sjcl 怎么解释AES加密

Question

比如我用gibberish-aes加密得到一段AES密文

var a = AES.enc('test', '123456789');
//result > U2FsdGVkX191FDEpDVIHpqXYVVGzeT83v4C4KktKsbM=

var b = AES.dec(a, '123456789');
//result > test

然后我想用sjcl去解密这段密文

var p = {};
var iter = 1000;
var salt = sjcl.random.randomWords('4','0');
var password = "123456789";
p.salt = salt;
p.iter = iter;
p = sjcl.misc.cachedPbkdf2(password, p);

var key = p.key;

var aes = new sjcl.cipher.aes(key);
var ct = aes.encrypt("U2FsdGVkX191FDEpDVIHpqXYVVGzeT83v4C4KktKsbM=");
//最后得到错误结果
//Uncaught invalid {message: "invalid aes block size"}

官方文档也是看得云里雾里的
求解哪一步出了错?
或者直接来一个可行的代码示例!
感激!!