1------------------------------------------------------------------------------
2--                                                                          --
3--                         GNAT LIBRARY COMPONENTS                          --
4--                                                                          --
5--       G N A T . S E C U R E _ H A S H E S . S H A 2 _ C O M M O N        --
6--                                                                          --
7--                                 B o d y                                  --
8--                                                                          --
9--           Copyright (C) 2009-2021, Free Software Foundation, Inc.        --
10--                                                                          --
11-- GNAT is free software;  you can  redistribute it  and/or modify it under --
12-- terms of the  GNU General Public License as published  by the Free Soft- --
13-- ware  Foundation;  either version 3,  or (at your option) any later ver- --
14-- sion.  GNAT is distributed in the hope that it will be useful, but WITH- --
15-- OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY --
16-- or FITNESS FOR A PARTICULAR PURPOSE.                                     --
17--                                                                          --
18-- As a special exception under Section 7 of GPL version 3, you are granted --
19-- additional permissions described in the GCC Runtime Library Exception,   --
20-- version 3.1, as published by the Free Software Foundation.               --
21--                                                                          --
22-- You should have received a copy of the GNU General Public License and    --
23-- a copy of the GCC Runtime Library Exception along with this program;     --
24-- see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see    --
25-- <http://www.gnu.org/licenses/>.                                          --
26--                                                                          --
27-- GNAT was originally developed  by the GNAT team at  New York University. --
28-- Extensive contributions were provided by Ada Core Technologies Inc.      --
29--                                                                          --
30------------------------------------------------------------------------------
31
32package body GNAT.Secure_Hashes.SHA2_Common is
33
34   ---------------
35   -- Transform --
36   ---------------
37
38   procedure Transform
39     (H_St : in out Hash_State.State;
40      M_St : in out Message_State)
41   is
42      use System;
43
44      subtype Word is Hash_State.Word;
45      use type Hash_State.Word;
46
47      function Ch (X, Y, Z : Word) return Word;
48      function Maj (X, Y, Z : Word) return Word;
49      pragma Inline (Ch, Maj);
50      --  Elementary functions from FIPS PUB 180-3
51
52      --------
53      -- Ch --
54      --------
55
56      function Ch (X, Y, Z : Word) return Word is
57      begin
58         return (X and Y) xor ((not X) and Z);
59      end Ch;
60
61      ---------
62      -- Maj --
63      ---------
64
65      function Maj (X, Y, Z : Word) return Word is
66      begin
67         return (X and Y) xor (X and Z) xor (Y and Z);
68      end Maj;
69
70      type Words is array (Natural range <>) of Word;
71
72      X : Words (0 .. 15);
73      for X'Address use M_St.Buffer'Address;
74      pragma Import (Ada, X);
75
76      W : Words (0 .. Rounds - 1);
77
78      A, B, C, D, E, F, G, H, T1, T2 : Word;
79
80   --  Start of processing for Transform
81
82   begin
83      if Default_Bit_Order /= High_Order_First then
84         for J in X'Range loop
85            Hash_State.Swap (X (J)'Address);
86         end loop;
87      end if;
88
89      --  1. Prepare message schedule
90
91      W (0 .. 15) := X;
92
93      for T in 16 .. Rounds - 1 loop
94         W (T) := S1 (W (T - 2)) + W (T - 7) + S0 (W (T - 15)) + W (T - 16);
95      end loop;
96
97      --  2. Initialize working variables
98
99      A := H_St (0);
100      B := H_St (1);
101      C := H_St (2);
102      D := H_St (3);
103      E := H_St (4);
104      F := H_St (5);
105      G := H_St (6);
106      H := H_St (7);
107
108      --  3. Perform transformation rounds
109
110      for T in 0 .. Rounds - 1 loop
111         T1 := H + Sigma1 (E) + Ch (E, F, G)
112             + K (Stream_Element_Offset (T)) + W (T);
113         T2 := Sigma0 (A) + Maj (A, B, C);
114         H := G;
115         G := F;
116         F := E;
117         E := D + T1;
118         D := C;
119         C := B;
120         B := A;
121         A := T1 + T2;
122      end loop;
123
124      --  4. Update hash state
125
126      H_St (0) := A + H_St (0);
127      H_St (1) := B + H_St (1);
128      H_St (2) := C + H_St (2);
129      H_St (3) := D + H_St (3);
130      H_St (4) := E + H_St (4);
131      H_St (5) := F + H_St (5);
132      H_St (6) := G + H_St (6);
133      H_St (7) := H + H_St (7);
134   end Transform;
135
136end GNAT.Secure_Hashes.SHA2_Common;
137