我并不十分熟悉的东西，但它似乎是试图MCRYPT_RIJNDAEL_256替代MCRYPT_RIJNDAEL_128将是一个明显的下一个步骤…
您是对的，这不是您所需要的。MCRYPT_RIJNDAEL_128实际上是正确的选择。根据您提供的链接，密钥和IV的长度是应有的两倍：
// How do you do 256-bit AES encryption in PHP vs. 128-bit AES encryption???
// The answer is: Give it a key that's 32 bytes long as opposed to 16 bytes long.
// For example:
$key256 = '12345678901234561234567890123456';
$key128 = '1234567890123456';
// Here's our 128-bit IV which is used for both 256-bit and 128-bit keys.
$iv = '1234567890123456';
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