/*
 * XMSS WOTS Public Key
 * (C) 2016 Matthias Gierlings
 *
 * Botan is released under the Simplified BSD License (see license.txt)
 **/

#ifndef BOTAN_XMSS_WOTS_PUBLICKEY_H__
#define BOTAN_XMSS_WOTS_PUBLICKEY_H__

#include <cstddef>
#include <string>
#include <vector>
#include <botan/alg_id.h>
#include <botan/asn1_oid.h>
#include <botan/assert.h>
#include <botan/exceptn.h>
#include <botan/pk_keys.h>
#include <botan/types.h>
#include <botan/xmss_wots_parameters.h>
#include <botan/xmss_address.h>
#include <botan/xmss_hash.h>

namespace Botan {

typedef std::vector<secure_vector<uint8_t>> wots_keysig_t;

/**
 * A Winternitz One Time Signature public key for use with Extended Hash-Based
 * Signatures.
 **/
class BOTAN_DLL XMSS_WOTS_PublicKey : virtual public Public_Key
   {
   public:
      class TreeSignature
         {
         public:
            TreeSignature() = default;

            TreeSignature(const wots_keysig_t& ots_sig,
                          const wots_keysig_t& auth_path)
               : m_ots_sig(ots_sig), m_auth_path(auth_path)
               {}

            TreeSignature(wots_keysig_t&& ots_sig,
                          wots_keysig_t&& auth_path)
               : m_ots_sig(std::move(ots_sig)),
                 m_auth_path(std::move(auth_path))
               {}

            const wots_keysig_t& ots_signature() const
               {
               return m_ots_sig;
               }

            wots_keysig_t& ots_signature()
               {
               return m_ots_sig;
               }

            const wots_keysig_t& authentication_path() const
               {
               return m_auth_path;
               }

            wots_keysig_t& authentication_path()
               {
               return m_auth_path;
               }

         private:
            wots_keysig_t m_ots_sig;
            wots_keysig_t m_auth_path;
         };

      /**
       * Creates a XMSS_WOTS_PublicKey for the signature method identified by
       * oid. The public seed for this key will be initialized with a
       * uniformly random n-byte value, where "n" is the element size of the
       * selected signature method.
       *
       * @param oid Identifier for the selected signature method.
       **/
      XMSS_WOTS_PublicKey(XMSS_WOTS_Parameters::ots_algorithm_t oid)
         : m_wots_params(oid),
           m_hash(m_wots_params.hash_function_name()) {}

      /**
       * Creates a XMSS_WOTS_PublicKey for the signature method identified by
       * oid. The public seed for this key will be initialized with a
       * uniformly random n-byte value, where "n" is the element size of the
       * selected signature method.
       *
       * @param oid Identifier for the selected signature method.
       * @param rng A random number generate used to generate the public seed.
       **/
      XMSS_WOTS_PublicKey(XMSS_WOTS_Parameters::ots_algorithm_t oid,
                          RandomNumberGenerator& rng)
         : m_wots_params(oid),
           m_hash(m_wots_params.hash_function_name()),
           m_public_seed(rng.random_vec(m_wots_params.element_size())) {}

      /**
       * Creates a XMSS_WOTS_PrivateKey for the signature method identified by
       * oid, with a precomputed public seed.
       *
       * @param oid Identifier for the selected signature method.
       * @param public_seed A precomputed public seed of n-bytes length.
       **/
      XMSS_WOTS_PublicKey(XMSS_WOTS_Parameters::ots_algorithm_t oid,
                          secure_vector<uint8_t> public_seed)
         : m_wots_params(oid),
           m_hash(m_wots_params.hash_function_name()),
           m_public_seed(public_seed) {}

      /**
       * Creates a XMSS_WOTS_PublicKey for the signature method identified by
       * oid. The public seed will be initialized with a precomputed seed and
       * and precomputed key data which should be derived from a
       * XMSS_WOTS_PrivateKey.
       *
       * @param oid Ident:s/ifier for the selected signature methods.
       * @param public_seed A precomputed public seed of n-bytes length.
       * @param key Precomputed raw key data of the XMSS_WOTS_PublicKey.
       **/
      XMSS_WOTS_PublicKey(XMSS_WOTS_Parameters::ots_algorithm_t oid,
                          secure_vector<uint8_t>&& public_seed,
                          wots_keysig_t&& key)
         : m_wots_params(oid),
           m_hash(m_wots_params.hash_function_name()),
           m_key(std::move(key)),
           m_public_seed(std::move(public_seed))
         {}

      /**
       * Creates a XMSS_WOTS_PublicKey for the signature method identified by
       * oid. The public seed will be initialized with a precomputed seed and
       * and precomputed key data which should be derived from a
       * XMSS_WOTS_PrivateKey.
       *
       * @param oid Identifier for the selected signature methods.
       * @param public_seed A precomputed public seed of n-bytes length.
       * @param key Precomputed raw key data of the XMSS_WOTS_PublicKey.
       **/
      XMSS_WOTS_PublicKey(XMSS_WOTS_Parameters::ots_algorithm_t oid,
                          const secure_vector<uint8_t>& public_seed,
                          const wots_keysig_t& key)
         : m_wots_params(oid),
           m_hash(m_wots_params.hash_function_name()),
           m_key(key),
           m_public_seed(public_seed)
         {}

      /**
       * Creates a XMSS_WOTS_PublicKey form a message and signature using
       * Algorithm 6 WOTS_pkFromSig defined in the XMSS standard. This
       * overload is used to verify a message using a public key.
       *
       * @param oid WOTSP algorithm identifier.
       * @param msg A message.
       * @param sig A WOTS signature for msg.
       * @param adrs An XMSS_Address.
       * @param public_seed The public public_seed.
       **/
      XMSS_WOTS_PublicKey(XMSS_WOTS_Parameters::ots_algorithm_t oid,
                          const secure_vector<uint8_t>& msg,
                          const wots_keysig_t& sig,
                          XMSS_Address& adrs,
                          const secure_vector<uint8_t>& public_seed)
         : m_wots_params(oid),
           m_hash(m_wots_params.hash_function_name()),
           m_key(pub_key_from_signature(msg,
                                        sig,
                                        adrs,
                                        public_seed)),
           m_public_seed(public_seed)
         {}

      /**
       * Retrieves the i-th element out of the length len chain of
       * n-byte elements contained in the public key.
       *
       * @param i index of the element.
       * @returns n-byte element addressed by i.
       **/
      const secure_vector<uint8_t>& operator[](size_t i) const { return m_key[i]; }
      secure_vector<uint8_t>& operator[](size_t i) { return m_key[i]; }

      /**
       * Convert the key into the raw key data. The key becomes a length
       * len vector of n-byte elements.
       **/
      operator const wots_keysig_t& () const { return m_key; }

      /**
       * Convert the key into the raw key data. The key becomes a length
       * len vector of n-byte elements.
       **/
      operator wots_keysig_t& () { return m_key; }

      const secure_vector<uint8_t>& public_seed() const { return m_public_seed; }

      secure_vector<uint8_t>& public_seed() { return m_public_seed; }

      void set_public_seed(const secure_vector<uint8_t>& public_seed)
         {
         m_public_seed = public_seed;
         }

      void set_public_seed(secure_vector<uint8_t>&& public_seed)
         {
         m_public_seed = std::move(public_seed);
         }

      const wots_keysig_t& key_data() const { return m_key; }

      wots_keysig_t& key_data() { return m_key; }

      void set_key_data(const wots_keysig_t& key_data)
         {
         m_key = key_data;
         }

      void set_key_data(wots_keysig_t&& key_data)
         {
         m_key = std::move(key_data);
         }

      const XMSS_WOTS_Parameters& wots_parameters() const
         {
         return m_wots_params;
         }

      virtual std::string algo_name() const override
         {
         return m_wots_params.name();
         }

      virtual AlgorithmIdentifier algorithm_identifier() const override
         {
         throw Not_Implemented("No AlgorithmIdentifier available for XMSS-WOTS.");
         }

      virtual bool check_key(RandomNumberGenerator&, bool) const override
         {
         return true;
         }

      virtual std::unique_ptr<PK_Ops::Verification>
         create_verification_op(const std::string&,
                                const std::string& provider) const override;

      virtual size_t estimated_strength() const override
         {
         return m_wots_params.estimated_strength();
         }

      virtual size_t key_length() const override
         {
         return m_wots_params.estimated_strength();
         }

      virtual std::vector<uint8_t> public_key_bits() const override
         {
         throw Not_Implemented("No key format defined for XMSS-WOTS");
         }

      bool operator==(const XMSS_WOTS_PublicKey& key)
         {
         return m_key == key.m_key;
         }

      bool operator!=(const XMSS_WOTS_PublicKey& key)
         {
         return !(*this == key);
         }

   protected:
      /**
       * Algorithm 2: Chaining Function.
       *
       * Takes an n-byte input string and transforms it into a the function
       * result iterating the cryptographic hash function "F" steps times on
       * the input x using the outputs of the PRNG "G".
       *
       *
       * @param[out] x An n-byte input string, that will be transformed into
       *               the chaining function result.
       * @param start_idx The start index.
       * @param steps A number of steps.
       * @param adrs An OTS Hash Address.
       * @param public_seed A public seed.
       *
       **/
      void chain(secure_vector<uint8_t>& x,
                 size_t start_idx,
                 size_t steps,
                 XMSS_Address& adrs,
                 const secure_vector<uint8_t>& public_seed);

      XMSS_WOTS_Parameters m_wots_params;
      XMSS_Hash m_hash;

      wots_keysig_t m_key;
      secure_vector<uint8_t> m_public_seed;

   private:
      /**
       * Algorithm 6: "WOTS_pkFromSig"
       * Computes a Winternitz One Time Signature+ public key from a message and
       * its signature.
       *
       * @param msg A message.
       * @param sig The signature for msg.
       * @param adrs An address.
       * @param public_seed A public_seed.
       *
       * @return Temporary WOTS+ public key.
       **/
      wots_keysig_t pub_key_from_signature(
         const secure_vector<uint8_t>& msg,
         const wots_keysig_t& sig,
         XMSS_Address& adrs,
         const secure_vector<uint8_t>& public_seed);
   };

}

#endif
