84 lines
2.7 KiB
C
84 lines
2.7 KiB
C
|
// //////////////////////////////////////////////////////////
|
||
|
|
// hmac.h
|
||
|
|
// Copyright (c) 2015 Stephan Brumme. All rights reserved.
|
||
|
|
// see http://create.stephan-brumme.com/disclaimer.html
|
||
|
|
//
|
||
|
|
|
||
|
|
#pragma once
|
||
|
|
|
||
|
|
// based on http://tools.ietf.org/html/rfc2104
|
||
|
|
// see also http://en.wikipedia.org/wiki/Hash-based_message_authentication_code
|
||
|
|
|
||
|
|
/** Usage:
|
||
|
|
std::string msg = "The quick brown fox jumps over the lazy dog";
|
||
|
|
std::string key = "key";
|
||
|
|
std::string md5hmac = hmac< MD5 >(msg, key);
|
||
|
|
std::string sha1hmac = hmac< SHA1 >(msg, key);
|
||
|
|
std::string sha2hmac = hmac<SHA256>(msg, key);
|
||
|
|
|
||
|
|
Note:
|
||
|
|
To keep my code simple, HMAC computation currently needs the whole message at once.
|
||
|
|
This is in contrast to the hashes MD5, SHA1, etc. where an add() method is available
|
||
|
|
for incremental computation.
|
||
|
|
You can use any hash for HMAC as long as it provides:
|
||
|
|
- constant HashMethod::BlockSize (typically 64)
|
||
|
|
- constant HashMethod::HashBytes (length of hash in bytes, e.g. 20 for SHA1)
|
||
|
|
- HashMethod::add(buffer, bufferSize)
|
||
|
|
- HashMethod::getHash(unsigned char buffer[HashMethod::BlockSize])
|
||
|
|
*/
|
||
|
|
|
||
|
|
#include <string>
|
||
|
|
#include <cstring> // memcpy
|
||
|
|
|
||
|
|
/// compute HMAC hash of data and key using MD5, SHA1 or SHA256
|
||
|
|
template <typename HashMethod>
|
||
|
|
std::string hmac(const void* data, size_t numDataBytes, const void* key, size_t numKeyBytes)
|
||
|
|
{
|
||
|
|
// initialize key with zeros
|
||
|
|
unsigned char usedKey[HashMethod::BlockSize] = {0};
|
||
|
|
|
||
|
|
// adjust length of key: must contain exactly blockSize bytes
|
||
|
|
if (numKeyBytes <= HashMethod::BlockSize)
|
||
|
|
{
|
||
|
|
// copy key
|
||
|
|
memcpy(usedKey, key, numKeyBytes);
|
||
|
|
}
|
||
|
|
else
|
||
|
|
{
|
||
|
|
// shorten key: usedKey = hashed(key)
|
||
|
|
HashMethod keyHasher;
|
||
|
|
keyHasher.add(key, numKeyBytes);
|
||
|
|
keyHasher.getHash(usedKey);
|
||
|
|
}
|
||
|
|
|
||
|
|
// create initial XOR padding
|
||
|
|
for (size_t i = 0; i < HashMethod::BlockSize; i++)
|
||
|
|
usedKey[i] ^= 0x36;
|
||
|
|
|
||
|
|
// inside = hash((usedKey ^ 0x36) + data)
|
||
|
|
unsigned char inside[HashMethod::HashBytes];
|
||
|
|
HashMethod insideHasher;
|
||
|
|
insideHasher.add(usedKey, HashMethod::BlockSize);
|
||
|
|
insideHasher.add(data, numDataBytes);
|
||
|
|
insideHasher.getHash(inside);
|
||
|
|
|
||
|
|
// undo usedKey's previous 0x36 XORing and apply a XOR by 0x5C
|
||
|
|
for (size_t i = 0; i < HashMethod::BlockSize; i++)
|
||
|
|
usedKey[i] ^= 0x5C ^ 0x36;
|
||
|
|
|
||
|
|
// hash((usedKey ^ 0x5C) + hash((usedKey ^ 0x36) + data))
|
||
|
|
HashMethod finalHasher;
|
||
|
|
finalHasher.add(usedKey, HashMethod::BlockSize);
|
||
|
|
finalHasher.add(inside, HashMethod::HashBytes);
|
||
|
|
|
||
|
|
return finalHasher.getHash();
|
||
|
|
}
|
||
|
|
|
||
|
|
|
||
|
|
/// convenience function for std::string
|
||
|
|
template <typename HashMethod>
|
||
|
|
std::string hmac(const std::string& data, const std::string& key)
|
||
|
|
{
|
||
|
|
return hmac<HashMethod>(data.c_str(), data.size(), key.c_str(), key.size());
|
||
|
|
}
|