220 12469 <833080F6-5FAB-4C71-860D-DB6BFA8CF2EF@gmail.com> article Path: news.gmane.org!not-for-mail From: Howard Hinnant Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Cryptographic hash functions reloaded [was Interest in cryptographic functions within the standard library] Date: Sun, 24 Aug 2014 19:21:17 -0400 Lines: 74 Approved: news@gmane.org Message-ID: <833080F6-5FAB-4C71-860D-DB6BFA8CF2EF@gmail.com> References: <53F8F620.3090701@gmx.de> <53F989E9.5090701@gmx.net> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 (Mac OS X Mail 7.3 \(1878.6\)) Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable X-Trace: ger.gmane.org 1408922492 21566 80.91.229.3 (24 Aug 2014 23:21:32 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Sun, 24 Aug 2014 23:21:32 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBCK2HM4L6YERB4PG5GPQKGQEED2UE5Q@isocpp.org Mon Aug 25 01:21:24 2014 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-oi0-f70.google.com ([209.85.218.70]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1XLh6A-0001Lt-TZ for gclcip-std-proposals@m.gmane.org; Mon, 25 Aug 2014 01:21:23 +0200 Original-Received: by mail-oi0-f70.google.com with SMTP id u20sf66860030oif.1 for ; Sun, 24 Aug 2014 16:21:21 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:mime-version:subject:from:in-reply-to:date :message-id:references:to:x-original-sender :x-original-authentication-results:reply-to:precedence:mailing-list :list-id:list-post:list-help:list-archive:list-subscribe :list-unsubscribe:content-type:content-transfer-encoding; bh=qWtHcziI6hzRBLBcBfTqw5ppahaXQ+jh+5A5M8fates=; b=KEpFv4q/VWx3mXp0rfrDDRlshtMylDdngMBtjcx+S1oz9fgoo8xkQE9B4AoQtW7FMz ffxp4oXLdFrsM15asUAR442qHdOTq8Is4UgGv65D7jAMmKLzMzEvLZlJFihxZ50CgWdF /20V+EHNqmGeUW0Yks973WbYimj9buN8HaSZdKX6T1QfCKWwiOk+G5+x/LKKVeHYSwih ZD89ZdusSrVuGNyYrOmCFY8vRxAWYZ81/zt+l7fUdoJ1kDiO5tZTWHgxhUHyYlVof28T t7+O0e7ovK/W7LRPKnn5NPoGNT7Eck7tm/iZTGtm9w8BZQUk7w7JVG64dACqu8RyWpTz vzdA== X-Gm-Message-State: ALoCoQnmA8NfeoK3XO+ViSiy4d02nmw+uOLCjcvxFG9J8gv7B9dxDYz/BREwI1beY3yvsaAs1mcb X-Received: by 10.42.97.138 with SMTP id o10mr2031963icn.33.1408922481708; Sun, 24 Aug 2014 16:21:21 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.50.164.169 with SMTP id yr9ls953299igb.11.canary; Sun, 24 Aug 2014 16:21:20 -0700 (PDT) X-Received: by 10.43.75.7 with SMTP id yy7mr238585icb.15.1408922480857; Sun, 24 Aug 2014 16:21:20 -0700 (PDT) Original-Received: from mail-ig0-x236.google.com (mail-ig0-x236.google.com [2607:f8b0:4001:c05::236]) by mx.google.com with ESMTPS id qc5si14769688icb.107.2014.08.24.16.21.20 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Sun, 24 Aug 2014 16:21:20 -0700 (PDT) Received-SPF: pass (google.com: domain of howard.hinnant@gmail.com designates 2607:f8b0:4001:c05::236 as permitted sender) client-ip=2607:f8b0:4001:c05::236; Original-Received: by mail-ig0-f182.google.com with SMTP id c1so1992968igq.15 for ; Sun, 24 Aug 2014 16:21:20 -0700 (PDT) X-Received: by 10.50.176.202 with SMTP id ck10mr12207456igc.2.1408922480735; Sun, 24 Aug 2014 16:21:20 -0700 (PDT) Original-Received: from [10.0.1.2] (cpe-24-58-234-96.twcny.res.rr.com. [24.58.234.96]) by mx.google.com with ESMTPSA id ig14sm30123391igb.13.2014.08.24.16.21.19 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Sun, 24 Aug 2014 16:21:19 -0700 (PDT) In-Reply-To: X-Mailer: Apple Mail (2.1878.6) X-Original-Sender: howard.hinnant@gmail.com X-Original-Authentication-Results: mx.google.com; spf=pass (google.com: domain of howard.hinnant@gmail.com designates 2607:f8b0:4001:c05::236 as permitted sender) smtp.mail=howard.hinnant@gmail.com; dkim=pass header.i=@gmail.com; dmarc=pass (p=NONE dis=NONE) header.from=gmail.com Precedence: list Mailing-list: list std-proposals@isocpp.org; contact std-proposals+owners@isocpp.org List-ID: X-Google-Group-Id: 399137483710 List-Post: , List-Help: , List-Archive: List-Subscribe: , List-Unsubscribe: , Xref: news.gmane.org gmane.comp.lang.c++.isocpp.proposals:12469 Archived-At: On Aug 24, 2014, at 5:01 PM, Myriachan wrote: > On Sunday, August 24, 2014 10:39:58 AM UTC-7, Howard Hinnant wrote: >>> I agree there is a choice for std::uhash<> when >>> converting a, say, "int" to a sequence of "unsigned char"s whether to >>> perform endian conversion or not, and that influences the cross-platfor= m >>> reproducibility of the hash when e.g. hashing a sequence of "int" >>> values. >=20 > Sadly, C++ still supports non-two's-complement architectures, so what hap= pens when you hash a negative int? I presume the int's bytes would be hashed just like any other scalar. >=20 >> This is the only role of the endian specifier, which can be any one of: >>=20 >> static constexpr std::endian endian =3D std::endian::big; >> static constexpr std::endian endian =3D std::endian::little; >> static constexpr std::endian endian =3D std::endian::native; >>=20 >> std::endian::native will be equal to one of std::endian::little or std::= endian::big. These enums are nothing more than the C++ version of the alre= ady popular macros: __BYTE_ORDER__, __ORDER_LITTLE_ENDIAN__, __ORDER_BIG_E= NDIAN__. >=20 > What about PDP-endian? I stand corrected. On PDP-endian std::endian::native has a value that is n= ot equal to either of std::endian::little or std::endian::big. If the Hash= Algorithm specifies little or big endian, the implementation is required to= map the bytes of the int (or whatever) to little or big endian prior to fe= eding it to the HashAlgorithm. For std::endian::big, this is the exact sam= e thing as inserting a call to hton() prior to the HashAlgorithm. > By the late 1990s, not only DEC but most of the New England computer indu= stry which had been built around minicomputers similar to the PDP-11 collap= sed in the face of microcomputer-based workstations and servers. >> A correct hash_append will be chosen (at compile time), which for scalar >> types that have endian issues, may or may not reverse the bytes of t >> depending on what the hash algorithm has requested, and what the >> platform's native endian is. >=20 > Does this mechanism support handling multiple scalars at once? On some s= ystems, byte swapping may be more efficient if does as vector math. An implementation could conceivably create a hash_append overload on arrays= of int and optimize that. >=20 >> See https://github.com/HowardHinnant/hash_append for complete code. >=20 > Its SHA-256 code is unsuitable for any platform for which "int" is larger= than 32 bits. It will have undefined behavior in those cases due to signe= d integer overflow or shifting left a negative number. Thanks, I'll put in a static_assert. Howard --=20 ---=20 You received this message because you are subscribed to the Google Groups "= ISO C++ Standard - Future Proposals" group. To unsubscribe from this group and stop receiving emails from it, send an e= mail to std-proposals+unsubscribe@isocpp.org. To post to this group, send email to std-proposals@isocpp.org. Visit this group at http://groups.google.com/a/isocpp.org/group/std-proposa= ls/. .