我需要在一个嵌入式项目中实现自己的HMAC-SHA256。但是我遇到了一些问题,甚至无法让伪代码手算出结果,所以我知道我做错了什么!
我的伪代码计算。按照维基百科上的图示进行操作。
1 function hmac (key, message)
2 if (length(key) > blocksize) then
3 // keys longer than blocksize are shortened
4 key = hash(key)
5 end if
6 if (length(key) < blocksize) then
7 // keys shorter than blocksize are zero-padded
8 key = key ∥ zeroes(blocksize - length(key))
9 end if
10
11 // Where blocksize is that of the underlying hash function
12 o_key_pad = [0x5c * blocksize] ⊕ key
13 i_key_pad = [0x36 * blocksize] ⊕ key // Where ⊕ is exclusive or (XOR)
14 // Where ∥ is concatenation
15 return hash(o_key_pad ∥ hash(i_key_pad ∥ message))
16 end function
当我手动计算key="mykey"和message="helloworld"时,得到以下结果:
key = 0x6d796b6579000000000000000000000000000000000000000000000000000000
o_key_pad = 0x31253739255c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c
i_key_pad = 0x5b4f5d534f363636363636363636363636363636363636363636363636363636
hash(i_key_pad ∥ message) = 6fb2e91de7b8b5ec6283846ff7245cd6eb4a4fd26056b529bd42d99fcf3314d2
整个hmac的值为0d76a16089f85cd2169bb64b6f2c818e6a404a218896483fcd97fee5cce185ae。