[Python-checkins] peps: Add default entropy.
steven.daprano
python-checkins at python.org
Tue Oct 6 08:11:23 EDT 2015
https://hg.python.org/peps/rev/850897ef2790
changeset: 6107:850897ef2790
user: Steven D'Aprano <steve+python at pearwood.info>
date: Mon Oct 05 03:11:17 2015 +1100
summary:
Add default entropy.
files:
pep-0506.txt | 96 ++++++++++++++++++++-------------------
1 files changed, 50 insertions(+), 46 deletions(-)
diff --git a/pep-0506.txt b/pep-0506.txt
--- a/pep-0506.txt
+++ b/pep-0506.txt
@@ -159,14 +159,19 @@
def randbelow(exclusive_upper_bound):
return _sysrand._randbelow(exclusive_upper_bound)
- def token_bytes(nbytes=32):
+ DEFAULT_ENTROPY = 32 # bytes
+
+ def token_bytes(nbytes=None):
+ if nbytes is None:
+ nbytes = DEFAULT_ENTROPY
return os.urandom(nbytes)
- def token_hex(nbytes=32):
+ def token_hex(nbytes=None):
return binascii.hexlify(token_bytes(nbytes)).decode('ascii')
- def token_url(nbytes=32):
- return base64.urlsafe_b64encode(token_bytes(nbytes)).decode('ascii')
+ def token_url(nbytes=None):
+ tok = token_bytes(nbytes)
+ return base64.urlsafe_b64encode(tok).rstrip(b'=').decode('ascii')
The ``secrets`` module itself will be pure Python, and other Python
@@ -176,18 +181,17 @@
Default arguments
~~~~~~~~~~~~~~~~~
-One difficult question is "How many bytes should my token be?" We can help
-with this question by giving the "token_*" functions a sensible default for
-the ``nbytes`` argument. This default value should be large enough to be
-expected to be secure for medium-security uses [xxx]_.
-
-It is expected that future versions will need to increase those default
-values, possibly even during
+One difficult question is "How many bytes should my token be?". We can
+help with this question by providing a default amount of entropy for the
+"token_*" functions. If the ``nbytes`` argument is None or not given, the
+default entropy will be used. This default value should be large enough
+to be expected to be secure for medium-security uses, but is expected to
+change in the future, possibly even in a maintenance release [13]_.
Naming conventions
~~~~~~~~~~~~~~~~~~
-One question is the naming conventions used in the module [13]_, whether to
+One question is the naming conventions used in the module [14]_, whether to
use C-like naming conventions such as "randrange" or more Pythonic names
such as "random_range".
@@ -200,7 +204,7 @@
============
One alternative is to change the default PRNG provided by the ``random``
-module [14]_. This received considerable scepticism and outright opposition:
+module [15]_. This received considerable scepticism and outright opposition:
* There is fear that a CSPRNG may be slower than the current PRNG (which
in the case of MT is already quite slow).
@@ -219,12 +223,12 @@
* Demonstrated attacks against MT are typically against PHP applications.
It is believed that PHP's version of MT is a significantly softer target
- than Python's version, due to a poor seeding technique [15]_. Consequently,
+ than Python's version, due to a poor seeding technique [16]_. Consequently,
without a proven attack against Python applications, many people object
to a backwards-incompatible change.
Nick Coghlan made an earlier suggestion for a globally configurable PRNG
-which uses the system CSPRNG by default [16]_, but has since withdrawn it
+which uses the system CSPRNG by default [17]_, but has since withdrawn it
in favour of this proposal.
@@ -233,7 +237,7 @@
* PHP
- PHP includes a function ``uniqid`` [17]_ which by default returns a
+ PHP includes a function ``uniqid`` [18]_ which by default returns a
thirteen character string based on the current time in microseconds.
Translated into Python syntax, it has the following signature::
@@ -244,7 +248,7 @@
applications use it for that purpose (citation needed).
PHP 5.3 and better also includes a function ``openssl_random_pseudo_bytes``
- [18]_. Translated into Python syntax, it has roughly the following
+ [19]_. Translated into Python syntax, it has roughly the following
signature::
def openssl_random_pseudo_bytes(length:int)->Tuple[str, bool]
@@ -256,16 +260,16 @@
* Javascript
- Based on a rather cursory search [19]_, there do not appear to be any
+ Based on a rather cursory search [20]_, there do not appear to be any
well-known standard functions for producing strong random values in
Javascript, although there may be good quality third-party libraries.
Standard Javascript doesn't seem to include an interface to the
system CSPRNG either, and people have extensively written about the
- weaknesses of Javascript's ``Math.random`` [20]_.
+ weaknesses of Javascript's ``Math.random`` [21]_.
* Ruby
- The Ruby standard library includes a module ``SecureRandom`` [21]_
+ The Ruby standard library includes a module ``SecureRandom`` [22]_
which includes the following methods:
* base64 - returns a Base64 encoded random string.
@@ -287,13 +291,13 @@
There was a proposal to add a "random.safe" submodule, quoting the Zen
of Python "Namespaces are one honking great idea" koan. However, the
-author of the Zen, Tim Peters, has come out against this idea [22]_, and
+author of the Zen, Tim Peters, has come out against this idea [23]_, and
recommends a top-level module.
In discussion on the python-ideas mailing list so far, the name "secrets"
has received some approval, and no strong opposition.
-There is already an existing third-party module with the same name [23]_,
+There is already an existing third-party module with the same name [24]_,
but it appears to be unused and abandoned.
@@ -305,9 +309,9 @@
A: The consensus among security professionals is that MT is not safe
in security contexts. It is not difficult to reconstruct the internal
- state of MT [24]_ [25]_ and so predict all past and future values. There
+ state of MT [25]_ [26]_ and so predict all past and future values. There
are a number of known, practical attacks on systems using MT for
- randomness [26]_.
+ randomness [27]_.
While there are currently no known direct attacks on applications
written in Python due to the use of MT, there is widespread agreement
@@ -318,7 +322,7 @@
A: No. This is a "batteries included" solution, not a full-featured
"nuclear reactor". It is intended to mitigate against some basic
security errors, not be a solution to all security-related issues. To
- quote Nick Coghlan referring to his earlier proposal [27]_::
+ quote Nick Coghlan referring to his earlier proposal [28]_::
"...folks really are better off learning to use things like
cryptography.io for security sensitive software, so this change
@@ -329,10 +333,10 @@
* Q: What about a password generator?
A: The consensus is that the requirements for password generators are too
- variable for it to be a good match for the standard library [28]_. No
+ variable for it to be a good match for the standard library [29]_. No
password generator will be included in the initial release of the
module, instead it will be given in the documentation as a recipe (à la
- the recipes in the ``itertools`` module) [29]_.
+ the recipes in the ``itertools`` module) [30]_.
References
@@ -367,46 +371,46 @@
.. [12] https://github.com/pyca/cryptography/issues/2347
-.. [xx] See discussion thread starting with
- https://mail.python.org/pipermail/python-ideas/2015-September/036509.html
+.. [13] https://mail.python.org/pipermail/python-ideas/2015-September/036517.html
+ https://mail.python.org/pipermail/python-ideas/2015-September/036515.html
-.. [13] https://mail.python.org/pipermail/python-ideas/2015-September/036474.html
+.. [14] https://mail.python.org/pipermail/python-ideas/2015-September/036474.html
-.. [14] Link needed.
+.. [15] Link needed.
-.. [15] By default PHP seeds the MT PRNG with the time (citation needed),
+.. [16] By default PHP seeds the MT PRNG with the time (citation needed),
which is exploitable by attackers, while Python seeds the PRNG with
output from the system CSPRNG, which is believed to be much harder to
exploit.
-.. [16] http://legacy.python.org/dev/peps/pep-0504/
+.. [17] http://legacy.python.org/dev/peps/pep-0504/
-.. [17] http://php.net/manual/en/function.uniqid.php
+.. [18] http://php.net/manual/en/function.uniqid.php
-.. [18] http://php.net/manual/en/function.openssl-random-pseudo-bytes.php
+.. [19] http://php.net/manual/en/function.openssl-random-pseudo-bytes.php
-.. [19] Volunteers and patches are welcome.
+.. [20] Volunteers and patches are welcome.
-.. [20] http://ifsec.blogspot.fr/2012/05/cross-domain-mathrandom-prediction.html
+.. [21] http://ifsec.blogspot.fr/2012/05/cross-domain-mathrandom-prediction.html
-.. [21] http://ruby-doc.org/stdlib-2.1.2/libdoc/securerandom/rdoc/SecureRandom.html
+.. [22] http://ruby-doc.org/stdlib-2.1.2/libdoc/securerandom/rdoc/SecureRandom.html
-.. [22] https://mail.python.org/pipermail/python-ideas/2015-September/036254.html
+.. [23] https://mail.python.org/pipermail/python-ideas/2015-September/036254.html
-.. [23] https://pypi.python.org/pypi/secrets
+.. [24] https://pypi.python.org/pypi/secrets
-.. [24] https://jazzy.id.au/2010/09/22/cracking_random_number_generators_part_3.html
+.. [25] https://jazzy.id.au/2010/09/22/cracking_random_number_generators_part_3.html
-.. [25] https://mail.python.org/pipermail/python-ideas/2015-September/036077.html
+.. [26] https://mail.python.org/pipermail/python-ideas/2015-September/036077.html
-.. [26] https://media.blackhat.com/bh-us-12/Briefings/Argyros/BH_US_12_Argyros_PRNG_WP.pdf
+.. [27] https://media.blackhat.com/bh-us-12/Briefings/Argyros/BH_US_12_Argyros_PRNG_WP.pdf
-.. [27] https://mail.python.org/pipermail/python-ideas/2015-September/036157.html
+.. [28] https://mail.python.org/pipermail/python-ideas/2015-September/036157.html
-.. [28] https://mail.python.org/pipermail/python-ideas/2015-September/036476.html
+.. [29] https://mail.python.org/pipermail/python-ideas/2015-September/036476.html
https://mail.python.org/pipermail/python-ideas/2015-September/036478.html
-.. [29] https://mail.python.org/pipermail/python-ideas/2015-September/036488.html
+.. [30] https://mail.python.org/pipermail/python-ideas/2015-September/036488.html
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