Generate HMAC SHA256 hash using key in C++ - c++

Question

I am looking for some function or a way that would return HMAC SHA256 hash in C++ using secret key. I have seen documentation of Crypto++ and OpenSSL but it does not accept an extra parameter of secret key for computation. Can someone help me by providing some info, code snippets or links.

Answer 1

You can use POCO library
Sample code:
class SHA256Engine : public Poco::Crypto::DigestEngine
{
public:
enum
{
BLOCK_SIZE = 64,
DIGEST_SIZE = 32
};
SHA256Engine()
: DigestEngine("SHA256")
{
}
};
Poco::HMACEngine<SHA256Engine> hmac{secretKey};
hmac.update(string);
std::cout << "HMACE hex:" << Poco::DigestEngine::digestToHex(hmac.digest()) << std::endl;// lookout difest() calls reset ;)
Sample integration with POCO using cmake install:
mkdir build_poco/
cd build_poco/ && cmake -DCMAKE_BUILD_TYPE=Release -DCMAKE_INSTALL_PREFIX=./install ../poco/
CMakeLists.txt
CMAKE_MINIMUM_REQUIRED(VERSION 3.8)
PROJECT(SamplePoco)
SET(CMAKE_CXX_STANDARD 14)
SET(SOURCE_FILES
src/main.cpp
)
SET(_IMPORT_PREFIX lib/build_poco/install)
INCLUDE(lib/build_poco/install/lib/cmake/Poco/PocoFoundationTargets.cmake)
INCLUDE(lib/build_poco/install/lib/cmake/Poco/PocoNetTargets.cmake)
INCLUDE(lib/build_poco/install/lib/cmake/Poco/PocoJSONTargets.cmake)
INCLUDE(lib/build_poco/install/lib/cmake/Poco/PocoXMLTargets.cmake)
INCLUDE(lib/build_poco/install/lib/cmake/Poco/PocoCryptoTargets.cmake)
INCLUDE(lib/build_poco/install/lib/cmake/Poco/PocoUtilTargets.cmake)
INCLUDE(lib/build_poco/install/lib/cmake/Poco/PocoNetSSLTargets.cmake)
ADD_EXECUTABLE(SamplePoco ${SOURCE_FILES})
TARGET_LINK_LIBRARIES(SamplePoco
Poco::Foundation
Poco::Crypto
Poco::Util
Poco::JSON
Poco::NetSSL
)
TARGET_INCLUDE_DIRECTORIES(SamplePoco PUBLIC src/)
Sample implementation used here: https://github.com/gelldur/abucoins-api-cpp

Answer 2

Following is a sample of function to generate SHA256-HMAC using Crypto++
#include <string>
#include <string_view>
#include <cryptopp/filters.h>
using CryptoPP::StringSink;
using CryptoPP::StringSource;
using CryptoPP::HashFilter;
#include <cryptopp/hmac.h>
using CryptoPP::HMAC;
#include <cryptopp/sha.h>
using CryptoPP::SHA256;
std::string CalcHmacSHA256(std::string_view decodedSecretKey, std::string_view request)
{
// Calculate HMAC
HMAC<SHA256> hmac(reinterpret_cast<CryptoPP::byte const*>(decodedSecretKey.data()), decodedSecretKey.size());
std::string calculated_hmac;
auto sink = std::make_unique<StringSink>(calculated_hmac);
auto filter = std::make_unique<HashFilter>(hmac, sink.get());
sink.release();
StringSource(reinterpret_cast<CryptoPP::byte const*>(request.data()), request.size(), true, filter.get()); // StringSource
filter.release();
return calculated_hmac;
}
#include <iostream>
int main() {
std::cout << CalcHmacSHA256("key", "data");
}
The source is CME iLink2 specification

Answer 3

For consistency, following is a sample of function to generate SHA256-HMAC using OpenSSL
#include <openssl/sha.h>
#include <openssl/hmac.h>
#include <string>
#include <string_view>
#include <array>
std::string CalcHmacSHA256(std::string_view decodedKey, std::string_view msg)
{
std::array<unsigned char, EVP_MAX_MD_SIZE> hash;
unsigned int hashLen;
HMAC(
EVP_sha256(),
decodedKey.data(),
static_cast<int>(decodedKey.size()),
reinterpret_cast<unsigned char const*>(msg.data()),
static_cast<int>(msg.size()),
hash.data(),
&hashLen
);
return std::string{reinterpret_cast<char const*>(hash.data()), hashLen};
}
For the record, I like Crypto++ better as in case of Crypto++ generated binary is smaller. The drawback is that Crypto++ does not have a CMake module.

Answer 4

OpenSSL docs for HMAC, clearly state the requirement of a 'key' as part of context initialization.
int HMAC_Init_ex(HMAC_CTX *ctx, const void *key, int key_len,
const EVP_MD *md, ENGINE *impl);
HMAC() computes the message authentication code of the n bytes at d
using the hash function evp_md and the key key which is key_len bytes
long.

Answer 5

You can use cpp-cryptlite to generate HMAC SHA256 hash, Following is the code snippet:
std::string src_str = "abcdefg";
std::string secret_key = "xxxxxx"; // this value is an example
boost::uint8_t digest[32]; // cryptlite::sha256::HASH_SIZE
cryptlite::hmac<cryptlite::sha256>::calc(src_str, secret_key, digest);
// and digest is the output hash

Answer 6

I had to modify #DmytroOvdiienko's answer a bit to get hexadecimal output:
#include <iomanip>
...
std::string CalcHmacSHA256(std::string_view decodedKey, std::string_view msg)
{
std::array<unsigned char, EVP_MAX_MD_SIZE> hash;
unsigned int hashLen;
HMAC(
EVP_sha256(),
decodedKey.data(),
static_cast<int>(decodedKey.size()),
reinterpret_cast<unsigned char const*>(msg.data()),
static_cast<int>(msg.size()),
hash.data(),
&hashLen
);
std::stringstream out;
for (unsigned int i=0; i < hashLen; i++) {
out << std::setfill('0') << std::setw(2) << std::right << std::hex << (int)hash.data()[i];
}
return out.str();
}
int main(int, char**) {
std::string key = "ESiFg448MqOmhQyxbt6HEHHPnAA1OE8nX0o9ANIVMIvWLISQS0MivDrkZvnBxMEI";
std::string msg = "foo";
std::string_view key_view{key};
std::string_view msg_view{msg};
std::cout << CalcHmacSHA256(key_view, msg_view) << std::endl;
}
The <iomanip>, setfill, setw, right are needed to make sure single-digit hex values are prefixed with a 0. An alternative is to use boost:
#include <boost/format.hpp>
...
out << boost::format("%02x") % (int)hash.data()[i];