/src/gnutls/lib/ext/pre_shared_key.c

Source
/*
 * Copyright (C) 2017-2018 Free Software Foundation, Inc.
 * Copyright (C) 2018 Red Hat, Inc.
 *
 * Author: Ander Juaristi, Nikos Mavrogiannopoulos
 *
 * This file is part of GnuTLS.
 *
 * The GnuTLS 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 program.  If not, see <https://www.gnu.org/licenses/>
 *
 */

#include "gnutls_int.h"
#include "auth/psk.h"
#include "handshake.h"
#include "kx.h"
#include "secrets.h"
#include "tls13/anti_replay.h"
#include "tls13/psk_ext_parser.h"
#include "tls13/finished.h"
#include "tls13/session_ticket.h"
#include "auth/psk_passwd.h"
#include "ext/session_ticket.h"
#include "ext/pre_shared_key.h"
#include <assert.h>

inline static bool
have_psk_credentials(const gnutls_psk_client_credentials_t cred,
         gnutls_session_t session)
{
  return (cred->get_function || cred->username.data) &&
         session->internals.priorities->have_psk;
}

static int compute_psk_from_ticket(const tls13_ticket_st *ticket,
           gnutls_datum_t *key)
{
  int ret;

  if (unlikely(ticket->prf == NULL || ticket->prf->output_size == 0))
    return gnutls_assert_val(GNUTLS_E_INTERNAL_ERROR);

  key->data = gnutls_malloc(ticket->prf->output_size);
  if (!key->data) {
    gnutls_assert();
    return GNUTLS_E_MEMORY_ERROR;
  }
  key->size = ticket->prf->output_size;

  ret = _tls13_expand_secret2(ticket->prf, RESUMPTION_LABEL,
            sizeof(RESUMPTION_LABEL) - 1, ticket->nonce,
            ticket->nonce_size,
            ticket->resumption_master_secret, key->size,
            key->data);
  if (ret < 0)
    gnutls_assert();

  return ret;
}

enum binder_type {
  BINDER_EXT,
  BINDER_RES,
  BINDER_IMP
};

static const char *get_binder_label(enum binder_type type, size_t *size)
{
  static const char ext_label[] = EXT_BINDER_LABEL;
  static const char res_label[] = RES_BINDER_LABEL;
  static const char imp_label[] = IMP_BINDER_LABEL;
  const char *label;

  switch (type) {
  case BINDER_EXT:
    label = ext_label;
    *size = sizeof(ext_label) - 1;
    break;
  case BINDER_RES:
    label = res_label;
    *size = sizeof(res_label) - 1;
    break;
  case BINDER_IMP:
    label = imp_label;
    *size = sizeof(imp_label) - 1;
    break;
  default:
    assert(0);
  }

  return label;
}

static int compute_binder_key(const mac_entry_st *prf, const uint8_t *key,
            size_t keylen, enum binder_type type, void *out)
{
  int ret;
  size_t label_len;
  const char *label = get_binder_label(type, &label_len);
  uint8_t tmp_key[MAX_HASH_SIZE];

  /* Compute HKDF-Extract(0, psk) */
  ret = _tls13_init_secret2(prf, key, keylen, tmp_key);
  if (ret < 0)
    return ret;

  /* Compute Derive-Secret(secret, label, transcript_hash) */
  ret = _tls13_derive_secret2(prf, label, label_len, NULL, 0, tmp_key,
            out);
  if (ret < 0)
    return ret;

  return 0;
}

static int compute_psk_binder(gnutls_session_t session, const mac_entry_st *prf,
            unsigned binders_length, int exts_length,
            int ext_offset, const gnutls_datum_t *psk,
            const gnutls_datum_t *client_hello,
            enum binder_type type, void *out)
{
  int ret;
  unsigned client_hello_pos, extensions_len_pos;
  gnutls_buffer_st handshake_buf;
  uint8_t binder_key[MAX_HASH_SIZE];

  _gnutls_buffer_init(&handshake_buf);

  if (session->security_parameters.entity == GNUTLS_CLIENT) {
    if (session->internals.hsk_flags & HSK_HRR_RECEIVED) {
      ret = gnutls_buffer_append_data(
        &handshake_buf,
        (const void *)session->internals
          .handshake_hash_buffer.data,
        session->internals.handshake_hash_buffer.length);
      if (ret < 0) {
        gnutls_assert();
        goto error;
      }
    }

    client_hello_pos = handshake_buf.length;
    ret = gnutls_buffer_append_data(
      &handshake_buf, client_hello->data, client_hello->size);
    if (ret < 0) {
      gnutls_assert();
      goto error;
    }

    /* This is a ClientHello message */
    handshake_buf.data[client_hello_pos] =
      GNUTLS_HANDSHAKE_CLIENT_HELLO;

    /* At this point we have not yet added the binders to the ClientHello,
     * but we have to overwrite the size field, pretending as if binders
     * of the correct length were present.
     */
    _gnutls_write_uint24(handshake_buf.length - client_hello_pos +
               binders_length - 2,
             &handshake_buf.data[client_hello_pos + 1]);
    _gnutls_write_uint16(
      handshake_buf.length - client_hello_pos +
        binders_length - ext_offset,
      &handshake_buf.data[client_hello_pos + ext_offset]);
    extensions_len_pos = handshake_buf.length - client_hello_pos -
             exts_length - 2;
    _gnutls_write_uint16(exts_length + binders_length + 2,
             &handshake_buf.data[client_hello_pos +
               extensions_len_pos]);
  } else {
    if (session->internals.hsk_flags & HSK_HRR_SENT) {
      if (unlikely(session->internals.handshake_hash_buffer
               .length <= client_hello->size)) {
        ret = gnutls_assert_val(
          GNUTLS_E_RECEIVED_ILLEGAL_PARAMETER);
        goto error;
      }

      ret = gnutls_buffer_append_data(
        &handshake_buf,
        session->internals.handshake_hash_buffer.data,
        session->internals.handshake_hash_buffer.length -
          client_hello->size);
      if (ret < 0) {
        gnutls_assert();
        goto error;
      }
    }

    if (unlikely(client_hello->size <= binders_length)) {
      ret = gnutls_assert_val(
        GNUTLS_E_RECEIVED_ILLEGAL_PARAMETER);
      goto error;
    }

    ret = gnutls_buffer_append_data(
      &handshake_buf, (const void *)client_hello->data,
      client_hello->size - binders_length);
    if (ret < 0) {
      gnutls_assert();
      goto error;
    }
  }

  ret = compute_binder_key(prf, psk->data, psk->size, type, binder_key);
  if (ret < 0) {
    gnutls_assert();
    goto error;
  }

  ret = _gnutls13_compute_finished(prf, binder_key, &handshake_buf, out);
  if (ret < 0) {
    gnutls_assert();
    goto error;
  }

  ret = 0;
error:
  _gnutls_buffer_clear(&handshake_buf);
  return ret;
}

static int generate_early_secrets(gnutls_session_t session,
          const mac_entry_st *prf)
{
  int ret;

  ret = _tls13_derive_secret2(
    prf, EARLY_TRAFFIC_LABEL, sizeof(EARLY_TRAFFIC_LABEL) - 1,
    session->internals.handshake_hash_buffer.data,
    session->internals.handshake_hash_buffer_client_hello_len,
    session->key.proto.tls13.temp_secret,
    session->key.proto.tls13.e_ckey);
  if (ret < 0)
    return gnutls_assert_val(ret);

  ret = _gnutls_call_keylog_func(session, "CLIENT_EARLY_TRAFFIC_SECRET",
               session->key.proto.tls13.e_ckey,
               prf->output_size);
  if (ret < 0)
    return gnutls_assert_val(ret);

  ret = _tls13_derive_secret2(
    prf, EARLY_EXPORTER_MASTER_LABEL,
    sizeof(EARLY_EXPORTER_MASTER_LABEL) - 1,
    session->internals.handshake_hash_buffer.data,
    session->internals.handshake_hash_buffer_client_hello_len,
    session->key.proto.tls13.temp_secret,
    session->key.proto.tls13.ap_expkey);
  if (ret < 0)
    return gnutls_assert_val(ret);

  ret = _gnutls_call_keylog_func(session, "EARLY_EXPORTER_SECRET",
               session->key.proto.tls13.ap_expkey,
               prf->output_size);
  if (ret < 0)
    return gnutls_assert_val(ret);

  return 0;
}

/* Calculate TLS 1.3 Early Secret and the derived secrets from the
 * selected PSK. */
int _gnutls_generate_early_secrets_for_psk(gnutls_session_t session)
{
  const uint8_t *psk;
  size_t psk_size;
  const mac_entry_st *prf;
  int ret;

  psk = session->key.binders[0].psk.data;
  psk_size = session->key.binders[0].psk.size;
  prf = session->key.binders[0].prf;

  if (unlikely(psk_size == 0))
    return gnutls_assert_val(GNUTLS_E_INVALID_REQUEST);

  ret = _tls13_init_secret2(prf, psk, psk_size,
          session->key.proto.tls13.temp_secret);
  if (ret < 0)
    return gnutls_assert_val(ret);

  session->key.proto.tls13.temp_secret_size = prf->output_size;

  ret = generate_early_secrets(session, session->key.binders[0].prf);
  if (ret < 0)
    return gnutls_assert_val(ret);

  return 0;
}

/**
 * gnutls_psk_format_imported_identity:
 * @identity: external identity
 * @context: optional contextual information
 * @version: protocol version to which the PSK is imported
 * @hash: hash algorithm used for KDF
 * @imported_identity: where the imported identity is stored
 *
 * This formats an external PSK identity @identity into an imported
 * form, described in RFC 9258 as ImportedIdentity.
 *
 * Upon success, the data field of @imported_identity is allocated
 * using gnutls_malloc() and the caller must free the memory after
 * use.
 *
 * Returns: %GNUTLS_E_SUCCESS (0) on success, otherwise a negative error code.
 * Since: 3.8.1
 */
int gnutls_psk_format_imported_identity(const gnutls_datum_t *identity,
          const gnutls_datum_t *context,
          gnutls_protocol_t version,
          gnutls_digest_algorithm_t hash,
          gnutls_datum_t *imported_identity)
{
  gnutls_buffer_st buf;
  const version_entry_st *ver = version_to_entry(version);
  const mac_entry_st *prf = hash_to_entry(hash);
  uint16_t target_protocol;
  uint16_t target_kdf;
  int ret;

  _gnutls_buffer_init(&buf);

  /* external_identity */
  ret = _gnutls_buffer_append_data_prefix16(&buf, identity->data,
              identity->size);
  if (ret < 0) {
    goto error;
  }

  /* context */
  ret = _gnutls_buffer_append_data_prefix16(&buf, context->data,
              context->size);
  if (ret < 0) {
    goto error;
  }

  /* target_protocol */
  target_protocol = ver->major << 8 | ver->minor;
  ret = _gnutls_buffer_append_uint16(&buf, target_protocol);
  if (ret < 0) {
    goto error;
  }

  /* target_kdf */
  switch (prf->id) {
  case GNUTLS_MAC_SHA256:
    target_kdf = 0x0001;
    break;
  case GNUTLS_MAC_SHA384:
    target_kdf = 0x0002;
    break;
  default:
    ret = gnutls_assert_val(GNUTLS_E_UNKNOWN_HASH_ALGORITHM);
    goto error;
  }
  ret = _gnutls_buffer_append_uint16(&buf, target_kdf);
  if (ret < 0) {
    goto error;
  }

  ret = _gnutls_buffer_to_datum(&buf, imported_identity, 0);
  if (ret < 0) {
    goto error;
  }
  return 0;

error:
  _gnutls_buffer_clear(&buf);
  return ret;
}

static int derive_ipsk(const mac_entry_st *prf,
           const gnutls_datum_t *imported_identity,
           const gnutls_datum_t *epsk, uint8_t ipsk[MAX_HASH_SIZE])
{
  uint8_t epskx[MAX_HASH_SIZE];
  uint8_t hashed_identity[MAX_HASH_SIZE];
  int ret;

  /* epskx = HKDF-Extract(0, epsk) */
  ret = _tls13_init_secret2(prf, epsk->data, epsk->size, epskx);
  if (ret < 0) {
    return ret;
  }
  ret = gnutls_hash_fast((gnutls_digest_algorithm_t)prf->id,
             imported_identity->data, imported_identity->size,
             hashed_identity);
  if (ret < 0) {
    return ret;
  }
  /* ipskx = HKDF-Expand-Label(epskx, "derived psk", Hash(ImportedIdentity), L) */
  return _tls13_expand_secret2(prf, DERIVED_PSK_LABEL,
             sizeof(DERIVED_PSK_LABEL) - 1,
             hashed_identity, prf->output_size, epskx,
             prf->output_size, ipsk);
}

/* This does the opposite of gnutls_psk_format_imported_identity.
 * Note that this does not allocate memory, and the data field of
 * identity and context must not be freed.
 */
static int parse_imported_identity(const gnutls_datum_t *imported_identity,
           gnutls_datum_t *identity,
           gnutls_datum_t *context,
           gnutls_protocol_t *version,
           gnutls_digest_algorithm_t *hash)
{
  uint16_t target_protocol;
  uint16_t target_kdf;
  gnutls_buffer_st buf;
  int ret;

  _gnutls_ro_buffer_from_datum(&buf, (gnutls_datum_t *)imported_identity);

  /* external_identity */
  ret = _gnutls_buffer_pop_datum_prefix16(&buf, identity);
  if (ret < 0) {
    return ret;
  }

  /* context */
  ret = _gnutls_buffer_pop_datum_prefix16(&buf, context);
  if (ret < 0) {
    return ret;
  }

  /* target_protocol */
  ret = _gnutls_buffer_pop_uint16(&buf, &target_protocol);
  if (ret < 0) {
    return ret;
  }
  *version = _gnutls_version_get((target_protocol >> 8) & 0xFF,
               target_protocol & 0xFF);

  /* target_kdf */
  ret = _gnutls_buffer_pop_uint16(&buf, &target_kdf);
  if (ret < 0) {
    return ret;
  }
  switch (target_kdf) {
  case 0x0001:
    *hash = GNUTLS_DIG_SHA256;
    break;
  case 0x0002:
    *hash = GNUTLS_DIG_SHA384;
    break;
  default:
    return gnutls_assert_val(GNUTLS_E_UNKNOWN_HASH_ALGORITHM);
  }
  return 0;
}

static int client_send_params(gnutls_session_t session, gnutls_buffer_t extdata,
            const gnutls_psk_client_credentials_t cred)
{
  int ret, ext_offset = 0;
  uint8_t binder_value[MAX_HASH_SIZE];
  size_t spos;
  gnutls_datum_t username = { NULL, 0 };
  gnutls_datum_t user_key = { NULL, 0 }, rkey = { NULL, 0 };
  unsigned client_hello_len;
  unsigned next_idx;
  const mac_entry_st *prf_res = NULL;
  const mac_entry_st *prf_psk = NULL;
  struct timespec cur_time;
  uint32_t ticket_age, ob_ticket_age;
  int free_username = 0;
  psk_auth_info_t info = NULL;
  unsigned psk_id_len = 0;
  unsigned binders_len, binders_pos;
  bool imported = false;
  tls13_ticket_st *ticket = &session->internals.tls13_ticket;

  if (((session->internals.flags & GNUTLS_NO_TICKETS) ||
       session->internals.tls13_ticket.ticket.data == NULL) &&
      (!cred || !have_psk_credentials(cred, session))) {
    return 0;
  }

  binders_len = 0;

  /* placeholder to be filled later */
  spos = extdata->length;
  ret = _gnutls_buffer_append_uint16(extdata, 0);
  if (ret < 0)
    return gnutls_assert_val(ret);

  /* First, let's see if we have a session ticket to send */
  if (!(session->internals.flags & GNUTLS_NO_TICKETS) &&
      ticket->ticket.data != NULL) {
    /* We found a session ticket */
    if (unlikely(ticket->prf == NULL)) {
      tls13_ticket_deinit(ticket);
      ret = gnutls_assert_val(GNUTLS_E_INTERNAL_ERROR);
      goto cleanup;
    }

    prf_res = ticket->prf;

    gnutls_gettime(&cur_time);
    if (unlikely(_gnutls_timespec_cmp(&cur_time,
              &ticket->arrival_time) < 0)) {
      gnutls_assert();
      tls13_ticket_deinit(ticket);
      goto ignore_ticket;
    }

    /* Check whether the ticket is stale */
    ticket_age = timespec_sub_ms(&cur_time, &ticket->arrival_time);
    if (ticket_age / 1000 > ticket->lifetime) {
      tls13_ticket_deinit(ticket);
      goto ignore_ticket;
    }

    ret = compute_psk_from_ticket(ticket, &rkey);
    if (ret < 0) {
      tls13_ticket_deinit(ticket);
      goto ignore_ticket;
    }

    /* Calculate obfuscated ticket age, in milliseconds, mod 2^32 */
    ob_ticket_age = ticket_age + ticket->age_add;

    if ((ret = _gnutls_buffer_append_data_prefix16(
           extdata, ticket->ticket.data,
           ticket->ticket.size)) < 0) {
      gnutls_assert();
      goto cleanup;
    }

    /* Now append the obfuscated ticket age */
    if ((ret = _gnutls_buffer_append_uint32(extdata,
              ob_ticket_age)) < 0) {
      gnutls_assert();
      goto cleanup;
    }

    psk_id_len += 6 + ticket->ticket.size;
    binders_len += 1 + _gnutls_mac_get_algo_len(prf_res);
  }

ignore_ticket:
  if (cred && have_psk_credentials(cred, session)) {
    gnutls_datum_t tkey;
    gnutls_psk_key_flags flags;

    if (cred->binder_algo == NULL) {
      gnutls_assert();
      ret = gnutls_assert_val(
        GNUTLS_E_INSUFFICIENT_CREDENTIALS);
      goto cleanup;
    }

    prf_psk = cred->binder_algo;

    ret = _gnutls_find_psk_key(session, cred, &username, &tkey,
             &flags, &free_username);
    if (ret < 0) {
      gnutls_assert();
      goto cleanup;
    }

    if (username.size == 0 || username.size > UINT16_MAX) {
      ret = gnutls_assert_val(GNUTLS_E_INVALID_PASSWORD);
      goto cleanup;
    }

    if (!free_username) {
      /* we need to copy the key */
      ret = _gnutls_set_datum(&user_key, tkey.data,
            tkey.size);
      if (ret < 0) {
        gnutls_assert();
        goto cleanup;
      }
    } else {
      user_key.data = tkey.data;
      user_key.size = tkey.size;
    }

    if (flags & GNUTLS_PSK_KEY_EXT) {
      uint8_t ipsk[MAX_HASH_SIZE];
      gnutls_datum_t imported_identity = { NULL, 0 };
      gnutls_datum_t context = { NULL, 0 };
      gnutls_protocol_t version;
      gnutls_digest_algorithm_t hash;
      const version_entry_st *vers;

      ret = parse_imported_identity(&username,
                  &imported_identity,
                  &context, &version,
                  &hash);
      if (ret < 0) {
        gnutls_assert();
        goto cleanup;
      }

      vers = version_to_entry(version);
      if (unlikely(!vers || !vers->tls13_sem)) {
        gnutls_assert();
        goto cleanup;
      }
      if (hash != MAC_TO_DIG(prf_psk->id)) {
        gnutls_assert();
        goto cleanup;
      }

      ret = derive_ipsk(prf_psk, &username, &user_key, ipsk);
      if (ret < 0) {
        gnutls_assert();
        goto cleanup;
      }

      _gnutls_free_datum(&user_key);
      ret = _gnutls_set_datum(&user_key, ipsk,
            prf_psk->output_size);
      zeroize_key(ipsk, sizeof(ipsk));
      if (ret < 0) {
        gnutls_assert();
        goto cleanup;
      }
      imported = true;
    }

    ret = _gnutls_auth_info_init(session, GNUTLS_CRD_PSK,
               sizeof(psk_auth_info_st), 1);
    if (ret < 0) {
      gnutls_assert();
      goto cleanup;
    }

    info = _gnutls_get_auth_info(session, GNUTLS_CRD_PSK);
    assert(info != NULL);

    ret = _gnutls_copy_psk_username(info, username);
    if (ret < 0) {
      gnutls_assert();
      goto cleanup;
    }

    if ((ret = _gnutls_buffer_append_data_prefix16(
           extdata, username.data, username.size)) < 0) {
      gnutls_assert();
      goto cleanup;
    }

    /* Now append the obfuscated ticket age */
    if ((ret = _gnutls_buffer_append_uint32(extdata, 0)) < 0) {
      gnutls_assert();
      goto cleanup;
    }

    psk_id_len += 6 + username.size;
    binders_len += 1 + _gnutls_mac_get_algo_len(prf_psk);
  }

  /* if no tickets or identities to be sent */
  if (psk_id_len == 0) {
    /* reset extensions buffer */
    extdata->length = spos;
    return 0;
  }

  _gnutls_write_uint16(psk_id_len, &extdata->data[spos]);

  binders_pos = extdata->length - spos;
  ext_offset = _gnutls_ext_get_extensions_offset(session);

  /* Compute the binders. extdata->data points to the start
   * of this client hello. */
  assert(extdata->length >= sizeof(mbuffer_st));
  assert(ext_offset >= (ssize_t)sizeof(mbuffer_st));
  ext_offset -= sizeof(mbuffer_st);
  client_hello_len = extdata->length - sizeof(mbuffer_st);

  next_idx = 0;

  ret = _gnutls_buffer_append_uint16(extdata, binders_len);
  if (ret < 0) {
    gnutls_assert_val(ret);
    goto cleanup;
  }

  if (prf_res && rkey.size > 0) {
    gnutls_datum_t client_hello;

    client_hello.data = extdata->data + sizeof(mbuffer_st);
    client_hello.size = client_hello_len;

    ret = compute_psk_binder(session, prf_res, binders_len,
           binders_pos, ext_offset, &rkey,
           &client_hello, BINDER_RES,
           binder_value);
    if (ret < 0) {
      gnutls_assert();
      goto cleanup;
    }

    /* Associate the selected pre-shared key with the session */
    gnutls_free(session->key.binders[next_idx].psk.data);
    session->key.binders[next_idx].psk.data = rkey.data;
    session->key.binders[next_idx].psk.size = rkey.size;
    rkey.data = NULL;

    session->key.binders[next_idx].prf = prf_res;
    session->key.binders[next_idx].resumption = 1;
    session->key.binders[next_idx].idx = next_idx;

    _gnutls_handshake_log(
      "EXT[%p]: sent PSK resumption identity (%d)\n", session,
      next_idx);

    next_idx++;

    /* Add the binder */
    ret = _gnutls_buffer_append_data_prefix8(extdata, binder_value,
               prf_res->output_size);
    if (ret < 0) {
      gnutls_assert();
      goto cleanup;
    }

    session->internals.hsk_flags |= HSK_TLS13_TICKET_SENT;
  }

  if (prf_psk && user_key.size > 0 && info) {
    gnutls_datum_t client_hello;

    client_hello.data = extdata->data + sizeof(mbuffer_st);
    client_hello.size = client_hello_len;

    ret = compute_psk_binder(session, prf_psk, binders_len,
           binders_pos, ext_offset, &user_key,
           &client_hello,
           imported ? BINDER_IMP : BINDER_EXT,
           binder_value);
    if (ret < 0) {
      gnutls_assert();
      goto cleanup;
    }

    /* Associate the selected pre-shared key with the session */
    gnutls_free(session->key.binders[next_idx].psk.data);
    session->key.binders[next_idx].psk.data = user_key.data;
    session->key.binders[next_idx].psk.size = user_key.size;
    user_key.data = NULL;

    session->key.binders[next_idx].prf = prf_psk;
    session->key.binders[next_idx].resumption = 0;
    session->key.binders[next_idx].idx = next_idx;

    _gnutls_handshake_log("EXT[%p]: sent PSK identity '%s' (%d)\n",
              session, info->username, next_idx);

    next_idx++;

    /* Add the binder */
    ret = _gnutls_buffer_append_data_prefix8(extdata, binder_value,
               prf_psk->output_size);
    if (ret < 0) {
      gnutls_assert();
      goto cleanup;
    }
  }

  ret = 0;

cleanup:
  if (free_username)
    _gnutls_free_datum(&username);

  _gnutls_free_key_datum(&user_key);
  _gnutls_free_key_datum(&rkey);

  return ret;
}

static int server_send_params(gnutls_session_t session, gnutls_buffer_t extdata)
{
  int ret;

  if (!(session->internals.hsk_flags & HSK_PSK_SELECTED))
    return 0;

  ret = _gnutls_buffer_append_uint16(extdata,
             session->key.binders[0].idx);
  if (ret < 0)
    return gnutls_assert_val(ret);

  return 2;
}

static int server_recv_params(gnutls_session_t session,
            const unsigned char *data, size_t len,
            const gnutls_psk_server_credentials_t pskcred)
{
  int ret;
  const mac_entry_st *prf;
  gnutls_datum_t full_client_hello;
  uint8_t binder_value[MAX_HASH_SIZE];
  uint16_t psk_index, i;
  gnutls_datum_t binder_recvd = { NULL, 0 };
  gnutls_datum_t key = { NULL, 0 };
  psk_ext_parser_st psk_parser;
  psk_ext_iter_st psk_iter;
  struct psk_st psk;
  psk_auth_info_t info;
  tls13_ticket_st ticket_data;
  /* These values should be set properly when session ticket is accepted. */
  uint32_t ticket_age = UINT32_MAX;
  struct timespec ticket_creation_time = { 0, 0 };
  enum binder_type binder_type;
  bool refuse_early_data = false;
  gnutls_mac_algorithm_t mac = GNUTLS_MAC_SHA384;

retry_binder:
  ret = _gnutls13_psk_ext_parser_init(&psk_parser, data, len);
  if (ret < 0) {
    /* No PSKs advertised by client */
    if (ret == GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE)
      return 0;
    return gnutls_assert_val(ret);
  }

  _gnutls13_psk_ext_iter_init(&psk_iter, &psk_parser);
  for (psk_index = 0;; psk_index++) {
    ret = _gnutls13_psk_ext_iter_next_identity(&psk_iter, &psk);
    if (ret < 0) {
      /* We couldn't find any usable PSK */
      if (ret == GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE)
        return 0;
      return gnutls_assert_val(ret);
    }

    /* This will unpack the session ticket if it is well
     * formed and has the expected name */
    if (!(session->internals.flags & GNUTLS_NO_TICKETS) &&
        _gnutls13_unpack_session_ticket(session, &psk.identity,
                &ticket_data) == 0) {
      prf = ticket_data.prf;

      session->internals.resumption_requested = 1;

      /* Check whether ticket is stale or not */
      ticket_age = psk.ob_ticket_age - ticket_data.age_add;
      if (ticket_age / 1000 > ticket_data.lifetime) {
        gnutls_assert();
        tls13_ticket_deinit(&ticket_data);
        continue;
      }

      ret = compute_psk_from_ticket(&ticket_data, &key);
      if (ret < 0) {
        gnutls_assert();
        tls13_ticket_deinit(&ticket_data);
        continue;
      }

      memcpy(&ticket_creation_time,
             &ticket_data.creation_time,
             sizeof(struct timespec));

      tls13_ticket_deinit(&ticket_data);

      binder_type = BINDER_RES;
      break;
    } else if (pskcred && psk.ob_ticket_age == 0 &&
         psk.identity.size > 0 &&
         psk.identity.size <= MAX_USERNAME_SIZE) {
      gnutls_psk_key_flags flags;
      uint8_t ipsk[MAX_HASH_SIZE];

      prf = pskcred->binder_algo == NULL ?
              _gnutls_mac_to_entry(mac) :
              pskcred->binder_algo;

      /* this fails only on configuration errors; as such we always
       * return its error code in that case */
      ret = _gnutls_psk_pwd_find_entry(
        session, (char *)psk.identity.data,
        psk.identity.size, &key, &flags);
      if (ret < 0) {
        return gnutls_assert_val(ret);
      }

      if (flags & GNUTLS_PSK_KEY_EXT) {
        gnutls_datum_t imported_identity = { NULL, 0 };
        gnutls_datum_t context = { NULL, 0 };
        gnutls_protocol_t version;
        gnutls_digest_algorithm_t hash;
        const version_entry_st *vers;

        ret = parse_imported_identity(
          &psk.identity, &imported_identity,
          &context, &version, &hash);
        if (ret < 0) {
          gnutls_assert();
          goto fail;
        }

        vers = version_to_entry(version);
        if (unlikely(!vers || !vers->tls13_sem)) {
          gnutls_assert();
          goto fail;
        }
        if (hash != MAC_TO_DIG(prf->id)) {
          gnutls_assert();
          goto fail;
        }

        ret = derive_ipsk(prf, &psk.identity, &key,
              ipsk);
        if (ret < 0) {
          gnutls_assert();
          goto fail;
        }
        _gnutls_free_key_datum(&key);
        ret = _gnutls_set_datum(&key, ipsk,
              prf->output_size);
        zeroize_key(ipsk, sizeof(ipsk));
        if (ret < 0) {
          gnutls_assert();
          goto fail;
        }

        binder_type = BINDER_IMP;
      } else {
        binder_type = BINDER_EXT;
      }
      break;
    }
  }

  _gnutls13_psk_ext_iter_init(&psk_iter, &psk_parser);
  for (i = 0; i <= psk_index; i++) {
    ret = _gnutls13_psk_ext_iter_next_binder(&psk_iter,
               &binder_recvd);
    if (ret < 0) {
      gnutls_assert();
      /* We couldn't extract binder */
      if (ret == GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE)
        ret = GNUTLS_E_RECEIVED_ILLEGAL_PARAMETER;
      goto fail;
    }
  }

  /* Get full ClientHello */
  if (!_gnutls_ext_get_full_client_hello(session, &full_client_hello)) {
    ret = GNUTLS_E_INTERNAL_ERROR;
    gnutls_assert();
    goto fail;
  }

  /* Compute the binder value for this PSK */
  ret = compute_psk_binder(session, prf, psk_parser.binders_len + 2, 0, 0,
         &key, &full_client_hello, binder_type,
         binder_value);
  if (ret < 0) {
    gnutls_assert();
    goto fail;
  }

  if (_gnutls_mac_get_algo_len(prf) != binder_recvd.size ||
      gnutls_memcmp(binder_value, binder_recvd.data, binder_recvd.size)) {
    /*
     * Older clients will always use SHA256 as binder algorithm
     * even for SHA384 PSKs, so we need to retry with SHA256
     * to calculate the correct binder value for those.
     */
    if (pskcred && pskcred->binder_algo == NULL &&
        mac == GNUTLS_MAC_SHA384) {
      mac = GNUTLS_MAC_SHA256;
      _gnutls_free_key_datum(&key);
      goto retry_binder;
    }
    gnutls_assert();
    ret = GNUTLS_E_RECEIVED_ILLEGAL_PARAMETER;
    goto fail;
  }

  if (session->internals.hsk_flags & HSK_PSK_KE_MODE_DHE_PSK)
    _gnutls_handshake_log("EXT[%p]: selected DHE-PSK mode\n",
              session);
  else {
    reset_cand_groups(session);
    _gnutls_handshake_log("EXT[%p]: selected PSK mode\n", session);
  }

  /* save the username in psk_auth_info to make it available
   * using gnutls_psk_server_get_username() */
  if (binder_type != BINDER_RES) {
    assert(psk.identity.size <= MAX_USERNAME_SIZE);

    ret = _gnutls_auth_info_init(session, GNUTLS_CRD_PSK,
               sizeof(psk_auth_info_st), 1);
    if (ret < 0) {
      gnutls_assert();
      goto fail;
    }

    info = _gnutls_get_auth_info(session, GNUTLS_CRD_PSK);
    assert(info != NULL);

    ret = _gnutls_copy_psk_username(info, psk.identity);
    if (ret < 0) {
      gnutls_assert();
      goto fail;
    }

    _gnutls_handshake_log(
      "EXT[%p]: selected PSK identity: %s (%d)\n", session,
      info->username, psk_index);

    /* We currently only support early data in resuming connection,
     * due to lack of API function to associate encryption
     * parameters with external PSK.
     */
    refuse_early_data = true;
  } else {
    if (session->internals.hsk_flags & HSK_EARLY_DATA_IN_FLIGHT) {
      if (session->internals.anti_replay) {
        ret = _gnutls_anti_replay_check(
          session->internals.anti_replay,
          ticket_age, &ticket_creation_time,
          &binder_recvd);
        if (ret < 0) {
          refuse_early_data = true;
          _gnutls_handshake_log(
            "EXT[%p]: replay detected; rejecting early data\n",
            session);
        }
      } else {
        refuse_early_data = true;
        _gnutls_handshake_log(
          "EXT[%p]: anti-replay is not enabled; rejecting early data\n",
          session);
      }
    }

    session->internals.resumed = true;
    _gnutls_handshake_log(
      "EXT[%p]: selected resumption PSK identity (%d)\n",
      session, psk_index);
  }

  session->internals.hsk_flags |= HSK_PSK_SELECTED;

  if ((session->internals.flags & GNUTLS_ENABLE_EARLY_DATA) &&
      (session->internals.hsk_flags & HSK_EARLY_DATA_IN_FLIGHT) &&
      !refuse_early_data &&
      !(session->internals.hsk_flags & HSK_HRR_SENT)) {
    session->internals.hsk_flags |= HSK_EARLY_DATA_ACCEPTED;
    _gnutls_handshake_log("EXT[%p]: early data accepted\n",
              session);
  }

  /* Reference the selected pre-shared key */
  session->key.binders[0].psk.data = key.data;
  session->key.binders[0].psk.size = key.size;
  key.data = NULL;
  key.size = 0;

  session->key.binders[0].idx = psk_index;
  session->key.binders[0].prf = prf;
  session->key.binders[0].resumption = binder_type == BINDER_RES;

  ret = _gnutls_generate_early_secrets_for_psk(session);
  if (ret < 0) {
    gnutls_assert();
    goto fail;
  }

fail:
  _gnutls_free_key_datum(&key);
  return ret;
}

/*
 * Return values for this function:
 *  -  0 : Not applicable.
 *  - >0 : Ok. Return size of extension data.
 *  - GNUTLS_E_INT_RET_0 : Size of extension data is zero.
 *  - <0 : There's been an error.
 *
 * In the client, generates the PskIdentity and PskBinderEntry messages.
 *
 *      PskIdentity identities<7..2^16-1>;
 *      PskBinderEntry binders<33..2^16-1>;
 *
 *      struct {
 *          opaque identity<1..2^16-1>;
 *          uint32 obfuscated_ticket_age;
 *      } PskIdentity;
 *
 *      opaque PskBinderEntry<32..255>;
 *
 * The server sends the selected identity, which is a zero-based index
 * of the PSKs offered by the client:
 *
 *      struct {
 *          uint16 selected_identity;
 *      } PreSharedKeyExtension;
 */
static int _gnutls_psk_send_params(gnutls_session_t session,
           gnutls_buffer_t extdata)
{
  gnutls_psk_client_credentials_t cred = NULL;
  const version_entry_st *vers;

  if (session->security_parameters.entity == GNUTLS_CLIENT) {
    vers = _gnutls_version_max(session);

    if (!vers || !vers->tls13_sem)
      return 0;

    if (session->internals.hsk_flags & HSK_PSK_KE_MODES_SENT) {
      cred = (gnutls_psk_client_credentials_t)
        _gnutls_get_cred(session, GNUTLS_CRD_PSK);
    }

    if ((session->internals.flags & GNUTLS_NO_TICKETS) &&
        !session->internals.priorities->have_psk)
      return 0;

    return client_send_params(session, extdata, cred);
  } else {
    vers = get_version(session);

    if (!vers || !vers->tls13_sem)
      return 0;

    if ((session->internals.flags & GNUTLS_NO_TICKETS) &&
        !session->internals.priorities->have_psk)
      return 0;

    if (session->internals.hsk_flags & HSK_PSK_KE_MODES_RECEIVED)
      return server_send_params(session, extdata);
    else
      return 0;
  }
}

static void swap_binders(gnutls_session_t session)
{
  struct binder_data_st tmp;

  memcpy(&tmp, &session->key.binders[0], sizeof(struct binder_data_st));
  memcpy(&session->key.binders[0], &session->key.binders[1],
         sizeof(struct binder_data_st));
  memcpy(&session->key.binders[1], &tmp, sizeof(struct binder_data_st));
}

/*
 * Return values for this function:
 *  -  0 : Not applicable.
 *  - >0 : Ok. Return size of extension data.
 *  - <0 : There's been an error.
 */
static int _gnutls_psk_recv_params(gnutls_session_t session,
           const unsigned char *data, size_t len)
{
  unsigned i;
  gnutls_psk_server_credentials_t pskcred;
  const version_entry_st *vers = get_version(session);
  int ret;

  if (!vers || !vers->tls13_sem)
    return 0;

  if (session->security_parameters.entity == GNUTLS_CLIENT) {
    if (session->internals.hsk_flags & HSK_PSK_KE_MODES_SENT) {
      DECR_LEN(len, 2);

      uint16_t selected_identity = _gnutls_read_uint16(data);

      for (i = 0; i < sizeof(session->key.binders) /
            sizeof(session->key.binders[0]);
           i++) {
        if (session->key.binders[i].prf != NULL &&
            session->key.binders[i].idx ==
              selected_identity) {
          if (session->key.binders[i].resumption) {
            session->internals.resumed =
              true;
            _gnutls_handshake_log(
              "EXT[%p]: selected PSK-resumption mode\n",
              session);
          } else {
            _gnutls_handshake_log(
              "EXT[%p]: selected PSK mode\n",
              session);
          }

          /* different PSK is selected, than the one we calculated early secrets */
          if (i != 0) {
            /* ensure that selected binder is set on (our) index zero */
            swap_binders(session);

            ret = _gnutls_generate_early_secrets_for_psk(
              session);
            if (ret < 0)
              return gnutls_assert_val(
                ret);
          }
          session->internals.hsk_flags |=
            HSK_PSK_SELECTED;
        }
      }

      return 0;
    } else {
      return gnutls_assert_val(
        GNUTLS_E_RECEIVED_ILLEGAL_EXTENSION);
    }
  } else {
    if (session->internals.hsk_flags & HSK_PSK_KE_MODES_RECEIVED) {
      if (session->internals.hsk_flags &
          HSK_PSK_KE_MODE_INVALID) {
        /* We received a "psk_ke_modes" extension, but with a value we don't support */
        return 0;
      }

      pskcred = (gnutls_psk_server_credentials_t)
        _gnutls_get_cred(session, GNUTLS_CRD_PSK);

      /* If there are no PSK credentials, this extension is not applicable,
       * so we return zero. */
      if (pskcred == NULL &&
          (session->internals.flags & GNUTLS_NO_TICKETS))
        return 0;

      return server_recv_params(session, data, len, pskcred);
    } else {
      return gnutls_assert_val(
        GNUTLS_E_RECEIVED_ILLEGAL_EXTENSION);
    }
  }
}

const hello_ext_entry_st ext_mod_pre_shared_key = {
  .name = "Pre Shared Key",
  .tls_id = PRE_SHARED_KEY_TLS_ID,
  .gid = GNUTLS_EXTENSION_PRE_SHARED_KEY,
  .client_parse_point = GNUTLS_EXT_TLS,
  .server_parse_point = GNUTLS_EXT_TLS,
  .validity = GNUTLS_EXT_FLAG_TLS | GNUTLS_EXT_FLAG_CLIENT_HELLO |
        GNUTLS_EXT_FLAG_TLS13_SERVER_HELLO,
  .send_func = _gnutls_psk_send_params,
  .recv_func = _gnutls_psk_recv_params
};

Coverage Report

Created: 2026-08-14 07:19