AES 并不等于Rijndael。
php 实现AES 加密解密
AES 的定义：
AES的区块长度固定为128比特，密钥长度则可以是128，192或256比特；
Rijndael使用的密钥和区块长度均可以是128，192或256比特。加密过程中使用的密钥是由Rijndael密钥生成方案产生。
大多数AES计算是在一个特别的有限域完成的。
AES不等于“Rijndael”，AES是Rigndael的子集。
- AES 固定块大小：128bit,key size.
- Rijndael block size 和 key size 可以是32bit的整数倍，最小128，最大256bits.
PHP提供了Rijndael 算法的一般实现，PHP mcrypt 无意中做了误导，很多用户认为MCRYPT_RIJNDAEL_256 的256是加密强度，其实他只是设置了算法的block size.
The AES encryption standard is defined as Rjindael encryption (128-bit, 192-bit, or 256-bit) using a block size of 16 bytes.
Chilkat implements the AES encryption standard.
When you specify MCRYPT_RIJNDAEL_256 in PHP, you are NOT setting the encryption strength to 256-bits. You are setting the block size to 256 bits. This is NOT AES encryption. To properly produce 256-bit AES encryption in PHP, you must provide a 32-byte encryption key (which implicitly sets the encryption strength), but the block size must be set to MCRYPT_RIJNDAEL_128 (16 bytes).
在PHP中实现256-bit AES算法，必须提供32位的密匙（设置加密强度），但block size 必须设置为128 bytes.
The Rijndael encyrption algorithm is a block cipher. It operates on discrete blocks of data. Padding MUST be added such that the data to be encrypted has a length that is a multiple of the block size.(PHP pads with NULL bytes)
Rijndael 是分组加密算法，需要对数据做填充以使得数据长度是块大小的整数倍
CBC mode requires an initialization vector. The size of the IV (initialization vector) is always equal to the block-size. (It is NOT equal to the key size.) Given that our block size is 128-bits, the IV is also 128-bits (i.e. 16 bytes). Thus, for AES encryption, the IV is always 16 bytes regardless of the strength of encryption.
IV 的size和block-size 一样
