This article examines the challenges of using random number generation in cryptography, highlighting the differences between PHP 5 and PHP 7. PHP 5 lacks readily available mechanisms for generating cryptographically secure random numbers, while PHP 7 introduces random_bytes
and random_int
functions for this purpose.
Understanding CSPRNGs
A Cryptographically Secure Pseudorandom Number Generator (CSPRNG) is a PRNG designed for cryptographic applications. Its key characteristic is high-quality randomness, crucial for:
- Key generation
- Random password creation
- Encryption algorithms
CSPRNGs in PHP 7
PHP 7 provides random_bytes
(returning a string of specified byte length) and random_int
(returning a random integer within a given range) for CSPRNG functionality.
random_bytes
example:
$bytes = random_bytes(10); var_dump(bin2hex($bytes)); // Possible output: string(20) "7dfab0af960d359388e6"
random_int
example:
var_dump(random_int(1, 100)); // Possible output: 27
These functions utilize various sources of randomness depending on the operating system, prioritizing secure options like CryptGenRandom
(Windows), arc4random_buf
(BSD), getrandom(2)
(Linux), and finally /dev/urandom
as a fallback. An error is thrown if no suitable source is found.
Testing Randomness
Evaluating the quality of a random number generator involves statistical tests. A simple example is simulating dice rolls. The expected distribution of outcomes for rolling three dice 1,000,000 times can be compared to the actual results generated by random_int
and the standard rand
function.
A code example (simplified for brevity) and a comparative graph (shown below) demonstrate that random_int
exhibits a distribution closer to the expected values, indicating superior randomness compared to rand
.
PHP 5 Alternatives
PHP 5 lacks built-in CSPRNGs. Workarounds include openssl_random_pseudo_bytes()
, mcrypt_create_iv()
, or direct access to /dev/random
or /dev/urandom
. Libraries like RandomLib or libsodium offer additional solutions.
The random_compat
Library
For PHP 5 compatibility, the Paragon Initiative Enterprises random_compat
library provides random_bytes
and random_int
functionality. It can be installed via Composer (composer require paragonie/random_compat
) and used as follows:
$bytes = random_bytes(10); var_dump(bin2hex($bytes)); // Possible output: string(20) "7dfab0af960d359388e6"
This library prioritizes different randomness sources compared to PHP 7, starting with /dev/urandom
.
A simple password generation example using random_compat
:
var_dump(random_int(1, 100)); // Possible output: 27
Conclusion
Using a CSPRNG is crucial for secure applications. The random_compat
library offers a backward-compatible solution for PHP 5, while PHP 7 developers should directly utilize random_bytes
and random_int
. Prioritizing reliable random number generation significantly enhances application security.
Further Reading
Description | Link |
---|---|
Die Hard Test | http://miracleart.cn/link/1852a2083dbe1c2ec33ab9366feb2862 |
Chi-square test with dice example | http://miracleart.cn/link/fb6a253729096c1e92e43c26a6fdadc3 |
Kolmogorov-Smirnov Test | http://miracleart.cn/link/030d13e49bb7d1add5ac5ea2e4a43231 |
Spectral Test | http://miracleart.cn/link/6bbd80b04535d39be5e02dbfd8730469 |
RaBiGeTe test suite | http://miracleart.cn/link/e626afbcdb83368b3491c0c473da19f1 |
Random Number Generation In PHP (2011) | http://miracleart.cn/link/f7ff233e4ed3e6b13c5d5c7a9201e4ec |
Testing RNG part 1 and 2 | http://miracleart.cn/link/a1c71b134d46d7f7ff00f488874a8d43, http://miracleart.cn/link/2e3517ba49c2a7c999b9c8381185ae4e |
Acknowledgements
Thanks to Scott Arciszewski for their peer review assistance.
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