The criteria for doing so have now been met:
* PHP 8.1+ is now the documented minimum, and the 1.42 branch already
enforces this in PHPVersionCheck. (T359868)
* OpenSSL support is also now required. (e4127e5864)
As stated in AbstractPbkdf2Password::canUseOpenSSL(), the version check
is no longer needed because PHP 8.1 requires OpenSSL >= 1.0.2. While the
the master branch may still work on PHP 7.4 for now, it is unlikely that
a site using it would still have a version of OpenSSL older than 1.0.1f.
(For example, WMF stopped using Ubuntu 14.04 "Trusty", which has exactly
that minimum version of OpenSSL, once Canonical started charging for
security updates in 2019.)
The reasons for the version check were:
* Old versions of OpenSSL appeared to perform at least as well as PHP
for reasonably long passwords (up to 128 bytes for SHA-512 hashes);
however, they had the same DoS issue that our own implementation for
PHP 5.3 had (see T64685). hash_pbkdf2() never had that problem.
* If PHP were to incorporate the major optimization of hashing the HMAC
key blocks only once, then the old OpenSSL versions would actually be
slower. So far, this has not happened.
Change-Id: I47eb1aabf3d0ae4792624f9ba1c392880d52d0b7
This at least doubles the speed, which would allow the number of
iterations to be doubled and computation of the password hash to
complete in the same amount of time as before, or maybe even a
slight bit less.
The doubling in speed is due to an optimization[1] that so far has not
been accepted into PHP's hash extension.[2] In addition, OpenSSL has
optimized assembly-language hash function implementations for several
common CPU architectures. These provide a further, yet more slight,
performance improvement.
While OpenSSL's PKCS5_PBKDF2_HMAC() is not the fastest implementation
around, using it does not add a new library dependency. And although
better password hashing functions exist, PBKDF2 is still the default
in MediaWiki. For these reasons, I think this change makes sense.
[1]: https://github.com/openssl/openssl/commit/c10e3f0cffb3820d
[2]: https://github.com/php/php-src/issues/9604
Change-Id: I7b06590d4c42581f8749336f9c17777f973a506c
