tls-crypt-v2: implement abstract metadata parser

The metadata that may be possibly be contained in the WKc has to be
verified by means of a user implemented behaviour.

Implement an abstract class that exports a verify() method to be
used for this purpose.

Users can extend this class and override the verify() method with
their own.

A basic implementation is also provided: it will just ignore the
metadata (if any) and report success to the core.

Signed-off-by: Antonio Quartulli <antonio@openvpn.net>

openvpn/client/cliopt.hpp

@@ -693,6 +693,7 @@ namespace openvpn {
       cp->dc_deferred = true; // defer data channel setup until after options pull
       cp->tls_auth_factory.reset(new CryptoOvpnHMACFactory<SSLLib::CryptoAPI>());
       cp->tls_crypt_factory.reset(new CryptoTLSCryptFactory<SSLLib::CryptoAPI>());
+      cp->tls_crypt_metadata_factory.reset(new CryptoTLSCryptMetadataFactory());
       cp->tlsprf_factory.reset(new CryptoTLSPRFFactory<SSLLib::CryptoAPI>());
       cp->ssl_factory = cc->new_factory();
       cp->load(opt, *proto_context_options, config.default_key_direction, false);

openvpn/crypto/tls_crypt_v2.hpp

@@ -155,6 +155,44 @@ namespace openvpn {
   };
 
   const std::string TLSCryptV2ClientKey::tls_crypt_v2_client_key_name = "OpenVPN tls-crypt-v2 client key";
+
+  // the user can extend the TLSCryptMetadata and the TLSCryptMetadataFactory
+  // classes to implement its own metadata verification method.
+  //
+  // default method is to *ignore* the metadata contained in the WKc sent by the client
+  class TLSCryptMetadata : public RC<thread_unsafe_refcount>
+  {
+  public:
+    typedef RCPtr<TLSCryptMetadata> Ptr;
+
+    // override this method with your own verification mechanism.
+    //
+    // If type is -1 it means that metadata is empty.
+    //
+    virtual bool verify(int type, Buffer& metadata) const
+    {
+      return true;
+    }
+  };
+
+  // abstract class to be extended when creating other factories
+  class TLSCryptMetadataFactory : public RC<thread_unsafe_refcount>
+  {
+  public:
+    typedef RCPtr<TLSCryptMetadataFactory> Ptr;
+
+    virtual TLSCryptMetadata::Ptr new_obj() = 0;
+  };
+
+  // factory implementation for the basic verification method
+  class CryptoTLSCryptMetadataFactory : public TLSCryptMetadataFactory
+  {
+  public:
+    TLSCryptMetadata::Ptr new_obj()
+    {
+      return new TLSCryptMetadata();
+    }
+  };
 }
 
 #endif /* OPENVPN_CRYPTO_TLS_CRYPT_V2_H */

openvpn/error/error.hpp

@@ -70,6 +70,7 @@ namespace openvpn {
       PRIMARY_EXPIRE,      // primary key context expired
       TLS_VERSION_MIN,     // peer cannot handshake at our minimum required TLS version
       TLS_AUTH_FAIL,       // tls-auth HMAC verification failed
+      TLS_CRYPT_META_FAIL, // tls-crypt-v2 metadata verification failed
       CERT_VERIFY_FAIL,    // peer certificate verification failure
       PEM_PASSWORD_FAIL,   // incorrect or missing PEM private key decryption password
       AUTH_FAILED,         // general authentication failure
@@ -145,6 +146,7 @@ namespace openvpn {
 	"PRIMARY_EXPIRE",
 	"TLS_VERSION_MIN",
 	"TLS_AUTH_FAIL",
+	"TLS_CRYPT_META_FAIL",
 	"CERT_VERIFY_FAIL",
 	"PEM_PASSWORD_FAIL",
 	"AUTH_FAILED",

openvpn/ssl/proto.hpp

@@ -305,6 +305,8 @@ namespace openvpn {
       TLSCryptFactory::Ptr tls_crypt_factory;
       TLSCryptContext::Ptr tls_crypt_context;
 
+      TLSCryptMetadataFactory::Ptr tls_crypt_metadata_factory;
+
       // reliability layer parms
       reliable::id_t reliable_window = 0;
       size_t max_ack_list = 0;
@@ -2690,11 +2692,16 @@ namespace openvpn {
 	plaintext.read(client_key.raw_alloc(), OpenVPNStaticKey::KEY_SIZE);
 	proto.reset_tls_crypt(*proto.config, client_key);
 
-	// check existence of optional metadata
-	size_t metadata_size = decrypt_bytes - OpenVPNStaticKey::KEY_SIZE;
-	if (metadata_size > 0)
-	  OPENVPN_LOG("tls-crypt-v2: received metadata (" << metadata_size << " bytes) - IGNORING");
-	// metadata is ignored at the moment
+	// verify metadata
+	int metadata_type = -1;
+	if (!plaintext.empty())
+	  metadata_type = plaintext.pop_front();
+
+	if (!proto.tls_crypt_metadata->verify(metadata_type, plaintext))
+	  {
+	    proto.stats->error(Error::TLS_CRYPT_META_FAIL);
+	    return false;
+	  }
 
 	// virtually remove the WKc from the packet
 	recv.set_size(tls_frame_size);
@@ -3048,6 +3055,8 @@ namespace openvpn {
       //mode should not be specified when slicing
       tls_crypt_server->init(c.tls_key.slice(OpenVPNStaticKey::HMAC),
 			     c.tls_key.slice(OpenVPNStaticKey::CIPHER));
+
+      tls_crypt_metadata = c.tls_crypt_metadata_factory->new_obj();
     }
 
     void reset()
@@ -3767,6 +3776,7 @@ namespace openvpn {
     TLSCryptInstance::Ptr tls_crypt_recv;
 
     TLSCryptInstance::Ptr tls_crypt_server;
+    TLSCryptMetadata::Ptr tls_crypt_metadata;
 
     PacketIDSend ta_pid_send;
     PacketIDReceive ta_pid_recv;

test/ssl/proto.cpp

@@ -835,6 +835,7 @@ int test(const int thread_num)
     const std::string server_key = read_text("server.key");
     const std::string dh_pem = read_text("dh.pem");
     const std::string tls_auth_key = read_text("tls-auth.key");
+    const std::string tls_crypt_v2_server_key = read_text("tls-crypt-v2-server.key");
     const std::string tls_crypt_v2_client_key = read_text("tls-crypt-v2-client.key");
 
     // client config
@@ -894,10 +895,12 @@ int test(const int thread_num)
 #ifdef USE_TLS_CRYPT_V2
     cp->tls_crypt_factory.reset(new CryptoTLSCryptFactory<ClientCryptoAPI>());
     cp->set_tls_crypt_algs(CryptoAlgs::lookup("SHA256"), CryptoAlgs::lookup("AES-256-CTR"));
-    TLSCryptV2ClientKey tls_crypt_v2_key(cp->tls_crypt_context);
-    tls_crypt_v2_key.parse(tls_crypt_v2_client_key);
-    tls_crypt_v2_key.extract_key(cp->tls_key);
-    tls_crypt_v2_key.extract_wkc(cp->wkc);
+    {
+      TLSCryptV2ClientKey tls_crypt_v2_key(cp->tls_crypt_context);
+      tls_crypt_v2_key.parse(tls_crypt_v2_client_key);
+      tls_crypt_v2_key.extract_key(cp->tls_key);
+      tls_crypt_v2_key.extract_wkc(cp->wkc);
+    }
     cp->tls_crypt_v2 = true;
 #endif
     cp->reliable_window = 4;
@@ -970,12 +973,20 @@ int test(const int thread_num)
     sp->set_tls_auth_digest(CryptoAlgs::lookup(PROTO_DIGEST));
     sp->key_direction = 1;
 #endif
-#if defined(USE_TLS_CRYPT) || defined(USE_TLS_CRYPT_V2)
+#if defined(USE_TLS_CRYPT)
     sp->tls_crypt_factory.reset(new CryptoTLSCryptFactory<ClientCryptoAPI>());
     sp->tls_key.parse(tls_auth_key);
     sp->set_tls_crypt_algs(CryptoAlgs::lookup("SHA256"), CryptoAlgs::lookup("AES-256-CTR"));
 #endif
 #ifdef USE_TLS_CRYPT_V2
+    sp->tls_crypt_factory.reset(new CryptoTLSCryptFactory<ClientCryptoAPI>());
+    {
+      TLSCryptV2ServerKey tls_crypt_v2_key;
+      tls_crypt_v2_key.parse(tls_crypt_v2_server_key);
+      tls_crypt_v2_key.extract_key(sp->tls_key);
+    }
+    sp->set_tls_crypt_algs(CryptoAlgs::lookup("SHA256"), CryptoAlgs::lookup("AES-256-CTR"));
+    sp->tls_crypt_metadata_factory.reset(new CryptoTLSCryptMetadataFactory());
     sp->tls_crypt_v2 = true;
 #endif
     sp->reliable_window = 4;

test/ssl/tls-crypt-v2-client.key

@@ -1,14 +1,14 @@
 -----BEGIN OpenVPN tls-crypt-v2 client key-----
-lxflRree2ic6dq7H6fR0nuNEv26m/kMm/Xt0kMPjAkLYfu5XFLTU3xELudrGMyWQ
-vVbHRBzN/14+BU+RW8rc1Ub14EX6rXwpKaQmCh28/FWKBK+4Bzcwb1bPXBMLEI1j
-aFmfgyKFYsOSGqkNtAT+PdRXTTZBwmvSfH2BwqhrwoIv+3W6KUnqLOlsjvDext6K
-/n6HXPyAgOBcCAVZUjIAzcd9HTc+oJKYFkp4zOPDCQ0RmcnCqWq/I6F9imzw8N+t
-vkv9yPaTQEINI6wzHWDNc18YsLyHbgGdeYyMZLBMSVWJzospQot6J7e5uVkEmc3N
-2dtPE0KnYeGqr0dihjgRZkKnKnwmsZ4rpu4Ue3+HITQ23v0bNdtwOAaHZkbdSM3c
-At3nKXzWT5jCoZlqZWGsy1gza3WUm4Z4pLFmfoaxaF3ImRvtEvqgHBurFbokYmGv
-VuCpuGeAJq3gQ0Z/lY89DKuj7B8htStSCzoubrh32dBwlYWkN1HrNrk+pwbVcTe7
-BX0nPnYILF+78F6y4VYI33PBiwtE8D69FGDq38zcK+LJIPJB7t1m42svJJ6u6mGN
-YRevm+zVYsbT/pA/wU+gIBoW1K5pe+euTBPSHe/PCxQ0Y+RiD7aOj8sScx+xfa8O
-RRJ0IwgoBTAkEyW7PmW4SEYUFZxEe9dAVlwmhCmoA99Vpz4I9hiS9a/TVEXCnLWy
-U/RPr7C84ehaZs7I8iY8ZQ==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 -----END OpenVPN tls-crypt-v2 client key-----

test/ssl/tls-crypt-v2-server.key

@@ -0,0 +1,5 @@
+-----BEGIN OpenVPN tls-crypt-v2 server key-----
+hn6VWraZG0o64iPI7faGYkwTMajjqhXqG2kC1X19jCl+aXhWPSgmDbRCT/pSfjLZ
+a2pKXP6DGdi3nuINKuPw4655AcuMaBe4b45+zJz5xk92NnNosLaTsanXtjfBNOK5
+S/M1f4cLZViVsJTDSMcINK/RCclWVK+IFi//CThZQM8=
+-----END OpenVPN tls-crypt-v2 server key-----