<html><head><meta http-equiv="Content-Type" content="text/html charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><br class=""><div><blockquote type="cite" class=""><div class="">Le 9 sept. 2017 à 03:07, Xiaodi Wu via swift-evolution <<a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a>> a écrit :</div><br class="Apple-interchange-newline"><div class=""><div dir="ltr" class="">On Fri, Sep 8, 2017 at 7:50 PM, Stephen Canon <span dir="ltr" class=""><<a href="mailto:scanon@apple.com" target="_blank" class="">scanon@apple.com</a>></span> wrote:<br class=""><div class="gmail_extra"><div class="gmail_quote"><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div style="word-wrap:break-word;line-break:after-white-space" class=""><span class=""><blockquote type="cite" class="">On Sep 8, 2017, at 8:09 PM, Xiaodi Wu via swift-evolution <<a href="mailto:swift-evolution@swift.org" target="_blank" class="">swift-evolution@swift.org</a>> wrote:<br class=""></blockquote><div class=""><blockquote type="cite" class=""><div class=""><div style="font-family:Helvetica;font-size:12px;font-style:normal;font-variant-caps:normal;font-weight:normal;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px" class=""><br class="m_2105560249099070811Apple-interchange-newline">This topic has been broached on Swift Evolution previously. It's interesting to me that Steve Canon is so certain that CSPRNGs are the way to go. I wasn't aware that hardware CSPRNGs have come such a long way and are so ubiquitous as to be feasible as a basis for Swift random numbers. If so, great.</div><div style="font-family:Helvetica;font-size:12px;font-style:normal;font-variant-caps:normal;font-weight:normal;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px" class=""><br class=""></div><div style="font-family:Helvetica;font-size:12px;font-style:normal;font-variant-caps:normal;font-weight:normal;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px" class="">Otherwise, if there is any way that a software, non-cryptographically secure PRNG is going to outperform a CSPRNG, then I think it's worthwhile to have a (carefully documented) choice between the two. I would imagine that for many uses, such as an animation in which you need a plausible source of noise to render a flame, whether that is cryptographically secure or not is absolutely irrelevant but performance may be key.</div></div></blockquote><br class=""></div></span><div class="">Let me be precise: it is absolutely possible to outperform CSPRNGs. They have simply become fast enough that the performance gap doesn’t matter for most uses (let’s say amortized ten cycles per byte or less—whatever you are going to do with the random bitstream will be much more expensive than getting the bits was).</div><div class=""><br class=""></div><div class="">That said, yes, there should definitely be other options. It should be possible for users to get reproducible results from a stdlib random interface run-to-run, and also across platforms. That alone requires that at least one other option for a generator be present. There may also be a place for a very high-throughput generator like xorshiro128+.</div><div class=""><br class=""></div><div class="">All I’m really saying is that the *default* generator should be an os-provided unseeded CSPRNG, and we should be very careful about documenting any generator options.</div></div></blockquote><div class=""><br class=""></div><div class=""><br class=""></div><div class="">Agree on all points. Much like Swift's strings are Unicode-correct instead of the fastest possible way of slicing and dicing sequences of ASCII characters, Swift's default PRNG should be cryptographically secure.</div></div></div></div></div></blockquote><div><br class=""></div></div><div>I agree too. Anyone that need a random generator but don’t know how it works and what’s a CSPRNG is need a CSPRNG.</div><div><br class=""></div><div>For other users, we still need a couple of other implementations.</div><div><br class=""></div><div><br class=""></div><br class=""></body></html>