PHP RFC: Easy User-land CSPRNG
- Version: 0.5
- Date: 2015-02-20
- Author: Sammy Kaye Powers me@sammyk.me & Leigh leigh@php.net
- Status: Implemented (in PHP 7.0)
- First Published at: http://wiki.php.net/rfc/easy_userland_csprng
Introduction
This RFC proposes adding a user-land API for an easy to use and reliable CSPRNG in PHP.
The Problem
By default PHP does not provide an easy mechanism for accessing cryptographically strong random numbers in user-land. Users have a few options like openssl_random_pseudo_bytes(), mcrypt_create_iv() or directly opening /dev/*random devices to obtain high quality pseudo-random bytes, but unfortunately system support for these functions and extensions varies between platforms and each come with their own set of problems
- The
mcrypt_create_iv()function has no dependency on MCrypt lib yet it requires the MCrypt extension to be installed before it can be used. Users are forced to include an entire library for no reason. openssl_random_pseudo_bytes()is provided by the OpenSSL lib. This function comes with a$crypto_strongthe meaning of which may just confuse users.- Falling back to
/dev/urandomis OS-specific.
In addition users may attempt to generate their own streams of random bytes relying on rand() or mt_rand(), and this is something we absolutely want to avoid.
Proposal
There should be a user-land API to easily return an arbitrary length of cryptographically secure pseudo-random bytes directly and work on any supported platform.
The initial proposal is to add two user-land functions that return the bytes as binary and integer. Arbitrary length strings of random bytes are important for salts, keys and initialisation vectors. Integers based on CS random are important for applications where unbiased results are critical (i.e. shuffling a Poker deck).
Signatures:
random_bytes(int length); random_int(int min, int max);
Examples:
$randomStr = random_bytes($length = 16); $randomInt = random_int($min = 0, $max = 127);
The sources of random used are as follows:
- On windows
CryptGenRandomis used exclusively arc4random_buf()is used if it is available (generally BSD specific)/dev/arandomis used where available/dev/urandomis used where none of the above is available- An error is thrown in the event that a sufficient source of randomness is unavailable.
Backward Incompatible Changes
Any user-land code that defines a random_bytes() or random_int() function would generate a fatal error, however it is likely that these functions provide the same or similar functionality as desired.
Proposed PHP Version(s)
PHP 7
RFC Impact
To SAPIs
This RFC should not impact the SAPI's.
To Existing Extensions
No existing extensions are affected.
To Opcache
Opcache is unaffected.
New Constants
There would be no new constants.
php.ini Defaults
There would be no new php.ini defaults.
Open Issues
- Nothing yet
Unaffected PHP Functionality
This change does not affect any of the existing rand() or mt_rand() functionality.
Future Scope
The concepts from the RFC could be used to:
- Deprecate
mcrypt_create_iv() - Improve
session_idrandomness generation - Detect LibreSSL-portable for arc4random() on Linux
Patches and Tests
The current patch can be found here: https://github.com/php/php-src/pull/1119
Proposed Voting Choices
The voting choices are yes (in favor for accepting this RFC for PHP 7) or no (against it).
Vote
Vote starts on March 14th, and will end two weeks later, on March 28th.
This RFC requires a 2/3 majority.
Changelog
- 0.5: Updated the function header for random_int() to reflect all args as required. - SammyK
- 0.4: Added BC info. Updated patch link to point to PR. - SammyK
- 0.2: Condensed the problem domain into something more focused. Added function sigs. - Leigh.
- 0.1: Mmmm drafty - Leigh
- 0.0: Initial draft - need Leigh's input - SammyK
Acknowledgements
Big thanks to Anthony Ferrara, Daniel Lowrey, E. Smith and all the kids in the PHP room for all the help with this one!