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smg_comms_skeys_s...    1  -- Message reader & writers for SMG Communication Protocol
smg_comms_skeys_s...    2  -- S.MG, 2018
smg_comms_skeys_s...    3 
smg_comms_skeys_s...    4 with Interfaces; use Interfaces;
smg_comms_skeys_s...    5 with Serpent;
smg_comms_skeys_s...    6 with System; use System;
smg_comms_skeys_s...    7 
smg_comms_skeys_s...    8 package body Messages is
smg_comms_skeys_s...    9 
smg_comms_skeys_s...   10   procedure Write_SKeys_SMsg( Keyset  : in Serpent_Keyset;
smg_comms_skeys_s...   11                               Counter : in Interfaces.Unsigned_16;
smg_comms_skeys_s...   12                               Msg     : out Raw_Types.Serpent_Msg) is
smg_comms_skeys_s...   13     Pos   : Integer := Msg'First;
smg_comms_skeys_s...   14     Check : CRC32.CRC32;
smg_comms_skeys_s...   15     PadLen: Integer;
smg_comms_skeys_s...   16     K     : Serpent.Key;
smg_comms_skeys_s...   17   begin
smg_comms_skeys_s...   18     -- write Type ID
smg_comms_skeys_s...   19     Msg(Pos) := SKeys_S_Type;
smg_comms_skeys_s...   20     Pos := Pos + 1;
smg_comms_skeys_s...   21 
smg_comms_skeys_s...   22     -- write count of keys (NB: this IS 8 bits by definition)
smg_comms_skeys_s...   23     Msg(Pos) := Keyset.Keys'Length;
smg_comms_skeys_s...   24     Pos := Pos + 1;
smg_comms_skeys_s...   25 
smg_comms_skeys_s...   26     -- write keys
smg_comms_skeys_s...   27     for I in Keyset.Keys'Range loop
smg_comms_skeys_s...   28       -- retrieve Key to write
smg_comms_skeys_s...   29       K := Keyset.Keys( I );
smg_comms_skeys_s...   30 
smg_comms_skeys_s...   31       -- write key itself
smg_comms_skeys_s...   32       Msg(Pos..Pos+K'Length-1) := K;
smg_comms_skeys_s...   33       -- ensure little endian order in message
smg_comms_skeys_s...   34       Cast_LE(Msg(Pos..Pos+K'Length-1));
smg_comms_skeys_s...   35       Pos := Pos + K'Length;
smg_comms_skeys_s...   36 
smg_comms_skeys_s...   37       -- write CRC of key
smg_comms_skeys_s...   38       Check := CRC32.CRC( K );
smg_comms_skeys_s...   39       Msg(Pos..Pos+3) := Raw_Types.Cast(Check);
smg_comms_skeys_s...   40       Cast_LE(Msg(Pos..Pos+3));
smg_comms_skeys_s...   41       Pos := Pos + 4;
smg_comms_skeys_s...   42     end loop;
smg_comms_skeys_s...   43 
smg_comms_skeys_s...   44     -- write flag
smg_comms_skeys_s...   45     Msg(Pos) := Keyset.Flag;
smg_comms_skeys_s...   46     Pos := Pos + 1;
smg_comms_skeys_s...   47 
smg_comms_skeys_s...   48     -- write message counter
smg_comms_skeys_s...   49     Msg(Pos..Pos+1) := Raw_Types.Cast(Counter);
smg_comms_skeys_s...   50     Cast_LE(Msg(Pos..Pos+1));
smg_comms_skeys_s...   51     Pos := Pos + 2;
smg_comms_skeys_s...   52 
smg_comms_skeys_s...   53     -- write padding as needed; endianness is irrelevant here
smg_comms_skeys_s...   54     PadLen := Msg'Last - Pos + 1;
smg_comms_skeys_s...   55     if PadLen > 0 then
smg_comms_skeys_s...   56       declare
smg_comms_skeys_s...   57         Pad : Raw_Types.Octets(1..PadLen);
smg_comms_skeys_s...   58       begin
smg_comms_skeys_s...   59         RNG.Get_Octets( Pad );
smg_comms_skeys_s...   60         Msg(Pos..Pos+PadLen-1) := Pad;
smg_comms_skeys_s...   61       end;
smg_comms_skeys_s...   62     end if;
smg_comms_skeys_s...   63   end Write_SKeys_SMsg;
smg_comms_skeys_s...   64 
smg_comms_skeys_s...   65 
smg_comms_skeys_s...   66   -- Reads a Serpent keyset from given Serpent Message
smg_comms_skeys_s...   67   procedure Read_SKeys_SMsg( Msg     : in Raw_Types.Serpent_Msg;
smg_comms_skeys_s...   68                              Counter : out Interfaces.Unsigned_16;
smg_comms_skeys_s...   69                              Keyset  : out Serpent_Keyset) is
smg_comms_skeys_s...   70     Pos: Integer := Msg'First;
smg_comms_skeys_s...   71   begin
smg_comms_skeys_s...   72     -- read type and check
smg_comms_skeys_s...   73     if Msg(Pos) = SKeys_S_Type then
smg_comms_skeys_s...   74       Pos := Pos + 1;
smg_comms_skeys_s...   75     else
smg_comms_skeys_s...   76       raise Invalid_Msg;
smg_comms_skeys_s...   77     end if;
smg_comms_skeys_s...   78 
smg_comms_skeys_s...   79     -- read count of keys and check
smg_comms_skeys_s...   80     if Msg(Pos) in Keys_Count'Range then
smg_comms_skeys_s...   81       declare
smg_comms_skeys_s...   82         N     : Keys_Count := Keys_Count(Msg(Pos));
smg_comms_skeys_s...   83         KS    : Serpent_Keyset(N);
smg_comms_skeys_s...   84         K     : Serpent.Key;
smg_comms_skeys_s...   85         Check : CRC32.CRC32;
smg_comms_skeys_s...   86         O4    : Raw_Types.Octets_4; 
smg_comms_skeys_s...   87         O2    : Raw_Types.Octets_2;
smg_comms_skeys_s...   88       begin
smg_comms_skeys_s...   89         Pos := Pos + 1;
smg_comms_skeys_s...   90         --read keys and check crc for each
smg_comms_skeys_s...   91         for I in 1 .. N loop
smg_comms_skeys_s...   92           -- read key and advance pos
smg_comms_skeys_s...   93           K := Msg(Pos..Pos+K'Length-1);
smg_comms_skeys_s...   94           Cast_LE(K);
smg_comms_skeys_s...   95           Pos := Pos + K'Length;
smg_comms_skeys_s...   96           -- read crc and compare to crc32(key)
smg_comms_skeys_s...   97           O4 := Msg(Pos..Pos+3);
smg_comms_skeys_s...   98           Cast_LE(O4);
smg_comms_skeys_s...   99           Check   := Raw_Types.Cast(O4);
smg_comms_skeys_s...  100           Pos := Pos + 4;
smg_comms_skeys_s...  101           if Check /= CRC32.CRC(K) then
smg_comms_skeys_s...  102             raise Invalid_Msg;
smg_comms_skeys_s...  103           end if;
smg_comms_skeys_s...  104           -- if it got here, key is fine so add to set
smg_comms_skeys_s...  105           KS.Keys(KS.Keys'First + I -1) := K;
smg_comms_skeys_s...  106         end loop;
smg_comms_skeys_s...  107         -- read and set flag
smg_comms_skeys_s...  108         KS.Flag := Msg(Pos);
smg_comms_skeys_s...  109         Pos := Pos + 1;
smg_comms_skeys_s...  110         -- read and set message counter
smg_comms_skeys_s...  111         O2 := Msg(Pos..Pos+1);
smg_comms_skeys_s...  112         Cast_LE(O2);
smg_comms_skeys_s...  113         Counter := Raw_Types.Cast(O2);
smg_comms_skeys_s...  114         -- rest of message is padding so it's ignored
smg_comms_skeys_s...  115         -- copy keyset to output variable
smg_comms_skeys_s...  116         Keyset := KS;
smg_comms_skeys_s...  117       end;
smg_comms_skeys_s...  118     else
smg_comms_skeys_s...  119       raise Invalid_Msg;
smg_comms_skeys_s...  120     end if;
smg_comms_skeys_s...  121   end Read_SKeys_SMsg;
smg_comms_skeys_s...  122 
smg_comms_skeys_s...  123   -- private part
smg_comms_skeys_s...  124   procedure Cast_LE( LE: in out Raw_Types.Octets ) is
smg_comms_skeys_s...  125   begin
smg_comms_skeys_s...  126     -- flip octets ONLY if native is big endian.
smg_comms_skeys_s...  127     if System.Default_Bit_Order = System.High_Order_First then
smg_comms_skeys_s...  128       declare
smg_comms_skeys_s...  129         BE: constant Raw_Types.Octets := LE;
smg_comms_skeys_s...  130       begin
smg_comms_skeys_s...  131         for I in 1..LE'Length loop
smg_comms_skeys_s...  132           LE(LE'First+I-1) := BE(BE'Last-I+1);
smg_comms_skeys_s...  133         end loop;
smg_comms_skeys_s...  134       end;
smg_comms_skeys_s...  135     end if;
smg_comms_skeys_s...  136     -- NOTHING to do for native little endian
smg_comms_skeys_s...  137   end Cast_LE;
smg_comms_skeys_s...  138 
smg_comms_skeys_s...  139 end Messages;