From patchwork Fri Oct 9 00:54:53 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Arne Schwabe X-Patchwork-Id: 1509 Return-Path: Delivered-To: patchwork@openvpn.net Delivered-To: patchwork@openvpn.net Received: from director8.mail.ord1d.rsapps.net ([172.31.255.6]) by backend30.mail.ord1d.rsapps.net with LMTP id IOz7M9BPgF9iYgAAIUCqbw (envelope-from ) for ; Fri, 09 Oct 2020 07:56:00 -0400 Received: from proxy1.mail.iad3b.rsapps.net ([172.31.255.6]) by director8.mail.ord1d.rsapps.net with LMTP id yKftM9BPgF8ldwAAfY0hYg (envelope-from ) for ; Fri, 09 Oct 2020 07:56:00 -0400 Received: from smtp31.gate.iad3b ([172.31.255.6]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) by proxy1.mail.iad3b.rsapps.net with LMTPS id YEyzLNBPgF8qNwAALM5PBw (envelope-from ) for ; Fri, 09 Oct 2020 07:56:00 -0400 X-Spam-Threshold: 95 X-Spam-Score: 0 X-Spam-Flag: NO X-Virus-Scanned: OK X-Orig-To: openvpnslackdevel@openvpn.net X-Originating-Ip: [216.105.38.7] Authentication-Results: smtp31.gate.iad3b.rsapps.net; iprev=pass policy.iprev="216.105.38.7"; spf=pass smtp.mailfrom="openvpn-devel-bounces@lists.sourceforge.net" smtp.helo="lists.sourceforge.net"; dkim=fail (signature verification failed) header.d=sourceforge.net; dkim=fail (signature verification failed) header.d=sf.net; dmarc=none (p=nil; dis=none) header.from=rfc2549.org X-Suspicious-Flag: YES X-Classification-ID: 65958a62-0a26-11eb-888c-52540005277f-1-1 Received: from [216.105.38.7] ([216.105.38.7:32826] helo=lists.sourceforge.net) by smtp31.gate.iad3b.rsapps.net (envelope-from ) (ecelerity 4.2.38.62370 r(:)) with ESMTPS (cipher=DHE-RSA-AES256-GCM-SHA384) id 8A/FC-00523-FCF408F5; Fri, 09 Oct 2020 07:56:00 -0400 Received: from [127.0.0.1] (helo=sfs-ml-1.v29.lw.sourceforge.com) by sfs-ml-1.v29.lw.sourceforge.com with esmtp (Exim 4.90_1) (envelope-from ) id 1kQqzU-0001yr-B6; Fri, 09 Oct 2020 11:55:16 +0000 Received: from [172.30.20.202] (helo=mx.sourceforge.net) by sfs-ml-1.v29.lw.sourceforge.com with esmtps (TLSv1.2:ECDHE-RSA-AES256-GCM-SHA384:256) (Exim 4.90_1) (envelope-from ) id 1kQqzT-0001ya-9O for openvpn-devel@lists.sourceforge.net; Fri, 09 Oct 2020 11:55:15 +0000 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=sourceforge.net; s=x; h=Message-Id:Date:Subject:To:From:Sender:Reply-To:Cc: MIME-Version:Content-Type:Content-Transfer-Encoding:Content-ID: Content-Description:Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc :Resent-Message-ID:In-Reply-To:References:List-Id:List-Help:List-Unsubscribe: List-Subscribe:List-Post:List-Owner:List-Archive; bh=M6On9pcDeGlFm/l6QqV1U+JHRq/YRjFA2ety8pQB31s=; b=LkVoa10pcZwZ4q8YGOx4iPrjl+ wyuFXwabn2KAjfWkk2RkDI+ZkuywNNGNYP0Ng/wbvG4FougUuzQ5sc3IgkYCXEw2F1zrKlwY27yZx HiY8/EYdlxGJuyhjQ3QUcOs0WWBJdyle0ainRfkIDuvmRkFAAuY3JkIQ7XQpPJ79n2Zw=; DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=sf.net; s=x ; h=Message-Id:Date:Subject:To:From:Sender:Reply-To:Cc:MIME-Version: Content-Type:Content-Transfer-Encoding:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: In-Reply-To:References:List-Id:List-Help:List-Unsubscribe:List-Subscribe: List-Post:List-Owner:List-Archive; bh=M6On9pcDeGlFm/l6QqV1U+JHRq/YRjFA2ety8pQB31s=; b=KTdY59CzUR97Spj+n4O7dcpBZQ Ocx/5p2mL6VvLHpSVeQj/lBPJhGUjyv8DtnOaQHm/gg9BdJ/tBqCD49wUua22gBNwInomi9PSEkNg hDyPUnxuS8XpDAj+f4zHD55aMJ+n3ILOpKM05jnMza0Jsdt/6BdQ+ziVi/UrWHw/HBFc=; Received: from mail.blinkt.de ([192.26.174.232]) by sfi-mx-3.v28.lw.sourceforge.com with esmtps (TLSv1.2:ECDHE-RSA-AES256-GCM-SHA384:256) (Exim 4.92.2) id 1kQqzN-004CPl-1f for openvpn-devel@lists.sourceforge.net; Fri, 09 Oct 2020 11:55:15 +0000 Received: from kamera.blinkt.de ([2001:638:502:390:20c:29ff:fec8:535c]) by mail.blinkt.de with smtp (Exim 4.94 (FreeBSD)) (envelope-from ) id 1kQqz7-000P7W-S0 for openvpn-devel@lists.sourceforge.net; Fri, 09 Oct 2020 13:54:53 +0200 Received: (nullmailer pid 4324 invoked by uid 10006); Fri, 09 Oct 2020 11:54:53 -0000 From: Arne Schwabe To: openvpn-devel@lists.sourceforge.net Date: Fri, 9 Oct 2020 13:54:53 +0200 Message-Id: <20201009115453.4279-1-arne@rfc2549.org> X-Mailer: git-send-email 2.17.1 X-Spam-Report: Spam Filtering performed by mx.sourceforge.net. See http://spamassassin.org/tag/ for more details. 0.0 URIBL_BLOCKED ADMINISTRATOR NOTICE: The query to URIBL was blocked. See http://wiki.apache.org/spamassassin/DnsBlocklists#dnsbl-block for more information. [URIs: rfc2549.org] 0.2 HEADER_FROM_DIFFERENT_DOMAINS From and EnvelopeFrom 2nd level mail domains are different 0.0 SPF_NONE SPF: sender does not publish an SPF Record 0.0 SPF_HELO_NONE SPF: HELO does not publish an SPF Record X-Headers-End: 1kQqzN-004CPl-1f Subject: [Openvpn-devel] [PATCH v5] Implement generating data channel keys via EKM/RFC 5705 X-BeenThere: openvpn-devel@lists.sourceforge.net X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , MIME-Version: 1.0 Errors-To: openvpn-devel-bounces@lists.sourceforge.net X-getmail-retrieved-from-mailbox: Inbox OpenVPN currently uses its own (based on TLS 1.0) key derivation mechanism to generate the 256 bytes key data in key2 struct that are then used used to generate encryption/hmac/iv vectors. While this mechanism is still secure, it is not state of the art. Instead of modernising our own approach, this commit implements key derivation using the Keying Material Exporters API introduced by RFC 5705. We also use an opportunistic approach of negotiating the use of EKM (exported key material) through an IV_PROTO flag and prefer EKM to our own PRF if both client and server support it. The use of EKM is pushed to the client as part of NCP as key-derivation tls-ekm. We still exchange the random data (112 bytes from client to server and 64 byte from server to client) for the OpenVPN PRF but do not use it. Removing that exchange would break the handshake and make a key-method 3 or similar necessary. As a side effect, this makes a little bit easier to have a FIPS compatible version of OpenVPN since we do not rely on calling MD5 anymore. Side note: this commit breaks the (not yet merged) WolfSSL support as it claims to support EKM in the OpenSSL compat API but always returns an error if you try to use it. Signed-off-by: Arne Schwabe Patch v2: rebase/change to V2 of EKM refactoring Patch v3: add Changes.rst Patch v4: Rebase on master. Patch v5: Refuse internal label to be used with --keying-material-exporter, polishing/fixes suggested by Steffan integrated Signed-off-by: Arne Schwabe Acked-by: Steffan Karger --- Changes.rst | 11 +++++++ doc/doxygen/doc_key_generation.h | 14 +++++++-- src/openvpn/crypto.h | 4 +++ src/openvpn/init.c | 1 + src/openvpn/multi.c | 4 +++ src/openvpn/options.c | 19 +++++++++++ src/openvpn/options.h | 3 ++ src/openvpn/push.c | 5 ++- src/openvpn/ssl.c | 54 ++++++++++++++++++++++++++++---- src/openvpn/ssl.h | 2 ++ src/openvpn/ssl_backend.h | 1 + src/openvpn/ssl_mbedtls.c | 7 ++--- 12 files changed, 111 insertions(+), 14 deletions(-) diff --git a/Changes.rst b/Changes.rst index f67e1d76..2a2829e7 100644 --- a/Changes.rst +++ b/Changes.rst @@ -1,3 +1,14 @@ +Overview of changes in 2.6 +========================== + + +New features +------------ +Keying Material Exporters (RFC 5705) based key generation + As part of the cipher negotiation OpenVPN will automatically prefer + the RFC5705 based key material generation to the current custom + OpenVPN PRF. This feature requires OpenSSL or mbed TLS 2.18+. + Overview of changes in 2.5 ========================== diff --git a/doc/doxygen/doc_key_generation.h b/doc/doxygen/doc_key_generation.h index 4bb9c708..cef773a9 100644 --- a/doc/doxygen/doc_key_generation.h +++ b/doc/doxygen/doc_key_generation.h @@ -58,6 +58,12 @@ * * @subsection key_generation_method_2 Key method 2 * + * There are two methods for generating key data when using key method 2 + * the first is OpenVPN's traditional approach that exchanges random + * data and uses a PRF and the other is using the RFC5705 keying material + * exporter to generate the key material. For both methods the random + * data is exchange but only used in the traditional method. + * * -# The client generates random material in the following amounts: * - Pre-master secret: 48 bytes * - Client's PRF seed for master secret: 32 bytes @@ -73,8 +79,12 @@ * server's random material. * * %Key method 2 %key expansion is performed by the \c - * generate_key_expansion() function. Please refer to its source code for - * details of the %key expansion process. + * generate_key_expansion_oepnvpn_prf() function. Please refer to its source + * code for details of the %key expansion process. + * + * When the client sends the IV_PROTO_TLS_KEY_EXPORT flag and the server replies + * with `key-derivation tls-ekm` the RFC5705 key material exporter with the + * label EXPORTER-OpenVPN-datakeys is used for the key data. * * @subsection key_generation_random Source of random material * diff --git a/src/openvpn/crypto.h b/src/openvpn/crypto.h index 999f643e..1ad669ce 100644 --- a/src/openvpn/crypto.h +++ b/src/openvpn/crypto.h @@ -254,6 +254,10 @@ struct crypto_options #define CO_MUTE_REPLAY_WARNINGS (1<<2) /**< Bit-flag indicating not to display * replay warnings. */ +#define CO_USE_TLS_KEY_MATERIAL_EXPORT (1<<3) + /**< Bit-flag indicating that data channel key derivation + * is done using TLS keying material export [RFC5705] + */ unsigned int flags; /**< Bit-flags determining behavior of * security operation functions. */ }; diff --git a/src/openvpn/init.c b/src/openvpn/init.c index f87c11e7..580a8550 100644 --- a/src/openvpn/init.c +++ b/src/openvpn/init.c @@ -687,6 +687,7 @@ restore_ncp_options(struct context *c) c->options.ciphername = c->c1.ciphername; c->options.authname = c->c1.authname; c->options.keysize = c->c1.keysize; + c->options.data_channel_use_ekm = false; } void diff --git a/src/openvpn/multi.c b/src/openvpn/multi.c index 13738180..a5862020 100644 --- a/src/openvpn/multi.c +++ b/src/openvpn/multi.c @@ -1817,6 +1817,10 @@ multi_client_set_protocol_options(struct context *c) c->c2.push_request_received = true; } +#ifdef HAVE_EXPORT_KEYING_MATERIAL + o->data_channel_use_ekm = (proto & IV_PROTO_TLS_KEY_EXPORT); +#endif + /* Select cipher if client supports Negotiable Crypto Parameters */ if (!o->ncp_enabled) { diff --git a/src/openvpn/options.c b/src/openvpn/options.c index 772323df..4e19d7cb 100644 --- a/src/openvpn/options.c +++ b/src/openvpn/options.c @@ -7979,6 +7979,20 @@ add_option(struct options *options, } options->ncp_ciphers = p[1]; } + else if (streq(p[0], "key-derivation") && p[1]) + { + VERIFY_PERMISSION(OPT_P_NCP) +#ifdef HAVE_EXPORT_KEYING_MATERIAL + if (streq(p[1], "tls-ekm")) + { + options->data_channel_use_ekm = true; + } + else +#endif + { + msg(msglevel, "Unknown key-derivation method %s", p[1]); + } + } else if (streq(p[0], "ncp-disable") && !p[1]) { VERIFY_PERMISSION(OPT_P_GENERAL|OPT_P_INSTANCE); @@ -8707,6 +8721,11 @@ add_option(struct options *options, "\"EXPORTER\""); goto err; } + if (streq(p[1], EXPORT_KEY_DATA_LABEL)) + { + msg(msglevel, "Keying material exporter label must not be '" + EXPORT_KEY_DATA_LABEL "'."); + } if (ekm_length < 16 || ekm_length > 4095) { msg(msglevel, "Invalid keying material exporter length"); diff --git a/src/openvpn/options.h b/src/openvpn/options.h index e527d70e..5d977793 100644 --- a/src/openvpn/options.h +++ b/src/openvpn/options.h @@ -648,6 +648,9 @@ struct options /* Useful when packets sent by openvpn itself are not subject * to the routing tables that would move packets into the tunnel. */ bool allow_recursive_routing; + + /* Use RFC5705 key export to generate data channel keys */ + bool data_channel_use_ekm; }; #define streq(x, y) (!strcmp((x), (y))) diff --git a/src/openvpn/push.c b/src/openvpn/push.c index e0d2eeaf..17bba948 100644 --- a/src/openvpn/push.c +++ b/src/openvpn/push.c @@ -479,7 +479,10 @@ prepare_push_reply(struct context *c, struct gc_arena *gc, { push_option_fmt(gc, push_list, M_USAGE, "cipher %s", o->ciphername); } - + if (o->data_channel_use_ekm) + { + push_option_fmt(gc, push_list, M_USAGE, "key-derivation tls-ekm"); + } return true; } diff --git a/src/openvpn/ssl.c b/src/openvpn/ssl.c index f90c6a85..b572b7b8 100644 --- a/src/openvpn/ssl.c +++ b/src/openvpn/ssl.c @@ -1783,6 +1783,29 @@ init_key_contexts(struct key_ctx_bi *key, } +static bool +generate_key_expansion_tls_export(struct tls_session *session, struct key2 *key2) +{ + struct gc_arena gc = gc_new(); + unsigned char *key2data; + + key2data = key_state_export_keying_material(session, + EXPORT_KEY_DATA_LABEL, + strlen(EXPORT_KEY_DATA_LABEL), + sizeof(key2->keys), + &gc); + if (!key2data) + { + return false; + } + memcpy(key2->keys, key2data, sizeof(key2->keys)); + secure_memzero(key2data, sizeof(key2->keys)); + key2->n = 2; + + gc_free(&gc); + return true; +} + static struct key2 generate_key_expansion_openvpn_prf(const struct tls_session *session) { @@ -1854,7 +1877,7 @@ generate_key_expansion_openvpn_prf(const struct tls_session *session) */ static bool generate_key_expansion(struct key_ctx_bi *key, - const struct tls_session *session) + struct tls_session *session) { bool ret = false; struct key2 key2; @@ -1865,10 +1888,20 @@ generate_key_expansion(struct key_ctx_bi *key, goto exit; } - bool server = session->opt->server; - key2 = generate_key_expansion_openvpn_prf(session); + if (session->opt->crypto_flags & CO_USE_TLS_KEY_MATERIAL_EXPORT) + { + if (!generate_key_expansion_tls_export(session, &key2)) + { + msg(D_TLS_ERRORS, "TLS Error: Keying material export failed"); + goto exit; + } + } + else + { + key2 = generate_key_expansion_openvpn_prf(session); + } key2_print(&key2, &session->opt->key_type, "Master Encrypt", "Master Decrypt"); @@ -1967,6 +2000,11 @@ tls_session_update_crypto_params(struct tls_session *session, return false; } + if (options->data_channel_use_ekm) + { + session->opt->crypto_flags |= CO_USE_TLS_KEY_MATERIAL_EXPORT; + } + if (strcmp(options->ciphername, session->opt->config_ciphername)) { msg(D_HANDSHAKE, "Data Channel: using negotiated cipher '%s'", @@ -2251,13 +2289,11 @@ push_peer_info(struct buffer *buf, struct tls_session *session) * push request, also signal that the client wants * to get push-reply messages without without requiring a round * trip for a push request message*/ - if(session->opt->pull) + if (session->opt->pull) { iv_proto |= IV_PROTO_REQUEST_PUSH; } - buf_printf(&out, "IV_PROTO=%d\n", iv_proto); - /* support for Negotiable Crypto Parameters */ if (session->opt->ncp_enabled && (session->opt->mode == MODE_SERVER || session->opt->pull)) @@ -2269,8 +2305,14 @@ push_peer_info(struct buffer *buf, struct tls_session *session) buf_printf(&out, "IV_NCP=2\n"); } buf_printf(&out, "IV_CIPHERS=%s\n", session->opt->config_ncp_ciphers); + +#ifdef HAVE_EXPORT_KEYING_MATERIAL + iv_proto |= IV_PROTO_TLS_KEY_EXPORT; +#endif } + buf_printf(&out, "IV_PROTO=%d\n", iv_proto); + /* push compression status */ #ifdef USE_COMP comp_generate_peer_info_string(&session->opt->comp_options, &out); diff --git a/src/openvpn/ssl.h b/src/openvpn/ssl.h index 005628f6..f00f8abd 100644 --- a/src/openvpn/ssl.h +++ b/src/openvpn/ssl.h @@ -116,6 +116,8 @@ * to wait for a push-request to send a push-reply */ #define IV_PROTO_REQUEST_PUSH (1<<2) +/** Supports key derivation via TLS key material exporter [RFC5705] */ +#define IV_PROTO_TLS_KEY_EXPORT (1<<3) /* Default field in X509 to be username */ #define X509_USERNAME_FIELD_DEFAULT "CN" diff --git a/src/openvpn/ssl_backend.h b/src/openvpn/ssl_backend.h index cf9fba25..4bcb3181 100644 --- a/src/openvpn/ssl_backend.h +++ b/src/openvpn/ssl_backend.h @@ -389,6 +389,7 @@ void key_state_ssl_free(struct key_state_ssl *ks_ssl); void backend_tls_ctx_reload_crl(struct tls_root_ctx *ssl_ctx, const char *crl_file, bool crl_inline); +#define EXPORT_KEY_DATA_LABEL "EXPORTER-OpenVPN-datakeys" /** * Keying Material Exporters [RFC 5705] allows additional keying material to be * derived from existing TLS channel. This exported keying material can then be diff --git a/src/openvpn/ssl_mbedtls.c b/src/openvpn/ssl_mbedtls.c index 4ec355a9..f375e957 100644 --- a/src/openvpn/ssl_mbedtls.c +++ b/src/openvpn/ssl_mbedtls.c @@ -1168,11 +1168,8 @@ key_state_ssl_init(struct key_state_ssl *ks_ssl, #ifdef HAVE_EXPORT_KEYING_MATERIAL /* Initialize keying material exporter */ - if (session->opt->ekm_size) - { - mbedtls_ssl_conf_export_keys_ext_cb(ks_ssl->ssl_config, - mbedtls_ssl_export_keys_cb, session); - } + mbedtls_ssl_conf_export_keys_ext_cb(ks_ssl->ssl_config, + mbedtls_ssl_export_keys_cb, session); #endif /* Initialise SSL context */