iwd/src/mschaputil.c

/*
 *
 *  Wireless daemon for Linux
 *
 *  Copyright (C) 2018  Intel Corporation. All rights reserved.
 *
 *  This library is free software; you can redistribute it and/or
 *  modify it under the terms of the GNU Lesser General Public
 *  License as published by the Free Software Foundation; either
 *  version 2.1 of the License, or (at your option) any later version.
 *
 *  This library 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
 *  Lesser General Public License for more details.
 *
 *  You should have received a copy of the GNU Lesser General Public
 *  License along with this library; if not, write to the Free Software
 *  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
 *
 */

#ifdef HAVE_CONFIG_H
#include <config.h>
#endif

#include <ell/ell.h>

#include "src/missing.h"
#include "src/mschaputil.h"

/**
 * Internal function for generate_nt_response.
 * The DES keys specified for generate_nt_response are 56bit, while the api we
 * use takes 64bit keys, so we have to generate the parity bits.
 **/
static bool mschap_des_encrypt(const uint8_t challenge[static 8],
						const uint8_t key[static 7],
						uint8_t cipher_text[static 8])
{
	uint8_t pkey[8], tmp;
	int i;
	struct l_cipher *cipher;
	uint8_t next;

	for (i = 0, next = 0; i < 7; ++i) {
		tmp = key[i];
		pkey[i] = (tmp >> i) | next | 1;
		next = tmp << (7 - i);
	}

	pkey[i] = next | 1;

	cipher = l_cipher_new(L_CIPHER_DES, pkey, 8);
	explicit_bzero(pkey, 8);

	if (!cipher)
		return false;

	l_cipher_encrypt(cipher, challenge, cipher_text, 8);
	l_cipher_free(cipher);

	return true;
}

bool mschap_challenge_response(const uint8_t *challenge,
				const uint8_t *password_hash, uint8_t *response)
{
	uint8_t buf[21];
	bool r;

	memset(buf, 0, sizeof(buf));
	memcpy(buf, password_hash, 16);

	r = mschap_des_encrypt(challenge, buf + 0, response + 0) &&
		mschap_des_encrypt(challenge, buf + 7, response + 8) &&
		mschap_des_encrypt(challenge, buf + 14, response + 16);

	explicit_bzero(buf, sizeof(buf));
	return r;
}

/**
 * Hash the utf8 encoded nt password.
 * It is asumed, that the password is valid utf8!
 * The rfc says "unicode-char", but never specifies which encoding.
 * This function converts the password to ucs-2.
 * The example in the code uses LE for the unicode chars, so it is forced here.
 * https://tools.ietf.org/html/draft-ietf-pppext-mschap-00#ref-8
 */
bool mschap_nt_password_hash(const char *password, uint8_t *password_hash)
{
	size_t size = l_utf8_strlen(password);
	size_t bsize = strlen(password);
	uint16_t buffer[size];
	unsigned int i, pos;
	struct l_checksum *check;
	bool r = false;

	for (i = 0, pos = 0; i < size; ++i) {
		wchar_t val;

		pos += l_utf8_get_codepoint(password + pos, bsize - pos, &val);

		if (val > 0xFFFF) {
			l_error("Encountered password with value not valid in "
								"ucs-2");
			goto cleanup;
		}

		buffer[i] = L_CPU_TO_LE16(val);
	}

	check = l_checksum_new(L_CHECKSUM_MD4);
	if (!check)
		goto cleanup;

	l_checksum_update(check, (uint8_t *) buffer, size * 2);
	l_checksum_get_digest(check, password_hash, 16);
	l_checksum_free(check);
	r = true;

cleanup:
	explicit_bzero(buffer, size * 2);
	return r;
}

static const char *mschapv2_exlude_domain_name(const char *username)
{
	const char *c;

	for (c = username; *c; c++) {
		if (*c != '\\')
			continue;

		return c + 1;
	}

	return username;
}

/**
 * Internal function to generate the challenge used in nt_response
 * https://tools.ietf.org/html/rfc2759
 *
 * @peer_challenge: The challenge generated by the peer (us)
 * @server_challenge: The challenge generated by the authenticator
 * @user: The username utf8 encoded
 * @challenge: The destination
 *
 * Returns: true on success, false if hash/encrypt couldn't be done
 **/
static bool mschapv2_challenge_hash(const uint8_t *peer_challenge,
					const uint8_t *server_challenge,
					const char *username,
					uint8_t challenge[static 8])
{
	struct l_checksum *check;

	check = l_checksum_new(L_CHECKSUM_SHA1);
	if (!check)
		return false;

	username = mschapv2_exlude_domain_name(username);

	l_checksum_update(check, peer_challenge, 16);
	l_checksum_update(check, server_challenge, 16);
	l_checksum_update(check, username, strlen(username));

	l_checksum_get_digest(check, challenge, 8);
	l_checksum_free(check);

	return true;
}

/**
 * Generate the nt_response for mschapv2.
 * This function is specified in:
 * https://tools.ietf.org/html/rfc2759
 *
 * @password_hash: The MD4 hash of the ucs2 encoded user password
 * @peer_challenge: the challenge generated by the peer (us)
 * @server_challenge: the challenge generated by the authenticator
 * @user: The username, utf8 encoded
 * @nt_response: The destination
 *
 * Returns: true on success, false if hash/encrypt couldn't be done
 **/
bool mschapv2_generate_nt_response(const uint8_t password_hash[static 16],
				const uint8_t peer_challenge[static 16],
				const uint8_t server_challenge[static 16],
				const char *user, uint8_t response[static 24])
{
	uint8_t challenge[8];
	uint8_t buffer[21];
	bool r;

	if (!mschapv2_challenge_hash(peer_challenge, server_challenge, user,
								challenge))
		return false;

	memset(buffer, 0, sizeof(buffer));
	memcpy(buffer, password_hash, 16);

	r = mschap_des_encrypt(challenge, buffer + 0, response + 0) &&
		mschap_des_encrypt(challenge, buffer + 7, response + 8) &&
		mschap_des_encrypt(challenge, buffer + 14, response + 16);

	explicit_bzero(buffer, sizeof(buffer));
	return r;
}

/**
 * Generate the hash of the password hash
 *
 * @password_hash: The hash of the password
 * @password_hash_hash: The MD4 hash of the password hash
 *
 * Returns: true on success, false if hash/encrypt couldn't be done
 **/
bool mschapv2_hash_nt_password_hash(const uint8_t password_hash[static 16],
					uint8_t password_hash_hash[static 16])
{
	struct l_checksum *check;

	check = l_checksum_new(L_CHECKSUM_MD4);
	if (!check)
		return false;

	l_checksum_update(check, password_hash, 16);
	l_checksum_get_digest(check, password_hash_hash, 16);
	l_checksum_free(check);

	return true;
}

/**
 * Generate the mschapv2 authenticator response for verifying authenticator
 * This function is specified in:
 * https://tools.ietf.org/html/rfc2759
 *
 * @password_hash_hash: The MD4 hash of the password hash
 * @nt_response: The nt_response generated for this exchange
 * @peer_challenge: The challenge generated by the peer (us)
 * @server_challenge: The challenge generated by the authenticator
 * @user: The username utf8 encoded
 * @response: The destination
 *
 * Returns: true on success, false if hash/encrypt couldn't be done
 **/
bool mschapv2_generate_authenticator_response(
				const uint8_t pw_hash_hash[static 16],
				const uint8_t nt_response[static 24],
				const uint8_t peer_challenge[static 16],
				const uint8_t server_challenge[static 16],
				const char *user, char response[static 42])
{
	static const uint8_t magic1[] = {
		0x4D, 0x61, 0x67, 0x69, 0x63, 0x20, 0x73, 0x65, 0x72, 0x76,
		0x65, 0x72, 0x20, 0x74, 0x6F, 0x20, 0x63, 0x6C, 0x69, 0x65,
		0x6E, 0x74, 0x20, 0x73, 0x69, 0x67, 0x6E, 0x69, 0x6E, 0x67,
		0x20, 0x63, 0x6F, 0x6E, 0x73, 0x74, 0x61, 0x6E, 0x74
	};

	static const uint8_t magic2[] = {
		0x50, 0x61, 0x64, 0x20, 0x74, 0x6F, 0x20, 0x6D, 0x61, 0x6B,
		0x65, 0x20, 0x69, 0x74, 0x20, 0x64, 0x6F, 0x20, 0x6D, 0x6F,
		0x72, 0x65, 0x20, 0x74, 0x68, 0x61, 0x6E, 0x20, 0x6F, 0x6E,
		0x65, 0x20, 0x69, 0x74, 0x65, 0x72, 0x61, 0x74, 0x69, 0x6F,
		0x6E
	};

	uint8_t digest[20];
	uint8_t challenge[8];
	char *ascii;
	struct l_checksum *check;

	check = l_checksum_new(L_CHECKSUM_SHA1);
	if (!check)
		return false;

	l_checksum_update(check, pw_hash_hash, 16);
	l_checksum_update(check, nt_response, 24);
	l_checksum_update(check, magic1, sizeof(magic1));
	l_checksum_get_digest(check, digest, sizeof(digest));
	l_checksum_free(check);

	if (!mschapv2_challenge_hash(peer_challenge, server_challenge, user,
								challenge))
		return false;

	check = l_checksum_new(L_CHECKSUM_SHA1);
	if (!check)
		return false;

	l_checksum_update(check, digest, sizeof(digest));
	l_checksum_update(check, challenge, sizeof(challenge));
	l_checksum_update(check, magic2, sizeof(magic2));
	l_checksum_get_digest(check, digest, sizeof(digest));
	l_checksum_free(check);

	response[0] = 'S';
	response[1] = '=';

	ascii = l_util_hexstring_upper(digest, sizeof(digest));
	if (!ascii)
		return false;

	memcpy(response + 2, ascii, 40);
	l_free(ascii);

	return true;
}