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PEP 506: Improve markup

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Berker Peksag 2015-09-20 03:21:55 +03:00
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@ -47,11 +47,11 @@ Rationale
This proposal is motivated by concerns that Python's standard library
makes it too easy for developers to inadvertently make serious security
errors. Theo de Raadt, the founder of OpenBSD, contacted Guido van Rossum
and expressed some concern[1] about the use of MT for generating sensitive
and expressed some concern [1]_ about the use of MT for generating sensitive
information such as passwords, secure tokens, session keys and similar.
Although the documentation for the random module explicitly states that
the default is not suitable for security purposes[2], it is strongly
the default is not suitable for security purposes [2]_, it is strongly
believed that this warning may be missed, ignored or misunderstood by
many Python developers. In particular:
@ -65,21 +65,21 @@ many Python developers. In particular:
(or learned techniques) from websites which don't offer best
practises.
The first[3] hit when searching for "python how to generate passwords" on
The first [3]_ hit when searching for "python how to generate passwords" on
Google is a tutorial that uses the default functions from the ``random``
module[4]. Although it is not intended for use in web applications, it is
module [4]_. Although it is not intended for use in web applications, it is
likely that similar techniques find themselves used in that situation.
The second hit is to a StackOverflow question about generating
passwords[5]. Most of the answers given, including the accepted one, use
passwords [5]_. Most of the answers given, including the accepted one, use
the default functions. When one user warned that the default could be
easily compromised, they were told "I think you worry too much."[6]
easily compromised, they were told "I think you worry too much." [6]_
This strongly suggests that the existing ``random`` module is an attractive
nuisance when it comes to generating (for example) passwords or secure
tokens.
Additional motivation (of a more philosophical bent) can be found in the
post which first proposed this idea[7].
post which first proposed this idea [7]_.
Proposal
@ -98,7 +98,7 @@ security. (See Alternatives below.) This proposes a different approach:
the most common needs, such as generating secure tokens. This code
will both directly satisfy a need ("How do I generate a password reset
token?"), and act as an example of acceptable practises which
developers can learn from[8].
developers can learn from [8]_.
To do this, this PEP proposes that we add a new module to the standard
library, with the suggested name ``secrets``. This module will contain a
@ -115,7 +115,7 @@ API and Implementation
The contents of the ``secrets`` module is expected to evolve over time, and
likely will evolve between the time of writing this PEP and actual release
in the standard library[9]. At the time of writing, the following functions
in the standard library [9]_. At the time of writing, the following functions
have been suggested:
* A high-level function for generating secure tokens suitable for use
@ -140,9 +140,9 @@ The consensus appears to be that there is no need to add a new CSPRNG to
the ``random`` module to support these uses, ``SystemRandom`` will be
sufficient.
Some illustrative implementations have been given by Nick Coghlan[10].
Some illustrative implementations have been given by Nick Coghlan [10]_.
This idea has also been discussed on the issue tracker for the
"cryptography" module[11].
"cryptography" module [11]_.
The ``secrets`` module itself will be pure Python, and other Python
implementations can easily make use of it unchanged, or adapt it as
@ -153,7 +153,7 @@ Alternatives
============
One alternative is to change the default PRNG provided by the ``random``
module[12]. This received considerable scepticism and outright opposition:
module [12]_. 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).
@ -172,13 +172,13 @@ module[12]. This received considerable scepticism and outright opposition:
* 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[13]. Consequently,
than Python's version, due to a poor seeding technique [13]_. 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[14], but has since hinted that he
may withdraw it in favour of this proposal[15].
which uses the system CSPRNG by default [14]_, but has since hinted that he
may withdraw it in favour of this proposal [15]_.
Comparison To Other Languages
@ -186,7 +186,7 @@ Comparison To Other Languages
* PHP
PHP includes a function ``uniqid`` [16] which by default returns a
PHP includes a function ``uniqid`` [16]_ which by default returns a
thirteen character string based on the current time in microseconds.
Translated into Python syntax, it has the following signature::
@ -196,8 +196,9 @@ Comparison To Other Languages
security purposes. Nevertheless, various mature, well-known PHP
applications use it for that purpose (citation needed).
PHP 5.3 and better also includes a function ``openssl_random_pseudo_bytes`` [17].
Translated into Python syntax, it has roughly the following signature::
PHP 5.3 and better also includes a function ``openssl_random_pseudo_bytes``
[17]_. Translated into Python syntax, it has roughly the following
signature::
def openssl_random_pseudo_bytes(length:int)->Tuple[str, bool]
@ -208,16 +209,16 @@ Comparison To Other Languages
* Javascript
Based on a rather cursory search[18], there doesn't appear to be any
Based on a rather cursory search [18]_, there doesn't 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[19].
weaknesses of Javascript's ``Math.random`` [19]_.
* Ruby
The Ruby standard library includes a module ``SecureRandom`` [20]
The Ruby standard library includes a module ``SecureRandom`` [20]_
which includes the following methods:
* base64 - returns a Base64 encoded random string.
@ -239,7 +240,7 @@ What Should Be The Name Of The Module?
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[21], and
author of the Zen, Tim Peters, has come out against this idea [21]_, and
recommends a top-level module.
In discussion on the python-ideas mailing list so far, the name "secrets"
@ -249,85 +250,93 @@ has received some approval, and no strong opposition.
Frequently Asked Questions
==========================
* Q: Is this a real problem? Surely MT is random enough that nobody can
predict its output.
* Q: Is this a real problem? Surely MT is random enough that nobody can
predict its output.
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[22][23] and so predict all past and future values. There
are a number of known, practical attacks on systems using MT for
randomness[24].
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 [22]_ [23]_ and so predict all past and future values. There
are a number of known, practical attacks on systems using MT for
randomness [24]_.
While there are currently no known direct attacks on applications
written in Python due to the use of MT, there is widespread agreement
that such usage is unsafe.
While there are currently no known direct attacks on applications
written in Python due to the use of MT, there is widespread agreement
that such usage is unsafe.
* Q: Is this an alternative to specialise cryptographic software such as SSL?
* Q: Is this an alternative to specialise cryptographic software such as SSL?
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::
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 [25]_::
"...folks really are better off learning to use things like
cryptography.io for security sensitive software, so this change
is just about harm mitigation given that it's inevitable that a
non-trivial proportion of the millions of current and future
Python developers won't do that."[25]
"...folks really are better off learning to use things like
cryptography.io for security sensitive software, so this change
is just about harm mitigation given that it's inevitable that a
non-trivial proportion of the millions of current and future
Python developers won't do that."
References
==========
[1] https://mail.python.org/pipermail/python-ideas/2015-September/035820.html
.. [1] https://mail.python.org/pipermail/python-ideas/2015-September/035820.html
[2] https://docs.python.org/3/library/random.html
.. [2] https://docs.python.org/3/library/random.html
[3] As of the date of writing. Also, as Google search terms may be automatically customised for the user without their knowledge, some readers may see different results.
.. [3] As of the date of writing. Also, as Google search terms may be
automatically customised for the user without their knowledge, some
readers may see different results.
[4] http://interactivepython.org/runestone/static/everyday/2013/01/3_password.html
.. [4] http://interactivepython.org/runestone/static/everyday/2013/01/3_password.html
[5] http://stackoverflow.com/questions/3854692/generate-password-in-python
.. [5] http://stackoverflow.com/questions/3854692/generate-password-in-python
[6] http://stackoverflow.com/questions/3854692/generate-password-in-python/3854766#3854766
.. [6] http://stackoverflow.com/questions/3854692/generate-password-in-python/3854766#3854766
[7] https://mail.python.org/pipermail/python-ideas/2015-September/036238.html
.. [7] https://mail.python.org/pipermail/python-ideas/2015-September/036238.html
[8] At least those who are motivated to read the source code and documentation.
.. [8] At least those who are motivated to read the source code and documentation.
[9] Tim Peters suggests that bike-shedding the contents of the module will be 10000 times more time consuming than actually implementing the module. Words do not begin to express how much I am looking forward to this.
.. [9] Tim Peters suggests that bike-shedding the contents of the module will
be 10000 times more time consuming than actually implementing the
module. Words do not begin to express how much I am looking forward to
this.
[10] https://mail.python.org/pipermail/python-ideas/2015-September/036271.html
.. [10] https://mail.python.org/pipermail/python-ideas/2015-September/036271.html
[11] https://github.com/pyca/cryptography/issues/2347
.. [11] https://github.com/pyca/cryptography/issues/2347
[12] Link needed.
.. [12] Link needed.
[13] 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.
.. [13] 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.
[14] http://legacy.python.org/dev/peps/pep-0504/
.. [14] http://legacy.python.org/dev/peps/pep-0504/
[15] https://mail.python.org/pipermail/python-ideas/2015-September/036243.html
.. [15] https://mail.python.org/pipermail/python-ideas/2015-September/036243.html
[16] http://php.net/manual/en/function.uniqid.php
.. [16] http://php.net/manual/en/function.uniqid.php
[17] http://php.net/manual/en/function.openssl-random-pseudo-bytes.php
.. [17] http://php.net/manual/en/function.openssl-random-pseudo-bytes.php
[18] Volunteers and patches are welcome.
.. [18] Volunteers and patches are welcome.
[19] http://ifsec.blogspot.fr/2012/05/cross-domain-mathrandom-prediction.html
.. [19] http://ifsec.blogspot.fr/2012/05/cross-domain-mathrandom-prediction.html
[20] http://ruby-doc.org/stdlib-2.1.2/libdoc/securerandom/rdoc/SecureRandom.html
.. [20] http://ruby-doc.org/stdlib-2.1.2/libdoc/securerandom/rdoc/SecureRandom.html
[21] https://mail.python.org/pipermail/python-ideas/2015-September/036254.html
.. [21] https://mail.python.org/pipermail/python-ideas/2015-September/036254.html
[22] https://jazzy.id.au/2010/09/22/cracking_random_number_generators_part_3.html
.. [22] https://jazzy.id.au/2010/09/22/cracking_random_number_generators_part_3.html
[23] https://mail.python.org/pipermail/python-ideas/2015-September/036077.html
.. [23] https://mail.python.org/pipermail/python-ideas/2015-September/036077.html
[24] https://media.blackhat.com/bh-us-12/Briefings/Argyros/BH_US_12_Argyros_PRNG_WP.pdf
.. [24] https://media.blackhat.com/bh-us-12/Briefings/Argyros/BH_US_12_Argyros_PRNG_WP.pdf
[25] https://mail.python.org/pipermail/python-ideas/2015-September/036157.html
.. [25] https://mail.python.org/pipermail/python-ideas/2015-September/036157.html
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