Make SRP6 support optional in TLS

Remove SRP_SHA from the default policy, since normal applications do
not need it.

Removes nullptr initializers of unique_ptrs in the Server_Key_Exchange
constructor, that's the default unique_ptr already.

10 files changed, 72 insertions, 20 deletions

diff --git a/src/lib/tls/info.txt b/src/lib/tls/info.txt
index 50b6dbbdf..a43d5619a 100644
--- a/src/lib/tls/info.txt
+++ b/src/lib/tls/info.txt
@@ -50,6 +50,5 @@ rng
 rsa
 sha1
 sha2_32
-srp6
 x509
 </requires>
diff --git a/src/lib/tls/msg_client_hello.cpp b/src/lib/tls/msg_client_hello.cpp
index 43ab84f33..23807215f 100644
--- a/src/lib/tls/msg_client_hello.cpp
+++ b/src/lib/tls/msg_client_hello.cpp
@@ -82,7 +82,7 @@ Client_Hello::Client_Hello(Handshake_IO& io,
    {
    m_extensions.add(new Extended_Master_Secret);
    m_extensions.add(new Renegotiation_Extension(reneg_info));
-   m_extensions.add(new SRP_Identifier(srp_identifier));
+
    m_extensions.add(new Server_Name_Indicator(hostname));
    m_extensions.add(new Session_Ticket());
    m_extensions.add(new Supported_Elliptic_Curves(policy.allowed_ecc_curves()));
@@ -97,6 +97,15 @@ Client_Hello::Client_Hello(Handshake_IO& io,
    if(reneg_info.empty() && !next_protocols.empty())
       m_extensions.add(new Application_Layer_Protocol_Notification(next_protocols));
 
+#if defined(BOTAN_HAS_SRP6)
+   m_extensions.add(new SRP_Identifier(srp_identifier));
+#else
+   if(!srp_identifier.empty())
+      {
+      throw Invalid_State("Attempting to initiate SRP session but TLS-SRP support disabled");
+      }
+#endif
+
    BOTAN_ASSERT(policy.acceptable_protocol_version(version),
                 "Our policy accepts the version we are offering");
 
@@ -136,7 +145,6 @@ Client_Hello::Client_Hello(Handshake_IO& io,
    m_extensions.add(new Extended_Master_Secret);
 
    m_extensions.add(new Renegotiation_Extension(reneg_info));
-   m_extensions.add(new SRP_Identifier(session.srp_identifier()));
    m_extensions.add(new Server_Name_Indicator(session.server_info().hostname()));
    m_extensions.add(new Session_Ticket(session.session_ticket()));
    m_extensions.add(new Supported_Elliptic_Curves(policy.allowed_ecc_curves()));
@@ -148,6 +156,15 @@ Client_Hello::Client_Hello(Handshake_IO& io,
    if(reneg_info.empty() && !next_protocols.empty())
       m_extensions.add(new Application_Layer_Protocol_Notification(next_protocols));
 
+#if defined(BOTAN_HAS_SRP6)
+   m_extensions.add(new SRP_Identifier(session.srp_identifier()));
+#else
+   if(!session.srp_identifier().empty())
+      {
+      throw Invalid_State("Attempting to resume SRP session but TLS-SRP support disabled");
+      }
+#endif
+
    hash.update(io.send(*this));
    }
 
diff --git a/src/lib/tls/msg_client_kex.cpp b/src/lib/tls/msg_client_kex.cpp
index 68809f22f..4bec9f3be 100644
--- a/src/lib/tls/msg_client_kex.cpp
+++ b/src/lib/tls/msg_client_kex.cpp
@@ -10,14 +10,19 @@
 #include <botan/internal/tls_extensions.h>
 #include <botan/internal/tls_handshake_io.h>
 #include <botan/credentials_manager.h>
+#include <botan/rng.h>
+#include <botan/loadstor.h>
+#include <botan/internal/ct_utils.h>
+
 #include <botan/pubkey.h>
+
 #include <botan/dh.h>
 #include <botan/ecdh.h>
 #include <botan/rsa.h>
+
+#if defined(BOTAN_HAS_SRP6)
 #include <botan/srp6.h>
-#include <botan/rng.h>
-#include <botan/loadstor.h>
-#include <botan/internal/ct_utils.h>
+#endif
 
 namespace Botan {
 
@@ -166,6 +171,7 @@ Client_Key_Exchange::Client_Key_Exchange(Handshake_IO& io,
 
          append_tls_length_value(m_key_material, priv_key.public_value(), 1);
          }
+#if defined(BOTAN_HAS_SRP6)
       else if(kex_algo == "SRP_SHA")
          {
          const BigInt N = BigInt::decode(reader.get_range<byte>(2, 1, 65535));
@@ -193,6 +199,7 @@ Client_Key_Exchange::Client_Key_Exchange(Handshake_IO& io,
          append_tls_length_value(m_key_material, BigInt::encode(srp_vals.first), 2);
          m_pre_master = srp_vals.second.bits_of();
          }
+#endif
       else
          {
          throw Internal_Error("Client_Key_Exchange: Unknown kex " +
@@ -323,12 +330,14 @@ Client_Key_Exchange::Client_Key_Exchange(const std::vector<byte>& contents,
          append_tls_length_value(m_pre_master, zeros, 2);
          append_tls_length_value(m_pre_master, psk.bits_of(), 2);
          }
+#if defined(BOTAN_HAS_SRP6)
       else if(kex_algo == "SRP_SHA")
          {
          SRP6_Server_Session& srp = state.server_kex()->server_srp_params();
 
          m_pre_master = srp.step2(BigInt::decode(reader.get_range<byte>(2, 0, 65535))).bits_of();
          }
+#endif
       else if(kex_algo == "DH" || kex_algo == "DHE_PSK" ||
               kex_algo == "ECDH" || kex_algo == "ECDHE_PSK")
          {
diff --git a/src/lib/tls/msg_server_kex.cpp b/src/lib/tls/msg_server_kex.cpp
index 0c3b5c704..fcff7349e 100644
--- a/src/lib/tls/msg_server_kex.cpp
+++ b/src/lib/tls/msg_server_kex.cpp
@@ -12,11 +12,14 @@
 #include <botan/credentials_manager.h>
 #include <botan/loadstor.h>
 #include <botan/pubkey.h>
+#include <botan/oids.h>
+
 #include <botan/dh.h>
 #include <botan/ecdh.h>
-#include <botan/rsa.h>
+
+#if defined(BOTAN_HAS_SRP6)
 #include <botan/srp6.h>
-#include <botan/oids.h>
+#endif
 
 namespace Botan {
 
@@ -86,6 +89,7 @@ Server_Key_Exchange::Server_Key_Exchange(Handshake_IO& io,
 
       m_kex_key.reset(ecdh.release());
       }
+#if defined(BOTAN_HAS_SRP6)
    else if(kex_algo == "SRP_SHA")
       {
       const std::string srp_identifier = state.client_hello()->srp_identifier();
@@ -115,6 +119,7 @@ Server_Key_Exchange::Server_Key_Exchange(Handshake_IO& io,
       append_tls_length_value(m_params, salt, 1);
       append_tls_length_value(m_params, BigInt::encode(B), 2);
       }
+#endif
    else if(kex_algo != "PSK")
       throw Internal_Error("Server_Key_Exchange: Unknown kex type " + kex_algo);
 
@@ -142,8 +147,7 @@ Server_Key_Exchange::Server_Key_Exchange(Handshake_IO& io,
 Server_Key_Exchange::Server_Key_Exchange(const std::vector<byte>& buf,
                                          const std::string& kex_algo,
                                          const std::string& sig_algo,
-                                         Protocol_Version version) :
-   m_kex_key(nullptr), m_srp_params(nullptr)
+                                         Protocol_Version version)
    {
    TLS_Data_Reader reader("ServerKeyExchange", buf);
 
@@ -249,12 +253,6 @@ const Private_Key& Server_Key_Exchange::server_kex_key() const
    return *m_kex_key;
    }
 
-// Only valid for SRP negotiation
-SRP6_Server_Session& Server_Key_Exchange::server_srp_params() const
-   {
-   BOTAN_ASSERT_NONNULL(m_srp_params);
-   return *m_srp_params;
-   }
 }
 
 }
diff --git a/src/lib/tls/tls_extensions.cpp b/src/lib/tls/tls_extensions.cpp
index b81a0dcb9..35c39ddab 100644
--- a/src/lib/tls/tls_extensions.cpp
+++ b/src/lib/tls/tls_extensions.cpp
@@ -24,8 +24,10 @@ Extension* make_extension(TLS_Data_Reader& reader,
       case TLSEXT_SERVER_NAME_INDICATION:
          return new Server_Name_Indicator(reader, size);
 
+#if defined(BOTAN_HAS_SRP6)
       case TLSEXT_SRP_IDENTIFIER:
          return new SRP_Identifier(reader, size);
+#endif
 
       case TLSEXT_USABLE_ELLIPTIC_CURVES:
          return new Supported_Elliptic_Curves(reader, size);
@@ -175,6 +177,8 @@ std::vector<byte> Server_Name_Indicator::serialize() const
    return buf;
    }
 
+#if defined(BOTAN_HAS_SRP6)
+
 SRP_Identifier::SRP_Identifier(TLS_Data_Reader& reader,
                                u16bit extension_size)
    {
@@ -196,6 +200,8 @@ std::vector<byte> SRP_Identifier::serialize() const
    return buf;
    }
 
+#endif
+
 Renegotiation_Extension::Renegotiation_Extension(TLS_Data_Reader& reader,
                                                  u16bit extension_size)
    {
diff --git a/src/lib/tls/tls_extensions.h b/src/lib/tls/tls_extensions.h
index a4ca31410..5a8aff9de 100644
--- a/src/lib/tls/tls_extensions.h
+++ b/src/lib/tls/tls_extensions.h
@@ -94,6 +94,7 @@ class Server_Name_Indicator final : public Extension
       std::string m_sni_host_name;
    };
 
+#if defined(BOTAN_HAS_SRP6)
 /**
 * SRP identifier extension (RFC 5054)
 */
@@ -119,6 +120,7 @@ class SRP_Identifier final : public Extension
    private:
       std::string m_srp_identifier;
    };
+#endif
 
 /**
 * Renegotiation Indication Extension (RFC 5746)
diff --git a/src/lib/tls/tls_handshake_state.cpp b/src/lib/tls/tls_handshake_state.cpp
index b085e378a..3799c9e7d 100644
--- a/src/lib/tls/tls_handshake_state.cpp
+++ b/src/lib/tls/tls_handshake_state.cpp
@@ -325,12 +325,16 @@ Handshake_State::get_next_handshake_msg()
 
 std::string Handshake_State::srp_identifier() const
    {
+#if defined(BOTAN_HAS_SRP6)
+   // Authenticated via the successful key exchange
    if(ciphersuite().valid() && ciphersuite().kex_algo() == "SRP_SHA")
       return client_hello()->srp_identifier();
+#endif
 
    return "";
    }
 
+
 std::vector<byte> Handshake_State::session_ticket() const
    {
    if(new_session_ticket() && !new_session_ticket()->ticket().empty())
diff --git a/src/lib/tls/tls_messages.h b/src/lib/tls/tls_messages.h
index 739eca23e..c648df720 100644
--- a/src/lib/tls/tls_messages.h
+++ b/src/lib/tls/tls_messages.h
@@ -22,7 +22,10 @@
 namespace Botan {
 
 class Credentials_Manager;
+
+#if defined(BOTAN_HAS_SRP6)
 class SRP6_Server_Session;
+#endif
 
 namespace TLS {
 
@@ -95,12 +98,14 @@ class Client_Hello final : public Handshake_Message
          return "";
          }
 
+#if defined(BOTAN_HAS_SRP6)
       std::string srp_identifier() const
          {
          if(SRP_Identifier* srp = m_extensions.get<SRP_Identifier>())
             return srp->identifier();
          return "";
          }
+#endif
 
       bool secure_renegotiation() const
          {
@@ -463,8 +468,14 @@ class Server_Key_Exchange final : public Handshake_Message
       // Only valid for certain kex types
       const Private_Key& server_kex_key() const;
 
+#if defined(BOTAN_HAS_SRP6)
       // Only valid for SRP negotiation
-      SRP6_Server_Session& server_srp_params() const;
+      SRP6_Server_Session& server_srp_params() const
+         {
+         BOTAN_ASSERT_NONNULL(m_srp_params);
+         return *m_srp_params;
+         }
+#endif
 
       Server_Key_Exchange(Handshake_IO& io,
                           Handshake_State& state,
@@ -482,8 +493,10 @@ class Server_Key_Exchange final : public Handshake_Message
    private:
       std::vector<byte> serialize() const override;
 
-      std::unique_ptr<Private_Key> m_kex_key;
+#if defined(BOTAN_HAS_SRP6)
       std::unique_ptr<SRP6_Server_Session> m_srp_params;
+#endif
+      std::unique_ptr<Private_Key> m_kex_key;
 
       std::vector<byte> m_params;
 
diff --git a/src/lib/tls/tls_policy.cpp b/src/lib/tls/tls_policy.cpp
index 096dffb4a..3100db50d 100644
--- a/src/lib/tls/tls_policy.cpp
+++ b/src/lib/tls/tls_policy.cpp
@@ -64,7 +64,7 @@ std::vector<std::string> Policy::allowed_macs() const
 std::vector<std::string> Policy::allowed_key_exchange_methods() const
    {
    return {
-      "SRP_SHA",
+      //"SRP_SHA",
       //"ECDHE_PSK",
       //"DHE_PSK",
       //"PSK",
@@ -80,7 +80,7 @@ std::vector<std::string> Policy::allowed_signature_methods() const
       "ECDSA",
       "RSA",
       "DSA",
-      //""
+      //"" (anon)
       };
    }
 
diff --git a/src/lib/tls/tls_server.cpp b/src/lib/tls/tls_server.cpp
index 6aed40479..5ababe621 100644
--- a/src/lib/tls/tls_server.cpp
+++ b/src/lib/tls/tls_server.cpp
@@ -84,12 +84,14 @@ bool check_for_resume(Session& session_info,
                     session_info.compression_method()))
       return false;
 
+#if defined(BOTAN_HAS_SRP6)
    // client sent a different SRP identity
    if(client_hello->srp_identifier() != "")
       {
       if(client_hello->srp_identifier() != session_info.srp_identifier())
          return false;
       }
+#endif
 
    // client sent a different SNI hostname
    if(client_hello->sni_hostname() != "")
@@ -160,6 +162,7 @@ u16bit choose_ciphersuite(
       if(suite.sig_algo() != "" && cert_chains.count(suite.sig_algo()) == 0)
          continue;
 
+#if defined(BOTAN_HAS_SRP6)
       /*
       The client may offer SRP cipher suites in the hello message but
       omit the SRP extension.  If the server would like to select an
@@ -171,6 +174,7 @@ u16bit choose_ciphersuite(
       if(suite.kex_algo() == "SRP_SHA" && client_hello->srp_identifier() == "")
          throw TLS_Exception(Alert::UNKNOWN_PSK_IDENTITY,
                              "Client wanted SRP but did not send username");
+#endif
 
       return suite_id;
       }