220 12599 <54035829.8060600@gmx.de> article Path: news.gmane.org!not-for-mail From: Markus Mayer Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Cryptographic hash functions reloaded [was Interest in cryptographic functions within the standard library] Date: Sun, 31 Aug 2014 19:15:21 +0200 Lines: 84 Approved: news@gmane.org Message-ID: <54035829.8060600@gmx.de> References: <53F8F620.3090701@gmx.de> <53F9AAF7.8030602@gmx.de> <53FA1DE1.9000603@gmx.de> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed X-Trace: ger.gmane.org 1409505333 21446 80.91.229.3 (31 Aug 2014 17:15:33 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Sun, 31 Aug 2014 17:15:33 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBDL3H4GM24GBBK5QRWQAKGQEW7R4RGQ@isocpp.org Sun Aug 31 19:15:26 2014 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-wi0-f198.google.com ([209.85.212.198]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1XO8ir-0007RA-6O for gclcip-std-proposals@m.gmane.org; Sun, 31 Aug 2014 19:15:25 +0200 Original-Received: by mail-wi0-f198.google.com with SMTP id ho1sf3018191wib.9 for ; Sun, 31 Aug 2014 10:15:24 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:message-id:date:from:user-agent:mime-version:to :subject:references:in-reply-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; bh=QRHJAfd5cC924kxU48VJG95WC+0IsVIbdQc0xCRFOCw=; b=UfdO/D0sAw1Qi2yOmh6LAmoQsFCiejyKe5sucq6GY5eRAEf3T4z/BOXjXb0imIvrdg ppCUWrSFtabzaOlgrxQ53nqHuJNnIJEQw2FgFgEucK2+sbMNuXS1/vlJ3vKl43tAdoRE CR106WYieTUBKYquqGCjbk73mi3aotDnY3s6B4tcnUfLMEwbnaZ0TQjep3r2JaLpvVTM P+YBR83ZGrb1NneH9TZMSo5LZTPLa5VMf21fxRg5dOleZFqG58TSfrdnMuYaw2MF/qo5 B6ItDomKmBS+ztkug43XNqwYuKpjmCjKL3sm2eSF49ECicEngmRvZyNayBw+W87pPnoY fZZg== X-Gm-Message-State: ALoCoQl96exc2vfM5RS3GfP0qBnHM+x9osoYqbYBDnBC2JdNNQ/5AHnRMnddc0ZSEM4MlZUoCaNv X-Received: by 10.194.79.34 with SMTP id g2mr218914wjx.3.1409505324619; Sun, 31 Aug 2014 10:15:24 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.152.115.231 with SMTP id jr7ls364199lab.102.gmail; Sun, 31 Aug 2014 10:15:22 -0700 (PDT) X-Received: by 10.112.157.132 with SMTP id wm4mr3027006lbb.89.1409505322948; Sun, 31 Aug 2014 10:15:22 -0700 (PDT) Original-Received: from mout.gmx.net (mout.gmx.net. [212.227.15.18]) by mx.google.com with ESMTPS id y10si8596630laj.52.2014.08.31.10.15.22 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Sun, 31 Aug 2014 10:15:22 -0700 (PDT) Received-SPF: pass (google.com: domain of lotharlutz@gmx.de designates 212.227.15.18 as permitted sender) client-ip=212.227.15.18; Original-Received: from [192.168.178.22] ([92.194.87.220]) by mail.gmx.com (mrgmx002) with ESMTPSA (Nemesis) id 0M4nYT-1YMPTz0jsL-00yves for ; Sun, 31 Aug 2014 19:15:22 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.7.0 In-Reply-To: <53FA1DE1.9000603@gmx.de> X-Provags-ID: V03:K0:hdyzc3Nq02a8keiFVBk3p78Q5dVQL2R4SIb4UQ+6K8ElbVKCykv 2pDD+I5KGrzXubNctLa6wSlbusFkym9Y+wMdSJAaBQlQsJmD54ttM+2Qup/VwKe0PnYhQu3 vBXq0meOp+NtokiOx+Ig1W5ZMJ78lbIs6BmohNACn8io7uOkSXVU6J9p9oqwlATVQuT9UTx kN7UDFh5Tzx0LOwkB0aKQ== X-UI-Out-Filterresults: notjunk:1; X-Original-Sender: lotharlutz@gmx.de X-Original-Authentication-Results: mx.google.com; spf=pass (google.com: domain of lotharlutz@gmx.de designates 212.227.15.18 as permitted sender) smtp.mail=lotharlutz@gmx.de 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:12599 Archived-At: Thanks for your valuable feedback. If checked the proposal for its feasibility for different byte-orders and for odd-sized architectures. Here are my findings and fixes: - The result type is a array of std::uint_least8_t. Each cell contains a value between 0 and 255 (including 0 and 255). This can be represented by every architecture. Byte-order is no problem because it is sequence of single bytes. - process_bytes take an address and a count. It hashes 'count' bytes (which have CHAR_BITS bits) starting a the given address in the order they are represented in memory. Every bit of this range contributes to the result. No byte-order conversion is performed. It is not the job of the hash function. It must be handled by an upper layer. With the current proposal your are unable to hash a range that is not a multiple of a byte. It is possible to add a process_bits(unsigned char byte, std::size_t bit_count), but I thinks it is not that useful. We can add it once we have experience how it is actually used. Regarding the 'const void* buffer vs. const unsinged char* buffer': I think 'const unsigned char*' is clearer, because it requires an explicit cast. This is like a warning sign "Warning: you have to care about byte-order, padding and other stuff by yourself!". The 'const void*' solution is more convenient when you want to hash a struct or a single variable. I came to the conclusion that it depends on how common the 'interprete this as a byte range' case is. I tried to come up with some actual numbers, but my google fun isn't strong enough. For my usage in 80% I do not have a unsigned char*. But what about your experience? Other changes: - Add a constexpr block_size. It specifies the smallest number of bytes (having CHAR_BITS bits), the buffer length have to be to achieve optimal performance. It is implementation defined, because it is a property of the specific implementation. Open questions: - process_bytes vs. operator(), or keep both - const void* buffer vs. const unsinged char* buffer class hash_function { public: typedef std::array result_type; static constexpr std::size_t block_size = IMPLEMENTATION_DEFINED; //Default contructable //Copyable //Moveable hash_function& process_bytes( const void *buffer, std::size_t byte_count); hash_function& operator() ( const void *buffer, std::size_t byte_count); void reset(); result_type hash_value() const; }; template process_blockwise(InputIt first, InputIt last, Hasher& hash_fn); //Maybe add process_blockwise_n regards Markus -- --- 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 email 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-proposals/. .