/*
 *
 * 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_CRYPT_GSEC_H
#define GRPC_CORE_TSI_ALTS_CRYPT_GSEC_H

#include <grpc/support/port_platform.h>

#include <assert.h>
#include <stdint.h>
#include <stdlib.h>

#include <grpc/grpc.h>

struct iovec {
  void* iov_base;
  size_t iov_len;
};

/**
 * A gsec interface for AEAD encryption schemes. The API is thread-compatible.
 * Each implementation of this interface should specify supported values for
 * key, nonce, and tag lengths.
 */

/* Key, nonce, and tag length in bytes */
const size_t kAesGcmNonceLength = 12;
const size_t kAesGcmTagLength = 16;
const size_t kAes128GcmKeyLength = 16;
const size_t kAes256GcmKeyLength = 32;

// The first 32 bytes are used as a KDF key and the remaining 12 bytes are used
// to mask the nonce.
const size_t kAes128GcmRekeyKeyLength = 44;

typedef struct gsec_aead_crypter gsec_aead_crypter;

/**
 * The gsec_aead_crypter is an API for different AEAD implementations such as
 * AES_GCM. It encapsulates all AEAD-related operations in the format of
 * V-table that stores pointers to functions implementing those operations.
 * It also provides helper functions to wrap each of those function pointers.
 *
 * A typical usage of this object would be:
 *
 *------------------------------------------------------------------------------
 * // Declare a gsec_aead_crypter object, and create and assign an instance
 * // of specific AEAD implementation e.g., AES_GCM to it. We assume both
 * // key and nonce contain cryptographically secure random bytes, and the key
 * // can be derived from an upper-layer application.
 * gsec_aead_crypter* crypter;
 * char* error_in_creation;
 * // User can populate the message with any 100 bytes data.
 * uint8_t* message = gpr_malloc(100);
 * grpc_status_code creation_status = gsec_aes_gcm_aead_crypter_create(key,
 *                                                      kAes128GcmKeyLength,
 *                                                      kAesGcmNonceLength,
 *                                                      kAesGcmTagLength,
 *                                                      &crypter,
 *                                                      false,
 *                                                      0
 *                                                      &error_in_creation);
 *
 * if (creation_status == GRPC_STATUS_OK) {
 *    // Allocate a correct amount of memory to hold a ciphertext.
 *    size_t clength = 0;
 *    gsec_aead_crypter_max_ciphertext_and_tag_length(crypter, 100, &clength,
 *                                                    nullptr);
 *    uint8_t* ciphertext = gpr_malloc(clength);
 *
 *    // Perform encryption
 *    size_t num_encrypted_bytes = 0;
 *    char* error_in_encryption = nullptr;
 *    grpc_status_code status = gsec_aead_crypter_encrypt(crypter, nonce,
 *                                                        kAesGcmNonceLength,
 *                                                        nullptr, 0, message,
 *                                                        100, ciphertext,
 *                                                        clength,
 *                                                        &num_encrypted_bytes,
 *                                                        &error_in_encryption);
 * if (status == GRPC_STATUS_OK) {
 *       // Allocate a correct amount of memory to hold a plaintext.
 *       size_t plength = 0;
 *       gsec_aead_crypter_max_plaintext_length(crypter, num_encrypted_bytes,
 *                                              &plength, nullptr);
 *       uint8_t* plaintext = gpr_malloc(plength);
 *
 *       // Perform decryption.
 *       size_t num_decrypted_bytes = 0;
 *       char* error_in_decryption = nullptr;
 *       status = gsec_aead_crypter_decrypt(crypter, nonce,
 *                                          kAesGcmNonceLength, nullptr, 0,
 *                                          ciphertext, num_encrypted_bytes,
 *                                          plaintext, plength,
 *                                          &num_decrypted_bytes,
 *                                          &error_in_decryption);
 *       if (status != GRPC_STATUS_OK) {
 *         fprintf(stderr, "AEAD decrypt operation failed with error code:"
 *                         "%d, message: %s\n", status, error_in_decryption);
 *       }
 *       ...
 *       gpr_free(plaintext);
 *       gpr_free(error_in_decryption);
 *    } else {
 *        fprintf(stderr, "AEAD encrypt operation failed with error code:"
 *                        "%d, message: %s\n", status, error_in_encryption);
 *    }
 *    ...
 *    gpr_free(ciphertext);
 *    gpr_free(error_in_encryption);
 * } else {
 *   fprintf(stderr, "Creation of AEAD crypter instance failed with error code:"
 *                   "%d, message: %s\n", creation_status, error_in_creation);
 * }
 *
 * // Destruct AEAD crypter instance.
 * if (creation_status == GRPC_STATUS_OK) {
 *   gsec_aead_crypter_destroy(crypter);
 * }
 * gpr_free(error_in_creation);
 * gpr_free(message);
 * -----------------------------------------------------------------------------
 */

/* V-table for gsec AEAD operations */
typedef struct gsec_aead_crypter_vtable {
  grpc_status_code (*encrypt_iovec)(
      gsec_aead_crypter* crypter, const uint8_t* nonce, size_t nonce_length,
      const struct iovec* aad_vec, size_t aad_vec_length,
      const struct iovec* plaintext_vec, size_t plaintext_vec_length,
      struct iovec ciphertext_vec, size_t* ciphertext_bytes_written,
      char** error_details);
  grpc_status_code (*decrypt_iovec)(
      gsec_aead_crypter* crypter, const uint8_t* nonce, size_t nonce_length,
      const struct iovec* aad_vec, size_t aad_vec_length,
      const struct iovec* ciphertext_vec, size_t ciphertext_vec_length,
      struct iovec plaintext_vec, size_t* plaintext_bytes_written,
      char** error_details);
  grpc_status_code (*max_ciphertext_and_tag_length)(
      const gsec_aead_crypter* crypter, size_t plaintext_length,
      size_t* max_ciphertext_and_tag_length_to_return, char** error_details);
  grpc_status_code (*max_plaintext_length)(
      const gsec_aead_crypter* crypter, size_t ciphertext_and_tag_length,
      size_t* max_plaintext_length_to_return, char** error_details);
  grpc_status_code (*nonce_length)(const gsec_aead_crypter* crypter,
                                   size_t* nonce_length_to_return,
                                   char** error_details);
  grpc_status_code (*key_length)(const gsec_aead_crypter* crypter,
                                 size_t* key_length_to_return,
                                 char** error_details);
  grpc_status_code (*tag_length)(const gsec_aead_crypter* crypter,
                                 size_t* tag_length_to_return,
                                 char** error_details);
  void (*destruct)(gsec_aead_crypter* crypter);
} gsec_aead_crypter_vtable;

/* Main struct for gsec interface */
struct gsec_aead_crypter {
  const struct gsec_aead_crypter_vtable* vtable;
};

/**
 * This method performs an AEAD encrypt operation.
 *
 * - crypter: AEAD crypter instance.
 * - nonce: buffer containing a nonce with its size equal to nonce_length.
 * - nonce_length: size of nonce buffer, and must be equal to the value returned
 *   from method gsec_aead_crypter_nonce_length.
 * - aad: buffer containing data that needs to be authenticated but not
 *   encrypted with its size equal to aad_length.
 * - aad_length: size of aad buffer, which should be zero if the buffer is
 *   nullptr.
 * - plaintext: buffer containing data that needs to be both encrypted and
 *   authenticated with its size equal to plaintext_length.
 * - plaintext_length: size of plaintext buffer, which should be zero if
 *   plaintext is nullptr.
 * - ciphertext_and_tag: buffer that will contain ciphertext and tags the method
 *   produced. The buffer should not overlap the plaintext buffer, and pointers
 *   to those buffers should not be equal. Also if the ciphertext+tag buffer is
 *   nullptr, the plaintext_length should be zero.
 * - ciphertext_and_tag_length: size of ciphertext+tag buffer, which should be
 *   at least as long as the one returned from method
 *   gsec_aead_crypter_max_ciphertext_and_tag_length.
 * - bytes_written: the actual number of bytes written to the ciphertext+tag
 *   buffer. If bytes_written is nullptr, the plaintext_length should be zero.
 * - 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 the success of encryption, 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 gsec_aead_crypter_encrypt(
    gsec_aead_crypter* crypter, const uint8_t* nonce, size_t nonce_length,
    const uint8_t* aad, size_t aad_length, const uint8_t* plaintext,
    size_t plaintext_length, uint8_t* ciphertext_and_tag,
    size_t ciphertext_and_tag_length, size_t* bytes_written,
    char** error_details);

/**
 * This method performs an AEAD encrypt operation.
 *
 * - crypter: AEAD crypter instance.
 * - nonce: buffer containing a nonce with its size equal to nonce_length.
 * - nonce_length: size of nonce buffer, and must be equal to the value returned
 *   from method gsec_aead_crypter_nonce_length.
 * - aad_vec: an iovec array containing data that needs to be authenticated but
 *   not encrypted.
 * - aad_vec_length: the array length of aad_vec.
 * - plaintext_vec: an iovec array containing data that needs to be both
 *   encrypted and authenticated.
 * - plaintext_vec_length: the array length of plaintext_vec.
 * - ciphertext_vec: an iovec containing a ciphertext buffer. The buffer should
 *   not overlap the plaintext buffer.
 * - ciphertext_bytes_written: the actual number of bytes written to
 *   ciphertext_vec.
 * - 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 the success of encryption, 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 gsec_aead_crypter_encrypt_iovec(
    gsec_aead_crypter* crypter, const uint8_t* nonce, size_t nonce_length,
    const struct iovec* aad_vec, size_t aad_vec_length,
    const struct iovec* plaintext_vec, size_t plaintext_vec_length,
    struct iovec ciphertext_vec, size_t* ciphertext_bytes_written,
    char** error_details);

/**
 * This method performs an AEAD decrypt operation.
 *
 * - crypter: AEAD crypter instance.
 * - nonce: buffer containing a nonce with its size equal to nonce_length.
 * - nonce_length: size of nonce buffer, and must be equal to the value returned
 *   from method gsec_aead_crypter_nonce_length.
 * - aad: buffer containing data that needs to be authenticated only.
 * - aad_length: size of aad buffer, which should be zero if the buffer is
 *   nullptr.
 * - ciphertext_and_tag: buffer containing ciphertext and tag.
 * - ciphertext_and_tag_length: length of ciphertext and tag. It should be zero
 *   if any of plaintext, ciphertext_and_tag, or bytes_written is nullptr. Also,
 *   ciphertext_and_tag_length should be at least as large as the tag length set
 *   at AEAD crypter instance construction time.
 * - plaintext: buffer containing decrypted and authenticated data the method
 *   produced. The buffer should not overlap with the ciphertext+tag buffer, and
 *   pointers to those buffers should not be equal.
 * - plaintext_length: size of plaintext buffer, which should be at least as
 *   long as the one returned from gsec_aead_crypter_max_plaintext_length
 *   method.
 * - bytes_written: the actual number of bytes written to the plaintext
 *   buffer.
 * - 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 the success of decryption, 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 gsec_aead_crypter_decrypt(
    gsec_aead_crypter* crypter, const uint8_t* nonce, size_t nonce_length,
    const uint8_t* aad, size_t aad_length, const uint8_t* ciphertext_and_tag,
    size_t ciphertext_and_tag_length, uint8_t* plaintext,
    size_t plaintext_length, size_t* bytes_written, char** error_details);

/**
 * This method performs an AEAD decrypt operation.
 *
 * - crypter: AEAD crypter instance.
 * - nonce: buffer containing a nonce with its size equal to nonce_length.
 * - nonce_length: size of nonce buffer, and must be equal to the value returned
 *   from method gsec_aead_crypter_nonce_length.
 * - aad_vec: an iovec array containing data that needs to be authenticated but
 *   not encrypted.
 * - aad_vec_length: the array length of aad_vec.
 * - ciphertext_vec: an iovec array containing the ciphertext and tag.
 * - ciphertext_vec_length: the array length of ciphertext_vec.
 * - plaintext_vec: an iovec containing a plaintext buffer. The buffer should
 *   not overlap the ciphertext buffer.
 * - plaintext_bytes_written: the actual number of bytes written to
 *   plaintext_vec.
 * - 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 the success of decryption, 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 gsec_aead_crypter_decrypt_iovec(
    gsec_aead_crypter* crypter, const uint8_t* nonce, size_t nonce_length,
    const struct iovec* aad_vec, size_t aad_vec_length,
    const struct iovec* ciphertext_vec, size_t ciphertext_vec_length,
    struct iovec plaintext_vec, size_t* plaintext_bytes_written,
    char** error_details);

/**
 * This method computes the size of ciphertext+tag buffer that must be passed to
 * gsec_aead_crypter_encrypt function to ensure correct encryption of a
 * plaintext. The actual size of ciphertext+tag written to the buffer could be
 * smaller.
 *
 * - crypter: AEAD crypter instance.
 * - plaintext_length: length of plaintext.
 * - max_ciphertext_and_tag_length_to_return: the size of ciphertext+tag buffer
 *   the method returns.
 * - 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 the success of execution, 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 gsec_aead_crypter_max_ciphertext_and_tag_length(
    const gsec_aead_crypter* crypter, size_t plaintext_length,
    size_t* max_ciphertext_and_tag_length_to_return, char** error_details);

/**
 * This method computes the size of plaintext buffer that must be passed to
 * gsec_aead_crypter_decrypt function to ensure correct decryption of a
 * ciphertext. The actual size of plaintext written to the buffer could be
 * smaller.
 *
 * - crypter: AEAD crypter instance.
 * - ciphertext_and_tag_length: length of ciphertext and tag.
 * - max_plaintext_length_to_return: the size of plaintext buffer the method
 *   returns.
 * - 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 the success of execution, 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 gsec_aead_crypter_max_plaintext_length(
    const gsec_aead_crypter* crypter, size_t ciphertext_and_tag_length,
    size_t* max_plaintext_length_to_return, char** error_details);

/**
 * This method returns a valid size of nonce array used at the construction of
 * AEAD crypter instance. It is also the size that should be passed to encrypt
 * and decrypt methods executed on the instance.
 *
 * - crypter: AEAD crypter instance.
 * - nonce_length_to_return: the length of nonce array the method returns.
 * - 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 the success of execution, 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 gsec_aead_crypter_nonce_length(
    const gsec_aead_crypter* crypter, size_t* nonce_length_to_return,
    char** error_details);

/**
 * This method returns a valid size of key array used at the construction of
 * AEAD crypter instance. It is also the size that should be passed to encrypt
 * and decrypt methods executed on the instance.
 *
 * - crypter: AEAD crypter instance.
 * - key_length_to_return: the length of key array the method returns.
 * - 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 the success of execution, 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 gsec_aead_crypter_key_length(const gsec_aead_crypter* crypter,
                                              size_t* key_length_to_return,
                                              char** error_details);
/**
 * This method returns a valid size of tag array used at the construction of
 * AEAD crypter instance. It is also the size that should be passed to encrypt
 * and decrypt methods executed on the instance.
 *
 * - crypter: AEAD crypter instance.
 * - tag_length_to_return: the length of tag array the method returns.
 * - 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 the success of execution, 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 gsec_aead_crypter_tag_length(const gsec_aead_crypter* crypter,
                                              size_t* tag_length_to_return,
                                              char** error_details);

/**
 * This method destroys an AEAD crypter instance by de-allocating all of its
 * occupied memory.
 *
 * - crypter: AEAD crypter instance that needs to be destroyed.
 */
void gsec_aead_crypter_destroy(gsec_aead_crypter* crypter);

/**
 * This method creates an AEAD crypter instance of AES-GCM encryption scheme
 * which supports 16 and 32 bytes long keys, 12 and 16 bytes long nonces, and
 * 16 bytes long tags. It should be noted that once the lengths of key, nonce,
 * and tag are determined at construction time, they cannot be modified later.
 *
 * - key: buffer containing a key which is binded with AEAD crypter instance.
 * - key_length: length of a key in bytes, which should be 44 if rekeying is
 *   enabled and 16 or 32 otherwise.
 * - nonce_length: length of a nonce in bytes, which should be either 12 or 16.
 * - tag_length: length of a tag in bytes, which should be always 16.
 * - rekey: enable nonce-based rekeying and nonce-masking.
 * - crypter: address of AES_GCM crypter instance 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 instance creation, it stores the address of instance at
 * crypter. Otherwise, it returns an error status code together with its details
 * specified in error_details.
 */
grpc_status_code gsec_aes_gcm_aead_crypter_create(const uint8_t* key,
                                                  size_t key_length,
                                                  size_t nonce_length,
                                                  size_t tag_length, bool rekey,
                                                  gsec_aead_crypter** crypter,
                                                  char** error_details);

#endif /* GRPC_CORE_TSI_ALTS_CRYPT_GSEC_H */