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smg_comms_rsa_oaep      1  -- S.MG, 2018
smg_comms_rsa_oaep      2 
smg_comms_rsa_oaep      3 with Interfaces; use Interfaces;
smg_comms_rsa_oaep      4 with OAEP;
smg_comms_rsa_oaep      5 with RNG;
smg_comms_rsa_oaep      6 
smg_comms_rsa_oaep      7 package body RSA_OAEP is
smg_comms_rsa_oaep      8 
smg_comms_rsa_oaep      9   -- OAEP + RSA with given public key.
smg_comms_rsa_oaep     10   -- Steps:
smg_comms_rsa_oaep     11   -- 1. repeat oaep.encrypt of Plain 
smg_comms_rsa_oaep     12   --      until the result has first octet < than first octet of Key's modulus.
smg_comms_rsa_oaep     13   -- 2. RSA.encrypt with Key on the result from 1.
smg_comms_rsa_oaep     14   procedure Encrypt( Plain: in Raw_Types.Octets;
smg_comms_rsa_oaep     15                      Key  : in RSA_pkey;
smg_comms_rsa_oaep     16                      Encr : out Raw_Types.RSA_len ) is
smg_comms_rsa_oaep     17     -- block obtained through OAEP padding of given input Plain
smg_comms_rsa_oaep     18     Blk     : OAEP.OAEP_Block := ( others => 0 );
smg_comms_rsa_oaep     19     Entropy : OAEP.OAEP_Block;
smg_comms_rsa_oaep     20     Len     : constant Natural := entropy'Length;
smg_comms_rsa_oaep     21   begin
smg_comms_rsa_oaep     22     -- loop cond: 1st octet of oaep block is < 1st octet of key's modulus
smg_comms_rsa_oaep     23     loop
smg_comms_rsa_oaep     24       -- get random bits via RNG (FG)
smg_comms_rsa_oaep     25       RNG.Get_Octets( Entropy );
smg_comms_rsa_oaep     26 
smg_comms_rsa_oaep     27       -- oaep encrypt
smg_comms_rsa_oaep     28       OAEP.OAEP_Encrypt( Plain, Entropy, Blk );
smg_comms_rsa_oaep     29 
smg_comms_rsa_oaep     30       -- check that the oaep block is suitable i.e. comparison of 1st octet
smg_comms_rsa_oaep     31       if Blk(Blk'First) < Key.n(Key.n'First) then exit; end if;
smg_comms_rsa_oaep     32 
smg_comms_rsa_oaep     33     end loop; -- oaep block < modulus
smg_comms_rsa_oaep     34 
smg_comms_rsa_oaep     35     -- RSA encrypt
smg_comms_rsa_oaep     36     Public_RSA( Blk, Key, Encr );
smg_comms_rsa_oaep     37   end; --Encrypt (OAEP+RSA)
smg_comms_rsa_oaep     38 
smg_comms_rsa_oaep     39   -- RSA+OAEP Decrypt
smg_comms_rsa_oaep     40   -- Steps:
smg_comms_rsa_oaep     41   -- 1. RSA Decrypt (secret key)
smg_comms_rsa_oaep     42   -- 2. OAEP Decrypt
smg_comms_rsa_oaep     43   procedure Decrypt( Encr : in Raw_Types.RSA_len;
smg_comms_rsa_oaep     44                      Key  : in RSA_skey;
smg_comms_rsa_oaep     45                      Plain: out Raw_Types.Octets;
smg_comms_rsa_oaep     46                      Plain_Len: out Natural;
smg_comms_rsa_oaep     47                      Success: out Boolean) is
smg_comms_rsa_oaep     48     Blk     : OAEP.OAEP_Block;
smg_comms_rsa_oaep     49     Msg     : OAEP.OAEP_HALF;
smg_comms_rsa_oaep     50     Msg_Len : Natural;
smg_comms_rsa_oaep     51   begin
smg_comms_rsa_oaep     52     -- RSA decrypt with provided secret key
smg_comms_rsa_oaep     53     -- NB: result HAS TO BE AN OAEP BLOCK HERE! Even if - potentially - 0 led!
smg_comms_rsa_oaep     54     Private_RSA( Encr, Key, Blk );
smg_comms_rsa_oaep     55 
smg_comms_rsa_oaep     56     -- OAEP decrypt
smg_comms_rsa_oaep     57     OAEP.OAEP_Decrypt(Blk, Msg_Len, Msg, Success);
smg_comms_rsa_oaep     58     -- switch to Length in OCTETS!
smg_comms_rsa_oaep     59     Msg_Len := Msg_Len / 8;
smg_comms_rsa_oaep     60 
smg_comms_rsa_oaep     61     -- check that result FITS in given output array - otherwise, fail
smg_comms_rsa_oaep     62     if Msg_Len > Plain'Length then
smg_comms_rsa_oaep     63       Success := FALSE;
smg_comms_rsa_oaep     64       Plain_Len := Msg_Len; --to give a clue to caller
smg_comms_rsa_oaep     65     else
smg_comms_rsa_oaep     66       Plain_Len := Msg_Len;
smg_comms_rsa_oaep     67       Plain( Plain'First .. 
smg_comms_rsa_oaep     68              Plain'First + Plain_Len-1) := Msg( Msg'First ..
smg_comms_rsa_oaep     69                                                 Msg'First + Plain_Len -1 );
smg_comms_rsa_oaep     70     end if;
smg_comms_rsa_oaep     71   end Decrypt;
smg_comms_rsa_oaep     72 
smg_comms_rsa_oaep     73   -- helper methods
smg_comms_rsa_oaep     74   -- encrypt with public RSA key given as struct, Ada style
smg_comms_rsa_oaep     75   procedure Public_RSA( Plain: in Raw_Types.Octets;
smg_comms_rsa_oaep     76                         Key  : in RSA_pkey;
smg_comms_rsa_oaep     77                         Encr : out Raw_Types.RSA_len) is
smg_comms_rsa_oaep     78     Encr_char  : char_array( size_t(Encr'First) .. size_t(Encr'Last));
smg_comms_rsa_oaep     79     Plain_char : char_array( size_t(Plain'First) .. size_t(Plain'Last));
smg_comms_rsa_oaep     80     N_char     : char_array( size_t(Key.n'First) .. size_t(Key.n'Last));
smg_comms_rsa_oaep     81     E_char     : char_array( size_t(Key.e'First) .. size_t(Key.e'Last));
smg_comms_rsa_oaep     82     out_len    : Integer;
smg_comms_rsa_oaep     83   begin
smg_comms_rsa_oaep     84     -- convert to char array
smg_comms_rsa_oaep     85     Octets_To_Char_Array( Plain, Plain_char );
smg_comms_rsa_oaep     86     Octets_To_Char_Array( Key.n, N_char );
smg_comms_rsa_oaep     87     Octets_To_Char_Array( Key.e, E_char );
smg_comms_rsa_oaep     88     -- call C imported function
smg_comms_rsa_oaep     89     out_len := Public_RSA_C( Encr_char  , Encr'Length, 
smg_comms_rsa_oaep     90                              Plain_char , Plain'Length,
smg_comms_rsa_oaep     91                              N_char     , Key.n'Length,
smg_comms_rsa_oaep     92                              E_char     , Key.e'Length);
smg_comms_rsa_oaep     93     -- convert back to octets
smg_comms_rsa_oaep     94     Char_Array_To_Octets( Encr_char, Encr );
smg_comms_rsa_oaep     95     -- C code trims leading 0s -> need to move octets if out_len<Encr'Length
smg_comms_rsa_oaep     96     if out_len < Encr'Length then
smg_comms_rsa_oaep     97       Encr(Encr'Last - out_len + 1 .. Encr'Last) := Encr(Encr'First .. 
smg_comms_rsa_oaep     98                                                       Encr'First+out_len-1);
smg_comms_rsa_oaep     99       Encr(Encr'First .. Encr'Last-out_len) := (others=>0);
smg_comms_rsa_oaep    100     end if;
smg_comms_rsa_oaep    101     -- no need to return anything!
smg_comms_rsa_oaep    102   end Public_RSA;
smg_comms_rsa_oaep    103 
smg_comms_rsa_oaep    104   procedure Private_RSA( Encr  : in Raw_Types.RSA_len;
smg_comms_rsa_oaep    105                          Key   : in RSA_skey;
smg_comms_rsa_oaep    106                          Plain : out Raw_Types.Octets) is
smg_comms_rsa_oaep    107     Plain_Char : char_array( size_t(Plain'First) .. size_t(Plain'Last) );
smg_comms_rsa_oaep    108     Plain_Len  : Integer;
smg_comms_rsa_oaep    109     Encr_Char  : char_array( size_t(Encr'First)  .. size_t(Encr'Last) );
smg_comms_rsa_oaep    110     N_Char     : char_array( size_t(Key.n'First) .. size_t(Key.n'Last) );
smg_comms_rsa_oaep    111     E_Char     : char_array( size_t(Key.e'First) .. size_t(Key.e'Last) );
smg_comms_rsa_oaep    112     D_Char     : char_array( size_t(Key.d'First) .. size_t(Key.d'Last) );
smg_comms_rsa_oaep    113     P_Char     : char_array( size_t(Key.p'First) .. size_t(Key.p'Last) );
smg_comms_rsa_oaep    114     Q_Char     : char_array( size_t(Key.q'First) .. size_t(Key.q'Last) );
smg_comms_rsa_oaep    115     U_Char     : char_array( size_t(Key.u'First) .. size_t(Key.u'Last) );
smg_comms_rsa_oaep    116   begin
smg_comms_rsa_oaep    117     -- convert key and encrypted message to C char_arrays
smg_comms_rsa_oaep    118     Octets_To_Char_Array( Encr, Encr_Char );
smg_comms_rsa_oaep    119     Octets_To_Char_Array( Key.n, N_Char );
smg_comms_rsa_oaep    120     Octets_To_Char_Array( Key.e, E_Char );
smg_comms_rsa_oaep    121     Octets_To_Char_Array( Key.d, D_Char );
smg_comms_rsa_oaep    122     Octets_To_Char_Array( Key.p, P_Char );
smg_comms_rsa_oaep    123     Octets_To_Char_Array( Key.q, Q_Char );
smg_comms_rsa_oaep    124     Octets_To_Char_Array( Key.u, U_Char );
smg_comms_rsa_oaep    125     -- call RSA decrypt via C_Wrappers
smg_comms_rsa_oaep    126     Plain_Len := Private_RSA_C( Plain_Char, Plain'Length,
smg_comms_rsa_oaep    127                                 Encr_Char , Encr'Length,
smg_comms_rsa_oaep    128                                 N_Char    , Key.n'Length,
smg_comms_rsa_oaep    129                                 E_Char    , Key.e'Length,
smg_comms_rsa_oaep    130                                 D_Char    , Key.d'Length,
smg_comms_rsa_oaep    131                                 P_Char    , Key.p'Length,
smg_comms_rsa_oaep    132                                 Q_Char    , Key.q'Length,
smg_comms_rsa_oaep    133                                 U_Char    , Key.u'Length);
smg_comms_rsa_oaep    134     -- convert result back to Octets
smg_comms_rsa_oaep    135     Char_Array_To_Octets( Plain_Char, Plain );
smg_comms_rsa_oaep    136     -- if length < OAEP_Block'Length,it's 0-led and got trimmed, so move it
smg_comms_rsa_oaep    137     if Plain_Len < Plain'Length then
smg_comms_rsa_oaep    138       Plain(Plain'Last-Plain_Len+1..Plain'Last):= Plain(Plain'First ..
smg_comms_rsa_oaep    139                                                    Plain'First + Plain_Len -1);
smg_comms_rsa_oaep    140       Plain(Plain'First .. Plain'Last-Plain_Len) := (others => 0);
smg_comms_rsa_oaep    141     end if;
smg_comms_rsa_oaep    142     -- no need to return anything!
smg_comms_rsa_oaep    143   end Private_RSA;
smg_comms_rsa_oaep    144 
smg_comms_rsa_oaep    145   procedure Octets_To_Char_Array( O   : in Raw_Types.Octets;
smg_comms_rsa_oaep    146                                   A   : out Interfaces.C.char_array) is
smg_comms_rsa_oaep    147   begin
smg_comms_rsa_oaep    148     -- check that lengths ARE THE SAME!
smg_comms_rsa_oaep    149     if A'Length /= O'Length then
smg_comms_rsa_oaep    150       raise Mismatched_Lengths_Error;
smg_comms_rsa_oaep    151     end if;
smg_comms_rsa_oaep    152     -- copy values over octet by octet
smg_comms_rsa_oaep    153     for I in 0 .. O'Length-1 loop
smg_comms_rsa_oaep    154       A( A'First + Interfaces.C.size_t( I )) := 
smg_comms_rsa_oaep    155                      Interfaces.C.Char( Character'Val(O(O'First + I)));
smg_comms_rsa_oaep    156     end loop;
smg_comms_rsa_oaep    157   end Octets_To_Char_Array;
smg_comms_rsa_oaep    158 
smg_comms_rsa_oaep    159   procedure Char_Array_To_Octets( A   : in Interfaces.C.char_array;
smg_comms_rsa_oaep    160                                   O   : out Raw_Types.Octets) is
smg_comms_rsa_oaep    161   begin
smg_comms_rsa_oaep    162     -- check that lengths ARE THE SAME!
smg_comms_rsa_oaep    163     if A'Length /= O'Length then
smg_comms_rsa_oaep    164       raise Mismatched_Lengths_Error;
smg_comms_rsa_oaep    165     end if;
smg_comms_rsa_oaep    166     -- copy values over octet by octet
smg_comms_rsa_oaep    167     for I in 0..O'Length -1 loop
smg_comms_rsa_oaep    168       O( O'First + I ) := Character'Pos( Character(
smg_comms_rsa_oaep    169                              A( A'First + Interfaces.C.size_t( I )) ));
smg_comms_rsa_oaep    170     end loop;
smg_comms_rsa_oaep    171   end Char_Array_To_Octets;
smg_comms_rsa_oaep    172 
smg_comms_rsa_oaep    173 end RSA_OAEP;