Add support for PAC-SERVER-CHECKSUM

lib/rex/proto/kerberos/pac.rb

@@ -12,3 +12,4 @@ end
 
 require 'rex/proto/kerberos/pac/element'
 require 'rex/proto/kerberos/pac/priv_svr_checksum'
+require 'rex/proto/kerberos/pac/server_checksum'

lib/rex/proto/kerberos/pac/server_checksum.rb

@@ -0,0 +1,28 @@
+# -*- coding: binary -*-
+
+module Rex
+  module Proto
+    module Kerberos
+      module Pac
+        class ServerChecksum < Element
+
+          # @!attribute version
+          #   @return [Fixnum] The checksum type
+          attr_accessor :checksum
+
+          # Encodes the Rex::Proto::Kerberos::Pac::ServerChecksum
+          #
+          # @return [String]
+          def encode
+            encoded = ''
+            encoded << [checksum].pack('V')
+            encoded << "\x00" * 16
+
+            encoded
+          end
+        end
+
+      end
+    end
+  end
+end

spec/lib/rex/proto/kerberos/pac/server_checksum_spec.rb

@@ -0,0 +1,26 @@
+# -*- coding:binary -*-
+require 'spec_helper'
+
+require 'rex/proto/kerberos'
+
+describe Rex::Proto::Kerberos::Pac::ServerChecksum do
+
+  subject(:server_checksum) do
+    described_class.new
+  end
+
+  let(:rsa_md5) { 7 }
+
+  let(:rsa_md5_sample) do
+    "\x07\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00"
+  end
+
+  describe "#encode" do
+    context "when RSA-MD5 checksum" do
+      it "encodes the ServerChecksums correctly" do
+        server_checksum.checksum = rsa_md5
+        expect(server_checksum.encode).to eq(rsa_md5_sample)
+      end
+    end
+  end
+end