Merge GH #673 X25519 TLS key exchange

4 files changed, 92 insertions, 36 deletions

diff --git a/src/lib/tls/msg_client_kex.cpp b/src/lib/tls/msg_client_kex.cpp
index 02ebcc2c8..81b01a704 100644
--- a/src/lib/tls/msg_client_kex.cpp
+++ b/src/lib/tls/msg_client_kex.cpp
@@ -20,8 +20,12 @@
 #include <botan/ecdh.h>
 #include <botan/rsa.h>
 
+#if defined(BOTAN_HAS_CURVE_25519)
+  #include <botan/curve25519.h>
+#endif
+
 #if defined(BOTAN_HAS_SRP6)
-#include <botan/srp6.h>
+  #include <botan/srp6.h>
 #endif
 
 namespace Botan {
@@ -138,31 +142,53 @@ Client_Key_Exchange::Client_Key_Exchange(Handshake_IO& io,
 
          const u16bit curve_id = reader.get_u16bit();
 
-         const std::string name = Supported_Elliptic_Curves::curve_id_to_name(curve_id);
+         const std::string curve_name = Supported_Elliptic_Curves::curve_id_to_name(curve_id);
 
-         if(name == "")
+         if(curve_name == "")
             throw Decoding_Error("Server sent unknown named curve " + std::to_string(curve_id));
 
-         if(!policy.allowed_ecc_curve(name))
+         if(!policy.allowed_ecc_curve(curve_name))
             {
             throw TLS_Exception(Alert::HANDSHAKE_FAILURE,
                                 "Server sent ECC curve prohibited by policy");
             }
 
-         EC_Group group(name);
-
-         std::vector<byte> ecdh_key = reader.get_range<byte>(1, 1, 255);
+         const std::vector<byte> ecdh_key = reader.get_range<byte>(1, 1, 255);
 
-         ECDH_PublicKey counterparty_key(group, OS2ECP(ecdh_key, group.get_curve()));
+         std::vector<byte> our_ecdh_public;
+         secure_vector<byte> ecdh_secret;
 
-         policy.check_peer_key_acceptable(counterparty_key);
-         
-         ECDH_PrivateKey priv_key(rng, group);
-
-         PK_Key_Agreement ka(priv_key, rng, "Raw");
+         if(curve_name == "x25519")
+            {
+#if defined(BOTAN_HAS_CURVE_25519)
+            if(ecdh_key.size() != 32)
+               throw TLS_Exception(Alert::HANDSHAKE_FAILURE, "Invalid X25519 key size");
+
+            Curve25519_PublicKey counterparty_key(ecdh_key);
+            policy.check_peer_key_acceptable(counterparty_key);
+            Curve25519_PrivateKey priv_key(rng);
+            PK_Key_Agreement ka(priv_key, rng, "Raw");
+            ecdh_secret = ka.derive_key(0, counterparty_key.public_value()).bits_of();
+#else
+            throw Internal_Error("Negotiated X25519 somehow, but it is disabled");
+#endif
 
-         secure_vector<byte> ecdh_secret =
-            ka.derive_key(0, counterparty_key.public_value()).bits_of();
+            // X25519 is always compressed but sent as "uncompressed" in TLS
+            our_ecdh_public = priv_key.public_value();
+            }
+         else
+            {
+            EC_Group group(curve_name);
+            ECDH_PublicKey counterparty_key(group, OS2ECP(ecdh_key, group.get_curve()));
+            policy.check_peer_key_acceptable(counterparty_key);
+            ECDH_PrivateKey priv_key(rng, group);
+            PK_Key_Agreement ka(priv_key, rng, "Raw");
+            ecdh_secret = ka.derive_key(0, counterparty_key.public_value()).bits_of();
+
+            // follow server's preference for point compression
+            our_ecdh_public = priv_key.public_value(
+               state.server_hello()->prefers_compressed_ec_points() ? PointGFp::COMPRESSED : PointGFp::UNCOMPRESSED);
+            }
 
          if(kex_algo == "ECDH")
             m_pre_master = ecdh_secret;
@@ -172,10 +198,7 @@ Client_Key_Exchange::Client_Key_Exchange(Handshake_IO& io,
             append_tls_length_value(m_pre_master, psk.bits_of(), 2);
             }
 
-         // follow server's preference for point compression
-         append_tls_length_value(m_key_material,
-               priv_key.public_value(state.server_hello()->prefers_compressed_ec_points() ?
-               PointGFp::COMPRESSED : PointGFp::UNCOMPRESSED ), 1);
+         append_tls_length_value(m_key_material, our_ecdh_public, 1);
          }
 #if defined(BOTAN_HAS_SRP6)
       else if(kex_algo == "SRP_SHA")
diff --git a/src/lib/tls/msg_server_kex.cpp b/src/lib/tls/msg_server_kex.cpp
index 325e5d1b0..4515ea450 100644
--- a/src/lib/tls/msg_server_kex.cpp
+++ b/src/lib/tls/msg_server_kex.cpp
@@ -17,8 +17,12 @@
 #include <botan/dh.h>
 #include <botan/ecdh.h>
 
+#if defined(BOTAN_HAS_CURVE_25519)
+  #include <botan/curve25519.h>
+#endif
+
 #if defined(BOTAN_HAS_SRP6)
-#include <botan/srp6.h>
+  #include <botan/srp6.h>
 #endif
 
 namespace Botan {
@@ -69,28 +73,40 @@ Server_Key_Exchange::Server_Key_Exchange(Handshake_IO& io,
          throw TLS_Exception(Alert::HANDSHAKE_FAILURE,
                              "Could not agree on an ECC curve with the client");
 
-      EC_Group ec_group(curve_name);
+      const uint16_t named_curve_id = Supported_Elliptic_Curves::name_to_curve_id(curve_name);
+      if(named_curve_id == 0)
+         throw Internal_Error("TLS does not support ECC with " + curve_name);
 
-      std::unique_ptr<ECDH_PrivateKey> ecdh(new ECDH_PrivateKey(rng, ec_group));
+      std::vector<byte> ecdh_public_val;
 
-      const std::string ecdh_domain_oid = ecdh->domain().get_oid();
-      const std::string domain = OIDS::lookup(OID(ecdh_domain_oid));
+      if(curve_name == "x25519")
+         {
+#if defined(BOTAN_HAS_CURVE_25519)
+         std::unique_ptr<Curve25519_PrivateKey> x25519(new Curve25519_PrivateKey(rng));
+         ecdh_public_val = x25519->public_value();
+         m_kex_key.reset(x25519.release());
+#else
+         throw Internal_Error("Negotiated X25519 somehow, but it is disabled");
+#endif
+         }
+      else
+         {
+         EC_Group ec_group(curve_name);
+         std::unique_ptr<ECDH_PrivateKey> ecdh(new ECDH_PrivateKey(rng, ec_group));
 
-      if(domain == "")
-         throw Internal_Error("Could not find name of ECDH domain " + ecdh_domain_oid);
+         // follow client's preference for point compression
+         ecdh_public_val = ecdh->public_value(
+            state.client_hello()->prefers_compressed_ec_points() ?
+            PointGFp::COMPRESSED : PointGFp::UNCOMPRESSED);
 
-      const u16bit named_curve_id = Supported_Elliptic_Curves::name_to_curve_id(domain);
+         m_kex_key.reset(ecdh.release());
+         }
 
       m_params.push_back(3); // named curve
       m_params.push_back(get_byte(0, named_curve_id));
       m_params.push_back(get_byte(1, named_curve_id));
 
-      // follow client's preference for point compression
-      append_tls_length_value(m_params,
-            ecdh->public_value(state.client_hello()->prefers_compressed_ec_points() ?
-            PointGFp::COMPRESSED : PointGFp::UNCOMPRESSED), 1);
-
-      m_kex_key.reset(ecdh.release());
+      append_tls_length_value(m_params, ecdh_public_val, 1);
       }
 #if defined(BOTAN_HAS_SRP6)
    else if(kex_algo == "SRP_SHA")
diff --git a/src/lib/tls/tls_extensions.cpp b/src/lib/tls/tls_extensions.cpp
index df265d915..a2db1faaf 100644
--- a/src/lib/tls/tls_extensions.cpp
+++ b/src/lib/tls/tls_extensions.cpp
@@ -293,6 +293,12 @@ std::string Supported_Elliptic_Curves::curve_id_to_name(u16bit id)
          return "brainpool384r1";
       case 28:
          return "brainpool512r1";
+
+#if defined(BOTAN_HAS_CURVE_25519)
+      case 29:
+         return "x25519";
+#endif
+
       default:
          return ""; // something we don't know or support
       }
@@ -313,7 +319,13 @@ u16bit Supported_Elliptic_Curves::name_to_curve_id(const std::string& name)
    if(name == "brainpool512r1")
       return 28;
 
-   throw Invalid_Argument("name_to_curve_id unknown name " + name);
+#if defined(BOTAN_HAS_CURVE_25519)
+   if(name == "x25519")
+      return 29;
+#endif
+
+   // Unknown/unavailable EC curves are ignored
+   return 0;
    }
 
 std::vector<byte> Supported_Elliptic_Curves::serialize() const
@@ -323,8 +335,12 @@ std::vector<byte> Supported_Elliptic_Curves::serialize() const
    for(size_t i = 0; i != m_curves.size(); ++i)
       {
       const u16bit id = name_to_curve_id(m_curves[i]);
-      buf.push_back(get_byte(0, id));
-      buf.push_back(get_byte(1, id));
+
+      if(id > 0)
+         {
+         buf.push_back(get_byte(0, id));
+         buf.push_back(get_byte(1, id));
+         }
       }
 
    buf[0] = get_byte(0, static_cast<u16bit>(buf.size()-2));
diff --git a/src/lib/tls/tls_policy.cpp b/src/lib/tls/tls_policy.cpp
index 53ef8e46d..6ee1e0eac 100644
--- a/src/lib/tls/tls_policy.cpp
+++ b/src/lib/tls/tls_policy.cpp
@@ -96,6 +96,7 @@ std::vector<std::string> Policy::allowed_ecc_curves() const
       "secp384r1",
       "brainpool256r1",
       "secp256r1",
+      "x25519",
       };
    }