/* toxencryptsave.h
 *
 * The Tox encrypted save functions.
 *
 *  Copyright (C) 2013 Tox project All Rights Reserved.
 *
 *  This file is part of Tox.
 *
 *  Tox is free software: you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation, either version 3 of the License, or
 *  (at your option) any later version.
 *
 *  Tox is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with Tox.  If not, see <http://www.gnu.org/licenses/>.
 *
 */

#ifndef TOXENCRYPTSAVE_H
#define TOXENCRYPTSAVE_H

#ifdef __cplusplus
extern "C" {
#endif

#include <stdint.h>
#include <stddef.h>
#include <stdbool.h>

#ifndef TOX_DEFINED
#define TOX_DEFINED
typedef struct Tox Tox;
struct Tox_Options;
#endif

#define TOX_PASS_SALT_LENGTH 32
#define TOX_PASS_KEY_LENGTH 32
#define TOX_PASS_ENCRYPTION_EXTRA_LENGTH 80

/* This module is conceptually organized into two parts. The first part are the functions
 * with "key" in the name. To use these functions, first derive an encryption key
 * from a password with tox_derive_key_from_pass, and use the returned key to
 * encrypt the data. The second part takes the password itself instead of the key,
 * and then delegates to the first part to derive the key before de/encryption,
 * which can simplify client code; however, key derivation is very expensive
 * compared to the actual encryption, so clients that do a lot of encryption should
 * favor using the first part intead of the second part.
 *
 * The encrypted data is prepended with a magic number, to aid validity checking
 * (no guarantees are made of course). Any data to be decrypted must start with
 * the magic number.
 *
 * Clients should consider alerting their users that, unlike plain data, if even one bit
 * becomes corrupted, the data will be entirely unrecoverable.
 * Ditto if they forget their password, there is no way to recover the data.
 */

/* Since apparently no one actually bothered to learn about the module previously,
 * the recently removed functions tox_encrypted_new and tox_get_encrypted_savedata
 * may be trivially replaced by calls to tox_pass_decrypt -> tox_new or
 * tox_get_savedata -> tox_pass_encrypt as appropriate. The removed functions
 * were never more than 5 line wrappers of the other public API functions anyways.
 * (As has always been, tox_pass_decrypt and tox_pass_encrypt are interchangeable
 *  with tox_pass_key_decrypt and tox_pass_key_encrypt, as the client program requires.)
 */

typedef enum TOX_ERR_KEY_DERIVATION {
    TOX_ERR_KEY_DERIVATION_OK,
    /**
     * Some input data, or maybe the output pointer, was null.
     */
    TOX_ERR_KEY_DERIVATION_NULL,
    /**
     * The crypto lib was unable to derive a key from the given passphrase,
     * which is usually a lack of memory issue. The functions accepting keys
     * do not produce this error.
     */
    TOX_ERR_KEY_DERIVATION_FAILED
} TOX_ERR_KEY_DERIVATION;

typedef enum TOX_ERR_ENCRYPTION {
    TOX_ERR_ENCRYPTION_OK,
    /**
     * Some input data, or maybe the output pointer, was null.
     */
    TOX_ERR_ENCRYPTION_NULL,
    /**
     * The crypto lib was unable to derive a key from the given passphrase,
     * which is usually a lack of memory issue. The functions accepting keys
     * do not produce this error.
     */
    TOX_ERR_ENCRYPTION_KEY_DERIVATION_FAILED,
    /**
     * The encryption itself failed.
     */
    TOX_ERR_ENCRYPTION_FAILED
} TOX_ERR_ENCRYPTION;

typedef enum TOX_ERR_DECRYPTION {
    TOX_ERR_DECRYPTION_OK,
    /**
     * Some input data, or maybe the output pointer, was null.
     */
    TOX_ERR_DECRYPTION_NULL,
    /**
     * The input data was shorter than TOX_PASS_ENCRYPTION_EXTRA_LENGTH bytes
     */
    TOX_ERR_DECRYPTION_INVALID_LENGTH,
    /**
     * The input data is missing the magic number (i.e. wasn't created by this
     * module, or is corrupted)
     */
    TOX_ERR_DECRYPTION_BAD_FORMAT,
    /**
     * The crypto lib was unable to derive a key from the given passphrase,
     * which is usually a lack of memory issue. The functions accepting keys
     * do not produce this error.
     */
    TOX_ERR_DECRYPTION_KEY_DERIVATION_FAILED,
    /**
     * The encrypted byte array could not be decrypted. Either the data was
     * corrupt or the password/key was incorrect.
     */
    TOX_ERR_DECRYPTION_FAILED
} TOX_ERR_DECRYPTION;


/******************************* BEGIN PART 2 *******************************
 * For simplicty, the second part of the module is presented first. The API for
 * the first part is analgous, with some extra functions for key handling. If
 * your code spends too much time using these functions, consider using the part
 * 1 functions instead.
 */

/* Encrypts the given data with the given passphrase. The output array must be
 * at least data_len + TOX_PASS_ENCRYPTION_EXTRA_LENGTH bytes long. This delegates
 * to tox_derive_key_from_pass and tox_pass_key_encrypt.
 *
 * returns true on success
 */
bool tox_pass_encrypt(const uint8_t *data, size_t data_len, const uint8_t *passphrase, size_t pplength, uint8_t *out,
                      TOX_ERR_ENCRYPTION *error);


/* Decrypts the given data with the given passphrase. The output array must be
 * at least data_len - TOX_PASS_ENCRYPTION_EXTRA_LENGTH bytes long. This delegates
 * to tox_pass_key_decrypt.
 *
 * the output data has size data_length - TOX_PASS_ENCRYPTION_EXTRA_LENGTH
 *
 * returns true on success
 */
bool tox_pass_decrypt(const uint8_t *data, size_t length, const uint8_t *passphrase, size_t pplength, uint8_t *out,
                      TOX_ERR_DECRYPTION *error);


/******************************* BEGIN PART 1 *******************************
 * And now part "1", which does the actual encryption, and is rather less cpu
 * intensive than part one. The first 3 functions are for key handling.
 */

/* This key structure's internals should not be used by any client program, even
 * if they are straightforward here.
 */
typedef struct {
    uint8_t salt[TOX_PASS_SALT_LENGTH];
    uint8_t key[TOX_PASS_KEY_LENGTH];
} TOX_PASS_KEY;

/* Generates a secret symmetric key from the given passphrase. out_key must be at least
 * TOX_PASS_KEY_LENGTH bytes long.
 * Be sure to not compromise the key! Only keep it in memory, do not write to disk.
 * The password is zeroed after key derivation.
 * The key should only be used with the other functions in this module, as it
 * includes a salt.
 * Note that this function is not deterministic; to derive the same key from a
 * password, you also must know the random salt that was used. See below.
 *
 * returns true on success
 */
bool tox_derive_key_from_pass(const uint8_t *passphrase, size_t pplength, TOX_PASS_KEY *out_key,
                              TOX_ERR_KEY_DERIVATION *error);

/* Same as above, except use the given salt for deterministic key derivation.
 * The salt must be TOX_PASS_SALT_LENGTH bytes in length.
 */
bool tox_derive_key_with_salt(const uint8_t *passphrase, size_t pplength, const uint8_t *salt, TOX_PASS_KEY *out_key,
                              TOX_ERR_KEY_DERIVATION *error);

/* This retrieves the salt used to encrypt the given data, which can then be passed to
 * derive_key_with_salt to produce the same key as was previously used. Any encrpyted
 * data with this module can be used as input.
 *
 * returns true if magic number matches
 * success does not say anything about the validity of the data, only that data of
 * the appropriate size was copied
 */
bool tox_get_salt(const uint8_t *data, uint8_t *salt);

/* Now come the functions that are analogous to the part 2 functions. */

/* Encrypt arbitrary with a key produced by tox_derive_key_*. The output
 * array must be at least data_len + TOX_PASS_ENCRYPTION_EXTRA_LENGTH bytes long.
 * key must be TOX_PASS_KEY_LENGTH bytes.
 * If you already have a symmetric key from somewhere besides this module, simply
 * call encrypt_data_symmetric in toxcore/crypto_core directly.
 *
 * returns true on success
 */
bool tox_pass_key_encrypt(const uint8_t *data, size_t data_len, const TOX_PASS_KEY *key, uint8_t *out,
                          TOX_ERR_ENCRYPTION *error);

/* This is the inverse of tox_pass_key_encrypt, also using only keys produced by
 * tox_derive_key_from_pass.
 *
 * the output data has size data_length - TOX_PASS_ENCRYPTION_EXTRA_LENGTH
 *
 * returns true on success
 */
bool tox_pass_key_decrypt(const uint8_t *data, size_t length, const TOX_PASS_KEY *key, uint8_t *out,
                          TOX_ERR_DECRYPTION *error);

/* Determines whether or not the given data is encrypted (by checking the magic number)
 */
bool tox_is_data_encrypted(const uint8_t *data);

#ifdef __cplusplus
}
#endif

#endif