tor/src/or/onion.c

/* Copyright 2001 Matej Pfajfar.
 * Copyright 2001-2004 Roger Dingledine.
 * Copyright 2004 Roger Dingledine, Nick Mathewson. */
/* See LICENSE for licensing information */
/* $Id$ */

/**
 * \file onion.c
 * \brief Functions to queue create cells, and handle onionskin
 * parsing and creation.
 **/

#include "or.h"

struct onion_queue_t {
  circuit_t *circ;
  struct onion_queue_t *next;
};

/** global (within this file) variables used by the next few functions */
static struct onion_queue_t *ol_list=NULL;
static struct onion_queue_t *ol_tail=NULL;
/** length of ol_list */
static int ol_length=0;

/** Add <b>circ</b> to the end of ol_list and return 0, except
 * if ol_list is too long, in which case do nothing and return -1.
 */
int onion_pending_add(circuit_t *circ) {
  struct onion_queue_t *tmp;

  tmp = tor_malloc_zero(sizeof(struct onion_queue_t));
  tmp->circ = circ;

  if (!ol_tail) {
    tor_assert(!ol_list);
    tor_assert(!ol_length);
    ol_list = tmp;
    ol_tail = tmp;
    ol_length++;
    return 0;
  }

  tor_assert(ol_list);
  tor_assert(!ol_tail->next);

  if (ol_length >= get_options()->MaxOnionsPending) {
    log_fn(LOG_WARN,"Already have %d onions queued. Closing.", ol_length);
    tor_free(tmp);
    return -1;
  }

  ol_length++;
  ol_tail->next = tmp;
  ol_tail = tmp;
  return 0;
}

/** Remove the first item from ol_list and return it, or return
 * NULL if the list is empty.
 */
circuit_t *onion_next_task(void) {
  circuit_t *circ;

  if (!ol_list)
    return NULL; /* no onions pending, we're done */

  tor_assert(ol_list->circ);
  tor_assert(ol_list->circ->p_conn); /* make sure it's still valid */
  tor_assert(ol_length > 0);
  circ = ol_list->circ;
  onion_pending_remove(ol_list->circ);
  return circ;
}

/** Go through ol_list, find the onion_queue_t element which points to
 * circ, remove and free that element. Leave circ itself alone.
 */
void onion_pending_remove(circuit_t *circ) {
  struct onion_queue_t *tmpo, *victim;

  if (!ol_list)
    return; /* nothing here. */

  /* first check to see if it's the first entry */
  tmpo = ol_list;
  if (tmpo->circ == circ) {
    /* it's the first one. remove it from the list. */
    ol_list = tmpo->next;
    if (!ol_list)
      ol_tail = NULL;
    ol_length--;
    victim = tmpo;
  } else { /* we need to hunt through the rest of the list */
    for ( ;tmpo->next && tmpo->next->circ != circ; tmpo=tmpo->next) ;
    if (!tmpo->next) {
      log_fn(LOG_DEBUG,"circ (p_circ_id %d) not in list, probably at cpuworker.",circ->p_circ_id);
      return;
    }
    /* now we know tmpo->next->circ == circ */
    victim = tmpo->next;
    tmpo->next = victim->next;
    if (ol_tail == victim)
      ol_tail = tmpo;
    ol_length--;
  }

  /* now victim points to the element that needs to be removed */

  tor_free(victim);
}

/*----------------------------------------------------------------------*/

/** Given a router's 128 byte public key,
 * stores the following in onion_skin_out:
 *   - [42 bytes] OAEP padding
 *   - [16 bytes] Symmetric key for encrypting blob past RSA
 *   - [70 bytes] g^x part 1 (inside the RSA)
 *   - [58 bytes] g^x part 2 (symmetrically encrypted)
 *
 * Stores the DH private key into handshake_state_out for later completion
 * of the handshake.
 *
 * The meeting point/cookies and auth are zeroed out for now.
 */
int
onion_skin_create(crypto_pk_env_t *dest_router_key,
                  crypto_dh_env_t **handshake_state_out,
                  char *onion_skin_out) /* Must be ONIONSKIN_CHALLENGE_LEN bytes */
{
  char *challenge = NULL;
  crypto_dh_env_t *dh = NULL;
  int dhbytes, pkbytes;

  *handshake_state_out = NULL;
  memset(onion_skin_out, 0, ONIONSKIN_CHALLENGE_LEN);

  if (!(dh = crypto_dh_new()))
    goto err;

  dhbytes = crypto_dh_get_bytes(dh);
  pkbytes = crypto_pk_keysize(dest_router_key);
  tor_assert(dhbytes == 128);
  tor_assert(pkbytes == 128);
  challenge = tor_malloc_zero(DH_KEY_LEN);

  if (crypto_dh_get_public(dh, challenge, dhbytes))
    goto err;

#ifdef DEBUG_ONION_SKINS
#define PA(a,n) \
  { int _i; for (_i = 0; _i<n; ++_i) printf("%02x ",((int)(a)[_i])&0xFF); }

  printf("Client: client g^x:");
  PA(challenge+16,3);
  printf("...");
  PA(challenge+141,3);
  puts("");

  printf("Client: client symkey:");
  PA(challenge+0,16);
  puts("");
#endif

  /* set meeting point, meeting cookie, etc here. Leave zero for now. */
  if (crypto_pk_public_hybrid_encrypt(dest_router_key, onion_skin_out,
                                      challenge, DH_KEY_LEN,
                                      PK_PKCS1_OAEP_PADDING, 1)<0)
    goto err;

  tor_free(challenge);
  *handshake_state_out = dh;

  return 0;
 err:
  tor_free(challenge);
  if (dh) crypto_dh_free(dh);
  return -1;
}

/** Given an encrypted DH public key as generated by onion_skin_create,
 * and the private key for this onion router, generate the reply (128-byte
 * DH plus the first 20 bytes of shared key material), and store the
 * next key_out_len bytes of key material in key_out.
 */
int
onion_skin_server_handshake(char *onion_skin, /* ONIONSKIN_CHALLENGE_LEN bytes */
                            crypto_pk_env_t *private_key,
                            crypto_pk_env_t *prev_private_key,
                            char *handshake_reply_out, /* ONIONSKIN_REPLY_LEN bytes */
                            char *key_out,
                            size_t key_out_len)
{
  char challenge[ONIONSKIN_CHALLENGE_LEN];
  crypto_dh_env_t *dh = NULL;
  int len;
  char *key_material=NULL;
  int i;
  crypto_pk_env_t *k;

  len = -1;
  for (i=0;i<2;++i) {
    k = i==0?private_key:prev_private_key;
    if (!k)
      break;
    len = crypto_pk_private_hybrid_decrypt(k, challenge,
                                           onion_skin, ONIONSKIN_CHALLENGE_LEN,
                                           PK_PKCS1_OAEP_PADDING,0);
    if (len>0)
      break;
  }
  if (len<0) {
    log_fn(LOG_WARN, "Couldn't decrypt onionskin: client may be using old onion key");
    goto err;
  } else if (len != DH_KEY_LEN) {
    log_fn(LOG_WARN, "Unexpected onionskin length after decryption: %d",
           len);
    goto err;
  }

  dh = crypto_dh_new();
  if (crypto_dh_get_public(dh, handshake_reply_out, DH_KEY_LEN))
    goto err;

#ifdef DEBUG_ONION_SKINS
  printf("Server: server g^y:");
  PA(handshake_reply_out+0,3);
  printf("...");
  PA(handshake_reply_out+125,3);
  puts("");
#endif

  key_material = tor_malloc(DIGEST_LEN+key_out_len);
  len = crypto_dh_compute_secret(dh, challenge, DH_KEY_LEN,
                                 key_material, DIGEST_LEN+key_out_len);
  if (len < 0)
    goto err;

  /* send back H(K|0) as proof that we learned K. */
  memcpy(handshake_reply_out+DH_KEY_LEN, key_material, DIGEST_LEN);

  /* use the rest of the key material for our shared keys, digests, etc */
  memcpy(key_out, key_material+DIGEST_LEN, key_out_len);

#ifdef DEBUG_ONION_SKINS
  printf("Server: key material:");
  PA(buf, DH_KEY_LEN);
  puts("");
  printf("Server: keys out:");
  PA(key_out, key_out_len);
  puts("");
#endif

  tor_free(key_material);
  crypto_dh_free(dh);
  return 0;
 err:
  tor_free(key_material);
  if (dh) crypto_dh_free(dh);

  return -1;
}

/** Finish the client side of the DH handshake.
 * Given the 128 byte DH reply + 20 byte hash as generated by
 * onion_skin_server_handshake and the handshake state generated by
 * onion_skin_create, verify H(K) with the first 20 bytes of shared
 * key material, then generate key_out_len more bytes of shared key
 * material and store them in key_out.
 *
 * After the invocation, call crypto_dh_free on handshake_state.
 */
int
onion_skin_client_handshake(crypto_dh_env_t *handshake_state,
                            char *handshake_reply, /* Must be ONIONSKIN_REPLY_LEN bytes */
                            char *key_out,
                            size_t key_out_len)
{
  int len;
  char *key_material=NULL;
  tor_assert(crypto_dh_get_bytes(handshake_state) == DH_KEY_LEN);

#ifdef DEBUG_ONION_SKINS
  printf("Client: server g^y:");
  PA(handshake_reply+0,3);
  printf("...");
  PA(handshake_reply+125,3);
  puts("");
#endif

  key_material = tor_malloc(20+key_out_len);
  len = crypto_dh_compute_secret(handshake_state, handshake_reply, DH_KEY_LEN,
                                 key_material, 20+key_out_len);
  if (len < 0)
    return -1;

  if (memcmp(key_material, handshake_reply+DH_KEY_LEN, 20)) {
    /* H(K) does *not* match. Something fishy. */
    tor_free(key_material);
    log_fn(LOG_WARN,"Digest DOES NOT MATCH on onion handshake. Bug or attack.");
    return -1;
  }

  /* use the rest of the key material for our shared keys, digests, etc */
  memcpy(key_out, key_material+20, key_out_len);

#ifdef DEBUG_ONION_SKINS
  printf("Client: keys out:");
  PA(key_out, key_out_len);
  puts("");
#endif

  tor_free(key_material);
  return 0;
}