/*

* HKDF

* (C) 2013,2015,2017 Jack Lloyd

* (C) 2016 René Korthaus, Rohde & Schwarz Cybersecurity

*

* Botan is released under the Simplified BSD License (see license.txt)

*/

#include <botan/internal/hkdf.h>

#include <botan/internal/loadstor.h>

#include <botan/exceptn.h>

namespace Botan {

void HKDF::kdf(uint8_t key[], size_t key_len,

               const uint8_t secret[], size_t secret_len,

               const uint8_t salt[], size_t salt_len,

               const uint8_t label[], size_t label_len) const

   {

   HKDF_Extract extract(m_prf->clone());

   HKDF_Expand expand(m_prf->clone());

   secure_vector<uint8_t> prk(m_prf->output_length());

   extract.kdf(prk.data(), prk.size(), secret, secret_len, salt, salt_len, nullptr, 0);

   expand.kdf(key, key_len, prk.data(), prk.size(), nullptr, 0, label, label_len);

   }

void HKDF_Extract::kdf(uint8_t key[], size_t key_len,

                       const uint8_t secret[], size_t secret_len,

                       const uint8_t salt[], size_t salt_len,

                       const uint8_t[], size_t) const

   {

   if(key_len == 0)

      return;

   const size_t prf_output_len = m_prf->output_length();

   if(key_len > prf_output_len)

      throw Invalid_Argument("HKDF-Extract maximum output length exceeeded");

   if(salt_len == 0)

      {

      m_prf->set_key(std::vector<uint8_t>(prf_output_len));

      }

   else

      {

      m_prf->set_key(salt, salt_len);

      }

   m_prf->update(secret, secret_len);

   if(key_len == prf_output_len)

      {

      m_prf->final(key);

      }

   else

      {

      secure_vector<uint8_t> prk;

      m_prf->final(prk);

      copy_mem(&key[0], prk.data(), key_len);

      }

   }

void HKDF_Expand::kdf(uint8_t key[], size_t key_len,

                      const uint8_t secret[], size_t secret_len,

                      const uint8_t salt[], size_t salt_len,

                      const uint8_t label[], size_t label_len) const

   {

   if(key_len == 0)

      return;

   const size_t blocks_required = key_len / m_prf->output_length();

   if(blocks_required >= 0xFF)

      throw Invalid_Argument("HKDF-Expand maximum output length exceeeded");

   m_prf->set_key(secret, secret_len);

   uint8_t counter = 1;

   secure_vector<uint8_t> h;

   size_t offset = 0;

   while(offset != key_len)

      {

      m_prf->update(h);

      m_prf->update(label, label_len);

      m_prf->update(salt, salt_len);

      m_prf->update(counter++);

      m_prf->final(h);

      const size_t written = std::min(h.size(), key_len - offset);

      copy_mem(&key[offset], h.data(), written);

      offset += written;

      }

   }

secure_vector<uint8_t>

hkdf_expand_label(const std::string& hash_fn,

                  const uint8_t secret[], size_t secret_len,

                  const std::string& label,

                  const uint8_t hash_val[], size_t hash_val_len,

                  size_t length)

   {

   BOTAN_ARG_CHECK(length <= 0xFFFF, "HKDF-Expand-Label requested output too large");

   BOTAN_ARG_CHECK(label.size() <= 0xFF, "HKDF-Expand-Label label too long");

   BOTAN_ARG_CHECK(hash_val_len <= 0xFF, "HKDF-Expand-Label hash too long");

   const uint16_t length16 = static_cast<uint16_t>(length);

   auto mac = MessageAuthenticationCode::create_or_throw("HMAC(" + hash_fn + ")");

   HKDF_Expand hkdf(mac.release());

   secure_vector<uint8_t> output(length16);

   std::vector<uint8_t> prefix(3 + label.size() + 1);

   prefix[0] = get_byte(0, length16);

   prefix[1] = get_byte(1, length16);

   prefix[2] = static_cast<uint8_t>(label.size());

   copy_mem(prefix.data() + 3,

            cast_char_ptr_to_uint8(label.data()),

            label.size());

   prefix[3 + label.size()] = static_cast<uint8_t>(hash_val_len);

   /*

   * We do something a little dirty here to avoid copying the hash_val,

   * making use of the fact that Botan's KDF interface supports label+salt,

   * and knowing that our HKDF hashes first param label then param salt.

   */

   hkdf.kdf(output.data(), output.size(),

            secret, secret_len,

            hash_val, hash_val_len,

            prefix.data(), prefix.size());

   return output;

   }

}