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Fix: null string error in hkdf encryption #1956

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Fix: null string error in hkdf encryption #1956

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5 changes: 4 additions & 1 deletion system/libraries/Encryption.php
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Original file line number Diff line number Diff line change
Expand Up @@ -863,7 +863,10 @@ public function hkdf($key, $digest = 'sha512', $salt = NULL, $length = NULL, $in
return FALSE;
}

self::strlen($salt) OR $salt = str_repeat("\0", $this->_digests[$digest]);
// PHP 8.1+ deprecates passing NULL to strlen() - $salt defaults to NULL (see docblock: "Optional
// salt"), and both encrypt() and decrypt() call hkdf() with an explicit NULL salt for their HMAC key
// derivation, so this is hit on every encrypt/decrypt call, not just an edge case.
self::strlen($salt ?? '') OR $salt = str_repeat("\0", $this->_digests[$digest]);

$prk = hash_hmac($digest, $key, $salt, TRUE);
$key = '';
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