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client: reject handshakes with DH parameters < 768 bits.

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Since the client has no way of communicating her supported parameter
range to the server, connections to servers that choose weak DH will
simply fail.

Reviewed-by: Kurt Roeckx <kurt@openssl.org>
This commit is contained in:
Emilia Kasper
2015-05-19 11:53:31 +02:00
parent dcbc03ede7
commit 10a70da729
4 changed files with 57 additions and 25 deletions
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73
ssl/s3_clnt.c
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@@ -2361,6 +2361,25 @@ int ssl3_get_server_done(SSL *s)
return (ret);
}
#ifndef OPENSSL_NO_DH
static DH *get_server_static_dh_key(SESS_CERT *scert)
{
DH *dh_srvr = NULL;
EVP_PKEY *spkey = NULL;
int idx = scert->peer_cert_type;
if (idx >= 0)
spkey = X509_get_pubkey(scert->peer_pkeys[idx].x509);
if (spkey) {
dh_srvr = EVP_PKEY_get1_DH(spkey);
EVP_PKEY_free(spkey);
}
if (dh_srvr == NULL)
SSLerr(SSL_F_GET_SERVER_STATIC_DH_KEY, ERR_R_INTERNAL_ERROR);
return dh_srvr;
}
#endif
int ssl3_send_client_key_exchange(SSL *s)
{
unsigned char *p;
@@ -2603,25 +2622,14 @@ int ssl3_send_client_key_exchange(SSL *s)
goto err;
}
if (scert->peer_dh_tmp != NULL)
if (scert->peer_dh_tmp != NULL) {
dh_srvr = scert->peer_dh_tmp;
else {
/* we get them from the cert */
int idx = scert->peer_cert_type;
EVP_PKEY *spkey = NULL;
dh_srvr = NULL;
if (idx >= 0)
spkey = X509_get_pubkey(scert->peer_pkeys[idx].x509);
if (spkey) {
dh_srvr = EVP_PKEY_get1_DH(spkey);
EVP_PKEY_free(spkey);
}
if (dh_srvr == NULL) {
SSLerr(SSL_F_SSL3_SEND_CLIENT_KEY_EXCHANGE,
ERR_R_INTERNAL_ERROR);
} else {
dh_srvr = get_server_static_dh_key(scert);
if (dh_srvr == NULL)
goto err;
}
}
if (s->s3->flags & TLS1_FLAGS_SKIP_CERT_VERIFY) {
/* Use client certificate key */
EVP_PKEY *clkey = s->cert->key->privatekey;
@@ -3464,25 +3472,44 @@ int ssl3_check_cert_and_algorithm(SSL *s)
}
#endif
#ifndef OPENSSL_NO_DH
if ((alg_k & SSL_kEDH) &&
!(has_bits(i, EVP_PK_DH | EVP_PKT_EXCH) || (dh != NULL))) {
SSLerr(SSL_F_SSL3_CHECK_CERT_AND_ALGORITHM, SSL_R_MISSING_DH_KEY);
if ((alg_k & SSL_kEDH) && dh == NULL) {
SSLerr(SSL_F_SSL3_CHECK_CERT_AND_ALGORITHM, ERR_R_INTERNAL_ERROR);
goto f_err;
} else if ((alg_k & SSL_kDHr) && !SSL_USE_SIGALGS(s) &&
}
if ((alg_k & SSL_kDHr) && !SSL_USE_SIGALGS(s) &&
!has_bits(i, EVP_PK_DH | EVP_PKS_RSA)) {
SSLerr(SSL_F_SSL3_CHECK_CERT_AND_ALGORITHM,
SSL_R_MISSING_DH_RSA_CERT);
goto f_err;
}
# ifndef OPENSSL_NO_DSA
else if ((alg_k & SSL_kDHd) && !SSL_USE_SIGALGS(s) &&
!has_bits(i, EVP_PK_DH | EVP_PKS_DSA)) {
if ((alg_k & SSL_kDHd) && !SSL_USE_SIGALGS(s) &&
!has_bits(i, EVP_PK_DH | EVP_PKS_DSA)) {
SSLerr(SSL_F_SSL3_CHECK_CERT_AND_ALGORITHM,
SSL_R_MISSING_DH_DSA_CERT);
goto f_err;
}
# endif
#endif
if (alg_k & (SSL_kDHE | SSL_kDHr | SSL_kDHd)) {
int dh_size;
if (alg_k & SSL_kDHE) {
dh_size = BN_num_bits(dh->p);
} else {
DH *dh_srvr = get_server_static_dh_key(sc);
if (dh_srvr == NULL)
goto f_err;
dh_size = BN_num_bits(dh_srvr->p);
DH_free(dh_srvr);
}
if ((!SSL_C_IS_EXPORT(s->s3->tmp.new_cipher) && dh_size < 768)
|| (SSL_C_IS_EXPORT(s->s3->tmp.new_cipher) && dh_size < 512)) {
SSLerr(SSL_F_SSL3_CHECK_CERT_AND_ALGORITHM, SSL_R_DH_KEY_TOO_SMALL);
goto f_err;
}
}
#endif /* !OPENSSL_NO_DH */
if (SSL_C_IS_EXPORT(s->s3->tmp.new_cipher) && !has_bits(i, EVP_PKT_EXP)) {
#ifndef OPENSSL_NO_RSA