Add os.urandom_info

[vstinner]

BPO	27249
Nosy	@vstinner, @tiran, @alex
Superseder	bpo-27266: Always use getrandom() in os.random() on Linux and add block=False parameter to os.urandom()

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = <Date 2016-06-08.22:33:02.413>
created_at = <Date 2016-06-07.12:06:14.678>
labels = []
title = 'Add os.urandom_info'
updated_at = <Date 2016-06-08.22:33:02.411>
user = 'https://github.com/vstinner'

bugs.python.org fields:

activity = <Date 2016-06-08.22:33:02.411>
actor = 'vstinner'
assignee = 'none'
closed = True
closed_date = <Date 2016-06-08.22:33:02.413>
closer = 'vstinner'
components = []
creation = <Date 2016-06-07.12:06:14.678>
creator = 'vstinner'
dependencies = []
files = []
hgrepos = []
issue_num = 27249
keywords = []
message_count = 3.0
messages = ['267641', '267659', '267918']
nosy_count = 3.0
nosy_names = ['vstinner', 'christian.heimes', 'alex']
pr_nums = []
priority = 'normal'
resolution = 'postponed'
stage = None
status = 'closed'
superseder = '27266'
type = None
url = 'https://bugs.python.org/issue27249'
versions = ['Python 3.6']

[vstinner]

It seems like in some cases, you do need to know how os.urandom() generates random numbers. On Linux, using getrandom() to read /dev/urandom in blocking mode or reading from /dev/urandom give a different level of security if the urandom entropy pool is not feeded with enough entropy yet. See the issue bpo-26839 for the background.

[tiran]

+1

How are you planning to handle initialization? Run getentropy() and check if the syscall succeeds?

[vstinner]

The current trend in the random discussion (see https://haypo-notes.readthedocs.io/pep_random.html and the issue bpo-26839) is more to use weak entropy to start Python (hash seed and random constructor) and os.urandom() blocks until the kernel collected enough entropy. In this case, such information is no more needed. So I close this issue, superseded by the issue bpo-27266.