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eucrypt_ch10_oaep...    1 -- Implementation of TMSR's OAEP with Keccak as hash function
eucrypt_ch10_oaep...    2 --
eucrypt_ch10_oaep...    3 -- S.MG, 2018
eucrypt_ch10_oaep...    4 
eucrypt_ch10_oaep...    5 with SMG_Keccak; use SMG_Keccak; -- Keccak is used as hash function
eucrypt_ch10_oaep...    6 with Interfaces; use Interfaces; -- for Unsigned_8 type and bit-level ops
eucrypt_ch10_oaep...    7 with Interfaces.C; use Interfaces.C; -- for interop with C
eucrypt_ch10_oaep...    8 
eucrypt_ch10_oaep...    9 package SMG_OAEP is
eucrypt_ch10_oaep...   10   pragma Pure( SMG_OAEP ); -- stateless, no side effects -> can cache calls
eucrypt_ch10_oaep...   11 
eucrypt_ch10_oaep...   12   -- fixed length of OAEP block in bits and in octets
eucrypt_ch10_oaep...   13   OAEP_LENGTH_BITS   : constant := 4096;
eucrypt_ch10_oaep...   14   OAEP_LENGTH_OCTETS : constant := 512;
eucrypt_ch10_oaep...   15   OAEP_HALF_OCTETS   : constant := OAEP_LENGTH_OCTETS / 2;
eucrypt_ch10_oaep...   16 
eucrypt_ch10_oaep...   17   -- subtypes used by the OAEP encrypt/decrypt
eucrypt_ch10_oaep...   18   subtype OAEP_Block is String( 1 .. OAEP_LENGTH_OCTETS );
eucrypt_ch10_oaep...   19   subtype OAEP_HALF is String( 1 .. OAEP_HALF_OCTETS );
eucrypt_ch10_oaep...   20 
eucrypt_ch10_oaep...   21   -- padding & formatting of maximum 1960 bits of the given String 
eucrypt_ch10_oaep...   22   -- uses TMSR's OAEP schema:
eucrypt_ch10_oaep...   23   -- 1.format M00 as: [random octet][sz1][sz2]"TMSR-RSA"[random]*Message
eucrypt_ch10_oaep...   24   --    where sz1 and sz2 store the length of the message in bits
eucrypt_ch10_oaep...   25   --    the random octets before message are padding to make OAEP_LENGTH_OCTETS
eucrypt_ch10_oaep...   26   -- 2. R = OAEP_HALF_OCTETS random bits
eucrypt_ch10_oaep...   27   -- 3. X = M00 xor hash(R)
eucrypt_ch10_oaep...   28   -- 4. Y = R xor hash(X)
eucrypt_ch10_oaep...   29   -- 5. Result is X || Y 
eucrypt_ch10_oaep...   30   -- NB: the Entropy parameter should be random octets from which this method 
eucrypt_ch10_oaep...   31   -- will use as many as required for the OAEP encryption of given Msg
eucrypt_ch10_oaep...   32   -- NB: at MOST OAEP_LENGTH_OCTETS - 11 octets of Msg! (Msg at most 1960 bits)
eucrypt_ch10_oaep...   33   procedure OAEP_Encrypt( Msg     : in String;
eucrypt_ch10_oaep...   34                           Entropy : in OAEP_Block;
eucrypt_ch10_oaep...   35                           Output  : out OAEP_Block);
eucrypt_ch10_oaep...   36 
eucrypt_ch10_oaep...   37   -- This is the opposite of OAEP_Encrypt above.
eucrypt_ch10_oaep...   38   -- @param Encr - an OAEP block previously obtained from OAEP_Encrypt
eucrypt_ch10_oaep...   39   -- @param Len - this will hold the length of the obtained message (in bits!)
eucrypt_ch10_oaep...   40   -- @param Output - the first Len octets of this are the recovered message
eucrypt_ch10_oaep...   41   -- @param Success - set to TRUE if message was recovered, false otherwise
eucrypt_ch10_oaep...   42   -- NB: when Success is FALSE, both Len and Output have undefined values
eucrypt_ch10_oaep...   43   procedure OAEP_Decrypt( Encr    : in OAEP_Block;
eucrypt_ch10_oaep...   44                           Len     : out Natural;
eucrypt_ch10_oaep...   45                           Output  : out OAEP_HALF;
eucrypt_ch10_oaep...   46                           Success : out Boolean);
eucrypt_ch10_oaep...   47 
eucrypt_ch10_oaep...   48   -- helper method, xor on strings
eucrypt_ch10_oaep...   49   -- NB: only Output'Length bits will be considered from S1 and S2
eucrypt_ch10_oaep...   50   -- NB: caller is responsible for S1 and S2 being long enough!
eucrypt_ch10_oaep...   51   procedure XOR_Strings( S1: in String; S2: in String; Output: out String );
eucrypt_ch10_oaep...   52 
eucrypt_ch10_oaep...   53   -- gnat-specific methods for bit-level operations
eucrypt_ch10_oaep...   54 	function Shift_Right( Value  : Unsigned_8; 
eucrypt_ch10_oaep...   55                         Amount : Natural ) 
eucrypt_ch10_oaep...   56                         return Unsigned_8;
eucrypt_ch10_oaep...   57   pragma Import(Intrinsic, Shift_Right); 
eucrypt_ch10_oaep...   58 
eucrypt_ch10_oaep...   59 	function Shift_Left( Value  : Unsigned_8; 
eucrypt_ch10_oaep...   60                         Amount : Natural ) 
eucrypt_ch10_oaep...   61                         return Unsigned_8;
eucrypt_ch10_oaep...   62   pragma Import(Intrinsic, Shift_Left); 
eucrypt_ch10_oaep...   63 
eucrypt_ch10_oaep...   64   -- conversions between bitstream and string
eucrypt_ch10_oaep...   65   -- NB: caller has to ensure correct size of output parameter! no checks here.
eucrypt_ch10_oaep...   66   procedure ToString( B: in Bitstream; S: out String );
eucrypt_ch10_oaep...   67   procedure ToBitstream( S: in String; B: out Bitstream );
eucrypt_ch10_oaep...   68 
eucrypt_ch10_oaep...   69   -- public wrapper for Sponge to use String for input/output
eucrypt_ch10_oaep...   70   procedure HashKeccak( Input     : in String;
eucrypt_ch10_oaep...   71                         Output    : out String;
eucrypt_ch10_oaep...   72                         Block_Len : in Keccak_Rate := Default_Bitrate);
eucrypt_ch10_oaep...   73 
eucrypt_ch10_oaep...   74   -- wrapper for calling from C
eucrypt_ch10_oaep...   75   -- @param Input the input string, as array of characters (C style)
eucrypt_ch10_oaep...   76   -- @param LenIn the length of the input string (as number of BITS)
eucrypt_ch10_oaep...   77   -- @param LenOut the desired number of bits to be returned as output
eucrypt_ch10_oaep...   78   -- @param Block_Len the bitrate used by the Keccak sponge (number of BITS)
eucrypt_ch10_oaep...   79   -- @return an array of characters with first LenOut bits set to Keccak output
eucrypt_ch10_oaep...   80 
eucrypt_ch10_oaep...   81   -- NB: caller HAS TO provide the length of the Input (parameter LenIn)
eucrypt_ch10_oaep...   82   -- NB: caller HAS TO provide the length of the Output (parameter LenOut)
eucrypt_ch10_oaep...   83   function Hash( Input     : Interfaces.C.Char_Array;
eucrypt_ch10_oaep...   84                  LenIn     : Interfaces.C.size_t;
eucrypt_ch10_oaep...   85                  LenOut    : Interfaces.C.size_t;
eucrypt_ch10_oaep...   86                  Block_Len : Interfaces.C.int := Default_Bitrate)
eucrypt_ch10_oaep...   87                  return Interfaces.C.Char_Array;
eucrypt_ch10_oaep...   88   pragma Export( C, Hash, "hash" );
eucrypt_ch10_oaep...   89 
eucrypt_ch10_oaep...   90 end SMG_OAEP;