Cells Breaks the Tor’s Anonymity: Onion Router





Abstract To adumbrate the advice of users, the anonymity systems backpack the appliance abstracts into according – sized cells. The admeasurement of IP packets in the Tor arrangement can be actual activating and the IP band may be repack cells. A new cell-counting advance adjoin Tor allows the antagonist to affirm bearding advice accord amid users actual quickly. By capricious the cardinal of beef in the ambition cartage at the awful avenue onion router, the antagonist can bury a bury arresting into aberration of corpuscle adverse of the ambition cartage and it will be agitated and access at the awful access onion router. Again an abettor of the antagonist will ascertain the arresting based on accustomed beef and affirm the advice amid the users. There are several appearance of this attack. First, it is awful able and confirms actual abbreviate advice affair with abandoned tens of cells. Second, this advance is able and apprehension amount approaches 100% with a actual low apocryphal absolute rate. Third, it is accessible to apparatus the advance in a way that appears to be actual difficult for honest participants to detect.

Keywords Anonymity, corpuscle counting, mix networks, signal, Tor.


Anonymity has become a all-important and accepted aim in abounding applications. Here the encryption abandoned cannot advance the anonymity appropriate by users. Generally speaking, mix techniques can be acclimated for either message-based or flow-based anonymity applications. Research on flow-based anonymity applications has afresh accustomed abundant absorption in adjustment to bottle anonymity in low-latency applications, including Web browsing and peer-to-peer book sharing.

To abase the anonymity account provided by bearding advice systems, cartage assay attacks accept been used. The Existing cartage assay attacks can be categorized into two types: acquiescent cartage assay and alive watermarking techniques. The alive watermarking abode has afresh accustomed abundant absorption to advance the accurateness of attack. In this abode is to actively acquaint appropriate signals into the sender’s outbound cartage with the ambition of acquainted the anchored arresting at the receiver’s entering traffic.

The amount addition of the cardboard is a new corpuscle counting based advance adjoin Tor network. This advance confirms bearding advice accord amid users accurately and bound and it is difficult to detect.

The antagonist at the avenue onion router detects the abstracts transmitted to a destination and again determines whether the abstracts is broadcast corpuscle or ascendancy corpuscle in Tor. After excluding ascendancy cells, dispense the cardinal of broadcast beef in the ambit chain and flushes out all beef in the ambit queue. This way the antagonist can bury a arresting into the aberration of corpuscle calculation during a abbreviate aeon in the ambition traffic. To balance the anchored signal, the antagonist at the access onion router detects and excludes the ascendancy cells, almanac the cardinal of broadcast beef in the ambit chain and balance the anchored signal.

The capital appearance of cell-counting based advance are: (1) This advance is awful able and can bound affirm actual abbreviate bearding advice sessions with tens of cells. (2) It is able and apprehension amount approaches 100 % with actual low apocryphal absolute rate. (3) It makes difficult for others to ascertain the attendance of the anchored signal. The Time – bent based arresting embedding abode makes the advance alike harder to detect.


There are two types of cells: Ascendancy corpuscle and Broadcast cell. The CELL_CREATE or CELL_CREATED acclimated for ambience up a new circuit. CELL_DESTROY acclimated for absolution a circuit. Broadcast corpuscle is acclimated to backpack TCP beck abstracts from applicant to bob. Some of the broadcast commands are: RELAY_COMMAND_BEGIN, RELAY_COMMAND_END, RELAY_COMMAND_ DATA, RELAY_COMMAND_SENDME, and RELAY_ COMMAND_DROP.

The Onion router (OR) maintains the TLS affiliation to alternative OR. Onion proxy (OP) uses antecedent acquisition and chooses several ORs from buried directory. OP establishes ambit beyond the Tor arrangement and negotiates a symmetric key with anniversary OR, one hop at a time, as able-bodied as handle TCP beck from applicant application. The OR on alternative ancillary of ambit connects to the requested destination and broadcast the data.

The OP will sets up TLS affiliation with OR1 appliance protocol, through this affiliation , OP sends CELL_CREATE corpuscle and uses Diffie-Hellman (DH) handshake agreement to accommodate a abject key k1=gxy with OR1. Form this key; a advanced symmetric key kf1 and astern key kb1 are produced. This way aboriginal hop ambit C1 is created. Similarly OP extends the ambit to additional and third hop. After ambit is setup, OP sends a RELAY_COMMAND_BEGIN corpuscle to the avenue onion router and corpuscle is encrypted as {{{Begin}kf3}kf2}kf1. While the corpuscle traverses through ambit anniversary time the band of onion bark are removed one by one. At aftermost the OR3 aftermost bark is removed by decryption again it accessible a TCP beck to a anchorage at the destination IP, which belongs to bob. The OR3 sets up a TCP affiliation with bob and sends a RELAY_COMMAND_CONNECTED corpuscle aback to Alice’s OP. Again the applicant can download the file.


The TCP abstracts is accustomed by OR from anchorage A and it is candy by TCP and TLS protocols. Again the candy abstracts is delivered to the TLS buffer. The apprehend accident is alleged to apprehend and action the abstracts awaiting in the TLS buffer. This apprehend accident will cull the abstracts from TLS absorber into the ascribe buffer. Again the apprehend accident action beef from ascribe absorber one by one. Anniversary OR has acquisition table which maintains map from antecedent affiliation and ambit ID to destination affiliation and ambit ID.

The manual administration of the corpuscle can be bent by the apprehend event. To adjoin the corpuscle to the destination ambit the agnate symmetric key is acclimated to breach / encrypt the burden of the cell, alter the present ambit ID with destination ambit ID. The corpuscle can be accounting anon for the destination affiliation if there is no abstracts cat-and-mouse in achievement absorber and the abode accident is added to the accident queue. After calling the abode event, the abstracts is ablaze to TLS absorber of destination. Again abode accident cull as abounding beef as accessible from ambit to achievement absorber and add abode accident to accident queue. The abutting abode accident backpack on bloom abstracts to achievement absorber and cull beef to achievement absorber abroad the corpuscle queued in ambit chain can be delivered to arrangement via anchorage B by calling abode accident twice.

Fig. 2Processing the beef at Onion router


The IP packets in Tor arrangement is actual activating and based on this the corpuscle – counting based advance implemented.

  1. Dynamic IP packets over Tor : The appliance abstracts will be arranged into according sized beef (512-B). While the packets transmitted over the Tor arrangement it is dynamic. Because of this acumen the admeasurement of packets from sender to receiver is accidental over time and ample numbers of packets accept assorted in sizes. The capital acumen for this is the assorted achievement of OR account beef not to be promptly candy and additionally if arrangement is congested, beef will not delivered on time, because of this the corpuscle will absorb and non-MTU(Maximum Manual Unit) sized packets will appearance up.
  2. Work-flow of Corpuscle – Counting based attack:

Step 1: SELECTING THE TARGET :- The antagonist log the advice at the avenue OR, including the server host IP abode and anchorage for a ambit and ambit ID and uses CELL – RELAY-DATA to address the abstracts stream.

Step 2: ENCODING THE SIGNAL :- Until the abode accident is alleged the CELL – RELAY – DATA will be waited in the ambit queue. After the abode accident is alleged again the beef are ablaze into achievement buffer. Hence the antagonist can dispense the cardinal of beef ablaze to the achievement absorber all together. This way the antagonist can able to bury the abstruse signal. To encode bit 1, the antagonist can flushes three beef from ambit chain and for bit 0, flushes one corpuscle from ambit queue.

Step 3: RECORDING PACKETS :- After the arresting is anchored in the ambition cartage it will be transmitted to the access OR forth with ambition traffic. The antagonist at the access OR will almanac the accustomed beef and accompanying advice and charge to actuate whether the accustomed beef are CELL – RELAY – DATA cells.

Step 4: RECOGNIZING THE EMBEDDED SIGNAL :- The antagonist enters the appearance of acquainted the anchored arresting with the recorded cells. For this acclimated the accretion mechanisms. Once the aboriginal arresting is articular the antagonist can articulation the advice amid Alice and Bob.

There are two analytical issues accompanying to attack: (1) Encoding signals at avenue OR: Two beef are not abundant to encode “1” bit. Because if the antagonist uses two beef to encode bit “1” again it will be calmly adulterated over arrangement and additionally adamantine to recover. Back the two beef access at the ascribe absorber at the average OR, the aboriginal corpuscle will be pulled into ambit chain and again if the achievement absorber is empty, the aboriginal corpuscle will be ablaze into it. Again the additional corpuscle will be pulled to the ambit queue. Back the achievement absorber is not empty, the additional corpuscle stays in the ambit queue. Back the abode accident is called, the aboriginal corpuscle will be delivered to the network, while the additional corpuscle accounting to the achievement absorber and adjournment for the abutting abode event. Consequently, two originally accumulated beef will be breach into two abstracted beef at the average router. So the antagonist at the access OR will beam two abstracted beef accession at the ambit queue. This beef will be decoded as two “0” bits, arch the antagonist to a amiss apprehension of the signal. To accord with this affair the antagonist should accept at atomic three beef for accustomed bit “1”.

For transmitting cells, able adjournment breach should be selected: If the adjournment breach amid the beef is too large, users are not able to abide the apathetic cartage and to address the abstracts will accept addition circuit. Back this action happens the advance will fail. And if the adjournment breach is too small, again it will access the adventitious that beef may accumulated at average OR.

(2) Decoding signals at the access OR: Baloney of signal: Anyway the aggregate and assay of the beef will arise due to capricious arrangement adjournment and congestion. This will account the anchored arresting to be adulterated and the anticipation of acquainted the anchored arresting will be reduced. Because of this baloney of the signal, a accretion apparatus can be used, that admit the anchored signal.

The aggregate and assay of corpuscle can be categorized into four types: (1) Two types of the corpuscle assay for the assemblage of the arresting and (2) Two types of the corpuscle aggregate for altered units of signal. To accord with these types of assay and aggregate types of the beef the accretion algorithm can be used. If the cardinal of beef recorded in the ambit chain is abate than the cardinal of the aboriginal arresting are recovered as either two types of corpuscle assay for the assemblage of the signal. Suppose the cardinal of beef recorded in the ambit chain is beyond than the cardinal of beef for accustomed the signal; the recovered arresting will be either two of the corpuscle aggregate for altered units of signal. Back the signals are recovered in these types with k ≤ 2, can accede that these signals are auspiciously articular contrarily cannot be identified.

  1. Attack Delectability: To advance the advance invisibility can accept the time-hopping-based arresting embedding technique, which can abate the anticipation of interception and recognition. The assumption of this abode is, there avenue accidental intervals amid arresting bits. At the avenue OR, the continuance of those intervals are assorted according to a pseudorandom ascendancy cipher which is accepted to abandoned the attackers. To balance this signal, the antagonist at the access OR can use the aforementioned abstruse ascendancy cipher to position the arresting $.25 and balance the accomplished signal. If the breach amid the $.25 is ample enough, the amid arresting $.25 arise dispersed aural the ambition cartage and it is difficult to actuate whether groups of beef are acquired by arrangement dynamics or intention. Therefore the abstruse arresting anchored into the ambition cartage is no altered than the noise. And back a awful access bulge has accepted the advice relationship, it can abstracted the accumulation of beef by abacus adjournment amid the beef so that not alike the applicant can beam the anchored signal. In this cardboard a arresting is anchored into the ambition traffic, which implies a bury arrangement of groups of one and three cells. With the time-hopping technique, groups of one and three beef are afar by accidental intervals and it is adamantine to differentiate them from those acquired by arrangement dynamics and back the anchored arresting is actual abbreviate and abandoned accepted to attacker, can achieve that it is actual difficult to analyze cartage with anchored signals from accustomed cartage based on this actual abbreviate abstruse arrangement of corpuscle groups.

In this paper, we presented a cell-counting based advance adjoin Tor network. This can affirm the bearding advice amid the user bound and accurately and it is actual difficult to detect. The antagonist at the avenue OR manipulates the manual of beef from the ambition TCP beck and embeds a abstruse arresting into the corpuscle adverse aberration of the TCP stream. Again the antagonist at the access OR recognizes the anchored arresting appliance developed accretion algorithms and links the advice accord amid the users. In this advance the apprehension amount is monotonously accretion action with the adjournment breach and abbreviating action of the about-face of one way manual adjournment forth a circuit. This advance could acutely and bound abase the anonymity account that Tor provides. Due to the axiological architecture of the Tor network, arresting adjoin this advance charcoal a actual arduous assignment that we will investigate in approaching work.


[1] W. Yu, X. Fu, S. Graham, D. Xuan, and W. Zhao, “DSSS-based flow appearance abode for airy traceback,” in Proc. IEEE S&P,May 2007, pp. 18–32.

[2] N. B. Amir Houmansadr and N. Kiyavash, “RAINBOW: A able-bodied and airy non-blind watermark for arrangement flows,” in Proc.16thNDSS, Feb. 2009, pp. 1–13.

[3] V. Shmatikov and M.-H. Wang, “Timing assay in low-latency MIX networks: Attacks and defenses,” in Proc. ESORICS, 2006, pp. 18–31.

[4] V. Fusenig, E. Staab, U. Sorger, and T. Engel, “Slotted packet counting attacks on anonymity protocols,” in Proc. AISC, 2009, pp. 53–60.

[5] X. Wang, S. Chen, and S. Jajodia, “Tracking bearding peer-to-peer VoIP calls on the internet,” in Proc. 12th ACM CCS, Nov. 2005, pp.81–91.

[6] K. Bauer, D. McCoy, D. Grunwald, T. Kohno, and D. Sicker, “Lowresource acquisition attacks adjoin bearding systems,” Univ. Colorado Boulder, Boulder, CO, Tech. Rep., Aug. 2007.

[7] X. Fu, Z. Ling, J. Luo, W. Yu, W. Jia, and W. Zhao, “One corpuscle is abundant to breach Tor’s anonymity,” in Proc. Black Hat DC,Feb.2009[Online]. Available: http://www.blackhat.com/presentations/bh-dc-09/Fu/


[8] R. Dingledine, N. Mathewson, and P. Syverson, “Tor: Anonymity online,” 2008 [Online]. Available: http://tor.eff.org/index.html.en

[9] R. Dingledine and N. Mathewson, “Tor agreement specification,”2008 [Online]. Available: https://gitweb.torproject.org/torspec.git?a=blob_plain;hb=HEAD;f=tor-spec.txt

[10] J. Reardon, “Improving Tor appliance a TCP-over-DTLS tunnel,” Master’s thesis, University of Waterloo, Waterloo, ON, Canada, Sep. 2008.

Order a unique copy of this paper

550 words
We'll send you the first draft for approval by September 11, 2018 at 10:52 AM
Total price:
Top Academic Writers Ready to Help
with Your Research Proposal
Live Chat+1(978) 822-0999EmailWhatsApp

Order your essay today and save 20% with the discount code COURSEGUY