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Cipherspaces/Darknets: An Overview Of Attack Strategies (Hacking
Illustrated Series InfoSec Tutorial Videos)
Cipherspaces/Darknets: An Overview Of Attack
Strategies
Darknets/Cipherspaces such as Tor and I2P have been covered before in great
detail. Sometimes it can be hard to follow attack strategies that have been used
against them as the papers written on the topic have been academic and abstract.
What this talk will attempt to do is step back and give an overview of the topic
in a manner hopefully more conducive to the understanding of security
practitioners, giving more concrete examples. While little to nothing in this
talk will be "new and groundbreaking" it should lead to a better understanding
of how encrypted anonymizing networks can be subverted to reveal identities.
Cipherspaces/Darknets: An overview of attack strategies
Adrian Crenshaw
About Adrian
I run Irongeek.com
I have an interest in InfoSec education
I don’t know everything - I’m just a geek with time on my hands
(ir)Regular on the ISDPodcast http://www.isdpodcast.com
Researcher for Tenacity Institute http://www.tenacitysolutions.com
A little background…
Darknets: There are many definitions, but the one I’m working from is
“anonymizing networks”
Use of encryption and proxies (some times other peers) to obfuscate who is
communicating to whom
Sometimes referred to as Cipherspace
(I love that term)
Tor and I2P will be my reference examples, but there are others
…and some notes
Things get subtle
Terms vary from researcher to researcher
Many weaknesses are interrelated
Other anonymizing networks: Morphmix/Tarzan/Mixminion/Mixmaster/JAP/
MUTE/AntsP2P/Haystack
Focus on Tor and I2P for illustrations when needed
Academic vs. real world
Threat Model and Adversaries matter
Threat Model: You can’t protect against everything!
Some protocols may be lost causes
Users may do something to reveal themselves
Does an attack reveal the Client/Host or just reduces the anonymity set?
Active vs. Passive attackers
Location, Location, Location:
Internal vs. External
Adversaries: Vary by power and interest
Nation States
Western Democracies vs. Others
Government agency with limited resources
ISP/Someone with a lot of nodes on the network
Private interests groups (RIAA/MPAA)
Adrian (AKA: Some shmuck with time on his hands)
Tor: The Onion Router
Layered encryption
Bi-directional tunnels
Has directory servers
Mostly focused on out proxying to the Internet
More info at https://www.torproject.org
I2P
Unidirectional connections: In tunnels and out tunnels
Information about network distributed via distributed hash table (netDB)
Layered encryption
Mostly focused on anonymous services
More info at http://www.i2p2.de/
I2P Encryption Layers
EIGamal/SessionTag+AES from A to H
Private Key AES from A to D and E to H
Diffie–Hellman/Station-To-Station protocol + AES
Silly Garlic Routing
Animation
Un-trusted exit points
You are only as anonymous as the data you send!
Overview
Mostly Tor centric:
Is the exit point for traffic looking at the data?
Traffic may be encrypted inside the network, but not once it is outbound!
Incidents
Dan Egerstad and the “Embassy Hack” http://www.wired.com/politics/security/news/2007/09/embassy_hacks
Tons of passwords sent via plain text protocols (POP3/SMTP/HTTP Basic/Etc)
Moxie Marlinspike did something similar with SSLStrip http://intrepidusgroup.com/insight/2009/02/moxie-marlinspike-un-masks-tor-users/
Do you trust your exit node?
Mitigation
Tor is for anonymity, not necessarily security
Use end-to-end encryption/Don’t use plain-text protocols
Plain text protocols that send usernames/email addresses in the clear are not
very anonymous now are they?
DNS Leaks, Other Protocol leaks and application layer problems
Overview
Does all traffic go though the proxy?
DNS Leaks are a classic example
Badly configured proxy setting could lead some types of traffic to go
elsewhere (outside of cipherspace)
Snooper can use web bugs to figure out your location http://www.irongeek.com/i.php?page=security/webbugs
HTTPS is a good example, but plugins can also be an issue
Application level stuff in general is a problem
Javascript is just hosed as far as reducing you anonymity set
See: Gregory Fleischer, DEFCON 17: Attacking Tor at the Application Layer
DNS Leaks
Mitigating DNS Leaks
Sniff for traffic leaving your box on port 53. The libPcap capture filter:
port 53
should work in most cases.
In Firefox, under about:config set network.proxy.socks_remote_dns to true
Torbutton should help
Other applications vary
May have to firewall off 53 in some cases
May want to edit torrc, and add:
DNSPort 53
AutomapHostsOnResolve 1
Then set your box’s DNS to point to 127.0.0.1
Grabbing content outside of the Darknet
Slightly Related: Cookies/Supercookies/Etc
Make hidden server contact you over public Internet
Another example, Bittorrent Issues
Yet Another Example:
IRC Ident
General Mitigations
Client wise:
Make sure your browser is set to send all traffic though the darknet, or none
at all
Look into firewall rules
Limit plugins used
Use a separate browser
Check against: http://decloak.net/ http://panopticlick.eff.org/
Hidden server wise:
Patch your stuff
Don’t run on a box that routes to the Internet
Attacks on centralized resources/infrastructure attacks/DoS attacks
Overview
Not so much against individual nodes, but the network in general
Whole bunch of categories, not comprehensive:
Starvation attacks
Partition attacks
Flooding
Standard DDoS attacks against resources inside and outside of the network (if
going though the network) are likely to be soaked by other peers
Shared known infrastructure can be a problem
Total (or at least severe) blocking of the Internet
Incidents
China blocked access to the core directory servers of Tor on September 25th
2009 https://blog.torproject.org/blog/tor-partially-blocked-china
Other blocking of Internet access. (Egypt, Libya, Iran)
DoS of directory servers
Mitigation
Bridge nodes (Tor)
Distributed infrastructure (I2P)
Taking out dev site would still be an issue
Distributed Hash Table
Protocol obfuscation
Total/Severe blocking will take a bit more:
(see next slide)
Mesh/Store and forward
For more info on mesh networks
Needs a clear front runner for setting up such a system
Wikipedia if nothing else http://en.wikipedia.org/wiki/Wireless_mesh_network
Village Infrastructure in a Kit-Alpha (VIKA) Project http://www.cuwin.net/node/325
U.S. Underwrites Internet Detour Around Censors http://www.nytimes.com/2011/06/12/world/12internet.html?_r=2&pagewanted=all
Clock based attacks
Overview
Some protocols allow you to check the remote system’s clock
Clock difference could be an issue
Major difference are easy to spot
Minor clock issues may need statistical analysis
Incidents
For skew, see:
Steven J. Murdoch, "Hot or Not: Revealing Hidden Services by their Clock Skew"
University of Cambridge, Cambridge, 2006 http://www.freehaven.net/anonbib/cache/HotOrNot.pdf
I2P Clock differences in I2P http://www.irongeek.com/i.php?page=security/darknets-i2p-identifying-hidden-servers
Clock Issues
Clock Differences
Mitigation
Attack can be hard to pull off because of network jitter
Set clocks with a reliably and often used NTP server
Some mitigation may take place in the darknet protocol itself
Metadata in files
Overview
Metadata is data about data
Just a few files types that contain metadata
JPG
EXIF (Exchangeable image file format)
IPTC (International Press Telecommunications Council)
PDF
DOC
DOCX
EXE
XLS
XLSX
PNG
Too many to name them all
Things stored: User names, edits, GPS info, network paths, MAC addresses in
odd cases. It all depends on the file format.
Incidents: Pwned by Metadata
Mitigation
Well, clean out the metadata, duh!
Apps vary on how to do it
local attacks
(at this point, it is already probably a lost cause)
Overview
If they have access to the local box, your hosed
Comes down to mostly traditional forensics
Data on hard drive
Cached data and URLs
Memory Forensics
Mitigations
Anti-forensics http://www.irongeek.com/i.php?page=videos/anti-forensics-occult-computing
Live CD/USB, but see Andrew Case’s work: https://media.blackhat.com/bh-dc-11/Case/BlackHat_DC_2011_Case_De-Anonymizing_Live_CDs-wp.pdf
Full hard drive encryption
Sybil attacks
Sock puppetry
Overview
Ever heard of Sybil attacks?
Think sock puppet, one entity acting as many
May allow for control of routing, elections, etc.
Makes many of the other attacks easier
Sock puppetry/Sybil
Mitigation
No absolute fixes
Make it cost something to have nodes (hashcash)
IP restrictions:
Both Tor and I2P restrict peering between IPs on the same /16
Central infrastructure may be more resilient against Sybil attacks (but has
other issues)
Peering/Profiling strategies
SybilLimit/SybilGuard/SybilInfer
Traffic Analysis Attacks
First/Last in chain attacks
Tagging attacks
Timing attacks
Overview
There’s much focus on this in academia, but I imagine application layer flaws
are more likely to snag someone
So many subtle variation on profiling traffic
Could be:
Timing of data exchanges
Amount of traffic
Tagging of traffic by colluding peers
Generally takes a powerful adversary
Hard to defeat in “low latency” networks
I2P one-way tunnel mesh network: Logical view
I2P one-way tunnel mesh network:
ISP view
End point and exit point
Timing Correlation
Mitigation
More routers
More cover traffic
(smaller needle in a larger haystack)
Entry Guards for first hop
One way tunnels
Short lived tunnels may help
Better peer profiling
Signing of the data
Fixed speeds
Padding and Chaff
Non-trivial delays and Batching
Intersection/Correlation Attacks
Overview
Could be as simple as knowing who is up when a hidden service can be accessed
Techniques can be used to reduce the search set
Application flaws and information leaks can narrow the anonymity set
Harvesting attacks
Correlation
Cut down needed checks
Mitigation
More nodes
Give less data that could be used to reduce the anonymity set
Make harvesting/scrapping attacks harder
Checkout “De-anonymizing I2P” paper and talk I’ll link to later
Links
Selected Papers in Anonymity http://www.freehaven.net/anonbib/
I2P’s Threat Model Page http://www.i2p2.de/how_threatmodel.html
General Darknets Talk http://www.irongeek.com/i.php?page=videos/aide-winter-2011#Cipherspace/Darknets:_anonymizing_private_networks
De-anonymizing I2P http://www.irongeek.com/i.php?page=security/darknets-i2p-identifying-hidden-servers http://www.irongeek.com/i.php?page=videos/identifying-the-true-ip-network-identity-of-i2p-service-hosts-talk-adrian-crenshaw-blackhat-dc-2011
Thanks
Conference organizers for having me
Tenacity for helping get me to Defcon
By buddies from Derbycon and the ISDPodcast
Open Icon Library for some of my images http://openiconlibrary.sourceforge.net
Events
DerbyCon 2011, Louisville Ky
Sept 30 - Oct 2 http://derbycon.com
Louisville Infosec http://www.louisvilleinfosec.com
Other Cons: http://skydogcon.com http://hack3rcon.org http://phreaknic.info http://notacon.org http://outerz0ne.org
Questions?
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