/*
 * irc-sasl.c - SASL authentication with IRC server
 *
 * Copyright (C) 2003-2019 Sébastien Helleu <flashcode@flashtux.org>
 *
 * This file is part of WeeChat, the extensible chat client.
 *
 * WeeChat 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.
 *
 * WeeChat 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 WeeChat.  If not, see <https://www.gnu.org/licenses/>.
 */

#include <limits.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <arpa/inet.h>
#include <gcrypt.h>

#ifdef HAVE_GNUTLS
#include <gnutls/gnutls.h>
#if LIBGNUTLS_VERSION_NUMBER >= 0x020a01 /* 2.10.1 */
#include <gnutls/abstract.h>
#endif /* LIBGNUTLS_VERSION_NUMBER >= 0x020a01 */
#endif /* HAVE_GNUTLS */

#include "../weechat-plugin.h"
#include "irc.h"
#include "irc-sasl.h"
#include "irc-server.h"


/*
 * these names are sent to the IRC server (as upper case), so they must be
 * valid values for the AUTHENTICATE command (example: "AUTHENTICATE PLAIN")
 */
char *irc_sasl_mechanism_string[IRC_NUM_SASL_MECHANISMS] =
{ "plain", "ecdsa-nist256p-challenge", "external", "dh-blowfish", "dh-aes" };


/*
 * Builds answer for SASL authentication, using mechanism "PLAIN".
 *
 * Note: result must be freed after use.
 */

char *
irc_sasl_mechanism_plain (const char *sasl_username, const char *sasl_password)
{
    char *string, *answer_base64;
    int length_username, length;

    answer_base64 = NULL;
    length_username = strlen (sasl_username);
    length = ((length_username + 1) * 2) + strlen (sasl_password) + 1;
    string = malloc (length);
    if (string)
    {
        snprintf (string, length, "%s|%s|%s",
                  sasl_username, sasl_username, sasl_password);
        string[length_username] = '\0';
        string[(length_username * 2) + 1] = '\0';

        answer_base64 = malloc (length * 4);
        if (answer_base64)
        {
            if (weechat_string_base_encode (64, string, length - 1,
                                            answer_base64) < 0)
            {
                free (answer_base64);
                answer_base64 = NULL;
            }
        }

        free (string);
    }

    return answer_base64;
}

/*
 * Returns the content of file with SASL key.
 *
 * Note: result must be freed after use.
 */

char *
irc_sasl_get_key_content (struct t_irc_server *server, const char *sasl_key)
{
    char *weechat_dir, *key_path1, *key_path2, *content;

    if (!sasl_key)
        return NULL;

    content = NULL;

    weechat_dir = weechat_info_get ("weechat_dir", "");
    key_path1 = weechat_string_replace (sasl_key, "%h", weechat_dir);
    key_path2 = (key_path1) ?
        weechat_string_expand_home (key_path1) : NULL;

    if (key_path2)
        content = weechat_file_get_content (key_path2);

    if (!content)
    {
        weechat_printf (
            server->buffer,
            _("%s%s: unable to read private key in file \"%s\""),
            weechat_prefix ("error"),
            IRC_PLUGIN_NAME,
            (key_path2) ? key_path2 : ((key_path1) ? key_path1 : sasl_key));
    }

    if (weechat_dir)
        free (weechat_dir);
    if (key_path1)
        free (key_path1);
    if (key_path2)
        free (key_path2);

    return content;
}

/*
 * Builds answer for SASL authentication, using mechanism
 * "ECDSA-NIST256P-CHALLENGE".
 *
 * Note: result must be freed after use.
 */

char *
irc_sasl_mechanism_ecdsa_nist256p_challenge (struct t_irc_server *server,
                                             const char *data_base64,
                                             const char *sasl_username,
                                             const char *sasl_key)
{
#if defined(HAVE_GNUTLS) && (LIBGNUTLS_VERSION_NUMBER >= 0x030015) /* 3.0.21 */
    char *data, *string, *answer_base64;
    int length_data, length_username, length, ret;
    char *str_privkey;
    gnutls_x509_privkey_t x509_privkey;
    gnutls_privkey_t privkey;
    gnutls_datum_t filedatum, decoded_data, signature;
#if LIBGNUTLS_VERSION_NUMBER >= 0x030300 /* 3.3.0 */
    gnutls_ecc_curve_t curve;
    gnutls_datum_t x, y, k;
    char *pubkey, *pubkey_base64;
#endif /* LIBGNUTLS_VERSION_NUMBER >= 0x030300 */

    answer_base64 = NULL;
    string = NULL;

    if (strcmp (data_base64, "+") == 0)
    {
        /* send "username" + '\0' + "username" */
        answer_base64 = NULL;
        length_username = strlen (sasl_username);
        length = length_username + 1 + length_username;
        string = malloc (length + 1);
        if (string)
        {
            snprintf (string, length + 1, "%s|%s", sasl_username, sasl_username);
            string[length_username] = '\0';
        }
    }
    else
    {
        /* sign the challenge with the private key and return the result */

        /* decode the challenge */
        data = malloc (strlen (data_base64) + 1);
        if (!data)
            return NULL;
        length_data = weechat_string_base_decode (64, data_base64, data);

        /* read file with private key */
        str_privkey = irc_sasl_get_key_content (server, sasl_key);
        if (!str_privkey)
        {
            free (data);
            return NULL;
        }

        /* import key */
        gnutls_x509_privkey_init (&x509_privkey);
        gnutls_privkey_init (&privkey);
        filedatum.data = (unsigned char *)str_privkey;
        filedatum.size = strlen (str_privkey);
        ret = gnutls_x509_privkey_import (x509_privkey, &filedatum,
                                          GNUTLS_X509_FMT_PEM);
        free (str_privkey);
        if (ret != GNUTLS_E_SUCCESS)
        {
            weechat_printf (
                server->buffer,
                _("%sgnutls: invalid private key file: error %d %s"),
                weechat_prefix ("error"),
                ret,
                gnutls_strerror (ret));
            gnutls_x509_privkey_deinit (x509_privkey);
            gnutls_privkey_deinit (privkey);
            free (data);
            return NULL;
        }

#if LIBGNUTLS_VERSION_NUMBER >= 0x030300 /* 3.3.0 */
        /* read raw values in key, to display public key */
        ret = gnutls_x509_privkey_export_ecc_raw (x509_privkey,
                                                  &curve, &x, &y, &k);
        if (ret == GNUTLS_E_SUCCESS)
        {
            pubkey = malloc (x.size + 1);
            if (pubkey)
            {
                pubkey[0] = (y.data[y.size - 1] & 1) ? 0x03 : 0x02;
                memcpy (pubkey + 1, x.data, x.size);
                pubkey_base64 = malloc ((x.size + 1 + 1) * 4);
                if (pubkey_base64)
                {
                    if (weechat_string_base_encode (64, pubkey, x.size + 1,
                                                    pubkey_base64) >= 0)
                    {
                        weechat_printf (
                            server->buffer,
                            _("%s%s: signing the challenge with ECC public "
                              "key: %s"),
                            weechat_prefix ("network"),
                            IRC_PLUGIN_NAME,
                            pubkey_base64);
                    }
                    free (pubkey_base64);
                }
                free (pubkey);
            }
            gnutls_free (x.data);
            gnutls_free (y.data);
            gnutls_free (k.data);
        }
#endif /* LIBGNUTLS_VERSION_NUMBER >= 0x030300 */

        /* import private key in an abstract key structure */
        ret = gnutls_privkey_import_x509 (privkey, x509_privkey, 0); /* gnutls >= 2.11.0 */
        if (ret != GNUTLS_E_SUCCESS)
        {
            weechat_printf (
                server->buffer,
                _("%sgnutls: unable to import the private key: error %d %s"),
                weechat_prefix ("error"),
                ret,
                gnutls_strerror (ret));
            gnutls_x509_privkey_deinit (x509_privkey);
            gnutls_privkey_deinit (privkey);
            free (data);
            return NULL;
        }

        decoded_data.data = (unsigned char *)data;
        decoded_data.size = length_data;
        ret = gnutls_privkey_sign_hash (privkey, GNUTLS_DIG_SHA256, 0, /* gnutls >= 2.11.0 */
                                        &decoded_data, &signature);
        if (ret != GNUTLS_E_SUCCESS)
        {
            weechat_printf (
                server->buffer,
                _("%sgnutls: unable to sign the hashed data: error %d %s"),
                weechat_prefix ("error"),
                ret,
                gnutls_strerror (ret));
            gnutls_x509_privkey_deinit (x509_privkey);
            gnutls_privkey_deinit (privkey);
            free (data);
            return NULL;
        }

        gnutls_x509_privkey_deinit (x509_privkey);
        gnutls_privkey_deinit (privkey);

        string = malloc (signature.size);
        if (string)
            memcpy (string, signature.data, signature.size);
        length = signature.size;

        gnutls_free (signature.data);

        free (data);
    }

    if (string && (length > 0))
    {
        answer_base64 = malloc ((length + 1) * 4);
        if (answer_base64)
        {
            if (weechat_string_base_encode (64, string, length,
                                            answer_base64) < 0)
            {
                free (answer_base64);
                answer_base64 = NULL;
            }
        }
        free (string);
        string = NULL;
    }

    if (string)
        free (string);

    return answer_base64;

#else /* no gnutls or gnutls < 3.0.21 */

    /* make C compiler happy */
    (void) data_base64;
    (void) sasl_username;
    (void) sasl_key;

    weechat_printf (server->buffer,
                    _("%sgnutls: version >= 3.0.21 is required for SASL "
                      "\"ecdsa-nist256p-challenge\""),
                    weechat_prefix ("error"));

    return NULL;
#endif /* defined(HAVE_GNUTLS) && (LIBGNUTLS_VERSION_NUMBER >= 0x030015) */
}

/*
 * Reads key sent by server (Diffie-Hellman key exchange).
 *
 * Returns:
 *   1: OK
 *   0: error
 */

int
irc_sasl_dh (const char *data_base64,
             unsigned char **public_bin, unsigned char **secret_bin,
             int *length_key)
{
    char *data;
    unsigned char *ptr_data;
    int length_data, size, num_bits_prime_number, rc;
    size_t num_written;
    gcry_mpi_t data_prime_number, data_generator_number, data_server_pub_key;
    gcry_mpi_t pub_key, priv_key, secret_mpi;

    rc = 0;

    data = NULL;
    data_prime_number = NULL;
    data_generator_number = NULL;
    data_server_pub_key = NULL;
    pub_key = NULL;
    priv_key = NULL;
    secret_mpi = NULL;

    /* decode data */
    data = malloc (strlen (data_base64) + 1);
    if (!data)
	goto dhend;
    length_data = weechat_string_base_decode (64, data_base64, data);
    ptr_data = (unsigned char *)data;

    /* extract prime number */
    size = ntohs ((((unsigned int)ptr_data[1]) << 8) | ptr_data[0]);
    ptr_data += 2;
    length_data -= 2;
    if (size > length_data)
        goto dhend;
    data_prime_number = gcry_mpi_new (size * 8);
    gcry_mpi_scan (&data_prime_number, GCRYMPI_FMT_USG, ptr_data, size, NULL);
    num_bits_prime_number = gcry_mpi_get_nbits (data_prime_number);
    if (num_bits_prime_number == 0 || INT_MAX - 7 < num_bits_prime_number)
	goto dhend;
    ptr_data += size;
    length_data -= size;

    /* extract generator number */
    size = ntohs ((((unsigned int)ptr_data[1]) << 8) | ptr_data[0]);
    ptr_data += 2;
    length_data -= 2;
    if (size > length_data)
        goto dhend;
    data_generator_number = gcry_mpi_new (size * 8);
    gcry_mpi_scan (&data_generator_number, GCRYMPI_FMT_USG, ptr_data, size, NULL);
    ptr_data += size;
    length_data -= size;

    /* extract server-generated public key */
    size = ntohs ((((unsigned int)ptr_data[1]) << 8) | ptr_data[0]);
    ptr_data += 2;
    length_data -= 2;
    if (size > length_data)
        goto dhend;
    data_server_pub_key = gcry_mpi_new (size * 8);
    gcry_mpi_scan (&data_server_pub_key, GCRYMPI_FMT_USG, ptr_data, size, NULL);

    /* generate keys */
    pub_key = gcry_mpi_new (num_bits_prime_number);
    priv_key = gcry_mpi_new (num_bits_prime_number);
    gcry_mpi_randomize (priv_key, num_bits_prime_number, GCRY_STRONG_RANDOM);
    /* pub_key = (g ^ priv_key) % p */
    gcry_mpi_powm (pub_key, data_generator_number, priv_key, data_prime_number);

    /* compute secret_bin */
    *length_key = (num_bits_prime_number + 7) / 8;
    *secret_bin = malloc (*length_key);
    secret_mpi = gcry_mpi_new (num_bits_prime_number);
    /* secret_mpi = (y ^ priv_key) % p */
    gcry_mpi_powm (secret_mpi, data_server_pub_key, priv_key, data_prime_number);
    gcry_mpi_print (GCRYMPI_FMT_USG, *secret_bin, *length_key,
                    &num_written, secret_mpi);

    /* create public_bin */
    *public_bin = malloc (*length_key);
    gcry_mpi_print (GCRYMPI_FMT_USG, *public_bin, *length_key,
                    &num_written, pub_key);
    rc = 1;

dhend:
    if (data)
        free (data);
    if (data_prime_number)
        gcry_mpi_release (data_prime_number);
    if (data_generator_number)
        gcry_mpi_release (data_generator_number);
    if (data_server_pub_key)
        gcry_mpi_release (data_server_pub_key);
    if (pub_key)
        gcry_mpi_release (pub_key);
    if (priv_key)
        gcry_mpi_release (priv_key);
    if (secret_mpi)
        gcry_mpi_release (secret_mpi);

    return rc;
}

/*
 * Builds answer for SASL authentication, using mechanism "DH-BLOWFISH".
 *
 * Argument data_base64 is a concatenation of 3 strings, each string is composed
 * of 2 bytes (length of string), followed by content of string:
 *   1. a prime number
 *   2. a generator number
 *   3. server-generated public key
 *
 * Note: result must be freed after use.
 */

char *
irc_sasl_mechanism_dh_blowfish (const char *data_base64,
                                const char *sasl_username,
                                const char *sasl_password)
{
    char *answer, *ptr_answer, *answer_base64;
    unsigned char *password_clear, *password_crypted;
    int length_key, length_username, length_password, length_answer;
    unsigned char *public_bin, *secret_bin;
    gcry_cipher_hd_t gcrypt_handle;

    password_clear = NULL;
    password_crypted = NULL;
    answer = NULL;
    answer_base64 = NULL;
    secret_bin = NULL;
    public_bin = NULL;

    if (!irc_sasl_dh (data_base64, &public_bin, &secret_bin, &length_key))
        goto bfend;

    /* create password buffers (clear and crypted) */
    length_password = strlen (sasl_password) +
        ((8 - (strlen (sasl_password) % 8)) % 8);
    password_clear = malloc (length_password);
    password_crypted = malloc (length_password);
    memset (password_clear, 0, length_password);
    memset (password_crypted, 0, length_password);
    memcpy (password_clear, sasl_password, strlen (sasl_password));

    /* crypt password using blowfish */
    if (gcry_cipher_open (&gcrypt_handle, GCRY_CIPHER_BLOWFISH,
                          GCRY_CIPHER_MODE_ECB, 0) != 0)
        goto bfend;
    if (gcry_cipher_setkey (gcrypt_handle, secret_bin, length_key) != 0)
        goto bfend;
    if (gcry_cipher_encrypt (gcrypt_handle,
                             password_crypted, length_password,
                             password_clear, length_password) != 0)
        goto bfend;

    gcry_cipher_close (gcrypt_handle);

    /*
     * build answer for server, it is concatenation of:
     *   1. key length (2 bytes)
     *   2. public key ('length_key' bytes)
     *   3. sasl_username ('length_username'+1 bytes)
     *   4. encrypted password ('length_password' bytes)
     */
    length_username = strlen (sasl_username) + 1;
    length_answer = 2 + length_key + length_username + length_password;
    answer = malloc (length_answer);
    ptr_answer = answer;
    *((unsigned int *)ptr_answer) = htons (length_key);
    ptr_answer += 2;
    memcpy (ptr_answer, public_bin, length_key);
    ptr_answer += length_key;
    memcpy (ptr_answer, sasl_username, length_username);
    ptr_answer += length_username;
    memcpy (ptr_answer, password_crypted, length_password);

    /* encode answer to base64 */
    answer_base64 = malloc ((length_answer + 1) * 4);
    if (answer_base64)
    {
        if (weechat_string_base_encode (64, answer, length_answer,
                                        answer_base64) < 0)
        {
            free (answer_base64);
            answer_base64 = NULL;
        }
    }

bfend:
    if (secret_bin)
        free (secret_bin);
    if (public_bin)
        free (public_bin);
    if (password_clear)
        free (password_clear);
    if (password_crypted)
        free (password_crypted);
    if (answer)
        free (answer);

    return answer_base64;
}

/*
 * Builds answer for SASL authentication, using mechanism "DH-AES".
 *
 * Argument data_base64 is a concatenation of 3 strings, each string is composed
 * of 2 bytes (length of string), followed by content of string:
 *   1. a prime number
 *   2. a generator number
 *   3. server-generated public key
 *
 * Note: result must be freed after use.
 */

char *
irc_sasl_mechanism_dh_aes (const char *data_base64,
                           const char *sasl_username,
                           const char *sasl_password)
{
    char *answer, *ptr_answer, *answer_base64;
    unsigned char *ptr_userpass, *userpass_clear, *userpass_crypted;
    int length_key, length_answer;
    int length_username, length_password, length_userpass;
    unsigned char *public_bin, *secret_bin;
    char iv[16];
    int cipher_algo;
    gcry_cipher_hd_t gcrypt_handle;

    userpass_clear = NULL;
    userpass_crypted = NULL;
    answer = NULL;
    answer_base64 = NULL;
    secret_bin = NULL;
    public_bin = NULL;

    if (irc_sasl_dh (data_base64, &public_bin, &secret_bin, &length_key) == 0)
        goto aesend;

    /* Select cipher algorithm: key length * 8 = cipher bit size */
    switch (length_key)
    {
        case 32:
            cipher_algo = GCRY_CIPHER_AES256;
            break;
        case 24:
            cipher_algo = GCRY_CIPHER_AES192;
            break;
        case 16:
            cipher_algo = GCRY_CIPHER_AES128;
            break;
        default:
            /* Invalid bit length */
            goto aesend;
    }

    /* Generate the IV */
    gcry_randomize (iv, sizeof (iv), GCRY_STRONG_RANDOM);

    /* create user/pass buffers (clear and crypted) */
    length_username = strlen (sasl_username) + 1;
    length_password = strlen (sasl_password) + 1;
    length_userpass = length_username + length_password +
        ((16 - ((length_username + length_password) % 16)) % 16);
    ptr_userpass = userpass_clear = malloc (length_userpass);
    userpass_crypted = malloc (length_userpass);
    memset (userpass_clear, 0, length_password);
    memset (userpass_crypted, 0, length_password);
    memcpy (ptr_userpass, sasl_username, length_username);
    ptr_userpass += length_username;
    memcpy (ptr_userpass, sasl_password, length_password);

    /* crypt password using AES in CBC mode */
    if (gcry_cipher_open (&gcrypt_handle, cipher_algo,
                          GCRY_CIPHER_MODE_CBC, 0) != 0)
        goto aesend;
    if (gcry_cipher_setkey (gcrypt_handle, secret_bin, length_key) != 0)
        goto aesend;
    if (gcry_cipher_setiv (gcrypt_handle, iv, sizeof (iv)) != 0)
        goto aesend;
    if (gcry_cipher_encrypt (gcrypt_handle,
                             userpass_crypted, length_userpass,
                             userpass_clear, length_userpass) != 0)
        goto aesend;

    gcry_cipher_close (gcrypt_handle);

    /*
     * build answer for server, it is concatenation of:
     *   1. key length (2 bytes)
     *   2. public key ('length_key' bytes)
     *   3. IV (sizeof (iv) bytes)
     *   4. encrypted password ('length_userpass' bytes)
     */
    length_answer = 2 + length_key + sizeof (iv) + length_userpass;
    answer = malloc (length_answer);
    ptr_answer = answer;
    *((unsigned int *)ptr_answer) = htons (length_key);
    ptr_answer += 2;
    memcpy (ptr_answer, public_bin, length_key);
    ptr_answer += length_key;
    memcpy (ptr_answer, iv, sizeof (iv));
    ptr_answer += sizeof (iv);
    memcpy (ptr_answer, userpass_crypted, length_userpass);

    /* encode answer to base64 */
    answer_base64 = malloc ((length_answer + 1) * 4);
    if (answer_base64)
    {
        if (weechat_string_base_encode (64, answer, length_answer,
                                        answer_base64) < 0)
        {
            free (answer_base64);
            answer_base64 = NULL;
        }
    }

aesend:
    if (secret_bin)
        free (secret_bin);
    if (public_bin)
        free (public_bin);
    if (userpass_clear)
        free (userpass_clear);
    if (userpass_crypted)
        free (userpass_crypted);
    if (answer)
        free (answer);

    return answer_base64;
}
