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1 281 jeremybenn
------------------------------------------------------------------------------
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--                                                                          --
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--                         GNAT LIBRARY COMPONENTS                          --
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--                                                                          --
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--                   G N A T . S E C U R E _ H A S H E S                    --
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--                                                                          --
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--                                 S p e c                                  --
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--                                                                          --
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--           Copyright (C) 2009, Free Software Foundation, Inc.             --
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--                                                                          --
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-- GNAT is free software;  you can  redistribute it  and/or modify it under --
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-- terms of the  GNU General Public License as published  by the Free Soft- --
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-- ware  Foundation;  either version 3,  or (at your option) any later ver- --
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-- sion.  GNAT is distributed in the hope that it will be useful, but WITH- --
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-- OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY --
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-- or FITNESS FOR A PARTICULAR PURPOSE.                                     --
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--                                                                          --
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-- As a special exception under Section 7 of GPL version 3, you are granted --
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-- additional permissions described in the GCC Runtime Library Exception,   --
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-- version 3.1, as published by the Free Software Foundation.               --
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--                                                                          --
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-- You should have received a copy of the GNU General Public License and    --
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-- a copy of the GCC Runtime Library Exception along with this program;     --
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-- see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see    --
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-- <http://www.gnu.org/licenses/>.                                          --
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--                                                                          --
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-- GNAT was originally developed  by the GNAT team at  New York University. --
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-- Extensive contributions were provided by Ada Core Technologies Inc.      --
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--                                                                          --
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------------------------------------------------------------------------------
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--  This package provides common suporting code for a family of secure
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--  hash functions (including MD5 and the FIPS PUB 180-3 functions SHA-1,
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--  SHA-224, SHA-256, SHA-384 and SHA-512).
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--  This is an internal unit and should be not used directly in applications.
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--  Use GNAT.MD5 and GNAT.SHA* instead.
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with Ada.Streams;
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with Interfaces;
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with System;
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package GNAT.Secure_Hashes is
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   type Buffer_Type is new String;
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   for Buffer_Type'Alignment use 8;
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   --  Secure hash functions use a string buffer that is also accessed as an
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   --  array of words, which may require up to 64 bit alignment.
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   --  The function-independent part of processing state: A buffer of data
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   --  being accumulated until a complete block is ready for hashing.
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   type Message_State (Block_Length : Natural) is record
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      Last : Natural := 0;
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      --  Index of last used element in Buffer
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      Length : Interfaces.Unsigned_64 := 0;
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      --  Total length of processed data
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      Buffer : Buffer_Type (1 .. Block_Length);
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      --  Data buffer
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   end record;
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   --  The function-specific part of processing state:
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   --  Each hash function maintains an internal state as an array of words,
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   --  which is ultimately converted to a stream representation with the
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   --  appropriate bit order.
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   generic
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      type Word is mod <>;
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      --  Either 32 or 64 bits
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      with procedure Swap (X : System.Address);
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      --  Byte swapping function for a Word at X
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      Hash_Bit_Order : System.Bit_Order;
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      --  Bit order of the produced hash
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   package Hash_Function_State is
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      type State is array (Natural range <>) of Word;
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      --  Used to store a hash function's internal state
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      procedure To_Hash
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        (H      : State;
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         H_Bits : out Ada.Streams.Stream_Element_Array);
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      --  Convert H to stream representation with the given bit order.
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      --  If H_Bits is smaller than the internal hash state, then the state
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      --  is truncated.
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   end Hash_Function_State;
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   --  Generic hashing framework:
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   --  The user interface for each implemented secure hash function is an
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   --  instance of this generic package.
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   generic
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      Block_Words : Natural;
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      --  Number of words in each block
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      State_Words : Natural;
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      --  Number of words in internal state
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      Hash_Words : Natural;
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      --  Number of words in the final hash (must be no greater than
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      --  State_Words).
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      Hash_Bit_Order : System.Bit_Order;
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      --  Bit order used for conversion between bit representation and word
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      --  representation.
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      with package Hash_State is new Hash_Function_State (<>);
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      --  Hash function state package
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      Initial_State : Hash_State.State;
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      --  Initial value of the hash function state
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      with procedure Transform
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        (H : in out Hash_State.State;
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         M : in out Message_State);
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      --  Transformation function updating H by processing a complete data
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      --  block from M.
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   package H is
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      --  The visible part of H is the interface to secure hashing functions
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      --  that is exposed to user applications, and is intended to remain
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      --  a stable interface.
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      pragma Assert (Hash_Words <= State_Words);
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      type Context is private;
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      --  The internal processing state of the hashing function
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      function "=" (L, R : Context) return Boolean is abstract;
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      --  Context is the internal, implementation defined intermediate state
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      --  in a hash computation, and no specific semantics can be expected on
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      --  equality of context values. Only equality of final hash values (as
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      --  returned by the [Wide_]Digest functions below) is meaningful.
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      Initial_Context : constant Context;
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      --  Initial value of a Context object. May be used to reinitialize
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      --  a Context value by simple assignment of this value to the object.
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      procedure Update      (C : in out Context; Input : String);
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      procedure Wide_Update (C : in out Context; Input : Wide_String);
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      procedure Update
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        (C     : in out Context;
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         Input : Ada.Streams.Stream_Element_Array);
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      --  Update C to process the given input. Successive calls to Update are
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      --  equivalent to a single call with the concatenation of the inputs. For
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      --  the Wide_String version, each Wide_Character is processed low order
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      --  byte first.
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      Word_Length : constant Natural := Hash_State.Word'Size / 8;
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      Hash_Length : constant Natural := Hash_Words * Word_Length;
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      subtype Message_Digest is String (1 .. 2 * Hash_Length);
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      --  The fixed-length string returned by Digest, providing the hash in
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      --  hexadecimal representation.
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      function Digest (C : Context) return Message_Digest;
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      --  Return hash for the data accumulated with C in hexadecimal
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      --  representation.
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      function Digest      (S : String)      return Message_Digest;
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      function Wide_Digest (W : Wide_String) return Message_Digest;
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      function Digest
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        (A : Ada.Streams.Stream_Element_Array) return Message_Digest;
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      --  These functions are equivalent to the corresponding Update (or
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      --  Wide_Update) on a default initialized Context, followed by Digest
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      --  on the resulting Context.
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   private
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      Block_Length : constant Natural := Block_Words * Word_Length;
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      --  Length in bytes of a data block
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      type Context is record
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         H_State : Hash_State.State (0 .. State_Words - 1) := Initial_State;
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         --  Function-specific state
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         M_State : Message_State (Block_Length);
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         --  Function-independent state (block buffer)
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      end record;
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      Initial_Context : constant Context := (others => <>);
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      --  Initial values are provided by default initialization of Context
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   end H;
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end GNAT.Secure_Hashes;

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