/*

 * XMSS Verification Operation

 * Provides signature verification capabilities for Extended Hash-Based

 * Signatures (XMSS).

 *

 * (C) 2016,2017 Matthias Gierlings

 *

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

 **/

#include <botan/internal/xmss_verification_operation.h>

namespace Botan {

XMSS_Verification_Operation::XMSS_Verification_Operation(

   const XMSS_PublicKey& public_key)

   : XMSS_Common_Ops(public_key.xmss_oid()),

     m_pub_key(public_key),

     m_msg_buf(0)

   {

   }

Unexecuted instantiation: Botan::XMSS_Verification_Operation::XMSS_Verification_Operation(Botan::XMSS_PublicKey const&)

Unexecuted instantiation: Botan::XMSS_Verification_Operation::XMSS_Verification_Operation(Botan::XMSS_PublicKey const&)

secure_vector<uint8_t>

XMSS_Verification_Operation::root_from_signature(const XMSS_Signature& sig,

      const secure_vector<uint8_t>& msg,

      XMSS_Address& adrs,

      const secure_vector<uint8_t>& seed)

   {

   const uint32_t next_index = static_cast<uint32_t>(sig.unused_leaf_index());

   adrs.set_type(XMSS_Address::Type::OTS_Hash_Address);

   adrs.set_ots_address(next_index);

   XMSS_WOTS_PublicKey pub_key_ots(m_pub_key.wots_parameters().oid(),

                                   msg,

                                   sig.tree().ots_signature(),

                                   adrs,

                                   seed);

   adrs.set_type(XMSS_Address::Type::LTree_Address);

   adrs.set_ltree_address(next_index);

   std::array<secure_vector<uint8_t>, 2> node;

   create_l_tree(node[0], pub_key_ots, adrs, seed);

   adrs.set_type(XMSS_Address::Type::Hash_Tree_Address);

   adrs.set_tree_index(next_index);

   for(size_t k = 0; k < m_xmss_params.tree_height(); k++)

      {

      adrs.set_tree_height(static_cast<uint32_t>(k));

      if(((next_index / (static_cast<size_t>(1) << k)) & 0x01) == 0)

         {

         adrs.set_tree_index(adrs.get_tree_index() >> 1);

         randomize_tree_hash(node[1],

                             node[0],

                             sig.tree().authentication_path()[k],

                             adrs,

                             seed);

         }

      else

         {

         adrs.set_tree_index((adrs.get_tree_index() - 1) >> 1);

         randomize_tree_hash(node[1],

                             sig.tree().authentication_path()[k],

                             node[0],

                             adrs,

                             seed);

         }

      node[0] = node[1];

      }

   return node[0];

   }

bool

XMSS_Verification_Operation::verify(const XMSS_Signature& sig,

                                    const secure_vector<uint8_t>& msg,

                                    const XMSS_PublicKey& public_key)

   {

   XMSS_Address adrs;

   secure_vector<uint8_t> index_bytes;

   XMSS_Tools::concat(index_bytes,

                      sig.unused_leaf_index(),

                      m_xmss_params.element_size());

   secure_vector<uint8_t> msg_digest =

      m_hash.h_msg(sig.randomness(),

                   public_key.root(),

                   index_bytes,

                   msg);

   secure_vector<uint8_t> node = root_from_signature(sig,

                                 msg_digest,

                                 adrs,

                                 public_key.public_seed());

   return (node == public_key.root());

   }

// FIXME: XMSS signature verification requires the "randomness" parameter out

// of the XMSS signature, which is part of the prefix that is hashed before

// msg. Since the signature is unknown till sign() is called all message

// content has to be buffered. For large messages this can be inconvenient or

// impossible.

// Possible solution: Change PK_Ops::Verification interface to take the

// signature as constructor argument, make sign a parameterless member call.

void XMSS_Verification_Operation::update(const uint8_t msg[], size_t msg_len)

   {

   std::copy(msg, msg + msg_len, std::back_inserter(m_msg_buf));

   }

bool XMSS_Verification_Operation::is_valid_signature(const uint8_t sig[],

      size_t sig_len)

   {

   try

      {

      XMSS_Signature signature(m_pub_key.xmss_parameters().oid(),

                               secure_vector<uint8_t>(sig, sig + sig_len));

      bool result = verify(signature, m_msg_buf, m_pub_key);

      m_msg_buf.clear();

      return result;

      }

   catch(...)

      {

      m_msg_buf.clear();

      return false;

      }

   }

}