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smg_comms_rsa_oaep      1 -- Implementation of TMSR's OAEP with Keccak as hash function
smg_comms_rsa_oaep      2 -- NB: this uses Eulora's protocol constants (esp. RSA key length) and types.
smg_comms_rsa_oaep      3 --
smg_comms_rsa_oaep      4 -- S.MG, 2018
smg_comms_rsa_oaep      5 
smg_comms_rsa_oaep      6 with Keccak;    -- Keccak is used as hash function
smg_comms_rsa_oaep      7 with Raw_Types; -- Eulora's protocol raw types and constant values
smg_comms_rsa_oaep      8 
smg_comms_rsa_oaep      9 with Interfaces; use Interfaces; -- for Unsigned_8 type and bit-level ops
smg_comms_rsa_oaep     10 
smg_comms_rsa_oaep     11 package OAEP is
smg_comms_rsa_oaep     12   pragma Pure( OAEP ); -- stateless, no side effects -> can cache calls
smg_comms_rsa_oaep     13 
smg_comms_rsa_oaep     14   -- constants for OAEP 
smg_comms_rsa_oaep     15   OAEP_LENGTH_OCTETS : constant := Raw_Types.RSA_KEY_OCTETS;
smg_comms_rsa_oaep     16   OAEP_LENGTH_BITS   : constant := OAEP_LENGTH_OCTETS * 8;
smg_comms_rsa_oaep     17   OAEP_HALF_OCTETS   : constant := OAEP_LENGTH_OCTETS / 2;
smg_comms_rsa_oaep     18   TMSR_STR           : constant String := "TMSR-RSA";
smg_comms_rsa_oaep     19     -- "TMSR-RSA" as unsigned_8 values:
smg_comms_rsa_oaep     20   TMSR               : constant Raw_Types.Octets := (84,77,83,82,45,82,83,65);
smg_comms_rsa_oaep     21   MAX_LEN_MSG        : constant Natural := OAEP_HALF_OCTETS - 
smg_comms_rsa_oaep     22                                            TMSR_STR'Length - 3;
smg_comms_rsa_oaep     23 
smg_comms_rsa_oaep     24   -- subtypes for OAEP encrypt/decrypt
smg_comms_rsa_oaep     25   subtype OAEP_Block is Raw_Types.Octets( 1 .. OAEP_LENGTH_OCTETS );
smg_comms_rsa_oaep     26   subtype OAEP_HALF is Raw_Types.Octets( 1 .. OAEP_HALF_OCTETS );
smg_comms_rsa_oaep     27 
smg_comms_rsa_oaep     28   -- padding & formatting of maximum MAX_LEN_MSG octets of the given input
smg_comms_rsa_oaep     29   -- uses TMSR's OAEP schema:
smg_comms_rsa_oaep     30   -- 1.format M00 as: [random octet][sz1][sz2]"TMSR-RSA"[random]*Message
smg_comms_rsa_oaep     31   --    where sz1 and sz2 store the length of the message in bits
smg_comms_rsa_oaep     32   --    the random octets before message are padding to make OAEP_LENGTH_OCTETS
smg_comms_rsa_oaep     33   -- 2. R = OAEP_HALF_OCTETS random bits
smg_comms_rsa_oaep     34   -- 3. X = M00 xor hash(R)
smg_comms_rsa_oaep     35   -- 4. Y = R xor hash(X)
smg_comms_rsa_oaep     36   -- 5. Result is X || Y 
smg_comms_rsa_oaep     37   -- NB: the Entropy parameter should be random octets from which this method 
smg_comms_rsa_oaep     38   -- will use as many as required for the OAEP encryption of given Msg
smg_comms_rsa_oaep     39   -- NB: at MOST MAX_LEN_MSG octets of Msg! (Msg at most MAX_LEN_MSG*8 bits!)
smg_comms_rsa_oaep     40   procedure OAEP_Encrypt( Msg      : in Raw_Types.Octets;
smg_comms_rsa_oaep     41                           Entropy  : in OAEP_Block;
smg_comms_rsa_oaep     42                           Output   : out OAEP_Block);
smg_comms_rsa_oaep     43 
smg_comms_rsa_oaep     44 
smg_comms_rsa_oaep     45   -- This is the opposite of OAEP_Encrypt above.
smg_comms_rsa_oaep     46   -- @param Encr - an OAEP block previously obtained from OAEP_Encrypt
smg_comms_rsa_oaep     47   -- @param Len - this will hold the length of the obtained message (in bits!)
smg_comms_rsa_oaep     48   -- @param Output - the first Len octets of this are the recovered message
smg_comms_rsa_oaep     49   -- @param Success - set to TRUE if message was recovered, false otherwise
smg_comms_rsa_oaep     50   -- NB: when Success is FALSE, both Len and Output have undefined values
smg_comms_rsa_oaep     51   procedure OAEP_Decrypt( Encr    : in OAEP_Block;
smg_comms_rsa_oaep     52                           Len     : out Natural;
smg_comms_rsa_oaep     53                           Output  : out OAEP_HALF;
smg_comms_rsa_oaep     54                           Success : out Boolean);
smg_comms_rsa_oaep     55 
smg_comms_rsa_oaep     56 private
smg_comms_rsa_oaep     57   -- gnat-specific methods for bit-level operations
smg_comms_rsa_oaep     58 	function Shift_Right( Value  : Unsigned_8; 
smg_comms_rsa_oaep     59                         Amount : Natural ) 
smg_comms_rsa_oaep     60                         return Unsigned_8;
smg_comms_rsa_oaep     61   pragma Import(Intrinsic, Shift_Right); 
smg_comms_rsa_oaep     62 
smg_comms_rsa_oaep     63 	function Shift_Left( Value  : Unsigned_8; 
smg_comms_rsa_oaep     64                         Amount : Natural ) 
smg_comms_rsa_oaep     65                         return Unsigned_8;
smg_comms_rsa_oaep     66   pragma Import(Intrinsic, Shift_Left); 
smg_comms_rsa_oaep     67 
smg_comms_rsa_oaep     68   -- helper method: xor 2 half-oaep blocks
smg_comms_rsa_oaep     69   function XOR_Octets(A : in OAEP_HALF; 
smg_comms_rsa_oaep     70                       B : in OAEP_HALF)
smg_comms_rsa_oaep     71                      return OAEP_HALF;
smg_comms_rsa_oaep     72 
smg_comms_rsa_oaep     73   -- conversions between bitstream and string
smg_comms_rsa_oaep     74   -- NB: caller has to ensure correct size of output parameter! no checks here.
smg_comms_rsa_oaep     75   procedure ToOctets   ( B : in Keccak.Bitstream; 
smg_comms_rsa_oaep     76                          O : out Raw_Types.Octets );
smg_comms_rsa_oaep     77 
smg_comms_rsa_oaep     78   procedure ToBitstream( O : in Raw_Types.Octets; 
smg_comms_rsa_oaep     79                          B : out Keccak.Bitstream );
smg_comms_rsa_oaep     80 
smg_comms_rsa_oaep     81   -- wrapper for Sponge to use Octets for input/output
smg_comms_rsa_oaep     82   procedure HashKeccak( Input     : in Raw_Types.Octets;
smg_comms_rsa_oaep     83                         Output    : out Raw_Types.Octets;
smg_comms_rsa_oaep     84                         Block_Len : in Keccak.Keccak_Rate := 
smg_comms_rsa_oaep     85                                        Keccak.Default_Bitrate);
smg_comms_rsa_oaep     86 
smg_comms_rsa_oaep     87 end OAEP;