Chrome自动填充的PHP mcrypt错误

I have a problem with my mcrypt code:

<?php
class Encryption {

    public function encrypt($value){
        $key = 'dfMsnopnM:kNas;ljn46tgskjdnkdnfn';
        if (!$value) {
            return false;
        }
        $iv = mcrypt_create_iv(mcrypt_get_iv_size(MCRYPT_RIJNDAEL_256, MCRYPT_MODE_ECB), MCRYPT_RAND);
        $encrypted_string = trim(base64_encode(mcrypt_encrypt(MCRYPT_RIJNDAEL_256, $key, $value, MCRYPT_MODE_ECB, mcrypt_create_iv(mcrypt_get_iv_size(MCRYPT_RIJNDAEL_256, MCRYPT_MODE_ECB), MCRYPT_RAND))));
        return $encrypted_string;
    }

    public function decrypt($value){
        $key = 'dfMsnopnM:kNas;ljn46tgskjdnkdnfn';
        if (!$value) {
            return false;
        }
        $iv = mcrypt_create_iv(mcrypt_get_iv_size(MCRYPT_RIJNDAEL_256, MCRYPT_MODE_ECB), MCRYPT_RAND);
        $decrypted_string = trim(mcrypt_decrypt(MCRYPT_RIJNDAEL_256, $key, base64_decode($value), MCRYPT_MODE_ECB, mcrypt_create_iv(mcrypt_get_iv_size(MCRYPT_RIJNDAEL_256, MCRYPT_MODE_ECB), MCRYPT_RAND)));
        return $decrypted_string;
    } 
}?>

Only some strings are decrypted in a wrong way. I can't find any matches between this strings. Only that they all saved in the chrome autofill. Can this be a reason for an error? Or can you find some wrong things in my Encryption class?