tevent: Add a utility function tevent_find_ops_byname().

[Samba.git] / libcli / auth / smbencrypt.c

/*
   Unix SMB/CIFS implementation.
   SMB parameters and setup
   Copyright (C) Andrew Tridgell 1992-1998
   Modified by Jeremy Allison 1995.
   Copyright (C) Jeremy Allison 1995-2000.
   Copyright (C) Luke Kennethc Casson Leighton 1996-2000.
   Copyright (C) Andrew Bartlett <abartlet@samba.org> 2002-2003

   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 3 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, see <http://www.gnu.org/licenses/>.
*/

#include "includes.h"
#include "system/time.h"
#include "../libcli/auth/msrpc_parse.h"
#include "../lib/crypto/crypto.h"
#include "../libcli/auth/libcli_auth.h"
#include "../librpc/gen_ndr/ntlmssp.h"

void SMBencrypt_hash(const uint8_t lm_hash[16], const uint8_t *c8, uint8_t p24[24])
{
        uint8_t p21[21];

        memset(p21,'\0',21);
        memcpy(p21, lm_hash, 16);

        SMBOWFencrypt(p21, c8, p24);

#ifdef DEBUG_PASSWORD
        DEBUG(100,("SMBencrypt_hash: lm#, challenge, response\n"));
        dump_data(100, p21, 16);
        dump_data(100, c8, 8);
        dump_data(100, p24, 24);
#endif
}

/*
   This implements the X/Open SMB password encryption
   It takes a password ('unix' string), a 8 byte "crypt key"
   and puts 24 bytes of encrypted password into p24

   Returns False if password must have been truncated to create LM hash
*/

bool SMBencrypt(const char *passwd, const uint8_t *c8, uint8_t p24[24])
{
        bool ret;
        uint8_t lm_hash[16];

        ret = E_deshash(passwd, lm_hash);
        SMBencrypt_hash(lm_hash, c8, p24);
        return ret;
}

/**
 * Creates the MD4 Hash of the users password in NT UNICODE.
 * @param passwd password in 'unix' charset.
 * @param p16 return password hashed with md4, caller allocated 16 byte buffer
 */

bool E_md4hash(const char *passwd, uint8_t p16[16])
{
        size_t len;
        smb_ucs2_t *wpwd;
        bool ret;

        ret = push_ucs2_talloc(NULL, &wpwd, passwd, &len);
        if (!ret || len < 2) {
                /* We don't want to return fixed data, as most callers
                 * don't check */
                mdfour(p16, (const uint8_t *)passwd, strlen(passwd));
                return false;
        }

        len -= 2;
        mdfour(p16, (const uint8_t *)wpwd, len);

        talloc_free(wpwd);
        return true;
}

/**
 * Creates the MD5 Hash of a combination of 16 byte salt and 16 byte NT hash.
 * @param 16 byte salt.
 * @param 16 byte NT hash.
 * @param 16 byte return hashed with md5, caller allocated 16 byte buffer
 */

void E_md5hash(const uint8_t salt[16], const uint8_t nthash[16], uint8_t hash_out[16])
{
        struct MD5Context tctx;
        MD5Init(&tctx);
        MD5Update(&tctx, salt, 16);
        MD5Update(&tctx, nthash, 16);
        MD5Final(hash_out, &tctx);
}

/**
 * Creates the DES forward-only Hash of the users password in DOS ASCII charset
 * @param passwd password in 'unix' charset.
 * @param p16 return password hashed with DES, caller allocated 16 byte buffer
 * @return false if password was > 14 characters, and therefore may be incorrect, otherwise true
 * @note p16 is filled in regardless
 */

bool E_deshash(const char *passwd, uint8_t p16[16])
{
        bool ret;
        uint8_t dospwd[14];
        TALLOC_CTX *frame = talloc_stackframe();

        size_t converted_size;

        char *tmpbuf;

        ZERO_STRUCT(dospwd);

        tmpbuf = strupper_talloc(frame, passwd);
        if (tmpbuf == NULL) {
                /* Too many callers don't check this result, we need to fill in the buffer with something */
                strlcpy((char *)dospwd, passwd ? passwd : "", sizeof(dospwd));
                E_P16(dospwd, p16);
                talloc_free(frame);
                return false;
        }

        ZERO_STRUCT(dospwd);

        ret = convert_string_error(CH_UNIX, CH_DOS, tmpbuf, strlen(tmpbuf), dospwd, sizeof(dospwd), &converted_size);
        talloc_free(frame);

        /* Only the first 14 chars are considered, password need not
         * be null terminated.  We do this in the error and success
         * case to avoid returning a fixed 'password' buffer, but
         * callers should not use it when E_deshash returns false */

        E_P16((const uint8_t *)dospwd, p16);

        ZERO_STRUCT(dospwd);

        return ret;
}

/**
 * Creates the MD4 and DES (LM) Hash of the users password.
 * MD4 is of the NT Unicode, DES is of the DOS UPPERCASE password.
 * @param passwd password in 'unix' charset.
 * @param nt_p16 return password hashed with md4, caller allocated 16 byte buffer
 * @param p16 return password hashed with des, caller allocated 16 byte buffer
 */

/* Does both the NT and LM owfs of a user's password */
void nt_lm_owf_gen(const char *pwd, uint8_t nt_p16[16], uint8_t p16[16])
{
        /* Calculate the MD4 hash (NT compatible) of the password */
        memset(nt_p16, '\0', 16);
        E_md4hash(pwd, nt_p16);

#ifdef DEBUG_PASSWORD
        DEBUG(100,("nt_lm_owf_gen: pwd, nt#\n"));
        dump_data(120, (const uint8_t *)pwd, strlen(pwd));
        dump_data(100, nt_p16, 16);
#endif

        E_deshash(pwd, (uint8_t *)p16);

#ifdef DEBUG_PASSWORD
        DEBUG(100,("nt_lm_owf_gen: pwd, lm#\n"));
        dump_data(120, (const uint8_t *)pwd, strlen(pwd));
        dump_data(100, p16, 16);
#endif
}

/* Does both the NTLMv2 owfs of a user's password */
bool ntv2_owf_gen(const uint8_t owf[16],
                  const char *user_in, const char *domain_in,
                  uint8_t kr_buf[16])
{
        smb_ucs2_t *user;
        smb_ucs2_t *domain;
        size_t user_byte_len;
        size_t domain_byte_len;
        bool ret;

        HMACMD5Context ctx;
        TALLOC_CTX *mem_ctx = talloc_init("ntv2_owf_gen for %s\\%s", domain_in, user_in);

        if (!mem_ctx) {
                return false;
        }

        if (!user_in) {
                user_in = "";
        }

        if (!domain_in) {
                domain_in = "";
        }

        user_in = strupper_talloc(mem_ctx, user_in);
        if (user_in == NULL) {
                talloc_free(mem_ctx);
                return false;
        }

        ret = push_ucs2_talloc(mem_ctx, &user, user_in, &user_byte_len );
        if (!ret) {
                DEBUG(0, ("push_uss2_talloc() for user failed)\n"));
                talloc_free(mem_ctx);
                return false;
        }

        ret = push_ucs2_talloc(mem_ctx, &domain, domain_in, &domain_byte_len);
        if (!ret) {
                DEBUG(0, ("push_ucs2_talloc() for domain failed\n"));
                talloc_free(mem_ctx);
                return false;
        }

        SMB_ASSERT(user_byte_len >= 2);
        SMB_ASSERT(domain_byte_len >= 2);

        /* We don't want null termination */
        user_byte_len = user_byte_len - 2;
        domain_byte_len = domain_byte_len - 2;

        hmac_md5_init_limK_to_64(owf, 16, &ctx);
        hmac_md5_update((uint8_t *)user, user_byte_len, &ctx);
        hmac_md5_update((uint8_t *)domain, domain_byte_len, &ctx);
        hmac_md5_final(kr_buf, &ctx);

#ifdef DEBUG_PASSWORD
        DEBUG(100, ("ntv2_owf_gen: user, domain, owfkey, kr\n"));
        dump_data(100, (uint8_t *)user, user_byte_len);
        dump_data(100, (uint8_t *)domain, domain_byte_len);
        dump_data(100, owf, 16);
        dump_data(100, kr_buf, 16);
#endif

        talloc_free(mem_ctx);
        return true;
}

/* Does the des encryption from the NT or LM MD4 hash. */
void SMBOWFencrypt(const uint8_t passwd[16], const uint8_t *c8, uint8_t p24[24])
{
        uint8_t p21[21];

        ZERO_STRUCT(p21);

        memcpy(p21, passwd, 16);
        E_P24(p21, c8, p24);
}

/* Does the des encryption. */

void SMBNTencrypt_hash(const uint8_t nt_hash[16], const uint8_t *c8, uint8_t *p24)
{
        uint8_t p21[21];

        memset(p21,'\0',21);
        memcpy(p21, nt_hash, 16);
        SMBOWFencrypt(p21, c8, p24);

#ifdef DEBUG_PASSWORD
        DEBUG(100,("SMBNTencrypt: nt#, challenge, response\n"));
        dump_data(100, p21, 16);
        dump_data(100, c8, 8);
        dump_data(100, p24, 24);
#endif
}

/* Does the NT MD4 hash then des encryption. Plaintext version of the above. */

void SMBNTencrypt(const char *passwd, const uint8_t *c8, uint8_t *p24)
{
        uint8_t nt_hash[16];
        E_md4hash(passwd, nt_hash);
        SMBNTencrypt_hash(nt_hash, c8, p24);
}


/* Does the md5 encryption from the Key Response for NTLMv2. */
void SMBOWFencrypt_ntv2(const uint8_t kr[16],
                        const DATA_BLOB *srv_chal,
                        const DATA_BLOB *smbcli_chal,
                        uint8_t resp_buf[16])
{
        HMACMD5Context ctx;

        hmac_md5_init_limK_to_64(kr, 16, &ctx);
        hmac_md5_update(srv_chal->data, srv_chal->length, &ctx);
        hmac_md5_update(smbcli_chal->data, smbcli_chal->length, &ctx);
        hmac_md5_final(resp_buf, &ctx);

#ifdef DEBUG_PASSWORD
        DEBUG(100, ("SMBOWFencrypt_ntv2: srv_chal, smbcli_chal, resp_buf\n"));
        dump_data(100, srv_chal->data, srv_chal->length);
        dump_data(100, smbcli_chal->data, smbcli_chal->length);
        dump_data(100, resp_buf, 16);
#endif
}

void SMBsesskeygen_ntv2(const uint8_t kr[16],
                        const uint8_t * nt_resp, uint8_t sess_key[16])
{
        /* a very nice, 128 bit, variable session key */

        HMACMD5Context ctx;

        hmac_md5_init_limK_to_64(kr, 16, &ctx);
        hmac_md5_update(nt_resp, 16, &ctx);
        hmac_md5_final((uint8_t *)sess_key, &ctx);

#ifdef DEBUG_PASSWORD
        DEBUG(100, ("SMBsesskeygen_ntv2:\n"));
        dump_data(100, sess_key, 16);
#endif
}

void SMBsesskeygen_ntv1(const uint8_t kr[16], uint8_t sess_key[16])
{
        /* yes, this session key does not change - yes, this
           is a problem - but it is 128 bits */

        mdfour((uint8_t *)sess_key, kr, 16);

#ifdef DEBUG_PASSWORD
        DEBUG(100, ("SMBsesskeygen_ntv1:\n"));
        dump_data(100, sess_key, 16);
#endif
}

void SMBsesskeygen_lm_sess_key(const uint8_t lm_hash[16],
                               const uint8_t lm_resp[24], /* only uses 8 */
                               uint8_t sess_key[16])
{
        /* Calculate the LM session key (effective length 40 bits,
           but changes with each session) */
        uint8_t p24[24];
        uint8_t partial_lm_hash[14];

        memcpy(partial_lm_hash, lm_hash, 8);
        memset(partial_lm_hash + 8, 0xbd, 6);

        des_crypt56(p24,   lm_resp, partial_lm_hash,     1);
        des_crypt56(p24+8, lm_resp, partial_lm_hash + 7, 1);

        memcpy(sess_key, p24, 16);

#ifdef DEBUG_PASSWORD
        DEBUG(100, ("SMBsesskeygen_lm_sess_key: \n"));
        dump_data(100, sess_key, 16);
#endif
}

DATA_BLOB NTLMv2_generate_names_blob(TALLOC_CTX *mem_ctx,
                                     const char *hostname,
                                     const char *domain)
{
        DATA_BLOB names_blob = data_blob_talloc(mem_ctx, NULL, 0);

        /* Deliberately ignore return here.. */
        if (hostname != NULL) {
                (void)msrpc_gen(mem_ctx, &names_blob,
                          "aaa",
                          MsvAvNbDomainName, domain,
                          MsvAvNbComputerName, hostname,
                          MsvAvEOL, "");
        } else {
                (void)msrpc_gen(mem_ctx, &names_blob,
                          "aa",
                          MsvAvNbDomainName, domain,
                          MsvAvEOL, "");
        }
        return names_blob;
}

static DATA_BLOB NTLMv2_generate_client_data(TALLOC_CTX *mem_ctx, const DATA_BLOB *names_blob)
{
        uint8_t client_chal[8];
        DATA_BLOB response = data_blob(NULL, 0);
        uint8_t long_date[8];
        NTTIME nttime;

        unix_to_nt_time(&nttime, time(NULL));

        generate_random_buffer(client_chal, sizeof(client_chal));

        push_nttime(long_date, 0, nttime);

        /* See http://www.ubiqx.org/cifs/SMB.html#SMB.8.5 */

        /* Deliberately ignore return here.. */
        (void)msrpc_gen(mem_ctx, &response, "ddbbdb",
                  0x00000101,     /* Header  */
                  0,              /* 'Reserved'  */
                  long_date, 8,   /* Timestamp */
                  client_chal, 8, /* client challenge */
                  0,              /* Unknown */
                  names_blob->data, names_blob->length);        /* End of name list */

        return response;
}

static DATA_BLOB NTLMv2_generate_response(TALLOC_CTX *out_mem_ctx,
                                          const uint8_t ntlm_v2_hash[16],
                                          const DATA_BLOB *server_chal,
                                          const DATA_BLOB *names_blob)
{
        uint8_t ntlmv2_response[16];
        DATA_BLOB ntlmv2_client_data;
        DATA_BLOB final_response;

        TALLOC_CTX *mem_ctx = talloc_named(out_mem_ctx, 0,
                                           "NTLMv2_generate_response internal context");

        if (!mem_ctx) {
                return data_blob(NULL, 0);
        }

        /* NTLMv2 */
        /* generate some data to pass into the response function - including
           the hostname and domain name of the server */
        ntlmv2_client_data = NTLMv2_generate_client_data(mem_ctx, names_blob);

        /* Given that data, and the challenge from the server, generate a response */
        SMBOWFencrypt_ntv2(ntlm_v2_hash, server_chal, &ntlmv2_client_data, ntlmv2_response);

        final_response = data_blob_talloc(out_mem_ctx, NULL, sizeof(ntlmv2_response) + ntlmv2_client_data.length);

        memcpy(final_response.data, ntlmv2_response, sizeof(ntlmv2_response));

        memcpy(final_response.data+sizeof(ntlmv2_response),
               ntlmv2_client_data.data, ntlmv2_client_data.length);

        talloc_free(mem_ctx);

        return final_response;
}

static DATA_BLOB LMv2_generate_response(TALLOC_CTX *mem_ctx,
                                        const uint8_t ntlm_v2_hash[16],
                                        const DATA_BLOB *server_chal)
{
        uint8_t lmv2_response[16];
        DATA_BLOB lmv2_client_data = data_blob_talloc(mem_ctx, NULL, 8);
        DATA_BLOB final_response = data_blob_talloc(mem_ctx, NULL,24);

        /* LMv2 */
        /* client-supplied random data */
        generate_random_buffer(lmv2_client_data.data, lmv2_client_data.length);

        /* Given that data, and the challenge from the server, generate a response */
        SMBOWFencrypt_ntv2(ntlm_v2_hash, server_chal, &lmv2_client_data, lmv2_response);
        memcpy(final_response.data, lmv2_response, sizeof(lmv2_response));

        /* after the first 16 bytes is the random data we generated above,
           so the server can verify us with it */
        memcpy(final_response.data+sizeof(lmv2_response),
               lmv2_client_data.data, lmv2_client_data.length);

        data_blob_free(&lmv2_client_data);

        return final_response;
}

bool SMBNTLMv2encrypt_hash(TALLOC_CTX *mem_ctx,
                           const char *user, const char *domain, const uint8_t nt_hash[16],
                           const DATA_BLOB *server_chal,
                           const DATA_BLOB *names_blob,
                           DATA_BLOB *lm_response, DATA_BLOB *nt_response,
                           DATA_BLOB *lm_session_key, DATA_BLOB *user_session_key)
{
        uint8_t ntlm_v2_hash[16];

        /* We don't use the NT# directly.  Instead we use it mashed up with
           the username and domain.
           This prevents username swapping during the auth exchange
        */
        if (!ntv2_owf_gen(nt_hash, user, domain, ntlm_v2_hash)) {
                return false;
        }

        if (nt_response) {
                *nt_response = NTLMv2_generate_response(mem_ctx,
                                                        ntlm_v2_hash, server_chal,
                                                        names_blob);
                if (user_session_key) {
                        *user_session_key = data_blob_talloc(mem_ctx, NULL, 16);

                        /* The NTLMv2 calculations also provide a session key, for signing etc later */
                        /* use only the first 16 bytes of nt_response for session key */
                        SMBsesskeygen_ntv2(ntlm_v2_hash, nt_response->data, user_session_key->data);
                }
        }

        /* LMv2 */

        if (lm_response) {
                *lm_response = LMv2_generate_response(mem_ctx,
                                                      ntlm_v2_hash, server_chal);
                if (lm_session_key) {
                        *lm_session_key = data_blob_talloc(mem_ctx, NULL, 16);

                        /* The NTLMv2 calculations also provide a session key, for signing etc later */
                        /* use only the first 16 bytes of lm_response for session key */
                        SMBsesskeygen_ntv2(ntlm_v2_hash, lm_response->data, lm_session_key->data);
                }
        }

        return true;
}

bool SMBNTLMv2encrypt(TALLOC_CTX *mem_ctx,
                      const char *user, const char *domain,
                      const char *password,
                      const DATA_BLOB *server_chal,
                      const DATA_BLOB *names_blob,
                      DATA_BLOB *lm_response, DATA_BLOB *nt_response,
                      DATA_BLOB *lm_session_key, DATA_BLOB *user_session_key)
{
        uint8_t nt_hash[16];
        E_md4hash(password, nt_hash);

        return SMBNTLMv2encrypt_hash(mem_ctx,
                                     user, domain, nt_hash, server_chal, names_blob,
                                     lm_response, nt_response, lm_session_key, user_session_key);
}

/***********************************************************
 encode a password buffer with a unicode password.  The buffer
 is filled with random data to make it harder to attack.
************************************************************/
bool encode_pw_buffer(uint8_t buffer[516], const char *password, int string_flags)
{
        uint8_t new_pw[512];
        ssize_t new_pw_len;

        /* the incoming buffer can be any alignment. */
        string_flags |= STR_NOALIGN;

        new_pw_len = push_string(new_pw,
                                 password,
                                 sizeof(new_pw), string_flags);
        if (new_pw_len == -1) {
                return false;
        }

        memcpy(&buffer[512 - new_pw_len], new_pw, new_pw_len);

        generate_random_buffer(buffer, 512 - new_pw_len);

        /*
         * The length of the new password is in the last 4 bytes of
         * the data buffer.
         */
        SIVAL(buffer, 512, new_pw_len);
        ZERO_STRUCT(new_pw);
        return true;
}


/***********************************************************
 decode a password buffer
 *new_pw_len is the length in bytes of the possibly mulitbyte
 returned password including termination.
************************************************************/

bool decode_pw_buffer(TALLOC_CTX *ctx,
                      uint8_t in_buffer[516],
                      char **pp_new_pwrd,
                      size_t *new_pw_len,
                      charset_t string_charset)
{
        int byte_len=0;

        *pp_new_pwrd = NULL;
        *new_pw_len = 0;

        /*
          Warning !!! : This function is called from some rpc call.
          The password IN the buffer may be a UNICODE string.
          The password IN new_pwrd is an ASCII string
          If you reuse that code somewhere else check first.
        */

        /* The length of the new password is in the last 4 bytes of the data buffer. */

        byte_len = IVAL(in_buffer, 512);

#ifdef DEBUG_PASSWORD
        dump_data(100, in_buffer, 516);
#endif

        /* Password cannot be longer than the size of the password buffer */
        if ( (byte_len < 0) || (byte_len > 512)) {
                DEBUG(0, ("decode_pw_buffer: incorrect password length (%d).\n", byte_len));
                DEBUG(0, ("decode_pw_buffer: check that 'encrypt passwords = yes'\n"));
                return false;
        }

        /* decode into the return buffer. */
        if (!convert_string_talloc(ctx, string_charset, CH_UNIX,
                                   &in_buffer[512 - byte_len],
                                   byte_len,
                                   (void *)pp_new_pwrd,
                                   new_pw_len)) {
                DEBUG(0, ("decode_pw_buffer: failed to convert incoming password\n"));
                return false;
        }

#ifdef DEBUG_PASSWORD
        DEBUG(100,("decode_pw_buffer: new_pwrd: "));
        dump_data(100, (uint8_t *)*pp_new_pwrd, *new_pw_len);
        DEBUG(100,("multibyte len:%lu\n", (unsigned long int)*new_pw_len));
        DEBUG(100,("original char len:%d\n", byte_len/2));
#endif

        return true;
}

/***********************************************************
 Decode an arc4 encrypted password change buffer.
************************************************************/

void encode_or_decode_arc4_passwd_buffer(unsigned char pw_buf[532], const DATA_BLOB *psession_key)
{
        struct MD5Context tctx;
        unsigned char key_out[16];

        /* Confounder is last 16 bytes. */

        MD5Init(&tctx);
        MD5Update(&tctx, &pw_buf[516], 16);
        MD5Update(&tctx, psession_key->data, psession_key->length);
        MD5Final(key_out, &tctx);
        /* arc4 with key_out. */
        arcfour_crypt(pw_buf, key_out, 516);
}

/***********************************************************
 encode a password buffer with an already unicode password.  The
 rest of the buffer is filled with random data to make it harder to attack.
************************************************************/
bool set_pw_in_buffer(uint8_t buffer[516], DATA_BLOB *password)
{
        if (password->length > 512) {
                return false;
        }

        memcpy(&buffer[512 - password->length], password->data, password->length);

        generate_random_buffer(buffer, 512 - password->length);

        /*
         * The length of the new password is in the last 4 bytes of
         * the data buffer.
         */
        SIVAL(buffer, 512, password->length);
        return true;
}

/***********************************************************
 decode a password buffer
 *new_pw_size is the length in bytes of the extracted unicode password
************************************************************/
bool extract_pw_from_buffer(TALLOC_CTX *mem_ctx,
                            uint8_t in_buffer[516], DATA_BLOB *new_pass)
{
        int byte_len=0;

        /* The length of the new password is in the last 4 bytes of the data buffer. */

        byte_len = IVAL(in_buffer, 512);

#ifdef DEBUG_PASSWORD
        dump_data(100, in_buffer, 516);
#endif

        /* Password cannot be longer than the size of the password buffer */
        if ( (byte_len < 0) || (byte_len > 512)) {
                return false;
        }

        *new_pass = data_blob_talloc(mem_ctx, &in_buffer[512 - byte_len], byte_len);

        if (!new_pass->data) {
                return false;
        }

        return true;
}


/* encode a wkssvc_PasswordBuffer:
 *
 * similar to samr_CryptPasswordEx. Different: 8byte confounder (instead of
 * 16byte), confounder in front of the 516 byte buffer (instead of after that
 * buffer), calling MD5Update() first with session_key and then with confounder
 * (vice versa in samr) - Guenther */

void encode_wkssvc_join_password_buffer(TALLOC_CTX *mem_ctx,
                                        const char *pwd,
                                        DATA_BLOB *session_key,
                                        struct wkssvc_PasswordBuffer **pwd_buf)
{
        uint8_t buffer[516];
        struct MD5Context ctx;
        struct wkssvc_PasswordBuffer *my_pwd_buf = NULL;
        DATA_BLOB confounded_session_key;
        int confounder_len = 8;
        uint8_t confounder[8];

        my_pwd_buf = talloc_zero(mem_ctx, struct wkssvc_PasswordBuffer);
        if (!my_pwd_buf) {
                return;
        }

        confounded_session_key = data_blob_talloc(mem_ctx, NULL, 16);

        encode_pw_buffer(buffer, pwd, STR_UNICODE);

        generate_random_buffer((uint8_t *)confounder, confounder_len);

        MD5Init(&ctx);
        MD5Update(&ctx, session_key->data, session_key->length);
        MD5Update(&ctx, confounder, confounder_len);
        MD5Final(confounded_session_key.data, &ctx);

        arcfour_crypt_blob(buffer, 516, &confounded_session_key);

        memcpy(&my_pwd_buf->data[0], confounder, confounder_len);
        memcpy(&my_pwd_buf->data[8], buffer, 516);

        data_blob_free(&confounded_session_key);

        *pwd_buf = my_pwd_buf;
}

WERROR decode_wkssvc_join_password_buffer(TALLOC_CTX *mem_ctx,
                                          struct wkssvc_PasswordBuffer *pwd_buf,
                                          DATA_BLOB *session_key,
                                          char **pwd)
{
        uint8_t buffer[516];
        struct MD5Context ctx;
        size_t pwd_len;

        DATA_BLOB confounded_session_key;

        int confounder_len = 8;
        uint8_t confounder[8];

        *pwd = NULL;

        if (!pwd_buf) {
                return WERR_BAD_PASSWORD;
        }

        if (session_key->length != 16) {
                DEBUG(10,("invalid session key\n"));
                return WERR_BAD_PASSWORD;
        }

        confounded_session_key = data_blob_talloc(mem_ctx, NULL, 16);

        memcpy(&confounder, &pwd_buf->data[0], confounder_len);
        memcpy(&buffer, &pwd_buf->data[8], 516);

        MD5Init(&ctx);
        MD5Update(&ctx, session_key->data, session_key->length);
        MD5Update(&ctx, confounder, confounder_len);
        MD5Final(confounded_session_key.data, &ctx);

        arcfour_crypt_blob(buffer, 516, &confounded_session_key);

        if (!decode_pw_buffer(mem_ctx, buffer, pwd, &pwd_len, CH_UTF16)) {
                data_blob_free(&confounded_session_key);
                return WERR_BAD_PASSWORD;
        }

        data_blob_free(&confounded_session_key);

        return WERR_OK;
}