What to trust on the Net

1
What to trust on the Net?
or Why do I get all these emails from LLoyds
Bank when I'm not a customer?

• Andrew McNab

2
Outline

• IP - the Network itself
• DNS - names like lloyds.com/
• Web - http//vvv.lloyds.com/e-banking/
• Signed objects like signed emails
• Provenance and authority
• Social Engineering

4 April 2006
Andrew McNab Trust on the Net
3
IP Addresses

• Internet Protocol (IP) is the standard for moving
  packets of data around the Internet
• Each node has its own address, like 192.168.0.9,
  and addresses are grouped into subnets, like
  192.168.0.
• Subnets generally correspond to a particular
  local network, so 192.168.0. might be your
  network at home, or the network for one building.
  
• Each packet has its source and destination
  addresses written in its header.

4 April 2006
Andrew McNab Trust on the Net
4
IP security

• The limitation with IP is that there is no
  authentication or authorization built into the
  system
• If you're physically on the network, you can send
  packets
• Some sites (including us) put limits on what you
  can do based on IP address (eg access local web
  pages.)
• However, an attacker can defeat this if
• they can get on the local network (eg with a
  notebook, or by getting on a wireless part of
  network)
• find a vulnerability in the router(s) which pass
  IP packets on to the right internal or external
  subnets.

4 April 2006
Andrew McNab Trust on the Net
5
IP solutions

• Strong physical security eg in a machine room
• Use WPA encryption of wireless access
• Limit access to network cards with one of a list
  of valid hardware MAC addresses, set in the
  factory
• numbers like 00458F4D92AB
• every device has one, but some allow users to
  change the MAC in software
• Push the security problem to a higher layer...
• IPSec IP over an encrypted channel
• Secure the protocols that run on top of IP

4 April 2006
Andrew McNab Trust on the Net
6
DNS

• The Domain Name System (DNS) maps human friendly
  names like www.amazon.com to the IP numbers the
  network really uses.
• Can use DNS names and domains to limit access to
  services
• Only machines in .cern.ch can see this page.
• But this has the same problems as IP based
  restrictions like 192.168.0.
• Furthermore, users contact DNS servers to find
  services which they trust so attacking DNS
  servers is a problem.

4 April 2006
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DNS server attacks

• For example, to make www.lloyds-bank.com point to
  my notebook rather than their server
• Most DNS servers use the same program, BIND, and
  vulnerabilities in this are regularly found
• so maybe I can hack the user's local DNS server,
  and make it lie about www.lloyds-bank.com
• It's possible to misconfigure DNS servers to
  allow attackers to inject fake data (ie
  pretending to know the truth about where
  www.lloyds-bank.com is)

4 April 2006
Andrew McNab Trust on the Net
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DNS solutions

• Use DNS-Sec
• Provides a way of using digital cryptography to
  sign responses from DNS servers
• Not at all universally deployed, which is
  necessary for it to work for random sites
• Can help with securing local friendly DNS
  servers against data injection attacks, but
  requires manually setting up private keys
• Push the security problem up to a higher level...

4 April 2006
Andrew McNab Trust on the Net
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Public/Private Keys

• Public Key Cryptography is a crypographic
  technique which uses the products of large prime
  numbers
• since it is a hard problem to factorise such
  products, we can publish the product without
  immediately revealing the prime factors
• Using that asymmetry, it's possible to build
  systems where I sign ( encrypt then hash) a
  message using my private key, and where you can
  verify the signature using my public key (which
  you know) but you can't sign it as me just with
  my public key

4 April 2006
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10
ssh

• Secure Shell (ssh) allows you to get command line
  access to your account on another Unix machine
• The secure part comes from using digital
  cryptography to establish trust (and encrypt the
  messages.)
• An ssh server creates a public and private key
  pair
• when you ssh to a machine, you're told it's
  public key and get the The authenticity of host
  can't be established. Are you sure you want to
  continue connecting (yes/no)? message
• If you're feeling trusting today, you say yes.
• ssh warns you if the public key change in the
  future

4 April 2006
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ssh problems

• First problem how to decide whether to trust a
  new machine
• how do you know?
• sometimes machines are reinstalled, the keys are
  not saved and new ones are generated
• or has the box been unplugged and replaced with a
  notebook today?
• Secondly, ssh allows user keys instead of
  passwords too
• great, no more passwords to steal
• not so great, can now steal ssh keys out of
  HOME/.ssh
• if I can do that at CERN, I can get into lots
  other sites too

4 April 2006
Andrew McNab Trust on the Net
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The Web

• We all know what this is!
• Web servers host pages/files identified by DNS
  names
• so the same DNS and IP problems as before
• HTTP protocol is used to request pages/files
• how do I know I'm really talking to Lloyds
  Bank?
• If the URL is like http//www.lloyds-bank.com/
  then you don't!
• If the URL is like https//www.lloyds-bank.com/
  and your browser has the padlock icon showing,
  then you probably do.

4 April 2006
Andrew McNab Trust on the Net
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HTTPS

• HTTPS is in effect HTTP over ssh
• In fact the SSL layer used by ssh was originally
  developed for HTTPS
• Requests and responses are encrypted
• so harder for eavesdroppers to steal your credit
  card number
• Like ssh, uses public/private keys to establish
  the authenticity of the web server
• but unlike ssh, they're not created by the web
  server

4 April 2006
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Certificates

• Public Key Cryptography allows us to sign
  things, in a way that other people can verify
• This means a trusted third party (TTP) can sign a
  server's public key
• The TTP can vouch for the authenticity of any
  name associated with the public key
• In practice, Certification Authorities issue
  signed public keys (certificates) with DNS
  names
• By trusting a few CAs, I can trust 1000s of
  certificates
• CAs exist both commercially (Verisign, BT etc)
  and in research projects (UK e-Science CA)

4 April 2006
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HTTPS certificates

• Certificates make HTTPS one of the most reliable
  security systems in production on the Net.
• So they're the basis of authentication on the
  Grid too
• Can also be used to identify users to servers
  signed user certificate instead of private ssh
  key
• But the certificates still just authenticate
  they don't tell you whether you can trust
  www.LL0YDS-BANK.com, just that the server is run
  by the owner of ll0yds-bank.com.
• So we push the problem up a level again, and
  manually squint at URLs to see if they're
  faked...

4 April 2006
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Virtual Organisations

• There isn't really a solution for this in the Web
  world yet
• people have to rely on brand image
• look carefully for odd spellings (0 not O
  etc)
• Within the Grid, we've faced the problem of how
  services authorized users
• not user who a user is, but are they really a
  current member of ATLAS?
• this offers some solutions we give users
  short-lived Attribute Certificates saying they're
  in ATLAS and what roles and groups they're in
• The UK FSA could do the same for UK Banking
  websites...

4 April 2006
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Email

• In terms of security, email really is a mess!
• it was designed to operate on a private Internet
  run by universities and labs
• Spam is largely a result of the unaccountability
  of sending email, since it can be very hard to
  determine who sent it
• Lots of solutions have been proposed
• they either involve putting limits on who can
  send email
• or don't have much effect until everyone adopts
  them
• Digital Certificates could play a part in this,
  but that would require most people to go and buy
  a commercial certificate

4 April 2006
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PGP and S/MIME

• PGP is a Public Key Cryptography system that can
  be used for emails, and in practice it works more
  like ssh keys than certificates
• need to establish bilateral trust between you and
  your friends (or friends of friends)
• so not very scalable
• S/MIME is IETF standard for signing emails with
  certificates
• the same kind of certificates used for WWW and
  Grid
• but UK e-Science CA certificates can't be used
  this way, since they don't contain the users
  email address

4 April 2006
Andrew McNab Trust on the Net
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Other signing

• Signing can also be used for programs you might
  download and install
• this again is widely implemented, like S/MIME,
  put not widely deployed in practice
• It's use is limited because of the cost
  associated with being checked out to get a
  signing certificate
• also works against Open Source software projects
• and smaller software companies
• There's no reason why you can't sign really
  important software/emails, and let people check
  them manually

4 April 2006
Andrew McNab Trust on the Net
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Phishing

• One major abuse of email's lack of security is
  Phishing
• This involves sending unsolicited email claiming
  to be an official notification from the user's
  bank, PayPal, eBay etc.
• Huge numbers of these are sent out if everyone
  gets an email from Lloyd's Bank, it will be right
  for 15 of people
• The email often tries to scare the user into
  following a link embedded in the email Account
  closure notice etc etc
• the link goes to the attacker's site, using one
  of the techniques mentioned already
• the fake site invites the user to reenter their
  password...

4 April 2006
Andrew McNab Trust on the Net
21
Social Engineering

• Phishing is an automated form of the ancient
  hacker technique of Social Engineering
• ie talking people into doing things that let you
  break in
• The ph comes from Phone Phreaking which
  involved hacking ATT's telephone network, and
  often required pretending to be a telephone
  engineer
• One of the problems of network security is the
  tendency to push the problem up to a higher
  level.
• Eventually, The Highest Level is a human, and
  we're much worse at following security procedures
  than computers

4 April 2006
Andrew McNab Trust on the Net
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SE examples

• The Art of Deception by Kevin Mitnick features
  a collection of social engineering stories, and
  ways to counteract them
• These are especially a problem in big
  organisations, because you're used to dealing
  with strangers who are nevertheless members
• so CERN, visiting other institutes, dealing with
  the University administration here
• Basic technique is to use publicly available
  details to create confidence, and extract more
  sensitive information
• Never give out numbers to strangers...

4 April 2006
Andrew McNab Trust on the Net
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The Network Outage

• (Phone calls adapted from Mitnick's book)
• Attacker Hey, Tom, this is Eddie Martin on the
  Help Desk. We're trying to troubleshoot a network
  problem. Have you seen any problems today?
• Tom Uh, not that I know of.
• Attacker Ok, but call if it does.
• Tom You better believe it!
• Attacker Sounds like it would be a problem.
  Call me on my cell phone [phone] if it
  happens. What's your network socket number, just
  in case...

4 April 2006
Andrew McNab Trust on the Net
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Network Outage (2)

• (The Next Day call to the network operations
  room)
• Attacker Hi, this is Bob, I'm in Tom DeLay's
  office in Bookkeeping. We're trying to
  troubleshoot a cabling problem. I need you to
  disable his network socket, number 6-47, for a
  few minutes...
• (The attacker then gets a call from Tom on his
  mobile...)
• Tom Help Eddie, my network just went down, like
  you said.
• Attacker Ok, I'll see if I can get it back
  online. Try again in a few minutes...
• Tom Thanks, I really appreciate that, Eddie.

4 April 2006
Andrew McNab Trust on the Net
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Network Outage (3)

• Attacker Hi again Tom. Is it working now?
• Tom Yes, thanks, I was really worried. But it's
  ok now.
• Attacker Ok, if you want to make sure it
  doesn't happen again, you need to make sure your
  computer is fully up to date.
• Tom Uh, ok. Up to date like what?
• Attacker I'll send you an email with
  instructions. Just click on the link in the email
  to http//www.M1CRS0FT.COM/ and download the
  updates.
• (So now Tom's computer is running some horrible
  Trojan program which allows the attacker to
  control it remotely, read his files etc)

4 April 2006
Andrew McNab Trust on the Net
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Summary

• You can trust HTTPS websites IF you make sure
  they've got sensible names
• you can minimise the risk of Phishing attacks by
  using Google to find sites, and not trusting URLs
  in emails
• ssh is great once you've made contact with a site
  and accepted its public key
• Everything else shouldn't be taken at face value
• especially helpful people who ask you about
  employment numbers, network numbers, addresses,
  office numbers, what Professor X's secretary's
  first name is etc that could be used to build
  confidence in an attacker...

4 April 2006
Andrew McNab Trust on the Net