +1258,16 @@ crypto_digest_assign(crypto_digest_env_t *into,
static BIGNUM *dh_param_p = NULL;
/** Shared G parameter for our DH key exchanges. */
static BIGNUM *dh_param_g = NULL;
#define N_XX_GX 10
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;
@ -1288,6 +1293,23 @@ static void init_dh_param(void) {
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.
@ -1363,6 +1385,29 @@ int crypto_dh_get_public(crypto_dh_env_t *dh, char *pubkey, size_t pubkey_len)
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
@ -1390,6 +1435,11 @@ int crypto_dh_compute_secret(crypto_dh_env_t *dh,
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) {