/*
 *
 * Copyright 2018 gRPC authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 *
 */

#ifndef GRPC_CORE_TSI_ALTS_FRAME_PROTECTOR_ALTS_CRYPTER_H
#define GRPC_CORE_TSI_ALTS_FRAME_PROTECTOR_ALTS_CRYPTER_H

#include <grpc/support/port_platform.h>

#include <stdbool.h>
#include <string.h>

#include <grpc/grpc.h>

#include "src/core/tsi/alts/crypt/gsec.h"

/**
 * An alts_crypter interface for an ALTS record protocol providing
 * seal/unseal functionality. The interface is thread-compatible.
 */

typedef struct alts_crypter alts_crypter;

/**
 * A typical usage of the interface would be
 *------------------------------------------------------------------------------
 * // Perform a seal operation. We assume the gsec_aead_crypter instance -
 * // client_aead_crypter is created beforehand with a 16-byte key and 12-byte
 * // nonce length.
 *
 * alts_crypter* client = nullptr;
 * char* client_error_in_creation = nullptr;
 * unsigned char* data = nullptr;
 * grpc_status_code client_status =
 *                 alts_seal_crypter_create(client_aead_crypter, 1, 5, &client,
 *                                          &client_error_in_creation);
 * if (client_status == GRPC_STATUS_OK) {
 *   size_t data_size = 100;
 *   size_t num_overhead_bytes = alts_crypter_num_overhead_bytes(client);
 *   size_t data_allocated_size = data_size + num_overhead_bytes;
 *   data = gpr_malloc(data_allocated_size);
 *   char* client_error_in_seal = nullptr;
 *   // Client performs a seal operation.
 *   client_status = alts_crypter_process_in_place(client, data,
 *                                                 data_allocated_size,
 *                                                 &data_size,
 *                                                 &client_error_in_seal);
 *   if (client_status != GRPC_STATUS_OK) {
 *     fprintf(stderr, "seal operation failed with error code:"
 *                     "%d, message: %s\n", client_status,
 *                      client_error_in_seal);
 *    }
 *    gpr_free(client_error_in_seal);
 * } else {
 *     fprintf(stderr, "alts_crypter instance creation failed with error"
 *                     "code: %d, message: %s\n", client_status,
 *                      client_error_in_creation);
 * }
 *
 * ...
 *
 * gpr_free(client_error_in_creation);
 * alts_crypter_destroy(client);
 *
 * ...
 *
 * // Perform an unseal operation. We assume the gsec_aead_crypter instance -
 * // server_aead_crypter is created beforehand with a 16-byte key and 12-byte
 * // nonce length. The key used in the creation of gsec_aead_crypter instances
 * // at server and client sides should be identical.
 *
 * alts_crypter* server = nullptr;
 * char* server_error_in_creation = nullptr;
 * grpc_status_code server_status =
 *               alts_unseal_crypter_create(server_aead_crypter, 0, 5, &server,
 *                                          &server_error_in_creation);
 * if (server_status == GRPC_STATUS_OK) {
 *   size_t num_overhead_bytes = alts_crypter_num_overhead_bytes(server);
 *   size_t data_size = 100 + num_overhead_bytes;
 *   size_t data_allocated_size = data_size;
 *   char* server_error_in_unseal = nullptr;
 *   // Server performs an unseal operation.
 *   server_status = alts_crypter_process_in_place(server, data,
 *                                                 data_allocated_size,
 *                                                 &data_size,
 *                                                 &server_error_in_unseal);
 *   if (server_status != GRPC_STATUS_OK) {
 *     fprintf(stderr, "unseal operation failed with error code:"
 *                     "%d, message: %s\n", server_status,
 *                      server_error_in_unseal);
 *   }
 *   gpr_free(server_error_in_unseal);
 * } else {
 *     fprintf(stderr, "alts_crypter instance creation failed with error"
 *                     "code: %d, message: %s\n", server_status,
 *                      server_error_in_creation);
 * }
 *
 * ...
 *
 * gpr_free(data);
 * gpr_free(server_error_in_creation);
 * alts_crypter_destroy(server);
 *
 * ...
 *------------------------------------------------------------------------------
 */

/* V-table for alts_crypter operations */
typedef struct alts_crypter_vtable {
  size_t (*num_overhead_bytes)(const alts_crypter* crypter);
  grpc_status_code (*process_in_place)(alts_crypter* crypter,
                                       unsigned char* data,
                                       size_t data_allocated_size,
                                       size_t data_size, size_t* output_size,
                                       char** error_details);
  void (*destruct)(alts_crypter* crypter);
} alts_crypter_vtable;

/* Main struct for alts_crypter interface */
struct alts_crypter {
  const alts_crypter_vtable* vtable;
};

/**
 * This method gets the number of overhead bytes needed for sealing data that
 * is the difference in size between the protected and raw data. The counter
 * value used in a seal or unseal operation is locally maintained (not sent or
 * received from the other peer) and therefore, will not be counted as part of
 * overhead bytes.
 *
 * - crypter: an alts_crypter instance.
 *
 * On success, the method returns the number of overhead bytes. Otherwise, it
 * returns zero.
 *
 */
size_t alts_crypter_num_overhead_bytes(const alts_crypter* crypter);

/**
 * This method performs either a seal or an unseal operation depending on the
 * alts_crypter instance - crypter passed to the method. If the crypter is
 * an instance implementing a seal operation, the method will perform a seal
 * operation. That is, it seals raw data and stores the result in-place, and the
 * memory allocated for data must be at least data_length +
 * alts_crypter_num_overhead_bytes(). If the crypter is an instance
 * implementing an unseal operation, the method will perform an unseal
 * operation. That is, it unseals protected data and stores the result in-place.
 * The size of unsealed data will be data_length -
 * alts_crypter_num_overhead_bytes(). Integrity tag will be verified during
 * the unseal operation, and if verification fails, the data will be wiped.
 * The counters used in both seal and unseal operations are managed internally.
 *
 * - crypter: an alts_crypter instance.
 * - data: if the method performs a seal operation, the data represents raw data
 *   that needs to be sealed. It also plays the role of buffer to hold the
 *   protected data as a result of seal. If the method performs an unseal
 *   operation, the data represents protected data that needs to be unsealed. It
 *   also plays the role of buffer to hold raw data as a result of unseal.
 * - data_allocated_size: the size of data buffer. The parameter is used to
 *   check whether the result of either seal or unseal can be safely written to
 *   the data buffer.
 * - data_size: if the method performs a seal operation, data_size
 *   represents the size of raw data that needs to be sealed, and if the method
 *   performs an unseal operation, data_size represents the size of protected
 *   data that needs to be unsealed.
 * - output_size: size of data written to the data buffer after a seal or an
 *   unseal operation.
 * - error_details: a buffer containing an error message if the method does not
 *   function correctly. It is legal to pass nullptr into error_details and
 *   otherwise, the parameter should be freed with gpr_free.
 *
 * On success, the method returns GRPC_STATUS_OK. Otherwise,
 * it returns an error status code along with its details specified in
 * error_details (if error_details is not nullptr).
 */
grpc_status_code alts_crypter_process_in_place(
    alts_crypter* crypter, unsigned char* data, size_t data_allocated_size,
    size_t data_size, size_t* output_size, char** error_details);

/**
 * This method creates an alts_crypter instance to be used to perform a seal
 * operation, given a gsec_aead_crypter instance and a flag indicating if the
 * created instance will be used at the client or server side. It takes
 * ownership of gsec_aead_crypter instance.
 *
 * - gc: a gsec_aead_crypter instance used to perform AEAD encryption.
 * - is_client: a flag indicating if the alts_crypter instance will be
 *   used at the client (is_client = true) or server (is_client =
 *   false) side.
 * - overflow_size: overflow size of counter in bytes.
 * - crypter: an alts_crypter instance to be returned from the method.
 * - error_details: a buffer containing an error message if the method does
 *   not function correctly. It is legal to pass nullptr into error_details, and
 *   otherwise, the parameter should be freed with gpr_free.
 *
 * On success of creation, the method returns GRPC_STATUS_OK.
 * Otherwise, it returns an error status code along with its details specified
 * in error_details (if error_details is not nullptr).
 */
grpc_status_code alts_seal_crypter_create(gsec_aead_crypter* gc, bool is_client,
                                          size_t overflow_size,
                                          alts_crypter** crypter,
                                          char** error_details);

/**
 * This method creates an alts_crypter instance used to perform an unseal
 * operation, given a gsec_aead_crypter instance and a flag indicating if the
 * created instance will be used at the client or server side. It takes
 * ownership of gsec_aead_crypter instance.
 *
 * - gc: a gsec_aead_crypter instance used to perform AEAD decryption.
 * - is_client: a flag indicating if the alts_crypter instance will be
 *   used at the client (is_client = true) or server (is_client =
 *   false) side.
 * - overflow_size: overflow size of counter in bytes.
 * - crypter: an alts_crypter instance to be returned from the method.
 * - error_details: a buffer containing an error message if the method does
 *   not function correctly. It is legal to pass nullptr into error_details, and
 *   otherwise, the parameter should be freed with gpr_free.
 *
 * On success of creation, the method returns GRPC_STATUS_OK.
 * Otherwise, it returns an error status code along with its details specified
 * in error_details (if error_details is not nullptr).
 */
grpc_status_code alts_unseal_crypter_create(gsec_aead_crypter* gc,
                                            bool is_client,
                                            size_t overflow_size,
                                            alts_crypter** crypter,
                                            char** error_details);

/**
 * This method destroys an alts_crypter instance by de-allocating all of its
 * occupied memory. A gsec_aead_crypter instance passed in at alts_crypter
 * instance creation time will be destroyed in this method.
 *
 * - crypter: an alts_crypter instance.
 */
void alts_crypter_destroy(alts_crypter* crypter);

#endif /* GRPC_CORE_TSI_ALTS_FRAME_PROTECTOR_ALTS_CRYPTER_H */