/*
 * Copyright (c) 2023-2024 Ian Marco Moffett and the Osmora Team.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 * 1. Redistributions of source code must retain the above copyright notice,
 *    this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of Hyra nor the names of its
 *    contributors may be used to endorse or promote products derived from
 *    this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 */

#include <sys/mman.h>
#include <openssl/evp.h>
#include <openssl/ec.h>
#include <openssl/pem.h>
#include <openssl/bn.h>
#include <openssl/err.h>
#include <crypto/ecdh.h>
#include <stdio.h>

#define KEY_SIZE 32

int
gen_x25519_keypair(struct x25519_keypair *res)
{
    EVP_PKEY_CTX *ctx;
    EVP_PKEY *keypair_raw = NULL;
    struct x25519_keypair keypair;
    int retor;

    if (res == NULL) {
        return -1;
    }

    ctx = EVP_PKEY_CTX_new_id(EVP_PKEY_X25519, NULL);
    if (ctx == NULL) {
        printf("ecdh: Failed to create X25519 keygen context\n");
        return -1;
    }

    if (EVP_PKEY_keygen_init(ctx) <= 0) {
        printf("ecdh: Failed to init X25519 keygen context\n");
        EVP_PKEY_CTX_free(ctx);
        return -1;
    }

    /* Create X25519 key pair */
    if (EVP_PKEY_keygen(ctx, &keypair_raw) <= 0) {
        printf("ecdh: Failed to generate X25519 keypair\n");
        EVP_PKEY_CTX_free(ctx);
        return -1;
    }

    /* Allocate a buffer for the public key */
    EVP_PKEY_get_raw_public_key(keypair_raw, NULL, &keypair.pubkey_len);
    keypair.pubkey = malloc(keypair.pubkey_len);

    if (keypair.pubkey == NULL) {
        printf(" ecdh: Failed to allocate memory for public key\n");
        EVP_PKEY_free(keypair_raw);
        EVP_PKEY_CTX_free(ctx);
        return -1;
    }

    /* Allocate a buffer for the private key */
    EVP_PKEY_get_raw_private_key(keypair_raw, NULL, &keypair.privkey_len);
    keypair.privkey = malloc(keypair.privkey_len);

    if (keypair.privkey == NULL) {
        printf("ecdh: Failed allocating memory for private key\n");
        EVP_PKEY_free(keypair_raw);
        EVP_PKEY_CTX_free(ctx);
        return -1;
    }

    retor = EVP_PKEY_get_raw_private_key(keypair_raw, keypair.privkey,
        &keypair.privkey_len);

    if (retor <= 0) {
        printf("Failed to extract private key\n");
        EVP_PKEY_free(keypair_raw);
        EVP_PKEY_CTX_free(ctx);
    }

    retor = EVP_PKEY_get_raw_public_key(keypair_raw, keypair.pubkey,
        &keypair.pubkey_len);

    if (retor <= 0) {
        printf("Failed to extract public key\n");
        EVP_PKEY_free(keypair_raw);
        EVP_PKEY_CTX_free(ctx);
    }

    EVP_PKEY_free(keypair_raw);
    EVP_PKEY_CTX_free(ctx);
    *res = keypair;
    return 0;
}

int
free_x25519_keypair(struct x25519_keypair *xkp)
{
    if (xkp == NULL) {
        return -1;
    }

    free(xkp->pubkey);
    free(xkp->privkey);
    return 0;
}

int
gen_session_key(const unsigned char *priv, const unsigned char *peer_key,
    unsigned char **res)
{
    size_t tmp;
    unsigned char *session_key;
    EVP_PKEY *own_key = NULL;
    EVP_PKEY *peer_pubkey = NULL;
    EVP_PKEY_CTX *ctx = NULL;

    /* Allocate memory for session key */
    session_key = malloc(KEY_SIZE);
    if (session_key == NULL) {
        printf("Failed to allocate session key memory\n");
        return -1;
    }

    /* Lock and load session key pages */
    if (mlock(session_key, KEY_SIZE) != 0) {
        printf("Failed to lock session key pages\n");
        free(session_key);
        return -1;
    }

    /* Create an EVP_PKEY from our private key */
    own_key = EVP_PKEY_new_raw_private_key(EVP_PKEY_X25519, NULL, priv,
        KEY_SIZE);

    if (own_key == NULL) {
        printf("Failed to serialize private key\n");
        free_session_key(session_key);
        return -1;
    }

    /* Create an EVP_PKEY for peer public key */
    peer_pubkey = EVP_PKEY_new_raw_public_key(EVP_PKEY_X25519, NULL,
        peer_key, KEY_SIZE);

    if (peer_pubkey == NULL) {
        printf("Failed to serialize peer public key\n");
        EVP_PKEY_free(own_key);
        free_session_key(session_key);
        return -1;
    }

    ctx = EVP_PKEY_CTX_new(own_key, NULL);
    if (ctx == NULL) {
        printf("Failed to create context\n");
        EVP_PKEY_free(own_key);
        EVP_PKEY_free(peer_pubkey);
        free_session_key(session_key);
        return -1;
    }

    /* Initialize key derivation */
    if (EVP_PKEY_derive_init(ctx) <= 0) {
        printf("Failed initializing key derivation\n");
        EVP_PKEY_CTX_free(ctx);
        EVP_PKEY_free(own_key);
        EVP_PKEY_free(peer_pubkey);
        free_session_key(session_key);
        return -1;
    }

    /* Set peer public key */
    if (EVP_PKEY_derive_set_peer(ctx, peer_pubkey) <= 0) {
        printf("Failed to set peer key\n");
        EVP_PKEY_CTX_free(ctx);
        EVP_PKEY_free(own_key);
        EVP_PKEY_free(peer_pubkey);
        free_session_key(session_key);
        return -1;
    }

    /* Derive the session key */
    tmp = KEY_SIZE;
    if (EVP_PKEY_derive(ctx, session_key, &tmp) <= 0) {
        printf("Failed to derive session key\n");
        EVP_PKEY_CTX_free(ctx);
        EVP_PKEY_free(own_key);
        EVP_PKEY_free(peer_pubkey);
        free_session_key(session_key);
        return -1;
    }

    EVP_PKEY_CTX_free(ctx);
    EVP_PKEY_free(own_key);
    EVP_PKEY_free(peer_pubkey);
    *res = session_key;
    return 0;
}

int
free_session_key(unsigned char *session_key)
{
    munlock(session_key, KEY_SIZE);
    free(session_key);
}