php mcrypt_encrypt 后 json_decode结果为null,该如何处理

php mcrypt_encrypt 后 json_decode结果为null

<br />$key = '1234567890123456';<br />    $iv = '1234567890123456';<br />    $os = array(<br />        'os' => php_uname('s'),<br />        'time' => time(),<br />        );<br />    $os = json_encode($os);<br />    $crypttext = base64_encode((mcrypt_encrypt(MCRYPT_RIJNDAEL_128, $key, $os, MCRYPT_MODE_CBC, $iv)));<br /><br />    $crypttext = base64_decode($crypttext);<br /><br />    $crypttext = (mcrypt_decrypt(MCRYPT_RIJNDAEL_128, $key, $crypttext, MCRYPT_MODE_CBC, $iv));<br />    $crypttext = json_decode($crypttext);<br />    var_dump($crypttext);<br />

求解
------解决思路----------------------

$key = '1234567890123456';<br />$iv = '1234567890123456';<br />$os = array(<br />  'os' => php_uname('s'),<br />  'time' => time(),<br />);<br />var_dump( $os = json_encode($os));<br />$crypttext = base64_encode((mcrypt_encrypt(MCRYPT_RIJNDAEL_128, $key, $os, MCRYPT_MODE_CBC, $iv)));<br /> <br />$crypttext = base64_decode($crypttext);<br /> <br />var_dump( $crypttext = (mcrypt_decrypt(MCRYPT_RIJNDAEL_128, $key, $crypttext, MCRYPT_MODE_CBC, $iv)));<br />echo bin2hex($crypttext), PHP_EOL;//尾部多了11个空字符<br />$crypttext = json_decode(trim($crypttext));//删掉就对了<br />var_dump($crypttext);

string(37) "{"os":"Windows NT","time":1428450826}"<br />string(48) "{"os":"Windows NT","time":1428450826}"<br />7b226f73223a2257696e646f7773204e54222c2274696d65223a313432383435303832367d0000000000000000000000<br />object(stdClass)#1 (2) {<br />  ["os"]=><br />  string(10) "Windows NT"<br />  ["time"]=><br />  int(1428450826)<br />}<br /><br />