What to trust on the Net? Andrew McNab or “Why do I get all these emails from LLoyds Bank when I'm...

What to trust on the Net?

Andrew McNab

“”

4 April 2006 Andrew McNab – Trust on the Net

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


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.


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.


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 00:45:8F:4D:92:AB– 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


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.

http://www.amazon.com/


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)


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...


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


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


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


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.


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


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)


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...

http://www.LL0YDS-BANK.com/


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...


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


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


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


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...


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


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...


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 555-567-7890 if it happens. What's your

network socket number, just in case...”


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.”


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)

http://www.M1CRS0FT.COM/


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...

What to trust on the Net? Andrew McNab or “Why do I get all these emails from LLoyds Bank when I'm...

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