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    1/*  Part of SWI-Prolog
    2
    3    Author:        Jan Wielemaker
    4    E-mail:        J.Wielemaker@vu.nl
    5    WWW:           http://www.swi-prolog.org
    6    Copyright (c)  2007-2013, University of Amsterdam
    7                              VU University Amsterdam
    8    All rights reserved.
    9
   10    Redistribution and use in source and binary forms, with or without
   11    modification, are permitted provided that the following conditions
   12    are met:
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   14    1. Redistributions of source code must retain the above copyright
   15       notice, this list of conditions and the following disclaimer.
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   20       distribution.
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   22    THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
   23    "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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   25    FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
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   34*/
   35
   36:- module(crypto_hash,
   37          [ sha_hash/3,                 % +Data, -Hash, +Options
   38            sha_new_ctx/2,              % -NewContext, +Options
   39            sha_hash_ctx/4,             % +OldCtx, +Data, -NewCtx, -Hash
   40            hmac_sha/4,                 % +Key, +Data, -Hash, +Options
   41            file_sha1/2,                % +File, -SHA1
   42            hash_atom/2                 % +Hash, -HexAtom
   43          ]).   44:- use_foreign_library(foreign(sha4pl)).

SHA secure hashes

This library provides a lightweight implementation for computing SHA secure hashes. A general secure hash interface is provided by library(crypto), part of the ssl package.

See also
- library(md5), library(hash_stream) and library(crypto). */
 sha_hash(+Data, -Hash, +Options) is det
Hash is the SHA hash of Data, The conversion is controlled by Options:
algorithm(+Algorithm)
One of sha1 (default), sha224, sha256, sha384 or sha512
encoding(+Encoding)
If Data is a sequence of character codes, this must be translated into a sequence of bytes, because that is what the hashing requires. The default encoding is utf8. The other meaningful value is octet, claiming that Data contains raw bytes.
Arguments:
Data- is either an atom, string or code-list
Hash- is a packed string
 sha_new_ctx(-NewContext, +Options) is det
NewContext is unified with the empty SHA computation context (which includes the Options.) It could later be passed to sha_hash_ctx/4. For Options, see sha_hash/3.
Arguments:
NewContext- is an opaque pure Prolog term that is subject to garbage collection.
 sha_hash_ctx(+OldContext, +Data, -NewContext, -Hash) is det
Hash is the SHA hash of Data. NewContext is the new SHA computation context, while OldContext is the old. OldContext may be produced by a prior invocation of either sha_new_ctx/3 or sha_hash_ctx/4 itself.

This predicate allows a SHA function to be computed in chunks, which may be important while working with Metalink (RFC 5854), BitTorrent or similar technologies, or simply with big files.

 hmac_sha(+Key, +Data, -Hash, +Options) is det
For Options, see sha_hash/3.
 file_sha1(+File, -SHA1:atom) is det
True when SHA1 is the SHA1 hash for the content of File. Options is passed to open/4 and typically used to control whether binary or text encoding must be used. The output is compatible to the sha1sum program found in many systems.
  104file_sha1(File, Hash) :-
  105    setup_call_cleanup(
  106        open(File, read, In, [type(binary)]),
  107        stream_sha1(In, Hash),
  108        close(In)).
  109
  110stream_sha1(Stream, Hash) :-
  111    sha_new_ctx(Ctx0, [encoding(octet)]),
  112    update_hash(Stream, Ctx0, _Ctx, 0, HashCodes),
  113    hash_atom(HashCodes, Hash).
  114
  115update_hash(In, Ctx0, Ctx, Hash0, Hash) :-
  116    at_end_of_stream(In),
  117    !,
  118    Ctx = Ctx0,
  119    Hash = Hash0.
  120update_hash(In, Ctx0, Ctx, _Hash0, Hash) :-
  121    read_pending_codes(In, Data, []),
  122    sha_hash_ctx(Ctx0, Data, Ctx1, Hash1),
  123    update_hash(In, Ctx1, Ctx, Hash1, Hash).
 hash_atom(+HashCodes, -HexAtom) is det
Convert a list of bytes (integers 0..255) into the usual hexadecimal notation. E.g.
?- sha_hash('SWI-Prolog', Hash, []),
   hash_atom(Hash, Hex).
Hash = [61, 128, 252, 38, 121, 69, 229, 85, 199|...],
Hex = '3d80fc267945e555c730403bd0ab0716e2a68c68'.
  139hash_atom(Codes, Hash) :-
  140    phrase(bytes_hex(Codes), HexCodes),
  141    atom_codes(Hash, HexCodes).
  142
  143bytes_hex([]) --> [].
  144bytes_hex([H|T]) -->
  145    { High is H>>4,
  146      Low is H /\ 0xf,
  147      code_type(C0, xdigit(High)),
  148      code_type(C1, xdigit(Low))
  149    },
  150    [C0,C1],
  151    bytes_hex(T)