trunk/rdesktop/secure.c

/* -*- 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_bpp;
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 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_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, uint8 * modulus, uint8 * exponent)
{
        BN_CTX *ctx;
        BIGNUM mod, exp, x, y;
        uint8 inr[SEC_MODULUS_SIZE];
        int outlen;

        reverse(modulus, SEC_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, SEC_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 < SEC_MODULUS_SIZE)
                memset(out + outlen, 0, SEC_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 = SEC_MODULUS_SIZE + SEC_PADDING_SIZE;
        uint32 flags = SEC_CLIENT_RANDOM;
        STREAM s;

        s = sec_init(flags, 76);

        out_uint32_le(s, length);
        out_uint8p(s, sec_crypted_random, SEC_MODULUS_SIZE);
        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_bpp);
        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);
                }
        }

        s_mark_end(s);
}

/* Parse a public key structure */
static BOOL
sec_parse_public_key(STREAM s, uint8 ** modulus, uint8 ** exponent)
{
        uint32 magic, modulus_len;

        in_uint32_le(s, magic);
        if (magic != SEC_RSA_MAGIC)
        {
                error("RSA magic 0x%x\n", magic);
                return False;
        }

        in_uint32_le(s, modulus_len);
        if (modulus_len != SEC_MODULUS_SIZE + SEC_PADDING_SIZE)
        {
                error("modulus len 0x%x\n", modulus_len);
                return False;
        }

        in_uint8s(s, 8);        /* modulus_bits, unknown */
        in_uint8p(s, *exponent, SEC_EXPONENT_SIZE);
        in_uint8p(s, *modulus, SEC_MODULUS_SIZE);
        in_uint8s(s, SEC_PADDING_SIZE);

        return s_check(s);
}

static BOOL
sec_parse_x509_key(X509 * cert)
{
        EVP_PKEY *epk = NULL;
        /* By some reason, Microsoft sets the OID of the Public RSA key to
           the oid for "MD5 with RSA Encryption" instead of "RSA Encryption"

           Kudos to Richard Levitte for the following (. intiutive .) 
           lines of code that resets the OID and let's us extract the key. */
        if (OBJ_obj2nid(cert->cert_info->key->algor->algorithm) == NID_md5WithRSAEncryption)
        {
                DEBUG_RDP5(("Re-setting algorithm type to RSA in server certificate\n"));
                cert->cert_info->key->algor->algorithm = OBJ_nid2obj(NID_rsaEncryption);
        }
        epk = X509_get_pubkey(cert);
        if (NULL == epk)
        {
                error("Failed to extract public key from certificate\n");
                return False;
        }

        server_public_key = (RSA *) epk->pkey.ptr;

        return True;
}


/* Parse a crypto information structure */
static BOOL
sec_parse_crypt_info(STREAM s, uint32 * rc4_key_size,
                     uint8 ** server_random, uint8 ** modulus, uint8 ** exponent)
{
        uint32 crypt_level, random_len, rsa_info_len;
        uint32 cacert_len, cert_len, flags;
        X509 *cacert, *server_cert;
        uint16 tag, length;
        uint8 *next_tag, *end;

        in_uint32_le(s, *rc4_key_size); /* 1 = 40-bit, 2 = 128-bit */
        in_uint32_le(s, crypt_level);   /* 1 = low, 2 = medium, 3 = high */
        if (crypt_level == 0)   /* no encryption */
                return False;
        in_uint32_le(s, random_len);
        in_uint32_le(s, rsa_info_len);

        if (random_len != SEC_RANDOM_SIZE)
        {
                error("random len %d, expected %d\n", random_len, SEC_RANDOM_SIZE);
                return False;
        }

        in_uint8p(s, *server_random, random_len);

        /* RSA info */
        end = s->p + rsa_info_len;
        if (end > s->end)
                return False;

        in_uint32_le(s, flags); /* 1 = RDP4-style, 0x80000002 = X.509 */
        if (flags & 1)
        {
                DEBUG_RDP5(("We're going for the RDP4-style encryption\n"));
                in_uint8s(s, 8);        /* unknown */

                while (s->p < end)
                {
                        in_uint16_le(s, tag);
                        in_uint16_le(s, length);

                        next_tag = s->p + length;

                        switch (tag)
                        {
                                case SEC_TAG_PUBKEY:
                                        if (!sec_parse_public_key(s, modulus, exponent))
                                                return False;
                                        DEBUG_RDP5(("Got Public key, RDP4-style\n"));

                                        break;

                                case SEC_TAG_KEYSIG:
                                        /* Is this a Microsoft key that we just got? */
                                        /* Care factor: zero! */
                                        /* Actually, it would probably be a good idea to check if the public key is signed with this key, and then store this 
                                           key as a known key of the hostname. This would prevent some MITM-attacks. */
                                        break;

                                default:
                                        unimpl("crypt tag 0x%x\n", tag);
                        }

                        s->p = next_tag;
                }
        }
        else
        {
                uint32 certcount;

                DEBUG_RDP5(("We're going for the RDP5-style encryption\n"));
                in_uint32_le(s, certcount);     /* Number of certificates */

                if (certcount < 2)
                {
                        error("Server didn't send enough X509 certificates\n");
                        return False;
                }

                for (; certcount > 2; certcount--)
                {               /* ignore all the certificates between the root and the signing CA */
                        uint32 ignorelen;
                        X509 *ignorecert;

                        DEBUG_RDP5(("Ignored certs left: %d\n", certcount));

                        in_uint32_le(s, ignorelen);
                        DEBUG_RDP5(("Ignored Certificate length is %d\n", ignorelen));
                        ignorecert = d2i_X509(NULL, &(s->p), ignorelen);

                        if (ignorecert == NULL)
                        {       /* XXX: error out? */
                                DEBUG_RDP5(("got a bad cert: this will probably screw up the rest of the communication\n"));
                        }

#ifdef WITH_DEBUG_RDP5
                        DEBUG_RDP5(("cert #%d (ignored):\n", certcount));
                        X509_print_fp(stdout, ignorecert);
#endif
                }

                /* Do da funky X.509 stuffy 

                   "How did I find out about this?  I looked up and saw a
                   bright light and when I came to I had a scar on my forehead
                   and knew about X.500"
                   - Peter Gutman in a early version of 
                   http://www.cs.auckland.ac.nz/~pgut001/pubs/x509guide.txt
                 */

                in_uint32_le(s, cacert_len);
                DEBUG_RDP5(("CA Certificate length is %d\n", cacert_len));
                cacert = d2i_X509(NULL, &(s->p), cacert_len);
                /* Note: We don't need to move s->p here - d2i_X509 is
                   "kind" enough to do it for us */
                if (NULL == cacert)
                {
                        error("Couldn't load CA Certificate from server\n");
                        return False;
                }

                /* Currently, we don't use the CA Certificate. 
                   FIXME: 
                   *) Verify the server certificate (server_cert) with the 
                   CA certificate.
                   *) Store the CA Certificate with the hostname of the 
                   server we are connecting to as key, and compare it
                   when we connect the next time, in order to prevent
                   MITM-attacks.
                 */

                in_uint32_le(s, cert_len);
                DEBUG_RDP5(("Certificate length is %d\n", cert_len));
                server_cert = d2i_X509(NULL, &(s->p), cert_len);
                if (NULL == server_cert)
                {
                        error("Couldn't load Certificate from server\n");
                        return False;
                }

                in_uint8s(s, 16);       /* Padding */

                /* Note: Verifying the server certificate must be done here, 
                   before sec_parse_public_key since we'll have to apply
                   serious violence to the key after this */

                if (!sec_parse_x509_key(server_cert))
                {
                        DEBUG_RDP5(("Didn't parse X509 correctly\n"));
                        return False;
                }
                return True;    /* There's some garbage here we don't care about */
        }
        return s_check_end(s);
}

/* Process crypto information blob */
static void
sec_process_crypt_info(STREAM s)
{
        uint8 *server_random, *modulus, *exponent;
        uint8 client_random[SEC_RANDOM_SIZE];
        uint32 rc4_key_size;
        uint8 inr[SEC_MODULUS_SIZE];

        if (!sec_parse_crypt_info(s, &rc4_key_size, &server_random, &modulus, &exponent))
        {
                DEBUG(("Failed to parse crypt info\n"));
                return;
        }

        DEBUG(("Generating client random\n"));
        /* Generate a client random, and hence determine encryption keys */
        /* This is what the MS client do: */
        memset(inr, 0, SEC_RANDOM_SIZE);
        /*  *ARIGL!* Plaintext attack, anyone?
           I tried doing:
           generate_random(inr);
           ..but that generates connection errors now and then (yes, 
           "now and then". Something like 0 to 3 attempts needed before a 
           successful connection. Nice. Not! 
         */

        generate_random(client_random);
        if (NULL != server_public_key)
        {                       /* Which means we should use 
                                   RDP5-style encryption */

                memcpy(inr + SEC_RANDOM_SIZE, client_random, SEC_RANDOM_SIZE);
                reverse(inr + SEC_RANDOM_SIZE, SEC_RANDOM_SIZE);

                RSA_public_encrypt(SEC_MODULUS_SIZE,
                                   inr, sec_crypted_random, server_public_key, RSA_NO_PADDING);

                reverse(sec_crypted_random, SEC_MODULUS_SIZE);

        }
        else
        {                       /* RDP4-style encryption */
                sec_rsa_encrypt(sec_crypted_random,
                                client_random, SEC_RANDOM_SIZE, modulus, exponent);
        }
        sec_generate_keys(client_random, server_random, rc4_key_size);
}


/* Process SRV_INFO, find RDP version supported by server */
static void
sec_process_srv_info(STREAM s)
{
        in_uint16_le(s, g_server_rdp_version);
        DEBUG_RDP5(("Server RDP version is %d\n", g_server_rdp_version));
        if (1 == g_server_rdp_version)
        {
                g_use_rdp5 = 0;
                g_server_bpp = 8;
        }
}


/* Process connect response data blob */
void
sec_process_mcs_data(STREAM s)
{
        uint16 tag, length;
        uint8 *next_tag;
        uint8 len;

        in_uint8s(s, 21);       /* header (T.124 ConferenceCreateResponse) */
        in_uint8(s, len);
        if (len & 0x80)
                in_uint8(s, len);

        while (s->p < s->end)
        {
                in_uint16_le(s, tag);
                in_uint16_le(s, length);

                if (length <= 4)
                        return;

                next_tag = s->p + length - 4;

                switch (tag)
                {
                        case SEC_TAG_SRV_INFO:
                                sec_process_srv_info(s);
                                break;

                        case SEC_TAG_SRV_CRYPT:
                                sec_process_crypt_info(s);
                                break;

                        case SEC_TAG_SRV_CHANNELS:
                                /* FIXME: We should parse this information and
                                   use it to map RDP5 channels to MCS 
                                   channels */
                                break;

                        default:
                                unimpl("response tag 0x%x\n", tag);
                }

                s->p = next_tag;
        }
}

/* Receive secure transport packet */
STREAM
sec_recv(uint8 * rdpver)
{
        uint32 sec_flags;
        uint16 channel;
        STREAM s;

        while ((s = mcs_recv(&channel, rdpver)) != NULL)
        {
                if (rdpver != NULL)
                {
                        if (*rdpver != 3)
                        {
                                if (*rdpver & 0x80)
                                {
                                        in_uint8s(s, 8);        /* signature */
                                        sec_decrypt(s->p, s->end - s->p);
                                }
                                return s;
                        }
                }
                if (g_encryption || !g_licence_issued)
                {
                        in_uint32_le(s, sec_flags);

                        if (sec_flags & SEC_ENCRYPT)
                        {
                                in_uint8s(s, 8);        /* signature */
                                sec_decrypt(s->p, s->end - s->p);
                        }

                        if (sec_flags & SEC_LICENCE_NEG)
                        {
                                licence_process(s);
                                continue;
                        }

                        if (sec_flags & 0x0400) /* SEC_REDIRECT_ENCRYPT */
                        {
                                uint8 swapbyte;

                                in_uint8s(s, 8);        /* signature */
                                sec_decrypt(s->p, s->end - s->p);

                                /* Check for a redirect packet, starts with 00 04 */
                                if (s->p[0] == 0 && s->p[1] == 4)
                                {
                                        /* for some reason the PDU and the length seem to be swapped.
                                           This isn't good, but we're going to do a byte for byte
                                           swap.  So the first foure value appear as: 00 04 XX YY,
                                           where XX YY is the little endian length. We're going to
                                           use 04 00 as the PDU type, so after our swap this will look
                                           like: XX YY 04 00 */
                                        swapbyte = s->p[0];
                                        s->p[0] = s->p[2];
                                        s->p[2] = swapbyte;

                                        swapbyte = s->p[1];
                                        s->p[1] = s->p[3];
                                        s->p[3] = swapbyte;

                                        swapbyte = s->p[2];
                                        s->p[2] = s->p[3];
                                        s->p[3] = swapbyte;
                                }
#ifdef WITH_DEBUG
                                /* warning!  this debug statement will show passwords in the clear! */
                                hexdump(s->p, s->end - s->p);
#endif
                        }

                }

                if (channel != MCS_GLOBAL_CHANNEL)
                {
                        channel_process(s, channel);
                        *rdpver = 0xff;
                        return s;
                }

                return s;
        }

        return NULL;
}

/* Establish a secure connection */
BOOL
sec_connect(char *server, char *username)
{
        struct stream mcs_data;

        /* We exchange some RDP data during the MCS-Connect */
        mcs_data.size = 512;
        mcs_data.p = mcs_data.data = (uint8 *) xmalloc(mcs_data.size);
        sec_out_mcs_data(&mcs_data);

        if (!mcs_connect(server, &mcs_data, username))
                return False;

        /*      sec_process_mcs_data(&mcs_data); */
        if (g_encryption)
                sec_establish_key();
        xfree(mcs_data.data);
        return True;
}

/* Establish a secure connection */
BOOL
sec_reconnect(char *server)
{
        struct stream mcs_data;

        /* We exchange some RDP data during the MCS-Connect */
        mcs_data.size = 512;
        mcs_data.p = mcs_data.data = (uint8 *) xmalloc(mcs_data.size);
        sec_out_mcs_data(&mcs_data);

        if (!mcs_reconnect(server, &mcs_data))
                return False;

        /*      sec_process_mcs_data(&mcs_data); */
        if (g_encryption)
                sec_establish_key();
        xfree(mcs_data.data);
        return True;
}

/* Disconnect a connection */
void
sec_disconnect(void)
{
        mcs_disconnect();
}

/* reset the state of the sec layer */
void
sec_reset_state(void)
{
        g_server_rdp_version = 0;
        sec_encrypt_use_count = 0;
        sec_decrypt_use_count = 0;
        mcs_reset_state();
}