SHA256算法变为HMAC-SHA256

算法道路千千万，各有千秋，莫要较真

现在很多都原生态支持SHA256，不如乐鑫的调用即用

然而对于别的偏向底层的开发，如需要自己实现算法，也不是不行！

公式为：
        HMAC_SHA256 (k,m)=SHA256(k`⊕opad∥SHA256(k`⊕ipad∥m))

其中：
SHA256 为SHA-256加密算法，其输出散列值长度256-bit；

∥ 拼接操作，将两个字符串拼接在一起；

B Hash函数明文分组长度，SHA-256算法中为512-bit；

k`为密钥（secret key）；

m 为要认证的消息；

k` 是从原始密钥 k 导出的另一个密钥（若 k 短于B，则向右填充零，直到与B相同；若k长于B，则对 k 进行一次SHA256散列计算）

opad 内部填充（0x5C5C5C…5C5C，512-bit常量）；

ipad 外部填充（0x363636…3636，512-bit常量）

以下是详细展开

假设 ProductSecret产品密钥：DMLMXLEBWOW6Voks                        16个字节

k="DMLMXLEBWOW6Voks"                                
k'=0x444d4c4d584c4542574f5736566f6b73000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000                64字节     512bit

opad=0x5C5C5C5C5C5C5C5C5C5C5C5C5C5C5C5C5C5C5C5C5C5C5C5C5C5C5C5C5C5C5C5C5C5C5C5C5C5C5C5C5C5C5C5C5C5C5C5C5C5C5C5C5C5C5C5C5C5C5C5C5C5C5C5C          64字节     512bit

ipad=0x36363636363636363636363636363636363636363636363636363636363636363636363636363636363636363636363636363636363636363636363636363636            64字节     512bit

k’⊕ipad = 0x727b7a7b6e7a73746179610060595d45363636363636363636363636363636363636363636363636363636363636363636363636363636363636363636363636
k’⊕opad = 0x181110110410191e0b130b6a0a33372f5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c

m="123456" = 0x313233343536

k’⊕ipad∥m =
0x727b7a7b6e7a73746179610060595d45363636363636363636363636363636363636363636363636363636363636363636363636363636363636363636363636313233343536

SHA256(k’⊕ipad∥m)=0x3abace516abbbe349f053a7e8a2f14049762646f70ddb1bc2c6536a7544f7ae6

k’⊕opad∥SHA256(k’⊕ipad∥m)=
0x181110110410191e0b130b6a0a33372f5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c3abace516abbbe349f053a7e8a2f14049762646f70ddb1bc2c6536a7544f7ae6

代入公式手动计算得
SHA256(k’⊕opad∥SHA256(k’⊕ipad∥m))=

4161df4e1022c4e2c4306982877c898bf9f807c886e0e9b59171d26d54407271

4161df4e1022c4e2c4306982877c898bf9f807c886e0e9b59171d26d54407271     

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