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synced 2024-09-21 13:34:59 +02:00
far far cleaner implementation of handshake checking logic. Backport candidate.
svn:r4736
This commit is contained in:
Nick Mathewson
parent
3b9991ef72
commit
9345323b18
@ -108,8 +108,8 @@ RSA *_crypto_pk_env_get_rsa(crypto_pk_env_t *env);
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EVP_PKEY *_crypto_pk_env_get_evp_pkey(crypto_pk_env_t *env, int private);
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DH *_crypto_dh_env_get_dh(crypto_dh_env_t *dh);
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static int tor_check_bignum(BIGNUM *bn);
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static int setup_openssl_threading(void);
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static int tor_check_dh_key(BIGNUM *bn);
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/** Return the number of bytes added by padding method <b>padding</b>.
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*/
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@ -1258,16 +1258,12 @@ crypto_digest_assign(crypto_digest_env_t *into,
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static BIGNUM *dh_param_p = NULL;
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/** Shared G parameter for our DH key exchanges. */
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static BIGNUM *dh_param_g = NULL;
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#define N_XX_GX 15
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static BIGNUM *dh_gx_xx[N_XX_GX];
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/** Initialize dh_param_p and dh_param_g if they are not already
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* set. */
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static void init_dh_param(void) {
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static int xx[] = { 0, 1, 2, -1, -2 };
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BIGNUM *p, *g;
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BN_CTX *ctx;
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int r, i;
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int r;
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if (dh_param_p && dh_param_g)
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return;
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@ -1292,29 +1288,6 @@ static void init_dh_param(void) {
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tor_assert(r);
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dh_param_p = p;
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dh_param_g = g;
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ctx = BN_CTX_new();
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for (i=0; i<5; ++i) {
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BIGNUM *x = BN_new(), *g_x = BN_new(), *p_x = BN_new();
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char *x_s, *g_x_s, *p_x_s;
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BN_copy(x, dh_param_p);
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BN_copy(p_x, dh_param_p);
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if (xx[i]<0) BN_sub_word(x,-xx[i]); else BN_set_word(x,xx[i]);
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if (xx[i]<0) BN_sub_word(p_x,-xx[i]); else BN_add_word(p_x,xx[i]);
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BN_mod_exp(g_x, dh_param_g, x, dh_param_p, ctx);
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x_s = BN_bn2hex(x);
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g_x_s = BN_bn2hex(g_x);
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p_x_s = BN_bn2hex(p_x);
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dh_gx_xx[i*3]=x;
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dh_gx_xx[i*3+1]=g_x;
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dh_gx_xx[i*3+2]=p_x;
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log_fn(LOG_DEBUG, "%d,%d,%d <- %s, %s, %s", i*3, i*3+1, i*3+2,
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x_s, g_x_s, p_x_s);
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OPENSSL_free(x_s);
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OPENSSL_free(g_x_s);
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OPENSSL_free(p_x_s);
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}
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BN_CTX_free(ctx);
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}
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/** Allocate and return a new DH object for a key exchange.
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@ -1358,10 +1331,19 @@ int crypto_dh_get_bytes(crypto_dh_env_t *dh)
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*/
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int crypto_dh_generate_public(crypto_dh_env_t *dh)
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{
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again:
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if (!DH_generate_key(dh->dh)) {
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crypto_log_errors(LOG_WARN, "generating DH key");
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return -1;
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}
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if (tor_check_dh_key(dh->dh->pub_key)<0) {
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log_fn(LOG_WARN, "Weird! Our own DH key was invalid. I guess once-in-the-universe chances really do happen. Trying again.");
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/* Free and clear the keys, so openssl will actually try again. */
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BN_free(dh->dh->pub_key);
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BN_free(dh->dh->priv_key);
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dh->dh->pub_key = dh->dh->priv_key = NULL;
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goto again;
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}
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return 0;
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}
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@ -1390,31 +1372,62 @@ int crypto_dh_get_public(crypto_dh_env_t *dh, char *pubkey, size_t pubkey_len)
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return 0;
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}
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/** DOCDOC later; 0 on ok, -1 on bad. */
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/** Check for bad diffie-hellman public keys (g^x). Return 0 if the key is
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* okay, or -1 if it's bad.
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*/
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static int
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tor_check_bignum(BIGNUM *bn)
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tor_check_dh_key(BIGNUM *bn)
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{
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int i;
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/* There are about 2^116 ways to have a 1024-bit key with <= 16 bits set,
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* and similarly for <= 16 bits unset. This is negligible compared to the
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* 2^1024 entry keyspace. */
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#define MIN_DIFFERING_BITS 16
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/* This covers another 2^25 keys, which is still negligible. */
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#define MIN_DIST_FROM_EDGE (1<<24)
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int i, n_bits, n_set;
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BIGNUM *x = NULL;
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char *s;
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tor_assert(bn);
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x = BN_new();
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if (!dh_param_p)
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init_dh_param();
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if (bn->neg) {
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log_fn(LOG_WARN, "bn<0");
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log_fn(LOG_WARN, "Rejecting DH key < 0");
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return -1;
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}
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if (BN_cmp(bn, dh_param_p)>=0){
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log_fn(LOG_WARN, "bn>=p");
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log_fn(LOG_WARN, "Rejecting DH key >= p");
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return -1;
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}
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for (i=0; i < N_XX_GX; ++i) {
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if (!BN_cmp(bn, dh_gx_xx[i])) {
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char *which = BN_bn2hex(dh_gx_xx[i]);
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log_fn(LOG_WARN, "Tell Nick and Roger: bn #%d [%s]",i,which);
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OPENSSL_free(which);
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return -1;
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}
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n_bits = BN_num_bits(bn);
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n_set = 0;
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for (i=0; i <= n_bits; ++i) {
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if (BN_is_bit_set(bn, i))
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++n_set;
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}
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if (n_set < MIN_DIFFERING_BITS || n_set >= n_bits-MIN_DIFFERING_BITS) {
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log_fn(LOG_WARN, "Too few/many bits in DH key (%d)", n_set);
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goto err;
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}
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BN_set_word(x, MIN_DIST_FROM_EDGE);
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if (BN_cmp(bn,x)<=0) {
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log_fn(LOG_WARN, "DH key is too close to 0");
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goto err;
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}
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BN_copy(x,dh_param_p);
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BN_sub_word(x, MIN_DIST_FROM_EDGE);
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if (BN_cmp(bn,x)>=0) {
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log_fn(LOG_WARN, "DH key is too close to p");
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goto err;
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}
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BN_free(x);
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return 0;
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err:
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BN_free(x);
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s = BN_bn2hex(bn);
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log_fn(LOG_WARN, "Rejecting invalid DH key [%s]", s);
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OPENSSL_free(s);
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return -1;
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}
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#undef MIN
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@ -1444,7 +1457,7 @@ int crypto_dh_compute_secret(crypto_dh_env_t *dh,
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if (!(pubkey_bn = BN_bin2bn((const unsigned char*)pubkey, pubkey_len, NULL)))
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goto error;
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if (tor_check_bignum(pubkey_bn)<0) {
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if (tor_check_dh_key(pubkey_bn)<0) {
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/* Check for invalid public keys. */
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log_fn(LOG_WARN,"Rejected invalid g^x");
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goto error;
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