Add chacha12 and chacha20

[godwasdog]

code form sectun

[godwasdog]

#251

[wangyu-]

Hi, thank you for your pull request. Sorry for the late response, cuz its a busy semester now.

I took a quick glance of the code, it looks good. I will merge& test it later, when I have more time..

[wangyu-]

There might be a problem in the use of fixed (zero) nonce.

Note that I also use zero IV for aes-cfb and aes-cbc, but a property of cbc/cfb is used, so the real IV is in the first data block (and it’s not fixed)...let’s call it a trick

Chacha12/20 works in counter mode(instead of cbc/cfb) and there is no such trick... So there might be a problem. I will confirm this later.

[godwasdog]

对，这个问题我也注意到了。本来想从 data block前面取uint8_t nonce[12]的。不过没通读源码，不敢乱改。考虑到前面有
`
//static send_bare[buf_len];
  iv_t iv=get_true_random_number_64();
  padding_t padding=get_true_random_number_64();

`
我这种不跨境、小流量的情况下，问题不大。
最后只能把问题留给您了，抱歉。

PS：AR9330(MIPS 24Kc)下比您编译的AES稍微快少少，希望您能测试下其他平台性能