Implement midpoint functionality for rendezvous points. (a981c409) · Commits · Benjamin J. Thompson / Tor

doc/rend-spec.txt

+2 −2

Original line number	Diff line number	Diff line
		@@ -111,7 +111,7 @@ Tor Rendezvous Spec
		TS A timestamp [4 octets]
		NI Number of introduction points [2 octets]
		Ipt A list of NUL-terminated OR nicknames [variable]
		SIG Signature of above fields [KL octets]
		SIG Signature of above fields [variable]

		KL is the length of PK, in octets. (Currently, KL must be 128.)
		TS is the number of seconds elapsed since Jan 1, 1970.
		@@ -131,7 +131,7 @@ Tor Rendezvous Spec
		KL Key length [2 octets]
		PK Bob's public key [KL octets]
		HS Hash of session info [20 octets]
		SIG Signature of above information [KL octets]
		SIG Signature of above information [variable]

		To prevent replay attacks, the HS field contains a SHA-1 hash based on the
		shared secret KH between Bob's OP and the introduction point, as

src/or/circuit.c

+38 −6

Original line number	Diff line number	Diff line
		@@ -88,7 +88,6 @@ void circuit_close_all_marked()
		}
		}


		circuit_t circuit_new(uint16_t p_circ_id, connection_t p_conn) {
		circuit_t *circ;

		@@ -307,14 +306,21 @@ circuit_t circuit_get_newest(connection_t conn,
		return NULL;
		}

		/* Return the first circuit in global_circuitlist whose rend_service
		* field is servid and whose purpose is purpose. Returns NULL if no circuit
		* is found.
		/* Return the first circuit in global_circuitlist after 'start' whose
		* rend_service field is servid and whose purpose is purpose. Returns
		* NULL if no circuit is found. If 'start' is null, begin at the start of
		* the list.
		*/
		circuit_t circuit_get_by_service_and_purpose(const char servid, int purpose)
		circuit_t circuit_get_next_by_service_and_purpose(circuit_t start,
		const char *servid, int purpose)
		{
		circuit_t *circ;
		for(circ=global_circuitlist; circ; circ = circ->next) {
		if (start == NULL)
		circ = global_circuitlist;
		else
		circ = start->next;

		for( ; circ; circ = circ->next) {
		if (circ->marked_for_close)
		continue;
		if (circ->purpose != purpose)
		@@ -325,6 +331,21 @@ circuit_t circuit_get_by_service_and_purpose(const char servid, int purpose)
		return NULL;
		}

		/* Return the circuit waiting for a rendezvous with the provided cookie.
		* Return NULL if no such circuit is found.
		*/
		circuit_t circuit_get_rendezvous(const char cookie)
		{
		circuit_t *circ;
		for (circ = global_circuitlist; circ; circ = circ->next) {
		if (! circ->marked_for_close &&
		circ->purpose == CIRCUIT_PURPOSE_REND_POINT_WAITING &&
		! memcmp(circ->rend_cookie, cookie, REND_COOKIE_LEN) )
		return circ;
		}
		return NULL;
		}

		#define MIN_SECONDS_BEFORE_EXPIRING_CIRC 10
		/* circuits that were born at the end of their second might be expired
		* after 10.1 seconds; circuits born at the beginning might be expired
		@@ -516,6 +537,17 @@ int circuit_receive_relay_cell(cell_t cell, circuit_t circ,
		}

		if(!conn) {
		if (circ->rend_splice && cell_direction == CELL_DIRECTION_OUT) {
		assert(circ->purpose == CIRCUIT_PURPOSE_REND_ESTABLISHED);
		assert(circ->rend_splice->purpose == CIRCUIT_PURPOSE_REND_ESTABLISHED);
		cell->circ_id = circ->rend_splice->p_circ_id;
		if (circuit_receive_relay_cell(cell, circ->rend_splice, CELL_DIRECTION_IN)<0) {
		log_fn(LOG_WARN, "Error relaying cell across rendezvous; closing circuits");
		circuit_mark_for_close(circ); /* XXXX Do this here, or just return -1? */
		return -1;
		}
		return 0;
		}
		log_fn(LOG_WARN,"Didn't recognize cell, but circ stops here! Closing circ.");
		return -1;
		}

src/or/or.h

+5 −3

Original line number	Diff line number	Diff line
		@@ -560,7 +560,7 @@ struct circuit_t {
		char rend_service[CRYPTO_SHA1_DIGEST_LEN];

		/* Holds rendezvous cookie if purpose is REND_POINT_WAITING or
		* S_RENDEZVOUSING or C_ESTABLISH_REND. Filled with zeroes otherwise.
		* C_ESTABLISH_REND. Filled with zeroes otherwise.
		*/
		char rend_cookie[REND_COOKIE_LEN];

		@@ -692,7 +692,9 @@ circuit_t circuit_get_by_circ_id_conn(uint16_t circ_id, connection_t conn);
		circuit_t circuit_get_by_conn(connection_t conn);
		circuit_t circuit_get_newest(connection_t conn,
		int must_be_open, int must_be_clean);
		circuit_t circuit_get_by_service_and_purpose(const char servid, int purpose);
		circuit_t circuit_get_next_by_service_and_purpose(circuit_t circuit,
		const char *servid, int purpose);
		circuit_t circuit_get_rendezvous(const char cookie);

		void circuit_expire_building(void);
		int circuit_count_building(void);

src/or/rendmid.c

+165 −0

Original line number	Diff line number	Diff line
		@@ -4,28 +4,193 @@

		#include "or.h"

		/* Respond to an ESTABLISH_INTRO cell by setting the circuit's purpose and
		* rendevous service.
		*/
		int
		rend_mid_establish_intro(circuit_t circ, char request, int request_len)
		{
		crypto_pk_env_t *pk = NULL;
		char buf[20+9];
		char expected_digest[20];
		char pk_digest[20];
		int asn1len;
		circuit_t *c;

		if (circ->purpose != CIRCUIT_PURPOSE_INTERMEDIATE) {
		log_fn(LOG_WARN, "Rejecting ESTABLISH_INTRO on non-intermediate circuit");
		goto err;
		}
		if (request_len < 22)
		goto truncated;
		/* First 2 bytes: length of asn1-encoded key. */
		asn1len = get_uint16(request);

		/* Next asn1len bytes: asn1-encoded key. */
		if (request_len < 22+asn1len)
		goto truncated;
		pk = crypto_pk_asn1_decode(request+2, asn1len);
		if (!pk) {
		log_fn(LOG_WARN, "Couldn't decode public key");
		goto err;
		}

		/* Next 20 bytes: Hash of handshake_digest \| "INTRODUCE" */
		memcpy(buf, circ->handshake_digest, 20);
		memcpy(buf+20, "INTRODUCE", 9);
		if (crypto_SHA_digest(buf, 29, expected_digest)<0) {
		log_fn(LOG_WARN, "Error computing digest");
		goto err;
		}
		if (memcmp(expected_digest, buf+2+asn1len, 20)) {
		log_fn(LOG_WARN, "Hash of session info was not as expected");
		goto err;
		}

		/* Rest of body: signature of previous data */
		if (crypto_pk_public_checksig_digest(pk, buf, 22+asn1len,
		buf+22+asn1len, request_len-(22+asn1len))<0) {
		log_fn(LOG_WARN, "Incorrect signature on ESTABLISH_INTRO cell; rejecting");
		goto err;
		}

		/* The request is valid. First, compute the hash of Bob's PK.*/
		if (crypto_pk_get_digest(pk, pk_digest)<0) {
		log_fn(LOG_WARN, "Couldn't hash public key.");
		goto err;
		}

		/* Close any other intro circuits with the same pk. */
		c = NULL;
		while ((c = circuit_get_next_by_service_and_purpose(
		c,pk_digest,CIRCUIT_PURPOSE_INTRO_POINT))) {
		circuit_mark_for_close(c);
		}

		/* Now, set up this circuit. */
		circ->purpose = CIRCUIT_PURPOSE_INTRO_POINT;
		memcpy(circ->rend_service, pk_digest, 20);

		return 0;
		truncated:
		log_fn(LOG_WARN, "Rejecting truncated ESTABLISH_INTRO cell");
		err:
		if (pk) crypto_free_pk_env(pk);
		circuit_mark_for_close(circ);
		return -1;
		}

		/* Process an INTRODUCE1 cell by finding the corresponding introduction
		* circuit, and relaying the body of the INTRODUCE1 cell inside an
		* INTRODUCE2 cell.
		*/
		int
		rend_mid_introduce(circuit_t circ, char request, int request_len)
		{
		circuit_t *intro_circ;

		if (request_len < 276) {
		log_fn(LOG_WARN, "Impossibly short INTRODUCE2 cell; dropping.");
		goto err;
		}

		/* The first 20 bytes are all we look at: they have a hash of Bob's PK. */
		intro_circ = circuit_get_next_by_service_and_purpose(
		NULL, request, CIRCUIT_PURPOSE_INTRO_POINT);
		if (!intro_circ) {
		log_fn(LOG_WARN,
		"No introduction circuit matching INTRODUCE2 cell; dropping");
		goto err;
		}

		/* Great. Now we just relay the cell down the circuit. */
		if (connection_edge_send_command(NULL, intro_circ,
		RELAY_COMMAND_INTRODUCE2,
		request, request_len, NULL)) {
		log_fn(LOG_WARN, "Unable to send INTRODUCE2 cell to OP.");
		goto err;
		}

		return 0;
		err:
		circuit_mark_for_close(circ); /* Is this right? */
		return -1;
		}

		/* Process an ESTABLISH_RENDEZVOUS cell by settingthe circuit's purpose and
		* rendezvous cookie.
		*/
		int
		rend_mid_establish_rendezvous(circuit_t circ, char request, int request_len)
		{
		if (circ->purpose != CIRCUIT_PURPOSE_INTERMEDIATE) {
		log_fn(LOG_WARN, "Tried to establish rendezvous on non-intermediate circuit");
		goto err;
		}

		if (request_len != REND_COOKIE_LEN) {
		log_fn(LOG_WARN, "Invalid length on ESTABLISH_RENDEZVOUS");
		goto err;
		}

		if (circuit_get_rendezvous(request)) {
		log_fn(LOG_WARN, "Duplicate rendezvous cookie in ESTABLISH_RENDEZVOUS");
		goto err;
		}

		circ->purpose = CIRCUIT_PURPOSE_REND_POINT_WAITING;
		memcpy(circ->rend_cookie, request, REND_COOKIE_LEN);

		return 0;
		err:
		circuit_mark_for_close(circ);
		return -1;
		}

		/* Process a RENDEZVOUS1 cell by looking up the correct rendezvous circuit by its
		* relaying the cell's body in a RENDEZVOUS2 cell, and connecting the two circuits.
		*/
		int
		rend_mid_rendezvous(circuit_t circ, char request, int request_len)
		{
		circuit_t *rend_circ;

		if (circ->purpose != CIRCUIT_PURPOSE_INTERMEDIATE) {
		log_fn(LOG_WARN, "Tried to complete rendezvous on non-intermediate circuit");
		goto err;
		}

		if (request_len < 20+128+20) {
		log_fn(LOG_WARN, "Rejecting impossibly short RENDEZVOUS1 cell");
		goto err;
		}

		rend_circ = circuit_get_rendezvous(request);
		if (!rend_circ) {
		log_fn(LOG_WARN, "Rejecting RENDEZVOUS1 cell with unrecognized rendezvous cookie");
		goto err;
		}

		/* Send the RENDEZVOUS2 cell to Alice. */
		if (connection_edge_send_command(NULL, rend_circ,
		RELAY_COMMAND_RENDEZVOUS2,
		request+20, request_len-20, NULL)) {
		log_fn(LOG_WARN, "Unable to send RENDEZVOUS2 cell to OP.");
		goto err;
		}

		/* Join the circuits. */
		circ->purpose = CIRCUIT_PURPOSE_REND_ESTABLISHED;
		rend_circ->purpose = CIRCUIT_PURPOSE_REND_ESTABLISHED;
		memset(circ->rend_cookie, 0, 20);

		rend_circ->rend_splice = circ;
		circ->rend_splice = rend_circ;

		return 0;
		err:
		circuit_mark_for_close(circ);
		return -1;
		}

		/*

src/or/rendservice.c

+1 −13

Original line number	Diff line number	Diff line
		@@ -235,8 +235,7 @@ int rend_service_init_keys(void)
		return 0;
		}

		/DOCDOC/
		rend_service_t *
		static rend_service_t *
		rend_service_get_by_pk_digest(const char* digest)
		{
		int i;
		@@ -253,17 +252,6 @@ rend_service_get_by_pk_digest(const char* digest)
		* Handle cells
		******/

		typedef struct rend_introduction_t {
		/* Digest of the hidden service's PK. */
		char key_digest[20];
		/* Nickname of OR running rendezvous point. */
		char *rendezvous_point;
		/* Cookie that we'll use to recognize the rendezvous point. */
		char cookie[20];
		/* g^xy */
		char shared_secret[128];
		} rend_introduction_t;

		/* Respond to an INTRODUCE2 cell by launching a circuit to the chosen
		* rendezvous points.
		*/