hmac.hh

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#pragma once

#include <vector>

#include <openssl/hmac.h>
#include <openssl/objects.h>

enum class hash_algorithms: unsigned char {
  sha_256, 
  sha_384  
}; // End of class hash_algorithms


class hmac {
  HMAC_CTX _ctx; 
  hash_algorithms _hash_algorithms;
public:
  hmac(const hash_algorithms p_hash_algorithms): _ctx{}, _hash_algorithms(p_hash_algorithms) { ::HMAC_CTX_init(&_ctx); };
  virtual ~hmac() { ::HMAC_CTX_cleanup(&_ctx); };

  inline int generate(const std::vector<unsigned char> p_buffer, const std::vector<unsigned char> p_secret_key, std::vector<unsigned char>& p_hmac) {
    // Sanity check
    if (p_buffer.size() == 0) {
      return -1;
    }

    return generate(p_buffer.data(), p_buffer.size(), p_secret_key.data(), p_secret_key.size(), p_hmac);
  };
  
  inline int generate(const unsigned char *p_buffer, const size_t p_buffer_length, const unsigned char *p_secret_key, const size_t p_secret_key_length, std::vector<unsigned char>& p_hmac) {
    // Sanity check
    if ((p_buffer == nullptr) || (p_secret_key == nullptr)) {
      return -1;
    }

    if (_hash_algorithms == hash_algorithms::sha_256) {
      p_hmac.resize(64);
      ::HMAC_Init_ex(&_ctx, (const void*)p_secret_key, (long unsigned int)p_secret_key_length, EVP_sha256(), NULL);
    } else if (_hash_algorithms == hash_algorithms::sha_384) {
      p_hmac.resize(128);
      ::HMAC_Init_ex(&_ctx, (const void*)p_secret_key, (long unsigned int)p_secret_key_length, EVP_sha384(), NULL);
    } else { // TODO To be continued
      return -1;
    }
    // Compute the hash value
    ::HMAC_Update(&_ctx, p_buffer, p_buffer_length);
    unsigned int length = p_hmac.size();
    ::HMAC_Final(&_ctx, static_cast<unsigned char*>(p_hmac.data()), &length);
    return 0;
  };
}; // End of class hmac