PHP 8.1: Phar: Added OpenSSL-256 and OpenSSL-512 signature algorithms
Phar extension in PHP can be used to package and run a PHP application using a single archive, called a Phar file. These Phar files can contain a signature to ensure it is not corrupted or incomplete.
Note that the integrity checks provided for Phar may not be suitable to avoid supply-chain attacks. While it can detect damaged or incomplete Phar files, it is trivial to modify a Phar archive and remove its integrity checks, rendering these checks fall short.
Phar::setSignatureAlgorithm sets the signature algorithm used in a Phar archive. Unless this value is set, PHP picks SHA256 (SHA1 prior to PHP 8.1) as the signature algorithm.
Phar also supports generating the signature using OpenSSL to generate the signature using a private key, validated with the file key. OpenSSL signatures require the OpenSSL extension enabled.
openssl genrsa -out private.pem 4096 openssl rsa -in private.pem -pubout -out public.pem
$pharFile = 'hello.phar'; $phar = new Phar($pharFile); $phar->buildFromDirectory('src/'); $phar->setDefaultStub('index.php', '/index.php'); $private_key = file_get_contents("private.pem"); $phar->setSignatureAlgorithm(Phar::OPENSSL, $private_key);
When the Phar file (
hello.phar from the example above) is executed, PHP refuses to run the Phar archive unless the public key is present at a file name with suffix
.pubkey in the same directory (
hello.phar.pubkey from the example).
In PHP 8.1, two new algorithms are introduced:
OpenSSL 256 and
OpenSSL 512. These two algorithms also require the OpenSSL extension enabled.
17, sets the signature algorithm to OpenSSL private key signing using SHA512.
18, sets the signature algorithm to OpenSSL private key signing using SHA256.
- $phar->setSignatureAlgorithm(Phar::OPENSSL, $private_key); + $phar->setSignatureAlgorithm(Phar::OPENSSL_SHA256, $private_key);
Backwards Compatibility Impact
Note that the new signature algorithms are not backwards compatible. Any Phar archive created using
OPENSSL_SHA512 will fail to run in PHP versions prior to PHP 8.1. All
OPENSSL signatures also require the OpenSSL extension enabled.
Attempting to use a Phar archive with an
OPENSSL_SHA512 signature fails with an
UnexpectedValueException exception (when loading use
Phar class) or a
PharException (on direct execution):
phar "hello.phar" has a broken or unsupported signature in hello.phar:8