/*
* SRP-6a (RFC 5054 compatatible)
* (C) 2011,2012,2019 Jack Lloyd
*
* Botan is released under the Simplified BSD License (see license.txt)
*/

#ifndef BOTAN_RFC5054_SRP6_H_
#define BOTAN_RFC5054_SRP6_H_

#include <botan/bigint.h>
#include <botan/dl_group.h>
#include <botan/symkey.h>
#include <string>

namespace Botan {

class RandomNumberGenerator;

/**
* SRP6a Client side
* @param username the username we are attempting login for
* @param password the password we are attempting to use
* @param group_id specifies the shared SRP group
* @param hash_id specifies a secure hash function
* @param salt is the salt value sent by the server
* @param B is the server's public value
* @param rng is a random number generator
*
* @return (A,K) the client public key and the shared secret key
*/
std::pair<BigInt, SymmetricKey> BOTAN_PUBLIC_API(2, 0) srp6_client_agree(std::string_view username,
                                                                         std::string_view password,
                                                                         std::string_view group_id,
                                                                         std::string_view hash_id,
                                                                         const std::vector<uint8_t>& salt,
                                                                         const BigInt& B,
                                                                         RandomNumberGenerator& rng);

/**
* SRP6a Client side
* @param username the username we are attempting login for
* @param password the password we are attempting to use
* @param group specifies the shared SRP group
* @param hash_id specifies a secure hash function
* @param salt is the salt value sent by the server
* @param B is the server's public value
* @param a_bits size of secret exponent in bits
* @param rng is a random number generator
*
* @return (A,K) the client public key and the shared secret key
*/
std::pair<BigInt, SymmetricKey> BOTAN_PUBLIC_API(2, 11) srp6_client_agree(std::string_view username,
                                                                          std::string_view password,
                                                                          const DL_Group& group,
                                                                          std::string_view hash_id,
                                                                          const std::vector<uint8_t>& salt,
                                                                          const BigInt& B,
                                                                          size_t a_bits,
                                                                          RandomNumberGenerator& rng);

/**
* Generate a new SRP-6 verifier
* @param identifier a username or other client identifier
* @param password the secret used to authenticate user
* @param salt a randomly chosen value, at least 128 bits long
* @param group_id specifies the shared SRP group
* @param hash_id specifies a secure hash function
*/
BigInt BOTAN_PUBLIC_API(2, 0) srp6_generate_verifier(std::string_view identifier,
                                                     std::string_view password,
                                                     const std::vector<uint8_t>& salt,
                                                     std::string_view group_id,
                                                     std::string_view hash_id);

/**
* Generate a new SRP-6 verifier
* @param identifier a username or other client identifier
* @param password the secret used to authenticate user
* @param salt a randomly chosen value, at least 128 bits long
* @param group specifies the shared SRP group
* @param hash_id specifies a secure hash function
*/
BigInt BOTAN_PUBLIC_API(2, 11) srp6_generate_verifier(std::string_view identifier,
                                                      std::string_view password,
                                                      const std::vector<uint8_t>& salt,
                                                      const DL_Group& group,
                                                      std::string_view hash_id);

/**
* Return the group id for this SRP param set, or else thrown an
* exception
* @param N the group modulus
* @param g the group generator
* @return group identifier
*/
std::string BOTAN_PUBLIC_API(2, 0) srp6_group_identifier(const BigInt& N, const BigInt& g);

/**
* Represents a SRP-6a server session
*/
class BOTAN_PUBLIC_API(2, 0) SRP6_Server_Session final {
   public:
      /**
      * Server side step 1
      * @param v the verification value saved from client registration
      * @param group_id the SRP group id
      * @param hash_id the SRP hash in use
      * @param rng a random number generator
      * @return SRP-6 B value
      */
      BigInt step1(const BigInt& v, std::string_view group_id, std::string_view hash_id, RandomNumberGenerator& rng);

      /**
      * Server side step 1
      * This version of step1 added in 2.11
      *
      * @param v the verification value saved from client registration
      * @param group the SRP group
      * @param hash_id the SRP hash in use
      * @param rng a random number generator
      * @param b_bits size of secret exponent in bits
      * @return SRP-6 B value
      */
      BigInt step1(
         const BigInt& v, const DL_Group& group, std::string_view hash_id, size_t b_bits, RandomNumberGenerator& rng);

      /**
      * Server side step 2
      * @param A the client's value
      * @return shared symmetric key
      */
      SymmetricKey step2(const BigInt& A);

   private:
      std::unique_ptr<DL_Group> m_group;
      std::string m_hash_id;
      BigInt m_B, m_b, m_v, m_S;
};

}  // namespace Botan

#endif
