From 15d0524327a10c2999f37375688196f8452f1029 Mon Sep 17 00:00:00 2001 From: Arne Schwabe Date: Tue, 25 Aug 2020 09:36:42 +0200 Subject: Move openvpn specific key expansion into its own function This moves the OpenVPN specific PRF into its own function also simplifies the code a bit by passing tls_session directly instead of 5 of its fields. Patch v2: Rebase Patch v4: rewrite/fix comments, fix potential not initialised before goto issue Signed-off-by: Arne Schwabe Acked-by: Steffan Karger Message-Id: <20200825073643.15920-1-arne@rfc2549.org> URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg20815.html Signed-off-by: Gert Doering --- src/openvpn/ssl.c | 116 +++++++++++++++++++++++++++++++++++------------------- 1 file changed, 76 insertions(+), 40 deletions(-) (limited to 'src/openvpn/ssl.c') diff --git a/src/openvpn/ssl.c b/src/openvpn/ssl.c index 3fcaa25..3535fc7 100644 --- a/src/openvpn/ssl.c +++ b/src/openvpn/ssl.c @@ -1765,27 +1765,36 @@ openvpn_PRF(const uint8_t *secret, VALGRIND_MAKE_READABLE((void *)output, output_len); } -/* - * Using source entropy from local and remote hosts, mix into - * master key. - */ -static bool -generate_key_expansion(struct key_ctx_bi *key, - const struct key_type *key_type, - const struct key_source2 *key_src, - const struct session_id *client_sid, - const struct session_id *server_sid, - bool server) +static void +init_key_contexts(struct key_ctx_bi *key, + const struct key_type *key_type, + bool server, + struct key2 *key2) +{ + /* Initialize key contexts */ + int key_direction = server ? KEY_DIRECTION_INVERSE : KEY_DIRECTION_NORMAL; + init_key_ctx_bi(key, key2, key_direction, key_type, "Data Channel"); + + /* Initialize implicit IVs */ + key_ctx_update_implicit_iv(&key->encrypt, (*key2).keys[(int)server].hmac, + MAX_HMAC_KEY_LENGTH); + key_ctx_update_implicit_iv(&key->decrypt, (*key2).keys[1-(int)server].hmac, + MAX_HMAC_KEY_LENGTH); + +} + +static struct key2 +generate_key_expansion_openvpn_prf(const struct tls_session *session) { uint8_t master[48] = { 0 }; - struct key2 key2 = { 0 }; - bool ret = false; - if (key->initialized) - { - msg(D_TLS_ERRORS, "TLS Error: key already initialized"); - goto exit; - } + const struct key_state *ks = &session->key[KS_PRIMARY]; + const struct key_source2 *key_src = ks->key_src; + + const struct session_id *client_sid = session->opt->server ? + &ks->session_id_remote : &session->session_id; + const struct session_id *server_sid = !session->opt->server ? + &ks->session_id_remote : &session->session_id; /* debugging print of source key material */ key_source2_print(key_src); @@ -1803,6 +1812,7 @@ generate_key_expansion(struct key_ctx_bi *key, master, sizeof(master)); + struct key2 key2; /* compute key expansion */ openvpn_PRF(master, sizeof(master), @@ -1815,36 +1825,67 @@ generate_key_expansion(struct key_ctx_bi *key, server_sid, (uint8_t *)key2.keys, sizeof(key2.keys)); + secure_memzero(&master, sizeof(master)); + /* + * fixup_key only correctly sets DES parity bits if the cipher is a + * DES variant. + * + * The newer OpenSSL and mbed TLS libraries (those that support EKM) + * ignore these bits. + * + * We keep the DES fixup here as compatibility. + * OpenVPN3 never did this fixup anyway. So this code is *probably* not + * required but we keep it for compatibility until we remove DES support + * since it does not hurt either. + */ + for (int i = 0; i < 2; ++i) + { + fixup_key(&key2.keys[i], &session->opt->key_type); + } key2.n = 2; - key2_print(&key2, key_type, "Master Encrypt", "Master Decrypt"); + return key2; +} + +/* + * Using source entropy from local and remote hosts, mix into + * master key. + */ +static bool +generate_key_expansion(struct key_ctx_bi *key, + const struct tls_session *session) +{ + bool ret = false; + struct key2 key2; + + if (key->initialized) + { + msg(D_TLS_ERRORS, "TLS Error: key already initialized"); + goto exit; + } + + + bool server = session->opt->server; + + key2 = generate_key_expansion_openvpn_prf(session); + + key2_print(&key2, &session->opt->key_type, + "Master Encrypt", "Master Decrypt"); /* check for weak keys */ for (int i = 0; i < 2; ++i) { - fixup_key(&key2.keys[i], key_type); - if (!check_key(&key2.keys[i], key_type)) + if (!check_key(&key2.keys[i], &session->opt->key_type)) { msg(D_TLS_ERRORS, "TLS Error: Bad dynamic key generated"); goto exit; } } - - /* Initialize OpenSSL key contexts */ - int key_direction = server ? KEY_DIRECTION_INVERSE : KEY_DIRECTION_NORMAL; - init_key_ctx_bi(key, &key2, key_direction, key_type, "Data Channel"); - - /* Initialize implicit IVs */ - key_ctx_update_implicit_iv(&key->encrypt, key2.keys[(int)server].hmac, - MAX_HMAC_KEY_LENGTH); - key_ctx_update_implicit_iv(&key->decrypt, key2.keys[1-(int)server].hmac, - MAX_HMAC_KEY_LENGTH); - + init_key_contexts(key, &session->opt->key_type, server, &key2); ret = true; exit: - secure_memzero(&master, sizeof(master)); secure_memzero(&key2, sizeof(key2)); return ret; @@ -1879,10 +1920,6 @@ tls_session_generate_data_channel_keys(struct tls_session *session) { bool ret = false; struct key_state *ks = &session->key[KS_PRIMARY]; /* primary key */ - const struct session_id *client_sid = session->opt->server ? - &ks->session_id_remote : &session->session_id; - const struct session_id *server_sid = !session->opt->server ? - &ks->session_id_remote : &session->session_id; if (ks->authenticated == KS_AUTH_FALSE) { @@ -1891,9 +1928,8 @@ tls_session_generate_data_channel_keys(struct tls_session *session) } ks->crypto_options.flags = session->opt->crypto_flags; - if (!generate_key_expansion(&ks->crypto_options.key_ctx_bi, - &session->opt->key_type, ks->key_src, client_sid, server_sid, - session->opt->server)) + + if (!generate_key_expansion(&ks->crypto_options.key_ctx_bi, session)) { msg(D_TLS_ERRORS, "TLS Error: generate_key_expansion failed"); goto cleanup; -- cgit v1.1