PHP Openssl descriptografa uma criptografia AES Mysql

openssl_encrypt() e openssl_decrypt() silencioso corta a chave para um comprimento máximo de 16 bytes (pelo menos para aes-128-ecb)

<?php
    $key1 = hex2bin(openssl_digest('mysecretphrase', 'sha512'));
    $key2 = substr($key1, 0, 16);
    $key3 = substr($key1, 0, 15);
    $method = 'aes-128-ecb';
    $in = 'testvalue';
    $data1 = base64_decode(openssl_encrypt($in, $method, $key1));
    $data2 = base64_decode(openssl_encrypt($in, $method, $key2));
    $data3 = base64_decode(openssl_encrypt($in, $method, $key3));
    var_dump(
        array(
            'key1'=>bin2hex($key1),
            'key2'=>bin2hex($key2),
            'key3'=>bin2hex($key3),
            'data1'=>bin2hex($data1),
            'data2'=>bin2hex($data2),
            'data3'=>bin2hex($data3),
            'data1==data2'=>($data1===$data2),
            'data1==data3'=>($data1===$data3)
        )
    );
?>

resultado:

   array(8) {
        ["key1"]=>string(128) "5fe76dfd5b75cf7cf68fae85d26fcc9b7951806ad6daaa71d843c6ec0e0ec9233a828ad9b60986a43d734983c8a0a50d3a0a49ec5ac196cfcc136aa16e0c5f89"
        ["key2"]=>string(32) "5fe76dfd5b75cf7cf68fae85d26fcc9b"
        ["key3"]=>string(30) "5fe76dfd5b75cf7cf68fae85d26fcc"
        ["data1"]=>string(32) "eb69e89312c1f7b9522d0e66346f2029"
        ["data2"]=>string(32) "eb69e89312c1f7b9522d0e66346f2029"
        ["data3"]=>string(32) "664f5a28d241f959beac350f2314b079"
        ["data1==data2"]=>bool(true)
        ["data1==data3"]=>bool(false)
    }

No mysql a chave de tamanho completo é usada por AES_ENCRYPT() e AES_DECRYPT()

SELECT 
    HEX(AES_ENCRYPT('testvalue',UNHEX(SHA2('mysecretphrase',512)))) AS l_full,
    HEX(AES_ENCRYPT('testvalue',SUBSTR(UNHEX(SHA2('mysecretphrase',512)),1,16))) AS l_16,
    HEX(AES_ENCRYPT('testvalue',SUBSTR(UNHEX(SHA2('mysecretphrase',512)),1,15))) AS l_15;

resultado:

l_full                           | l_16                             | l_15
---------------------------------|----------------------------------|----------------------------------------
A88DD1EFB377FD31A0EFA55EA29BA8C6 | EB69E89312C1F7B9522D0E66346F2029 | 664F5A28D241F959BEAC350F2314B079