<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=""><div class="">Ok, so you’re looking for how would you replicate the blocking behavior of os.urandom that exists in 3.5.0 and 3.5.1?</div><div class=""><br class=""></div><div class="">In that case, it’s hard. I don’t think linux provides any way to externally determine if /dev/urandom has been initialized or not. Probably the easiest thing to do would be to interface with the getrandom() function using a c-ext, CFFI, or ctypes. If you’re looking for a way of doing this without calling the getrandom() function.. I believe the answer is you can’t.</div><div class=""><br class=""></div><div class="">The closest thing you can get is checking the /proc/sys/kernel/random/entropy_avail file, but that tells you how much entropy the system currently thinks it has (which will go up and down over time) and corresponds to /dev/random on Linux not /dev/urandom.</div><div class=""><br class=""></div><div class="">You could read from /dev/random, but that’s going to randomly block outside of the pool initialization whenever the kernel things it doesn’t have enough entropy. Cryptographers and security experts alike consider this to be pretty stupid behavior and don’t recommend using it because of this “randomly block throughout the use of your application” behavior.</div><div class=""><br class=""></div><div class="">So really, out of the recommended solutions you really only have find a way to interface with the getrandom() function, or just consume /dev/urandom and hope it’s been initialized.</div><div class=""><br class=""></div><br class=""><div><blockquote type="cite" class=""><div class="">On Jun 10, 2016, at 2:43 PM, David Mertz <<a href="mailto:mertz@gnosis.cx" class="">mertz@gnosis.cx</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><div dir="ltr" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class="">My hypothetical is "Ensure good random bits (on Python 3.5.2 and Linux), and block rather than allow bad bits."<div class=""><br class=""></div><div class="">I'm not quite sure I understand all of your question, Donald. On Python 3.4—and by BDFL declaration on 3.5.2—os.urandom() *will not* block, although it might on 3.5.1.</div></div><div class="gmail_extra" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;"><br class=""><div class="gmail_quote">On Fri, Jun 10, 2016 at 11:33 AM, Donald Stufft<span class="Apple-converted-space"> </span><span dir="ltr" class=""><<a href="mailto:donald@stufft.io" target="_blank" class="">donald@stufft.io</a>></span><span class="Apple-converted-space"> </span>wrote:<br class=""><blockquote class="gmail_quote" style="margin: 0px 0px 0px 0.8ex; border-left-width: 1px; border-left-color: rgb(204, 204, 204); border-left-style: solid; padding-left: 1ex;"><div style="word-wrap: break-word;" class=""><span class=""><br class=""><div class=""><blockquote type="cite" class=""><div class="">On Jun 10, 2016, at 2:29 PM, David Mertz <<a href="mailto:mertz@gnosis.cx" target="_blank" class="">mertz@gnosis.cx</a>> wrote:</div><br class=""><div class=""><span style="font-family: Helvetica; font-size: 12px; font-style: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; float: none; display: inline !important;" class="">If I *were* someone who needed to write a Linux system initialization script using Python 3.5.2, what would the code look like. I think for this use case, requiring something with a little bit of "code smell" is fine, but I kinda hope it exists at all.</span></div></blockquote></div><div class=""><br class=""></div></span>Do you mean if os.urandom blocked and you wanted to call os.urandom from your boot script? Or if os.urandom doesn’t block and you wanted to ensure you got good random numbers on boot?<br class=""><div class=""><div style="font-family: Helvetica; font-style: normal; font-weight: normal; letter-spacing: normal; line-height: normal; text-align: -webkit-auto; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; word-wrap: break-word;" class=""><br class="">—<span class="HOEnZb"><font color="#888888" class=""><br class="">Donald Stufft<br class=""></font></span></div><div style="font-family: Helvetica; font-style: normal; font-weight: normal; letter-spacing: normal; line-height: normal; text-align: -webkit-auto; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; word-wrap: break-word;" class=""><br class=""></div><br class=""></div><br class=""></div></blockquote></div><br class=""><br clear="all" class=""><div class=""><br class=""></div>--<span class="Apple-converted-space"> </span><br class=""><div class="gmail_signature" data-smartmail="gmail_signature">Keeping medicines from the bloodstreams of the sick; food<span class="Apple-converted-space"> </span><br class="">from the bellies of the hungry; books from the hands of the<span class="Apple-converted-space"> </span><br class="">uneducated; technology from the underdeveloped; and putting<span class="Apple-converted-space"> </span><br class="">advocates of freedom in prisons. Intellectual property is<br class="">to the 21st century what the slave trade was to the 16th.</div></div></div></blockquote></div><br class=""><div class="">
<div style="color: rgb(0, 0, 0); font-family: Helvetica; font-style: normal; font-variant-ligatures: normal; font-variant-position: normal; font-variant-caps: normal; font-variant-numeric: normal; font-variant-alternates: normal; font-variant-east-asian: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-align: -webkit-auto; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><br class="">—<br class="">Donald Stufft<br class=""></div><div style="color: rgb(0, 0, 0); font-family: Helvetica; font-style: normal; font-variant-ligatures: normal; font-variant-position: normal; font-variant-caps: normal; font-variant-numeric: normal; font-variant-alternates: normal; font-variant-east-asian: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-align: -webkit-auto; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><br class=""></div><br class="Apple-interchange-newline">
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