Implement to_blob on OpenSSL::PKey::EC::Point

Fix an issue where writing an ECDSA public_key out to a Net::SSH::Buffer
fails when calling to_blob on the key due to the method being undefined.

Fixes #619

lib/net/ssh/transport/openssl.rb

@@ -225,6 +225,22 @@ def ssh_do_sign(data)
 
           return Net::SSH::Buffer.from(:bignum, sig_r, :bignum, sig_s).to_s
         end
+
+        class Point
+          # Returns the description of this key type used by the
+          # SSH2 protocol, like "ecdsa-sha2-nistp256"
+          def ssh_type
+            "ecdsa-sha2-#{CurveNameAliasInv[self.group.curve_name]}"
+          end
+
+          # Converts the key to a blob, according to the SSH2 protocol.
+          def to_blob
+            @blob ||= Net::SSH::Buffer.from(:string, ssh_type,
+                                            :string, CurveNameAliasInv[self.group.curve_name],
+                                            :mstring, self.to_bn.to_s(2)).to_s
+            @blob
+          end
+        end
       end
     else
       class OpenSSL::PKey::ECError < RuntimeError

test/test_buffer.rb

@@ -411,6 +411,14 @@ def test_write_ecdsa_sha2_nistp521_key_should_write_argument_to_end_of_buffer
       buffer.write_key(key)
       assert_equal "start\000\000\000\023ecdsa-sha2-nistp521\000\000\000\bnistp521\000\000\000\205\004\001\214\240:\005}T\217\024\310\2647\0049o\372\266\367z\317\256~\262\034\217\357\234\251\307=A\311\221\237m\3736%\221\257\375M+-\200*(\354\021\320\002\265\225\350\304\360\264\307\325l\366'\202\332\204~\000\323\201\271\2671>]\240\2109\301bo2\300\t\246\225{\017\344\034\2003^\344\367\260\263[\223\276g\373\216o\021\224\3178h]3\\\216\252@rHQT\247g\207\241K\376\262\236\225=-\005\210\276", buffer.to_s
     end
+
+    def test_write_ec_point_should_write_argument_to_end_of_buffer
+      buffer = new("start")
+      key = OpenSSL::PKey::EC::Point.new(OpenSSL::PKey::EC.new(OpenSSL::PKey::EC::CurveNameAlias['nistp256']).group)
+
+      buffer.write_key(key)
+      assert_equal "start\x00\x00\x00\x13ecdsa-sha2-nistp256\x00\x00\x00\bnistp256\x00\x00\x00\x00", buffer.to_s
+    end
   end
 
   private