自己写的HMAC函数，不能正常使用

Question

我编写了以下函数来生成 HMAC-SHA1 引用 https://www.rfc-editor.org/rfc/rfc2104, however, the values I generate seem to differ from the values given on https://www.rfc-editor.org/rfc/rfc2202 and from what I've tested on https://www.freeformatter.com/hmac-generator.html。

例如，函数应该为键为“key”的文本“The quick brown fox jumps over the lazy dog”生成 de7c9b85b8b78aa6bc8a7a36f70a90701c9db4d9，但它生成 d3c446dbd70f5db3693f63f96a5931d49eaa5bab。

谁能指出我的错误？

函数：

const int block_size = 64;
const int hash_output_size = 20;
const int ipadVal = 0x36;
const int opadVal = 0x5C;
std::string HMAC::getHMAC(const std::string &text)
{
// check if key length is block_size
// else, append 0x00 till the length of new key is block_size
int key_length = key.length();
std::string newkey = key;
if (key_length < block_size)
{
    int appended_zeros = block_size - key_length;
    // create new string with appended_zeros number of zeros
    std::string zeros = std::string(appended_zeros, '0');
    newkey = key + zeros;
}
if (key_length > block_size)
{
    SHA1 sha1;
    newkey = sha1(key);
}

// calculate hash of newkey XOR ipad and newkey XOR opad
std::string keyXipad = newkey;
std::string keyXopad = newkey;
for (int i = 0; i < 64; i++)
{
    keyXipad[i] ^= ipadVal;
    keyXopad[i] ^= opadVal;
}

// get first hash, hash of keyXipad+text
std::string inner_hash = getSHA1(keyXipad + text);

// get outer hash, hash of keyXopad+inner_hash
std::string outer_hash = getSHA1(keyXopad + inner_hash);

// return outer_hash
return outer_hash;
}

编辑：在行

std::string zeros = std::string(appended_zeros, '0');

'0' 应该改为 0：int 而不是 char。感谢@Igor Tandetnik。

Answer 1

好的..所以稍微环顾一下我就可以找到 HMAC produces wrong results。事实证明，我犯了同样的错误，将十六进制用作 ascii。

我使用一个函数将 inner_hash 从十六进制转换为 ascii，然后一切都变得完美。

函数的最终版本：

std::string HMAC::getHMAC(const std::string &text)
{
// check if key length is block_size
// else, append 0x00 till the length of new key is block_size
int key_length = key.length();
std::string newkey = key;
if (key_length < block_size)
{
    int appended_zeros = block_size - key_length;
    // create new string with appended_zeros number of zeros
    std::cout << "\nAppending " << appended_zeros << " 0s to key";
    std::string zeros = std::string(appended_zeros, 0);
    newkey = key + zeros;
}
if (key_length > block_size)
{
    SHA1 sha1;
    newkey = sha1(key);
}

// calculate hash of newkey XOR ipad and newkey XOR opad
std::string keyXipad = newkey;
std::string keyXopad = newkey;
for (int i = 0; i < 64; i++)
{
    keyXipad[i] ^= ipadVal;
    keyXopad[i] ^= opadVal;
}

// get first hash, hash of keyXipad+text
std::string toInnerHash = keyXipad + text;
std::string inner_hash = getHash(toInnerHash);

// get outer hash, hash of keyXopad+inner_hash
std::string toOuterHash = keyXopad + hex_to_string(inner_hash);
std::string outer_hash = getHash(toOuterHash);

// return outer_hash
return outer_hash;
}

hex_to_string 函数取自

自己写的HMAC函数，不能正常使用

Self written HMAC function, not working correctly

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