scram/client.c

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/* client.c --- SASL SCRAM client side functions.
 * Copyright (C) 2009  Simon Josefsson
 *
 * This file is part of GNU SASL Library.
 *
 * GNU SASL 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.
 *
 * GNU SASL 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 GNU SASL Library; if not, write to the Free
 * Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
 * Boston, MA 02110-1301, USA.
 *
 */

#ifdef HAVE_CONFIG_H
# include "config.h"
#endif

/* Get specification. */
#include "scram.h"

/* Get malloc, free. */
#include <stdlib.h>

/* Get memcpy, strlen, strchr. */
#include <string.h>

/* Get bool. */
#include <stdbool.h>

#include "tokens.h"
#include "parser.h"
#include "printer.h"
#include "gc.h"
#include "memxor.h"

#define CNONCE_ENTROPY_BYTES 18

struct scram_client_state
{
  int step;
  char *cfmb; /* client first message bare */
  char *serversignature;
  char *authmessage;
  struct scram_client_first cf;
  struct scram_server_first sf;
  struct scram_client_final cl;
  struct scram_server_final sl;
};

int
_gsasl_scram_sha1_client_start (Gsasl_session * sctx, void **mech_data)
{
  struct scram_client_state *state;
  char buf[CNONCE_ENTROPY_BYTES];
  int rc;

  state = (struct scram_client_state *) calloc (sizeof (*state), 1);
  if (state == NULL)
    return GSASL_MALLOC_ERROR;

  rc = gsasl_nonce (buf, CNONCE_ENTROPY_BYTES);
  if (rc != GSASL_OK)
    {
      free (state);
      return rc;
    }

  rc = gsasl_base64_to (buf, CNONCE_ENTROPY_BYTES,
                        &state->cf.client_nonce, NULL);
  if (rc != GSASL_OK)
    {
      free (state);
      return rc;
    }

  *mech_data = state;

  return GSASL_OK;
}

static char
hexdigit_to_char (char hexdigit)
{
  if (hexdigit >= '0' && hexdigit <= '9')
    return hexdigit - '0';
  if (hexdigit >= 'a' && hexdigit <= 'f')
    return hexdigit - 'a' + 10;
  return 0;
}

static char
hex_to_char (char u, char l)
{
  return (char) (((unsigned char) hexdigit_to_char (u)) * 16
                 + hexdigit_to_char (l));
}

static void
sha1_hex_to_byte (char *saltedpassword, const char *p)
{
  while (*p)
    {
      *saltedpassword = hex_to_char (p[0], p[1]);
      p += 2;
      saltedpassword++;
    }
}

static bool
hex_p (const char *hexstr)
{
  static const char hexalpha[] = "0123456789abcdef";

  for (; *hexstr; hexstr++)
    if (strchr (hexalpha, *hexstr) == NULL)
      return false;

  return true;
}

int
_gsasl_scram_sha1_client_step (Gsasl_session * sctx,
                               void *mech_data,
                               const char *input, size_t input_len,
                               char **output, size_t * output_len)
{
  struct scram_client_state *state = mech_data;
  int res = GSASL_MECHANISM_CALLED_TOO_MANY_TIMES;
  int rc;

  *output = NULL;
  *output_len = 0;

  switch (state->step)
    {
    case 0:
      {
        const char *p;

        /* We don't support channel bindings. */
        state->cf.cbflag = 'n';

        p = gsasl_property_get (sctx, GSASL_AUTHID);
        if (!p)
          return GSASL_NO_AUTHID;

        /* FIXME check that final document uses query strings. */
        rc = gsasl_saslprep (p, GSASL_ALLOW_UNASSIGNED,
                             &state->cf.username, NULL);
        if (rc != GSASL_OK)
          return rc;

        p = gsasl_property_get (sctx, GSASL_AUTHZID);
        if (p)
          state->cf.authzid = strdup (p);

        rc = scram_print_client_first (&state->cf, output);
        if (rc == -2)
          return GSASL_MALLOC_ERROR;
        else if (rc != 0)
          return GSASL_AUTHENTICATION_ERROR;

        *output_len = strlen (*output);

        /* Save "cbind" and "bare" for next step. */
        p = strchr (*output, ',');
        if (!p)
            return GSASL_AUTHENTICATION_ERROR;
        p++;
        p = strchr (p, ',');
        if (!p)
            return GSASL_AUTHENTICATION_ERROR;
        p++;
        rc = gsasl_base64_to (*output, p - *output, &state->cl.cbind, NULL);
        if (rc != 0)
          return rc;

        state->cfmb = strdup (p);
        if (!state->cfmb)
          return GSASL_MALLOC_ERROR;

        /* We are done. */
        state->step++;
        return GSASL_NEEDS_MORE;
        break;
      }

    case 1:
      {
        if (scram_parse_server_first (input, input_len, &state->sf) < 0)
          return GSASL_MECHANISM_PARSE_ERROR;

        if (strlen (state->sf.nonce) < strlen (state->cf.client_nonce) ||
            memcmp (state->cf.client_nonce, state->sf.nonce,
                    strlen (state->cf.client_nonce)) != 0)
          return GSASL_AUTHENTICATION_ERROR;

        state->cl.nonce = strdup (state->sf.nonce);
        if (!state->cl.nonce)
          return GSASL_MALLOC_ERROR;

        /* Save salt/iter as properties, so that client callback can
           access them. */
        {
          char *str = NULL;
          int n;
          n = asprintf (&str, "%d", state->sf.iter);
          if (n < 0 || str == NULL)
            return GSASL_MALLOC_ERROR;
          gsasl_property_set (sctx, GSASL_SCRAM_ITER, str);
          free (str);
        }

        gsasl_property_set (sctx, GSASL_SCRAM_SALT, state->sf.salt);

        /* Generate ClientProof. */
        {
          char saltedpassword[20];
          char *clientkey;
          char *storedkey;
          char *clientsignature;
          char clientproof[20];
          const char *p;

          /* Get SaltedPassword. */
          p = gsasl_property_get (sctx, GSASL_SCRAM_SALTED_PASSWORD);
          if (p && strlen (p) == 40 && hex_p (p))
            sha1_hex_to_byte (saltedpassword, p);
          else if ((p = gsasl_property_get (sctx, GSASL_PASSWORD)) != NULL)
            {
              Gc_rc err;
              char *salt;
              size_t saltlen;
              char *preppasswd;

              rc = gsasl_saslprep (p, 0, &preppasswd, NULL);
              if (rc != GSASL_OK)
                return rc;

              rc = gsasl_base64_from (state->sf.salt, strlen (state->sf.salt),
                                      &salt, &saltlen);
              if (rc != 0)
                {
                  gsasl_free (preppasswd);
                  return rc;
                }

              /* SaltedPassword := Hi(password, salt) */
              err = gc_pbkdf2_sha1 (preppasswd, strlen (preppasswd),
                                    salt, saltlen,
                                    state->sf.iter, saltedpassword, 20);
              gsasl_free (preppasswd);
              gsasl_free (salt);
              if (err != GC_OK)
                return GSASL_MALLOC_ERROR;
            }
          else
            return GSASL_NO_PASSWORD;

          /* Get client-final-message-without-proof. */
          {
            char *cfmwp;
            int n;

            state->cl.proof = strdup ("p");
            rc = scram_print_client_final (&state->cl, &cfmwp);
            if (rc != 0)
              return GSASL_MALLOC_ERROR;
            free (state->cl.proof);

            /* Compute AuthMessage */
            n = asprintf (&state->authmessage, "%s,%.*s,%.*s",
                          state->cfmb,
                          input_len, input,
                          strlen (cfmwp) - 4,
                          cfmwp);
            free (cfmwp);
            if (n <= 0 || !state->authmessage)
              return GSASL_MALLOC_ERROR;
          }

          /* ClientKey := HMAC(SaltedPassword, "Client Key") */
#define CLIENT_KEY "Client Key"
          rc = gsasl_hmac_sha1 (saltedpassword, 20,
                                CLIENT_KEY, strlen (CLIENT_KEY),
                                &clientkey);
          if (rc != 0)
            return rc;

          /* StoredKey := H(ClientKey) */
          rc = gsasl_sha1 (clientkey, 20, &storedkey);
          if (rc != 0)
            {
              free (clientkey);
              return rc;
            }

          /* ClientSignature := HMAC(StoredKey, AuthMessage) */
          rc = gsasl_hmac_sha1 (storedkey, 20,
                                state->authmessage,
                                strlen (state->authmessage),
                                &clientsignature);
          free (storedkey);
          if (rc != 0)
            {
              free (clientkey);
              return rc;
            }

          /* ClientProof := ClientKey XOR ClientSignature */
          memcpy (clientproof, clientkey, 20);
          memxor (clientproof, clientsignature, 20);

          free (clientkey);
          free (clientsignature);

          rc = gsasl_base64_to (clientproof, 20, &state->cl.proof, NULL);
          if (rc != 0)
            return rc;

          /* Generate ServerSignature, for comparison in next step. */
          {
            char *serverkey;
            char *serversignature;

            /* ServerKey := HMAC(SaltedPassword, "Server Key") */
#define SERVER_KEY "Server Key"
            rc = gsasl_hmac_sha1 (saltedpassword, 20,
                                  SERVER_KEY, strlen (SERVER_KEY),
                                  &serverkey);
            if (rc != 0)
              return rc;

            /* ServerSignature := HMAC(ServerKey, AuthMessage) */
            rc = gsasl_hmac_sha1 (serverkey, 20,
                                  state->authmessage,
                                  strlen (state->authmessage),
                                  &serversignature);
            gsasl_free (serverkey);
            if (rc != 0)
              return rc;

            rc = gsasl_base64_to (serversignature, 20,
                                  &state->serversignature, NULL);
            gsasl_free (serversignature);
            if (rc != 0)
              return rc;
          }
        }

        rc = scram_print_client_final (&state->cl, output);
        if (rc != 0)
          return GSASL_MALLOC_ERROR;

        *output_len = strlen (*output);

        state->step++;
        return GSASL_NEEDS_MORE;
        break;
      }

    case 2:
      {
        if (scram_parse_server_final (input, input_len, &state->sl) < 0)
          return GSASL_MECHANISM_PARSE_ERROR;

        if (strcmp (state->sl.verifier, state->serversignature) != 0)
          return GSASL_AUTHENTICATION_ERROR;

        state->step++;
        return GSASL_OK;
        break;
      }

    default:
      break;
    }

  return res;
}

void
_gsasl_scram_sha1_client_finish (Gsasl_session * sctx, void *mech_data)
{
  struct scram_client_state *state = mech_data;

  if (!state)
    return;

  free (state->cfmb);
  free (state->serversignature);
  free (state->authmessage);
  scram_free_client_first (&state->cf);
  scram_free_server_first (&state->sf);
  scram_free_client_final (&state->cl);
  scram_free_server_final (&state->sl);

  free (state);
}