secure.c

rdesktop is a client for Microsoft Windows NT Terminal Server, Windows 2000 Terminal Services, Wind

/* -*- c-basic-offset: 8 -*-
   rdesktop: A Remote Desktop Protocol client.
   Protocol services - RDP encryption and licensing
   Copyright (C) Matthew Chapman 1999-2005

   This program 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 2 of the License, or
   (at your option) any later version.

   This program 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 this program; if not, write to the Free Software
   Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
*/

#include "rdesktop.h"

#include <openssl/rc4.h>
#include <openssl/md5.h>
#include <openssl/sha.h>
#include <openssl/bn.h>
#include <openssl/x509v3.h>

extern char g_hostname[16];
extern int g_width;
extern int g_height;
extern unsigned int g_keylayout;
extern int g_keyboard_type;
extern int g_keyboard_subtype;
extern int g_keyboard_functionkeys;
extern BOOL g_encryption;
extern BOOL g_licence_issued;
extern BOOL g_use_rdp5;
extern BOOL g_console_session;
extern int g_server_depth;
extern uint16 mcs_userid;
extern VCHANNEL g_channels[];
extern unsigned int g_num_channels;

static int rc4_key_len;
static RC4_KEY rc4_decrypt_key;
static RC4_KEY rc4_encrypt_key;
static RSA *server_public_key;
static uint32 server_public_key_len;

static uint8 sec_sign_key[16];
static uint8 sec_decrypt_key[16];
static uint8 sec_encrypt_key[16];
static uint8 sec_decrypt_update_key[16];
static uint8 sec_encrypt_update_key[16];
static uint8 sec_crypted_random[SEC_MAX_MODULUS_SIZE];

uint16 g_server_rdp_version = 0;

/* These values must be available to reset state - Session Directory */
static int sec_encrypt_use_count = 0;
static int sec_decrypt_use_count = 0;

/*
 * I believe this is based on SSLv3 with the following differences:
 *  MAC algorithm (5.2.3.1) uses only 32-bit length in place of seq_num/type/length fields
 *  MAC algorithm uses SHA1 and MD5 for the two hash functions instead of one or other
 *  key_block algorithm (6.2.2) uses 'X', 'YY', 'ZZZ' instead of 'A', 'BB', 'CCC'
 *  key_block partitioning is different (16 bytes each: MAC secret, decrypt key, encrypt key)
 *  encryption/decryption keys updated every 4096 packets
 * See http://wp.netscape.com/eng/ssl3/draft302.txt
 */

/*
 * 48-byte transformation used to generate master secret (6.1) and key material (6.2.2).
 * Both SHA1 and MD5 algorithms are used.
 */
void
sec_hash_48(uint8 * out, uint8 * in, uint8 * salt1, uint8 * salt2, uint8 salt)
{
	uint8 shasig[20];
	uint8 pad[4];
	SHA_CTX sha;
	MD5_CTX md5;
	int i;

	for (i = 0; i < 3; i++)
	{
		memset(pad, salt + i, i + 1);

		SHA1_Init(&sha);
		SHA1_Update(&sha, pad, i + 1);
		SHA1_Update(&sha, in, 48);
		SHA1_Update(&sha, salt1, 32);
		SHA1_Update(&sha, salt2, 32);
		SHA1_Final(shasig, &sha);

		MD5_Init(&md5);
		MD5_Update(&md5, in, 48);
		MD5_Update(&md5, shasig, 20);
		MD5_Final(&out[i * 16], &md5);
	}
}

/*
 * 16-byte transformation used to generate export keys (6.2.2).
 */
void
sec_hash_16(uint8 * out, uint8 * in, uint8 * salt1, uint8 * salt2)
{
	MD5_CTX md5;

	MD5_Init(&md5);
	MD5_Update(&md5, in, 16);
	MD5_Update(&md5, salt1, 32);
	MD5_Update(&md5, salt2, 32);
	MD5_Final(out, &md5);
}

/* Reduce key entropy from 64 to 40 bits */
static void
sec_make_40bit(uint8 * key)
{
	key[0] = 0xd1;
	key[1] = 0x26;
	key[2] = 0x9e;
}

/* Generate encryption keys given client and server randoms */
static void
sec_generate_keys(uint8 * client_random, uint8 * server_random, int rc4_key_size)
{
	uint8 pre_master_secret[48];
	uint8 master_secret[48];
	uint8 key_block[48];

	/* Construct pre-master secret */
	memcpy(pre_master_secret, client_random, 24);
	memcpy(pre_master_secret + 24, server_random, 24);

	/* Generate master secret and then key material */
	sec_hash_48(master_secret, pre_master_secret, client_random, server_random, 'A');
	sec_hash_48(key_block, master_secret, client_random, server_random, 'X');

	/* First 16 bytes of key material is MAC secret */
	memcpy(sec_sign_key, key_block, 16);

	/* Generate export keys from next two blocks of 16 bytes */
	sec_hash_16(sec_decrypt_key, &key_block[16], client_random, server_random);
	sec_hash_16(sec_encrypt_key, &key_block[32], client_random, server_random);

	if (rc4_key_size == 1)
	{
		DEBUG(("40-bit encryption enabled\n"));
		sec_make_40bit(sec_sign_key);
		sec_make_40bit(sec_decrypt_key);
		sec_make_40bit(sec_encrypt_key);
		rc4_key_len = 8;
	}
	else
	{
		DEBUG(("rc_4_key_size == %d, 128-bit encryption enabled\n", rc4_key_size));
		rc4_key_len = 16;
	}

	/* Save initial RC4 keys as update keys */
	memcpy(sec_decrypt_update_key, sec_decrypt_key, 16);
	memcpy(sec_encrypt_update_key, sec_encrypt_key, 16);

	/* Initialise RC4 state arrays */
	RC4_set_key(&rc4_decrypt_key, rc4_key_len, sec_decrypt_key);
	RC4_set_key(&rc4_encrypt_key, rc4_key_len, sec_encrypt_key);
}

static uint8 pad_54[40] = {
	54, 54, 54, 54, 54, 54, 54, 54, 54, 54, 54, 54, 54, 54, 54, 54, 54,
	54, 54, 54,
	54, 54, 54, 54, 54, 54, 54, 54, 54, 54, 54, 54, 54, 54, 54, 54, 54,
	54, 54, 54
};

static uint8 pad_92[48] = {
	92, 92, 92, 92, 92, 92, 92, 92, 92, 92, 92, 92, 92, 92, 92, 92, 92,
	92, 92, 92, 92, 92, 92, 92,
	92, 92, 92, 92, 92, 92, 92, 92, 92, 92, 92, 92, 92, 92, 92, 92, 92,
	92, 92, 92, 92, 92, 92, 92
};

/* Output a uint32 into a buffer (little-endian) */
void
buf_out_uint32(uint8 * buffer, uint32 value)
{
	buffer[0] = (value) & 0xff;
	buffer[1] = (value >> 8) & 0xff;
	buffer[2] = (value >> 16) & 0xff;
	buffer[3] = (value >> 24) & 0xff;
}

/* Generate a MAC hash (5.2.3.1), using a combination of SHA1 and MD5 */
void
sec_sign(uint8 * signature, int siglen, uint8 * session_key, int keylen, uint8 * data, int datalen)
{
	uint8 shasig[20];
	uint8 md5sig[16];
	uint8 lenhdr[4];
	SHA_CTX sha;
	MD5_CTX md5;

	buf_out_uint32(lenhdr, datalen);

	SHA1_Init(&sha);
	SHA1_Update(&sha, session_key, keylen);
	SHA1_Update(&sha, pad_54, 40);
	SHA1_Update(&sha, lenhdr, 4);
	SHA1_Update(&sha, data, datalen);
	SHA1_Final(shasig, &sha);

	MD5_Init(&md5);
	MD5_Update(&md5, session_key, keylen);
	MD5_Update(&md5, pad_92, 48);
	MD5_Update(&md5, shasig, 20);
	MD5_Final(md5sig, &md5);

	memcpy(signature, md5sig, siglen);
}

/* Update an encryption key */
static void
sec_update(uint8 * key, uint8 * update_key)
{
	uint8 shasig[20];
	SHA_CTX sha;
	MD5_CTX md5;
	RC4_KEY update;

	SHA1_Init(&sha);
	SHA1_Update(&sha, update_key, rc4_key_len);
	SHA1_Update(&sha, pad_54, 40);
	SHA1_Update(&sha, key, rc4_key_len);
	SHA1_Final(shasig, &sha);

	MD5_Init(&md5);
	MD5_Update(&md5, update_key, rc4_key_len);
	MD5_Update(&md5, pad_92, 48);
	MD5_Update(&md5, shasig, 20);
	MD5_Final(key, &md5);

	RC4_set_key(&update, rc4_key_len, key);
	RC4(&update, rc4_key_len, key, key);

	if (rc4_key_len == 8)
		sec_make_40bit(key);
}

/* Encrypt data using RC4 */
static void
sec_encrypt(uint8 * data, int length)
{
	if (sec_encrypt_use_count == 4096)
	{
		sec_update(sec_encrypt_key, sec_encrypt_update_key);
		RC4_set_key(&rc4_encrypt_key, rc4_key_len, sec_encrypt_key);
		sec_encrypt_use_count = 0;
	}

	RC4(&rc4_encrypt_key, length, data, data);
	sec_encrypt_use_count++;
}

/* Decrypt data using RC4 */
void
sec_decrypt(uint8 * data, int length)
{
	if (sec_decrypt_use_count == 4096)
	{
		sec_update(sec_decrypt_key, sec_decrypt_update_key);
		RC4_set_key(&rc4_decrypt_key, rc4_key_len, sec_decrypt_key);
		sec_decrypt_use_count = 0;
	}

	RC4(&rc4_decrypt_key, length, data, data);
	sec_decrypt_use_count++;
}

static void
reverse(uint8 * p, int len)
{
	int i, j;
	uint8 temp;

	for (i = 0, j = len - 1; i < j; i++, j--)
	{
		temp = p[i];
		p[i] = p[j];
		p[j] = temp;
	}
}

/* Perform an RSA public key encryption operation */
static void
sec_rsa_encrypt(uint8 * out, uint8 * in, int len, uint32 modulus_size, uint8 * modulus,
		uint8 * exponent)
{
	BN_CTX *ctx;
	BIGNUM mod, exp, x, y;
	uint8 inr[SEC_MAX_MODULUS_SIZE];
	int outlen;

	reverse(modulus, modulus_size);
	reverse(exponent, SEC_EXPONENT_SIZE);
	memcpy(inr, in, len);
	reverse(inr, len);

	ctx = BN_CTX_new();
	BN_init(&mod);
	BN_init(&exp);
	BN_init(&x);
	BN_init(&y);

	BN_bin2bn(modulus, modulus_size, &mod);
	BN_bin2bn(exponent, SEC_EXPONENT_SIZE, &exp);
	BN_bin2bn(inr, len, &x);
	BN_mod_exp(&y, &x, &exp, &mod, ctx);
	outlen = BN_bn2bin(&y, out);
	reverse(out, outlen);
	if (outlen < modulus_size)
		memset(out + outlen, 0, modulus_size - outlen);

	BN_free(&y);
	BN_clear_free(&x);
	BN_free(&exp);
	BN_free(&mod);
	BN_CTX_free(ctx);
}

/* Initialise secure transport packet */
STREAM
sec_init(uint32 flags, int maxlen)
{
	int hdrlen;
	STREAM s;

	if (!g_licence_issued)
		hdrlen = (flags & SEC_ENCRYPT) ? 12 : 4;
	else
		hdrlen = (flags & SEC_ENCRYPT) ? 12 : 0;
	s = mcs_init(maxlen + hdrlen);
	s_push_layer(s, sec_hdr, hdrlen);

	return s;
}

/* Transmit secure transport packet over specified channel */
void
sec_send_to_channel(STREAM s, uint32 flags, uint16 channel)
{
	int datalen;

	s_pop_layer(s, sec_hdr);
	if (!g_licence_issued || (flags & SEC_ENCRYPT))
		out_uint32_le(s, flags);

	if (flags & SEC_ENCRYPT)
	{
		flags &= ~SEC_ENCRYPT;
		datalen = s->end - s->p - 8;

#if WITH_DEBUG
		DEBUG(("Sending encrypted packet:\n"));
		hexdump(s->p + 8, datalen);
#endif

		sec_sign(s->p, 8, sec_sign_key, rc4_key_len, s->p + 8, datalen);
		sec_encrypt(s->p + 8, datalen);
	}

	mcs_send_to_channel(s, channel);
}

/* Transmit secure transport packet */

void
sec_send(STREAM s, uint32 flags)
{
	sec_send_to_channel(s, flags, MCS_GLOBAL_CHANNEL);
}


/* Transfer the client random to the server */
static void
sec_establish_key(void)
{
	uint32 length = server_public_key_len + SEC_PADDING_SIZE;
	uint32 flags = SEC_CLIENT_RANDOM;
	STREAM s;

	s = sec_init(flags, length + 4);

	out_uint32_le(s, length);
	out_uint8p(s, sec_crypted_random, server_public_key_len);
	out_uint8s(s, SEC_PADDING_SIZE);

	s_mark_end(s);
	sec_send(s, flags);
}

/* Output connect initial data blob */
static void
sec_out_mcs_data(STREAM s)
{
	int hostlen = 2 * strlen(g_hostname);
	int length = 158 + 76 + 12 + 4;
	unsigned int i;

	if (g_num_channels > 0)
		length += g_num_channels * 12 + 8;

	if (hostlen > 30)
		hostlen = 30;

	/* Generic Conference Control (T.124) ConferenceCreateRequest */
	out_uint16_be(s, 5);
	out_uint16_be(s, 0x14);
	out_uint8(s, 0x7c);
	out_uint16_be(s, 1);

	out_uint16_be(s, (length | 0x8000));	/* remaining length */

	out_uint16_be(s, 8);	/* length? */
	out_uint16_be(s, 16);
	out_uint8(s, 0);
	out_uint16_le(s, 0xc001);
	out_uint8(s, 0);

	out_uint32_le(s, 0x61637544);	/* OEM ID: "Duca", as in Ducati. */
	out_uint16_be(s, ((length - 14) | 0x8000));	/* remaining length */

	/* Client information */
	out_uint16_le(s, SEC_TAG_CLI_INFO);
	out_uint16_le(s, 212);	/* length */
	out_uint16_le(s, g_use_rdp5 ? 4 : 1);	/* RDP version. 1 == RDP4, 4 == RDP5. */
	out_uint16_le(s, 8);
	out_uint16_le(s, g_width);
	out_uint16_le(s, g_height);
	out_uint16_le(s, 0xca01);
	out_uint16_le(s, 0xaa03);
	out_uint32_le(s, g_keylayout);
	out_uint32_le(s, 2600);	/* Client build. We are now 2600 compatible :-) */

	/* Unicode name of client, padded to 32 bytes */
	rdp_out_unistr(s, g_hostname, hostlen);
	out_uint8s(s, 30 - hostlen);

	/* See
	   http://msdn.microsoft.com/library/default.asp?url=/library/en-us/wceddk40/html/cxtsksupportingremotedesktopprotocol.asp */
	out_uint32_le(s, g_keyboard_type);
	out_uint32_le(s, g_keyboard_subtype);
	out_uint32_le(s, g_keyboard_functionkeys);
	out_uint8s(s, 64);	/* reserved? 4 + 12 doublewords */
	out_uint16_le(s, 0xca01);	/* colour depth? */
	out_uint16_le(s, 1);

	out_uint32(s, 0);
	out_uint8(s, g_server_depth);
	out_uint16_le(s, 0x0700);
	out_uint8(s, 0);
	out_uint32_le(s, 1);
	out_uint8s(s, 64);	/* End of client info */

	out_uint16_le(s, SEC_TAG_CLI_4);
	out_uint16_le(s, 12);
	out_uint32_le(s, g_console_session ? 0xb : 9);
	out_uint32(s, 0);

	/* Client encryption settings */
	out_uint16_le(s, SEC_TAG_CLI_CRYPT);
	out_uint16_le(s, 12);	/* length */
	out_uint32_le(s, g_encryption ? 0x3 : 0);	/* encryption supported, 128-bit supported */
	out_uint32(s, 0);	/* Unknown */

	DEBUG_RDP5(("g_num_channels is %d\n", g_num_channels));
	if (g_num_channels > 0)
	{
		out_uint16_le(s, SEC_TAG_CLI_CHANNELS);
		out_uint16_le(s, g_num_channels * 12 + 8);	/* length */
		out_uint32_le(s, g_num_channels);	/* number of virtual channels */
		for (i = 0; i < g_num_channels; i++)
		{
			DEBUG_RDP5(("Requesting channel %s\n", g_channels[i].name));
			out_uint8a(s, g_channels[i].name, 8);
			out_uint32_be(s, g_channels[i].flags);
		}