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smg_comms_packing...    1   -- Packing/unpacking for Eulora's communication protocol:
smg_comms_packing...    2   -- Serpent Message to/from Serpent Packet
smg_comms_packing...    3   -- RSA Message to/from RSA Packet
smg_comms_packing...    4   -- S.MG, 2018
smg_comms_packing...    5 
smg_comms_packing...    6 package body Packing is
smg_comms_packing...    7 
smg_comms_packing...    8   -- Packing a Serpent message into Serpent package, using the given key
smg_comms_packing...    9   function Pack( Msg : in Raw_Types.Serpent_Msg;
smg_comms_packing...   10                  K   : in Serpent.Key ) 
smg_comms_packing...   11                return Raw_Types.Serpent_Pkt is
smg_comms_packing...   12 
smg_comms_packing...   13     -- single Serpent blocks containing plain / encrypted data
smg_comms_packing...   14     Plain    : Serpent.Block;
smg_comms_packing...   15     Encr     : Serpent.Block;
smg_comms_packing...   16 
smg_comms_packing...   17     -- Serpent Key Schedule - needed for direct encr/decr calls
smg_comms_packing...   18     KS       : Serpent.Key_Schedule;
smg_comms_packing...   19 
smg_comms_packing...   20     -- final resulting Serpent package
smg_comms_packing...   21     Pkt      : Raw_Types.Serpent_Pkt := (others => 0);
smg_comms_packing...   22   begin
smg_comms_packing...   23     -- prepare the Serpent key schedule based on given key
smg_comms_packing...   24     Serpent.Prepare_Key( K, KS );
smg_comms_packing...   25 
smg_comms_packing...   26     -- encrypt message block by block and copy result in packet
smg_comms_packing...   27     for I in 1 .. S_Blocks loop
smg_comms_packing...   28       -- get current block to encrypt
smg_comms_packing...   29       Plain := Msg( Msg'First + (I-1) * Block_Len .. 
smg_comms_packing...   30                     Msg'First +  I    * Block_Len - 1 );
smg_comms_packing...   31       -- encrypt with Serpent
smg_comms_packing...   32       Serpent.Encrypt( KS, Plain, Encr );
smg_comms_packing...   33       -- copy result to output packet
smg_comms_packing...   34       Pkt( Pkt'First + (I-1) * Block_Len ..
smg_comms_packing...   35            Pkt'First +  I    * Block_Len - 1 ) 
smg_comms_packing...   36          := Encr;
smg_comms_packing...   37     end loop;
smg_comms_packing...   38 
smg_comms_packing...   39     -- return result
smg_comms_packing...   40     return Pkt;
smg_comms_packing...   41   end Pack;
smg_comms_packing...   42 
smg_comms_packing...   43   -- Unpacking a Serpent packet into contained message, using the given key
smg_comms_packing...   44   function Unpack( Pkt : in Raw_Types.Serpent_Pkt;
smg_comms_packing...   45                    K   : in Serpent.Key) 
smg_comms_packing...   46                  return Raw_Types.Serpent_Msg is
smg_comms_packing...   47     -- single Serpent blocks containing plain / encrypted data
smg_comms_packing...   48     Plain    : Serpent.Block;
smg_comms_packing...   49     Encr     : Serpent.Block;
smg_comms_packing...   50 
smg_comms_packing...   51     -- Serpent Key Schedule - needed for direct encr/decr calls
smg_comms_packing...   52     KS       : Serpent.Key_Schedule;
smg_comms_packing...   53 
smg_comms_packing...   54     -- the message extracted from the given packet
smg_comms_packing...   55     Msg : Raw_Types.Serpent_Msg := (others => 0);
smg_comms_packing...   56   begin
smg_comms_packing...   57     -- prepare the Serpent key for use
smg_comms_packing...   58     Serpent.Prepare_Key( K, KS );
smg_comms_packing...   59 
smg_comms_packing...   60     -- decrypt the Serpent packet block by block
smg_comms_packing...   61     for I in 1 .. S_Blocks loop
smg_comms_packing...   62       -- get current block from input and decrypt
smg_comms_packing...   63       Encr := Pkt( Pkt'First + (I-1) * Block_Len ..
smg_comms_packing...   64                    Pkt'First +  I    * Block_Len - 1 );
smg_comms_packing...   65       Serpent.Decrypt( KS, Encr, Plain );
smg_comms_packing...   66 
smg_comms_packing...   67       -- copy result to its correct position in final output
smg_comms_packing...   68       Msg( Msg'First + (I-1) * Block_Len ..
smg_comms_packing...   69            Msg'First +  I    * Block_Len - 1 )
smg_comms_packing...   70          := Plain;
smg_comms_packing...   71     end loop;
smg_comms_packing...   72 
smg_comms_packing...   73     -- return the result - the message content of given package
smg_comms_packing...   74     return Msg;
smg_comms_packing...   75   end Unpack;
smg_comms_packing...   76 
smg_comms_packing...   77   -- Packing a RSA message into RSA packet, using the given key
smg_comms_packing...   78   function Pack( Msg : in Raw_Types.RSA_Msg;
smg_comms_packing...   79                  K   : in RSA_OAEP.RSA_pkey)
smg_comms_packing...   80                 return Raw_Types.RSA_Pkt is
smg_comms_packing...   81 
smg_comms_packing...   82   -- a chunk that can be processed via rsa+oaep at any given time
smg_comms_packing...   83     Chunk: Raw_Types.Octets(1..Raw_Types.OAEP_MAX_LEN) := (others => 0);
smg_comms_packing...   84 
smg_comms_packing...   85   -- number of chunks in the message to process
smg_comms_packing...   86   -- NO incomplete chunks will be processed!
smg_comms_packing...   87   -- NB: values are set so that there are no incomplete blocks here
smg_comms_packing...   88     N   : constant Natural := Msg'Length / Chunk'Length;
smg_comms_packing...   89 
smg_comms_packing...   90   -- intermediate result, as obtained from rsa_oaep
smg_comms_packing...   91     Encr: Raw_Types.RSA_len := (others => 0);
smg_comms_packing...   92 
smg_comms_packing...   93   -- final resulting RSA Packet
smg_comms_packing...   94     Pkt : Raw_Types.RSA_Pkt := (others => 0);
smg_comms_packing...   95   begin 
smg_comms_packing...   96     -- there should ALWAYS be precisely N chunks in Msg to feed to rsa_oaep
smg_comms_packing...   97     -- process chunks of Msg one at a time
smg_comms_packing...   98     for I in 1..N loop
smg_comms_packing...   99       -- get current chunk
smg_comms_packing...  100       Chunk := Msg(Msg'First + (I-1) * Chunk'Length .. 
smg_comms_packing...  101                    Msg'First + I * Chunk'Length - 1 );
smg_comms_packing...  102       -- call rsa oaep encrypt on current chunk
smg_comms_packing...  103       RSA_OAEP.Encrypt( Chunk, K, Encr );
smg_comms_packing...  104       -- copy result to its place in final packet
smg_comms_packing...  105       Pkt( Pkt'First + (I-1) * Encr'Length .. 
smg_comms_packing...  106            Pkt'First + I * Encr'Length - 1 ) := Encr;
smg_comms_packing...  107     end loop;
smg_comms_packing...  108     -- return final result
smg_comms_packing...  109     return Pkt;
smg_comms_packing...  110   end Pack;
smg_comms_packing...  111 
smg_comms_packing...  112   -- Unpacking a RSA packet into contained message, using the given key
smg_comms_packing...  113   function Unpack( Pkt     : in Raw_Types.RSA_Pkt;
smg_comms_packing...  114                    K       : in RSA_OAEP.RSA_skey;
smg_comms_packing...  115                    Success : out Boolean)
smg_comms_packing...  116                   return Raw_Types.RSA_Msg is
smg_comms_packing...  117     -- a chunk - basically input for RSA_OAEP.Decrypt
smg_comms_packing...  118     Chunk : Raw_Types.RSA_len := (others => 0);
smg_comms_packing...  119 
smg_comms_packing...  120     -- intermediate result of rsa_oaep decrypt
smg_comms_packing...  121     Decr  : Raw_Types.Octets( 1..Raw_Types.OAEP_MAX_LEN ) := (others => 0);
smg_comms_packing...  122     Len   : Natural;
smg_comms_packing...  123     Flag  : Boolean;
smg_comms_packing...  124 
smg_comms_packing...  125     -- number of chunks in the packet
smg_comms_packing...  126     -- NB: there should be only FULL chunks! otherwise -> fail
smg_comms_packing...  127     N   : constant Natural := Pkt'Length / Chunk'Length;
smg_comms_packing...  128 
smg_comms_packing...  129     -- final resulting message content of the given RSA packet
smg_comms_packing...  130     Msg : Raw_Types.RSA_Msg := (others => 0);
smg_comms_packing...  131   begin
smg_comms_packing...  132     -- initialize Success flag
smg_comms_packing...  133     Success := True;
smg_comms_packing...  134 
smg_comms_packing...  135     -- process given packet, chunk by chunk
smg_comms_packing...  136     for I in 1..N loop
smg_comms_packing...  137       -- get current chunk
smg_comms_packing...  138       Chunk := Pkt( Pkt'First + (I-1) * Chunk'Length ..
smg_comms_packing...  139                     Pkt'First + I * Chunk'Length - 1 );
smg_comms_packing...  140       -- decrypt it via rsa+oaep
smg_comms_packing...  141       RSA_OAEP.Decrypt( Chunk, K, Decr, Len, Flag );
smg_comms_packing...  142       -- check result and if ok then copy it to final result at its place
smg_comms_packing...  143       -- NB: if returned length is EVER less than OAEP_MAX_LEN then -> fail!
smg_comms_packing...  144       -- the reason for above: there will be undefined bits in the output!
smg_comms_packing...  145       if Len /= Raw_Types.OAEP_MAX_LEN or (not Flag) then
smg_comms_packing...  146         Success := False;
smg_comms_packing...  147         return Msg;
smg_comms_packing...  148       else
smg_comms_packing...  149         Msg( Msg'First + (I-1) * Decr'Length ..
smg_comms_packing...  150              Msg'First + I * Decr'Length - 1 ) := Decr;
smg_comms_packing...  151       end if;
smg_comms_packing...  152     end loop;
smg_comms_packing...  153 
smg_comms_packing...  154     -- return obtained message
smg_comms_packing...  155     return Msg;
smg_comms_packing...  156   end Unpack;
smg_comms_packing...  157 
smg_comms_packing...  158 
smg_comms_packing...  159 end Packing;