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smg_comms_rsa_oaep      1 -- S.MG, 2018
smg_comms_rsa_oaep      2 
smg_comms_rsa_oaep      3 package body OAEP is
smg_comms_rsa_oaep      4 
smg_comms_rsa_oaep      5   -- padding & formatting of maximum MAX_LEN_MSG*8 bits of the given input
smg_comms_rsa_oaep      6   -- uses TMSR's OAEP schema:
smg_comms_rsa_oaep      7   -- 1.format M00 as: [random octet][sz1][sz2]"TMSR-RSA"[random]*Message
smg_comms_rsa_oaep      8   --    where sz1 and sz2 store the length of the message in bits
smg_comms_rsa_oaep      9   --    the random octets before message are padding to make OAEP_LENGTH_OCTETS
smg_comms_rsa_oaep     10   -- 2. R = OAEP_HALF_OCTETS random bits
smg_comms_rsa_oaep     11   -- 3. X = M00 xor hash(R)
smg_comms_rsa_oaep     12   -- 4. Y = R xor hash(X)
smg_comms_rsa_oaep     13   -- 5. Result is X || Y 
smg_comms_rsa_oaep     14   -- NB: the Entropy parameter should be random octets from which this method 
smg_comms_rsa_oaep     15   -- will use as many as required for the OAEP encryption of given Msg
smg_comms_rsa_oaep     16   -- NB: at MOST MAX_LEN_MSG octets of Msg! (Msg at most 1960 bits)
smg_comms_rsa_oaep     17   procedure OAEP_Encrypt( Msg     : in Raw_Types.Octets;
smg_comms_rsa_oaep     18                           Entropy : in OAEP_Block;
smg_comms_rsa_oaep     19                           Output  : out OAEP_Block) is
smg_comms_rsa_oaep     20     M00    : OAEP_HALF;
smg_comms_rsa_oaep     21     R      : OAEP_HALF;
smg_comms_rsa_oaep     22     HashR  : OAEP_HALF;
smg_comms_rsa_oaep     23     X      : OAEP_HALF;
smg_comms_rsa_oaep     24     HashX  : OAEP_HALF;
smg_comms_rsa_oaep     25     Y      : OAEP_HALF;
smg_comms_rsa_oaep     26     MsgLen : Natural;
smg_comms_rsa_oaep     27     PadLen : Natural;
smg_comms_rsa_oaep     28   begin
smg_comms_rsa_oaep     29     -- calculate maximum length of msg and needed amount of padding
smg_comms_rsa_oaep     30     -- make sure also that only MAX_LEN_MSG octets at most are used from Msg
smg_comms_rsa_oaep     31     MsgLen := Msg'Length;                          -- real msg length
smg_comms_rsa_oaep     32     if MsgLen > MAX_LEN_MSG then
smg_comms_rsa_oaep     33       MsgLen := MAX_LEN_MSG;  --only first MAX_LEN_MSG octets used
smg_comms_rsa_oaep     34       PadLen := 0;            --no padding needed
smg_comms_rsa_oaep     35     else
smg_comms_rsa_oaep     36       PadLen := MAX_LEN_MSG - MsgLen; -- add padding as needed
smg_comms_rsa_oaep     37     end if;
smg_comms_rsa_oaep     38 
smg_comms_rsa_oaep     39     -- step 1: header and format to obtain M00
smg_comms_rsa_oaep     40       -- first octet is random bits
smg_comms_rsa_oaep     41     M00( M00'First ) := Entropy( Entropy'First );
smg_comms_rsa_oaep     42 
smg_comms_rsa_oaep     43       -- next 2 octets hold the used length of Msg (number of octets)
smg_comms_rsa_oaep     44     M00( M00'First + 2) := Unsigned_8( ( MsgLen * 8 ) mod 256 );
smg_comms_rsa_oaep     45     M00( M00'First + 1) := Unsigned_8( ( (MsgLen * 8 ) / 256 ) mod 256 );
smg_comms_rsa_oaep     46 
smg_comms_rsa_oaep     47       -- next 8 octets are reserved for later use, currently "TMSR-RSA"
smg_comms_rsa_oaep     48     M00( M00'First + 3 .. M00'First + 10 ) := TMSR;
smg_comms_rsa_oaep     49 
smg_comms_rsa_oaep     50       -- random bits for padding, if Msg is less than maximum length
smg_comms_rsa_oaep     51     for I in 1 .. PadLen loop
smg_comms_rsa_oaep     52       M00( M00'First + 10 + I ) := Entropy( Entropy'First + I );
smg_comms_rsa_oaep     53     end loop;
smg_comms_rsa_oaep     54 
smg_comms_rsa_oaep     55       -- the message itself
smg_comms_rsa_oaep     56     M00( M00'Last - MsgLen + 1 .. M00'Last ) := 
smg_comms_rsa_oaep     57                                Msg( Msg'First .. Msg'First + MsgLen - 1 );
smg_comms_rsa_oaep     58 
smg_comms_rsa_oaep     59     -- step 2: R = Raw_Types.OAEP_HALF_OCTETS random octets
smg_comms_rsa_oaep     60     -- can take LAST octets from given entropy as they are NOT used before
smg_comms_rsa_oaep     61     -- (even if original message was empty, padding uses at most half - 10
smg_comms_rsa_oaep     62     --   while entropy has full block length)
smg_comms_rsa_oaep     63     R := Entropy( Entropy'Last - OAEP_HALF_OCTETS + 1 .. Entropy'Last );
smg_comms_rsa_oaep     64 
smg_comms_rsa_oaep     65     -- step 3: X = M00 xor hash(R)
smg_comms_rsa_oaep     66     HashKeccak( R, HashR );
smg_comms_rsa_oaep     67     X := XOR_Octets(M00, HashR);
smg_comms_rsa_oaep     68 
smg_comms_rsa_oaep     69     -- step 4: Y = R xor hash(X)
smg_comms_rsa_oaep     70     HashKeccak( X, HashX );
smg_comms_rsa_oaep     71     Y := XOR_Octets(R, HashX);
smg_comms_rsa_oaep     72 
smg_comms_rsa_oaep     73     -- step 5: Output is X || Y
smg_comms_rsa_oaep     74     Output( Output'First .. Output'First + X'Length - 1 ) := X;
smg_comms_rsa_oaep     75     Output( Output'Last - Y'Length + 1 .. Output'Last )   := Y;
smg_comms_rsa_oaep     76     
smg_comms_rsa_oaep     77   end OAEP_Encrypt;
smg_comms_rsa_oaep     78 
smg_comms_rsa_oaep     79   procedure OAEP_Decrypt( Encr    : in OAEP_Block;
smg_comms_rsa_oaep     80                           Len     : out Natural;
smg_comms_rsa_oaep     81                           Output  : out OAEP_HALF;
smg_comms_rsa_oaep     82                           Success : out Boolean ) is
smg_comms_rsa_oaep     83     X, Y, M, R   : OAEP_HALF;
smg_comms_rsa_oaep     84     HashX, HashR : OAEP_HALF;
smg_comms_rsa_oaep     85     LenOctets    : Natural;
smg_comms_rsa_oaep     86   begin
smg_comms_rsa_oaep     87     -- step 1: separate X and Y
smg_comms_rsa_oaep     88     X := Encr( Encr'First .. Encr'First + X'Length - 1 );
smg_comms_rsa_oaep     89     Y := Encr( Encr'Last - Y'Length + 1 .. Encr'Last );
smg_comms_rsa_oaep     90 
smg_comms_rsa_oaep     91     -- step 2: R = Y xor hash(X)
smg_comms_rsa_oaep     92     HashKeccak( X, HashX );
smg_comms_rsa_oaep     93     R := XOR_Octets(Y, HashX);
smg_comms_rsa_oaep     94 
smg_comms_rsa_oaep     95     -- step 3: M = X xor hash(R)
smg_comms_rsa_oaep     96     HashKeccak( R, HashR );
smg_comms_rsa_oaep     97     M := XOR_Octets(X, HashR);
smg_comms_rsa_oaep     98 
smg_comms_rsa_oaep     99     -- step 4: extract length and message
smg_comms_rsa_oaep    100     Len := Natural(M( M'First + 1 )) * 256 +
smg_comms_rsa_oaep    101            Natural(M( M'First + 2 ));
smg_comms_rsa_oaep    102     LenOctets := Len / 8; 
smg_comms_rsa_oaep    103 
smg_comms_rsa_oaep    104     if LenOctets > MAX_LEN_MSG or LenOctets < 0 then
smg_comms_rsa_oaep    105       Success := False;  -- error, failed to retrieve message
smg_comms_rsa_oaep    106     else
smg_comms_rsa_oaep    107       Success := True;
smg_comms_rsa_oaep    108       Output( Output'First .. Output'First + LenOctets - 1 ) := 
smg_comms_rsa_oaep    109         M( M'Last - LenOctets + 1 .. M'Last );
smg_comms_rsa_oaep    110     end if;
smg_comms_rsa_oaep    111 
smg_comms_rsa_oaep    112   end OAEP_Decrypt;
smg_comms_rsa_oaep    113 
smg_comms_rsa_oaep    114 -- private, helper methods
smg_comms_rsa_oaep    115   procedure HashKeccak(Input     : in Raw_Types.Octets;
smg_comms_rsa_oaep    116                        Output    : out Raw_Types.Octets;
smg_comms_rsa_oaep    117                        Block_Len : in Keccak.Keccak_Rate := 
smg_comms_rsa_oaep    118                                       Keccak.Default_Bitrate) is
smg_comms_rsa_oaep    119     BIn  : Keccak.Bitstream( 0 .. Input'Length * 8 - 1 );
smg_comms_rsa_oaep    120     BOut : Keccak.Bitstream( 0 .. Output'Length * 8 - 1 ); 
smg_comms_rsa_oaep    121   begin
smg_comms_rsa_oaep    122     ToBitstream( Input, BIn );
smg_comms_rsa_oaep    123     Keccak.Sponge( BIn, BOut, Block_Len );
smg_comms_rsa_oaep    124     ToOctets( BOut, Output );
smg_comms_rsa_oaep    125   end HashKeccak;
smg_comms_rsa_oaep    126 
smg_comms_rsa_oaep    127   function XOR_Octets(A : in OAEP_HALF; 
smg_comms_rsa_oaep    128                       B : in OAEP_HALF)
smg_comms_rsa_oaep    129                      return OAEP_HALF is
smg_comms_rsa_oaep    130     R : OAEP_HALF;
smg_comms_rsa_oaep    131   begin
smg_comms_rsa_oaep    132     for I in R'Range loop
smg_comms_rsa_oaep    133       R(I) := A(I) xor B(I);
smg_comms_rsa_oaep    134     end loop;
smg_comms_rsa_oaep    135     return R;
smg_comms_rsa_oaep    136   end XOR_Octets;
smg_comms_rsa_oaep    137 
smg_comms_rsa_oaep    138   -- conversion between types
smg_comms_rsa_oaep    139   procedure ToOctets(B: in Keccak.Bitstream; O: out Raw_Types.Octets ) is
smg_comms_rsa_oaep    140     Pos : Natural;
smg_comms_rsa_oaep    141   begin
smg_comms_rsa_oaep    142     Pos := B'First;
smg_comms_rsa_oaep    143     for I in O'Range loop
smg_comms_rsa_oaep    144       O(I) := Unsigned_8( B( Pos     ) ) +
smg_comms_rsa_oaep    145               Unsigned_8( B( Pos + 1 ) ) * 2 +
smg_comms_rsa_oaep    146               Unsigned_8( B( Pos + 2 ) ) * 4 +
smg_comms_rsa_oaep    147               Unsigned_8( B( Pos + 3 ) ) * 8 +
smg_comms_rsa_oaep    148               Unsigned_8( B( Pos + 4 ) ) * 16 +
smg_comms_rsa_oaep    149               Unsigned_8( B( Pos + 5 ) ) * 32 +
smg_comms_rsa_oaep    150               Unsigned_8( B( Pos + 6 ) ) * 64 +
smg_comms_rsa_oaep    151               Unsigned_8( B( Pos + 7 ) ) * 128;
smg_comms_rsa_oaep    152       Pos := Pos + 8;
smg_comms_rsa_oaep    153     end loop;
smg_comms_rsa_oaep    154   end ToOctets;
smg_comms_rsa_oaep    155 
smg_comms_rsa_oaep    156   procedure ToBitstream(O: in Raw_Types.Octets; B: out Keccak.Bitstream ) is
smg_comms_rsa_oaep    157     V   : Unsigned_8;
smg_comms_rsa_oaep    158     Pos : Natural;
smg_comms_rsa_oaep    159   begin
smg_comms_rsa_oaep    160     Pos := B'First;
smg_comms_rsa_oaep    161     for I in O'Range loop
smg_comms_rsa_oaep    162       V := O( I );
smg_comms_rsa_oaep    163       B( Pos     ) := Keccak.Bit( V and 1 );
smg_comms_rsa_oaep    164       B( Pos + 1 ) := Keccak.Bit( Shift_Right( V, 1 ) and 1 );
smg_comms_rsa_oaep    165       B( Pos + 2 ) := Keccak.Bit( Shift_Right( V, 2 ) and 1 );
smg_comms_rsa_oaep    166       B( Pos + 3 ) := Keccak.Bit( Shift_Right( V, 3 ) and 1 );
smg_comms_rsa_oaep    167       B( Pos + 4 ) := Keccak.Bit( Shift_Right( V, 4 ) and 1 );
smg_comms_rsa_oaep    168       B( Pos + 5 ) := Keccak.Bit( Shift_Right( V, 5 ) and 1 );
smg_comms_rsa_oaep    169       B( Pos + 6 ) := Keccak.Bit( Shift_Right( V, 6 ) and 1 );
smg_comms_rsa_oaep    170       B( Pos + 7 ) := Keccak.Bit( Shift_Right( V, 7 ) and 1 );
smg_comms_rsa_oaep    171 
smg_comms_rsa_oaep    172       Pos := Pos + 8;
smg_comms_rsa_oaep    173     end loop;
smg_comms_rsa_oaep    174   end ToBitstream;
smg_comms_rsa_oaep    175 
smg_comms_rsa_oaep    176 end OAEP;