onion_ntor.c 12 KB

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  1. /* Copyright (c) 2012-2016, The Tor Project, Inc. */
  2. /* See LICENSE for licensing information */
  3. /**
  4. * \file onion_ntor.c
  5. *
  6. * \brief Implementation for the ntor handshake.
  7. */
  8. #include "orconfig.h"
  9. #define ONION_NTOR_PRIVATE
  10. #include "crypto.h"
  11. #include "onion_ntor.h"
  12. #include "torlog.h"
  13. #include "util.h"
  14. /** Free storage held in an ntor handshake state. */
  15. void
  16. ntor_handshake_state_free(ntor_handshake_state_t *state)
  17. {
  18. if (!state)
  19. return;
  20. memwipe(state, 0, sizeof(*state));
  21. tor_free(state);
  22. }
  23. /** Convenience function to represent HMAC_SHA256 as our instantiation of
  24. * ntor's "tweaked hash'. Hash the <b>inp_len</b> bytes at <b>inp</b> into
  25. * a DIGEST256_LEN-byte digest at <b>out</b>, with the hash changing
  26. * depending on the value of <b>tweak</b>. */
  27. static void
  28. h_tweak(uint8_t *out,
  29. const uint8_t *inp, size_t inp_len,
  30. const char *tweak)
  31. {
  32. size_t tweak_len = strlen(tweak);
  33. crypto_hmac_sha256((char*)out, tweak, tweak_len, (const char*)inp, inp_len);
  34. }
  35. /** Wrapper around a set of tweak-values for use with the ntor handshake. */
  36. typedef struct tweakset_t {
  37. const char *t_mac;
  38. const char *t_key;
  39. const char *t_verify;
  40. const char *m_expand;
  41. } tweakset_t;
  42. /** The tweaks to be used with our handshake. */
  43. const tweakset_t proto1_tweaks = {
  44. #define PROTOID "ntor-curve25519-sha256-1"
  45. #define PROTOID_LEN 24
  46. PROTOID ":mac",
  47. PROTOID ":key_extract",
  48. PROTOID ":verify",
  49. PROTOID ":key_expand"
  50. };
  51. /** Convenience macro: copy <b>len</b> bytes from <b>inp</b> to <b>ptr</b>,
  52. * and advance <b>ptr</b> by the number of bytes copied. */
  53. #define APPEND(ptr, inp, len) \
  54. STMT_BEGIN { \
  55. memcpy(ptr, (inp), (len)); \
  56. ptr += len; \
  57. } STMT_END
  58. /**
  59. * Compute the first client-side step of the ntor handshake for communicating
  60. * with a server whose DIGEST_LEN-byte server identity is <b>router_id</b>,
  61. * and whose onion key is <b>router_key</b>. Store the NTOR_ONIONSKIN_LEN-byte
  62. * message in <b>onion_skin_out</b>, and store the handshake state in
  63. * *<b>handshake_state_out</b>. Return 0 on success, -1 on failure.
  64. */
  65. int
  66. onion_skin_ntor_create(const uint8_t *router_id,
  67. const curve25519_public_key_t *router_key,
  68. ntor_handshake_state_t **handshake_state_out,
  69. uint8_t *onion_skin_out)
  70. {
  71. ntor_handshake_state_t *state;
  72. uint8_t *op;
  73. state = tor_malloc_zero(sizeof(ntor_handshake_state_t));
  74. memcpy(state->router_id, router_id, DIGEST_LEN);
  75. memcpy(&state->pubkey_B, router_key, sizeof(curve25519_public_key_t));
  76. if (curve25519_secret_key_generate(&state->seckey_x, 0) < 0) {
  77. tor_free(state);
  78. return -1;
  79. }
  80. curve25519_public_key_generate(&state->pubkey_X, &state->seckey_x);
  81. op = onion_skin_out;
  82. APPEND(op, router_id, DIGEST_LEN);
  83. APPEND(op, router_key->public_key, CURVE25519_PUBKEY_LEN);
  84. APPEND(op, state->pubkey_X.public_key, CURVE25519_PUBKEY_LEN);
  85. tor_assert(op == onion_skin_out + NTOR_ONIONSKIN_LEN);
  86. *handshake_state_out = state;
  87. return 0;
  88. }
  89. #define SERVER_STR "Server"
  90. #define SERVER_STR_LEN 6
  91. #define SECRET_INPUT_LEN (CURVE25519_PUBKEY_LEN * 3 + \
  92. CURVE25519_OUTPUT_LEN * 2 + \
  93. DIGEST_LEN + PROTOID_LEN)
  94. #define AUTH_INPUT_LEN (DIGEST256_LEN + DIGEST_LEN + \
  95. CURVE25519_PUBKEY_LEN*3 + \
  96. PROTOID_LEN + SERVER_STR_LEN)
  97. /**
  98. * Perform the server side of an ntor handshake. Given an
  99. * NTOR_ONIONSKIN_LEN-byte message in <b>onion_skin</b>, our own identity
  100. * fingerprint as <b>my_node_id</b>, and an associative array mapping public
  101. * onion keys to curve25519_keypair_t in <b>private_keys</b>, attempt to
  102. * perform the handshake. Use <b>junk_keys</b> if present if the handshake
  103. * indicates an unrecognized public key. Write an NTOR_REPLY_LEN-byte
  104. * message to send back to the client into <b>handshake_reply_out</b>, and
  105. * generate <b>key_out_len</b> bytes of key material in <b>key_out</b>. Return
  106. * 0 on success, -1 on failure.
  107. */
  108. int
  109. onion_skin_ntor_server_handshake(const uint8_t *onion_skin,
  110. const di_digest256_map_t *private_keys,
  111. const curve25519_keypair_t *junk_keys,
  112. const uint8_t *my_node_id,
  113. uint8_t *handshake_reply_out,
  114. uint8_t *key_out,
  115. size_t key_out_len)
  116. {
  117. const tweakset_t *T = &proto1_tweaks;
  118. /* Sensitive stack-allocated material. Kept in an anonymous struct to make
  119. * it easy to wipe. */
  120. struct {
  121. uint8_t secret_input[SECRET_INPUT_LEN];
  122. uint8_t auth_input[AUTH_INPUT_LEN];
  123. curve25519_public_key_t pubkey_X;
  124. curve25519_secret_key_t seckey_y;
  125. curve25519_public_key_t pubkey_Y;
  126. uint8_t verify[DIGEST256_LEN];
  127. } s;
  128. uint8_t *si = s.secret_input, *ai = s.auth_input;
  129. const curve25519_keypair_t *keypair_bB;
  130. int bad;
  131. /* Decode the onion skin */
  132. /* XXXX Does this possible early-return business threaten our security? */
  133. if (tor_memneq(onion_skin, my_node_id, DIGEST_LEN))
  134. return -1;
  135. /* Note that on key-not-found, we go through with this operation anyway,
  136. * using "junk_keys". This will result in failed authentication, but won't
  137. * leak whether we recognized the key. */
  138. keypair_bB = dimap_search(private_keys, onion_skin + DIGEST_LEN,
  139. (void*)junk_keys);
  140. if (!keypair_bB)
  141. return -1;
  142. memcpy(s.pubkey_X.public_key, onion_skin+DIGEST_LEN+DIGEST256_LEN,
  143. CURVE25519_PUBKEY_LEN);
  144. /* Make y, Y */
  145. curve25519_secret_key_generate(&s.seckey_y, 0);
  146. curve25519_public_key_generate(&s.pubkey_Y, &s.seckey_y);
  147. /* NOTE: If we ever use a group other than curve25519, or a different
  148. * representation for its points, we may need to perform different or
  149. * additional checks on X here and on Y in the client handshake, or lose our
  150. * security properties. What checks we need would depend on the properties
  151. * of the group and its representation.
  152. *
  153. * In short: if you use anything other than curve25519, this aspect of the
  154. * code will need to be reconsidered carefully. */
  155. /* build secret_input */
  156. curve25519_handshake(si, &s.seckey_y, &s.pubkey_X);
  157. bad = safe_mem_is_zero(si, CURVE25519_OUTPUT_LEN);
  158. si += CURVE25519_OUTPUT_LEN;
  159. curve25519_handshake(si, &keypair_bB->seckey, &s.pubkey_X);
  160. bad |= safe_mem_is_zero(si, CURVE25519_OUTPUT_LEN);
  161. si += CURVE25519_OUTPUT_LEN;
  162. APPEND(si, my_node_id, DIGEST_LEN);
  163. APPEND(si, keypair_bB->pubkey.public_key, CURVE25519_PUBKEY_LEN);
  164. APPEND(si, s.pubkey_X.public_key, CURVE25519_PUBKEY_LEN);
  165. APPEND(si, s.pubkey_Y.public_key, CURVE25519_PUBKEY_LEN);
  166. APPEND(si, PROTOID, PROTOID_LEN);
  167. tor_assert(si == s.secret_input + sizeof(s.secret_input));
  168. /* Compute hashes of secret_input */
  169. h_tweak(s.verify, s.secret_input, sizeof(s.secret_input), T->t_verify);
  170. /* Compute auth_input */
  171. APPEND(ai, s.verify, DIGEST256_LEN);
  172. APPEND(ai, my_node_id, DIGEST_LEN);
  173. APPEND(ai, keypair_bB->pubkey.public_key, CURVE25519_PUBKEY_LEN);
  174. APPEND(ai, s.pubkey_Y.public_key, CURVE25519_PUBKEY_LEN);
  175. APPEND(ai, s.pubkey_X.public_key, CURVE25519_PUBKEY_LEN);
  176. APPEND(ai, PROTOID, PROTOID_LEN);
  177. APPEND(ai, SERVER_STR, SERVER_STR_LEN);
  178. tor_assert(ai == s.auth_input + sizeof(s.auth_input));
  179. /* Build the reply */
  180. memcpy(handshake_reply_out, s.pubkey_Y.public_key, CURVE25519_PUBKEY_LEN);
  181. h_tweak(handshake_reply_out+CURVE25519_PUBKEY_LEN,
  182. s.auth_input, sizeof(s.auth_input),
  183. T->t_mac);
  184. /* Generate the key material */
  185. crypto_expand_key_material_rfc5869_sha256(
  186. s.secret_input, sizeof(s.secret_input),
  187. (const uint8_t*)T->t_key, strlen(T->t_key),
  188. (const uint8_t*)T->m_expand, strlen(T->m_expand),
  189. key_out, key_out_len);
  190. /* Wipe all of our local state */
  191. memwipe(&s, 0, sizeof(s));
  192. return bad ? -1 : 0;
  193. }
  194. /**
  195. * Perform the final client side of the ntor handshake, using the state in
  196. * <b>handshake_state</b> and the server's NTOR_REPLY_LEN-byte reply in
  197. * <b>handshake_reply</b>. Generate <b>key_out_len</b> bytes of key material
  198. * in <b>key_out</b>. Return 0 on success, -1 on failure.
  199. */
  200. int
  201. onion_skin_ntor_client_handshake(
  202. const ntor_handshake_state_t *handshake_state,
  203. const uint8_t *handshake_reply,
  204. uint8_t *key_out,
  205. size_t key_out_len,
  206. const char **msg_out)
  207. {
  208. const tweakset_t *T = &proto1_tweaks;
  209. /* Sensitive stack-allocated material. Kept in an anonymous struct to make
  210. * it easy to wipe. */
  211. struct {
  212. curve25519_public_key_t pubkey_Y;
  213. uint8_t secret_input[SECRET_INPUT_LEN];
  214. uint8_t verify[DIGEST256_LEN];
  215. uint8_t auth_input[AUTH_INPUT_LEN];
  216. uint8_t auth[DIGEST256_LEN];
  217. } s;
  218. uint8_t *ai = s.auth_input, *si = s.secret_input;
  219. const uint8_t *auth_candidate;
  220. int bad;
  221. /* Decode input */
  222. memcpy(s.pubkey_Y.public_key, handshake_reply, CURVE25519_PUBKEY_LEN);
  223. auth_candidate = handshake_reply + CURVE25519_PUBKEY_LEN;
  224. /* See note in server_handshake above about checking points. The
  225. * circumstances under which we'd need to check Y for membership are
  226. * different than those under which we'd be checking X. */
  227. /* Compute secret_input */
  228. curve25519_handshake(si, &handshake_state->seckey_x, &s.pubkey_Y);
  229. bad = safe_mem_is_zero(si, CURVE25519_OUTPUT_LEN);
  230. si += CURVE25519_OUTPUT_LEN;
  231. curve25519_handshake(si, &handshake_state->seckey_x,
  232. &handshake_state->pubkey_B);
  233. bad |= (safe_mem_is_zero(si, CURVE25519_OUTPUT_LEN) << 1);
  234. si += CURVE25519_OUTPUT_LEN;
  235. APPEND(si, handshake_state->router_id, DIGEST_LEN);
  236. APPEND(si, handshake_state->pubkey_B.public_key, CURVE25519_PUBKEY_LEN);
  237. APPEND(si, handshake_state->pubkey_X.public_key, CURVE25519_PUBKEY_LEN);
  238. APPEND(si, s.pubkey_Y.public_key, CURVE25519_PUBKEY_LEN);
  239. APPEND(si, PROTOID, PROTOID_LEN);
  240. tor_assert(si == s.secret_input + sizeof(s.secret_input));
  241. /* Compute verify from secret_input */
  242. h_tweak(s.verify, s.secret_input, sizeof(s.secret_input), T->t_verify);
  243. /* Compute auth_input */
  244. APPEND(ai, s.verify, DIGEST256_LEN);
  245. APPEND(ai, handshake_state->router_id, DIGEST_LEN);
  246. APPEND(ai, handshake_state->pubkey_B.public_key, CURVE25519_PUBKEY_LEN);
  247. APPEND(ai, s.pubkey_Y.public_key, CURVE25519_PUBKEY_LEN);
  248. APPEND(ai, handshake_state->pubkey_X.public_key, CURVE25519_PUBKEY_LEN);
  249. APPEND(ai, PROTOID, PROTOID_LEN);
  250. APPEND(ai, SERVER_STR, SERVER_STR_LEN);
  251. tor_assert(ai == s.auth_input + sizeof(s.auth_input));
  252. /* Compute auth */
  253. h_tweak(s.auth, s.auth_input, sizeof(s.auth_input), T->t_mac);
  254. bad |= (tor_memneq(s.auth, auth_candidate, DIGEST256_LEN) << 2);
  255. crypto_expand_key_material_rfc5869_sha256(
  256. s.secret_input, sizeof(s.secret_input),
  257. (const uint8_t*)T->t_key, strlen(T->t_key),
  258. (const uint8_t*)T->m_expand, strlen(T->m_expand),
  259. key_out, key_out_len);
  260. memwipe(&s, 0, sizeof(s));
  261. if (bad) {
  262. if (bad & 4) {
  263. if (msg_out)
  264. *msg_out = NULL; /* Don't report this one; we probably just had the
  265. * wrong onion key.*/
  266. log_fn(LOG_INFO, LD_PROTOCOL,
  267. "Invalid result from curve25519 handshake: %d", bad);
  268. }
  269. if (bad & 3) {
  270. if (msg_out)
  271. *msg_out = "Zero output from curve25519 handshake";
  272. log_fn(LOG_WARN, LD_PROTOCOL,
  273. "Invalid result from curve25519 handshake: %d", bad);
  274. }
  275. }
  276. return bad ? -1 : 0;
  277. }