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keccak                  1  -- S.MG implementation of Keccak-f permutations
keccak                  2 
keccak                  3  -- (Based on The Keccak Reference, Version 3.0, January 14, 2011, by
keccak                  4  --   Guido Bertoni, Joan Daemen, Michael Peeters and Gilles Van Assche)
keccak                  5 
keccak                  6  -- S.MG, 2018
keccak                  7 
keccak                  8 package SMG_Keccak is
keccak                  9 	pragma Pure(SMG_Keccak);  --stateless, no side effects -> can cache calls
keccak                 10 
keccak                 11   --knobs (can change as per keccak design but fixed here for S.MG purposes)--
keccak                 12   Keccak_L: constant := 6;  --gives keccak z (word) dimension of 2^6=64 and 
keccak                 13                             --therefore keccak function 1600 with current 
keccak                 14                             --constants (5*5*2^6)
keccak                 15 
keccak                 16   Default_Bitrate: constant := 1344; --max bits the sponge can eat/spit without
keccak                 17                                      --needing to scramble the state
keccak                 18 
keccak                 19   --constants: dimensions of keccak state and number of rounds
keccak                 20   XY_Length: constant := 5;
keccak                 21   Z_Length: constant := 2**Keccak_L;
keccak                 22   Width: constant := XY_Length * XY_Length * Z_Length;
keccak                 23   N_Rounds: constant := 12 + 2*Keccak_L;
keccak                 24 
keccak                 25   --types
keccak                 26   type XYCoord is mod XY_Length;
keccak                 27   type ZCoord is mod Z_Length;
keccak                 28   type Round_Index is mod N_Rounds;
keccak                 29 
keccak                 30   type ZWord is mod 2**Z_Length;	--"lane" in keccak ref
keccak                 31   type Plane is array(XYCoord) of ZWord; --a "horizontal slice" of keccak state
keccak                 32   type State is array(XYCoord, XYCoord) of ZWord; --the full keccak state
keccak                 33 
keccak                 34   type Round_Constants is array(Round_Index) of ZWord;  --magic keccak constants
keccak                 35 
keccak                 36   -- rate can be chosen by caller at each call, between 1 and width of state
keccak                 37   -- higher rate means sponge "eats" more bits at a time but has fewer bits in 
keccak                 38   --   the "secret" part of the state (i.e. lower capacity)
keccak                 39   subtype Keccak_Rate is Positive range 1..Width;  -- capacity = width - rate
keccak                 40 
keccak                 41   type Bit is mod 2;
keccak                 42   type Bitstream is array( Natural range <> ) of Bit; -- any length; message
keccak                 43   subtype Bitword is Bitstream( 0..Z_Length - 1 ); -- bits of one state "word"
keccak                 44 
keccak                 45   -- type conversions
keccak                 46   function BitsToWord( BWord : in Bitword ) return ZWord;
keccak                 47   function WordToBits( Word  : in ZWord ) return Bitword;
keccak                 48 
keccak                 49   -- flip input octets (i.e. groups of 8 bits)
keccak                 50   function FlipOctets( BWord : in Bitword ) return Bitword;
keccak                 51 
keccak                 52   -- public function, the sponge itself
keccak                 53   -- Keccak sponge structure using Keccak_Function, Pad and a given bitrate;
keccak                 54   -- Input - the stream of bits to hash (the message)
keccak                 55   -- Output - a bitstream of desired size for holding output
keccak                 56   -- Block_Len - the bitrate to use; this is effectively the block length 
keccak                 57   --             for splitting Input AND squeezing output between scrambles 
keccak                 58   procedure Sponge(Input      : in Bitstream;
keccak                 59                    Output     : out Bitstream;
keccak                 60                    Block_Len  : in Keccak_Rate := Default_Bitrate );
keccak                 61 
keccak                 62 private
keccak                 63   -- these are internals of the keccak implementation, not meant to be directly 
keccak                 64   --  accessed/used
keccak                 65 
keccak                 66   -- this will squeeze Block'Length bits out of state S
keccak                 67   -- NO scramble of state in here!
keccak                 68   -- NB: make SURE that Block'Length is the correct bitrate for this sponge
keccak                 69   -- in particular, Block'Length should be a correct bitrate aka LESS than Width 
keccak                 70   procedure SqueezeBlock( Block: out Bitstream; S: in State);
keccak                 71 
keccak                 72   -- This absorbs into sponge the given block, modifying the state accordingly
keccak                 73   -- NO scramble of state in here so make sure the whole Block fits in state!
keccak                 74   -- NB: make SURE that Block'Length is *the correct bitrate* for this sponge
keccak                 75   -- in particular, Block'Length should be a correct bitrate aka LESS than Width 
keccak                 76   procedure AbsorbBlock( Block: in Bitstream; S: in out State );
keccak                 77 
keccak                 78   --Keccak magic numbers
keccak                 79   RC : constant Round_Constants :=
keccak                 80     (
keccak                 81      16#0000_0000_0000_0001#,
keccak                 82      16#0000_0000_0000_8082#,
keccak                 83      16#8000_0000_0000_808A#,
keccak                 84      16#8000_0000_8000_8000#,
keccak                 85      16#0000_0000_0000_808B#,
keccak                 86      16#0000_0000_8000_0001#,
keccak                 87      16#8000_0000_8000_8081#,
keccak                 88      16#8000_0000_0000_8009#,
keccak                 89      16#0000_0000_0000_008A#,
keccak                 90      16#0000_0000_0000_0088#,
keccak                 91      16#0000_0000_8000_8009#,
keccak                 92      16#0000_0000_8000_000A#,
keccak                 93      16#0000_0000_8000_808B#,
keccak                 94      16#8000_0000_0000_008B#,
keccak                 95      16#8000_0000_0000_8089#,
keccak                 96      16#8000_0000_0000_8003#,
keccak                 97      16#8000_0000_0000_8002#,
keccak                 98      16#8000_0000_0000_0080#,
keccak                 99      16#0000_0000_0000_800A#,
keccak                100      16#8000_0000_8000_000A#,
keccak                101      16#8000_0000_8000_8081#,
keccak                102      16#8000_0000_0000_8080#,
keccak                103      16#0000_0000_8000_0001#,
keccak                104      16#8000_0000_8000_8008#
keccak                105     );
keccak                106 
keccak                107   --gnat-specific methods to have bit-ops for modular types
keccak                108   function Rotate_Left( Value  : ZWord; 
keccak                109 	                      Amount : Natural) 
keccak                110 	                      return ZWord;
keccak                111 	pragma Import(Intrinsic, Rotate_Left); 
keccak                112 
keccak                113 	function Shift_Right( Value  : ZWord; 
keccak                114                         Amount : Natural) 
keccak                115                         return ZWord;
keccak                116   pragma Import(Intrinsic, Shift_Right); 
keccak                117 
keccak                118   function Shift_Left( Value  : ZWord;
keccak                119                        Amount : Natural)
keccak                120                        return ZWord;
keccak                121   pragma Import(Intrinsic, Shift_Left);
keccak                122 
keccak                123   --Keccak transformations of the internal state
keccak                124   function Theta ( Input       : in State) return State;
keccak                125   function Rho   ( Input       : in State) return State;
keccak                126   function Pi    ( Input       : in State) return State;
keccak                127   function Chi   ( Input       : in State) return State;
keccak                128   function Iota  ( Round_Const : in ZWord; Input : in State) return State;
keccak                129 
keccak                130   --Keccak function with block width currently 1600 (Width constant above)
keccak                131   --this simply applies *all* keccak transformations in the correct order, using
keccak                132   -- the keccak magic numbers (round constants) as per keccak reference
keccak                133   function Keccak_Function(Input: in State) return State;
keccak                134 
keccak                135 end SMG_Keccak;