Address some issues with PR 492

Adds copyright notices for Juraj Somorovsky and Christian Mainka of Hackmanit
for the changes in 7c7fcecbe6a and 6d327f879c

Add Policy::check_peer_key_acceptable which lets the app set an arbitrary
callback for examining keys - both the end entity signature keys from
certificates and the peer PFS public keys. Default impl checks that the
algorithm size matches the min keylength. This centralizes this logic
and lets the application do interesting things.

Adds a policy for ECDSA group size checks.

Increases default policy minimums to 2048 RSA and 256 ECC.
(Maybe I'm an optimist after all.)

1 files changed, 7 insertions, 13 deletions

diff --git a/src/lib/tls/msg_server_kex.cpp b/src/lib/tls/msg_server_kex.cpp
index 99f0d0f09..10581fe45 100644
--- a/src/lib/tls/msg_server_kex.cpp
+++ b/src/lib/tls/msg_server_kex.cpp
@@ -147,7 +147,6 @@ 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,
-                                         const Policy& policy,
                                          Protocol_Version version)
    {
    TLS_Data_Reader reader("ServerKeyExchange", buf);
@@ -166,18 +165,11 @@ Server_Key_Exchange::Server_Key_Exchange(const std::vector<byte>& buf,
    if(kex_algo == "DH" || kex_algo == "DHE_PSK")
       {
       // 3 bigints, DH p, g, Y
-      std::vector<byte> p = reader.get_range<byte>(2, 1, 65535);
-      reader.get_range<byte>(2, 1, 65535);
-      reader.get_range<byte>(2, 1, 65535);
-      
-      // protection against the LOGJAM attack
-      int key_size = p.size() * 8;
-      if(key_size < policy.minimum_dh_group_size())
-         throw TLS_Exception(Alert::INSUFFICIENT_SECURITY,
-                                "Server sent DH group of " +
-                                std::to_string(key_size) +
-                                " bits, policy requires at least " +
-                                std::to_string(policy.minimum_dh_group_size()));
+
+      for(size_t i = 0; i != 3; ++i)
+         {
+         reader.get_range<byte>(2, 1, 65535);
+         }
       }
    else if(kex_algo == "ECDH" || kex_algo == "ECDHE_PSK")
       {
@@ -244,6 +236,8 @@ bool Server_Key_Exchange::verify(const Public_Key& server_key,
                                  const Handshake_State& state,
                                  const Policy& policy) const
    {
+   policy.check_peer_key_acceptable(server_key);
+
    std::pair<std::string, Signature_Format> format =
       state.parse_sig_format(server_key, m_hash_algo, m_sig_algo,
                              false, policy);