Tài liệu Introduction to VPNs, PKI, and PGP ppt

• Dedicated leased lines are expensive • Most locations have low-cost connectivity to the Internet • Why not use the Internet as the communication media and use encryption for securit

Hello, in this module we continue our discussion of encryption and we look at some practical

applications of it We start off by looking at VPN’s or virtual private networks and see how you can use them to create secure communications using public networks such as the Internet We than briefly look at the problem of key management and finish our discussion with a look at PGP or Pretty Good Privacy, which is an application that allows you to encrypt files and send encrypted email

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Foundations of a VPN

• VPNs use cryptography to communicate

securely in the presence of adversaries

– Encryption: Scramble data into something difficult to read without a key.

– Decryption: the opposite process of encrypting

– Authentication: How are you sure you’re talking to the right person?

To architect and deploy a VPN, we need to understand how to apply these three tools These concepts are easy to grasp at the conceptual level, but the devil is in the details as they say Crypto has evolved from an abstract playground for mathematicians to something with widespread public awareness (those little solid, gold keys in the browser have people asking the darndest questions).Likewise, authentication is a discipline in its own right We’ll be discussing authentication systems and client-side web certificates

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What is a VPN?

• Dedicated leased lines are expensive

• Most locations have low-cost

connectivity to the Internet

• Why not use the Internet as the

communication media and use

encryption for security

• So, a VPN is a secure communication

path that utilizes public networks

In its most basic sense, VPN’s, or virtual private networks, are a secure communication path that utilizes public networks Having dedicated leased lines between locations provides for secure communications but can get very expensive With most leased lines, you pay by the distance So the greater the distance between two locations, the more expensive the line But most sites have fairly inexpensive connections to the Internet, so why not use those connections in order to communicate? The main problem is security Public networks, such as the Internet, have no security built-in However, if we encrypt the data that is sent over the lines, we now have the security we need with the costs that we like, thus a VPN

to load up software on their laptop and let them connect to the home office via a VPN over the Internet.

In looking for VPNs, ask about quality of service (QOS) Leased and dial-up lines offer both

bandwidth and latency guarantees, while dedicated connection technologies, like ATM and Frame Relay, have extensive mechanisms for similar guarantees As IP-based VPNs become more widely deployed, there will be market demand for similar guarantees, in order to ensure end-to-end

application transparency

Cost is another potential benefit With a frame or dedicated circuit, you typically pay a flat monthly fee so even if the circuit goes unused, its costing you money Also, crossing state and government boundaries with a dedicated circuit only increases their cost With a VPN, you pay for a local connection to the Internet with no “distance” charges

Given these benefits, its not surprising that Taylor and Hecht report that VPN technology is expected

to expand 300-1000% by 2003 (Taylor and Hecht)

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What VPN systems are

• Load balance, QOS, failover, redundancy

• Encryption

The fundamental components of VPN’s can usually be built on existing equipment Most routers and firewalls have capabilities for providing VPN capabilities, or dedicated boxes can also be purchased The thing to remember is in order to properly create a VPN, it requires several other components such as a PKI or public key infrastructure, X.509 certificates, key management schemes, etc One of the biggest problems that companies face is they try to setup a VPN without proper planning VPN’s can be straightforward to configure and setup but only if you do your homework and plan properly

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Security Issue

• If you are encrypting tunneled data

coming into your network, you lose

a number of checks and balances.

– What ELSE is connected to the VPN client that is connected to YOU?

192.68.0.10 Public IPNetwork

Security Gateway A Security

through Or to put it another way,allows un-trusted data into your network Since the firewall cannot read the data, it cannot provide proper filtering

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IPSec Review

• IETF standard enables encrypted

communication between users and devices

– Implemented transparently into the network

infrastructure

– Scales from small to very large networks

• Open standard enables multivendor

interoperability

• Most VPN devices and clients are IPSec

compliant

Now I’m going to spend some time discussing some of the aspects you should understand about

IPSec technology as part of your security solution IPSec is a Layer 3 method for providing tunnels

It is an IETF standard, enabling encrypted communication between users and devices as illustrated here The goal is enabling a lot of different types of devices to understand one another One of the first applications of IPSec is Remote Access VPNs

IPSec is transparent to the network infrastructure, and is scalable from very small applications to

very large networks

As an open standard, IPSec is available to everyone, so vendors can ensure interoperability As of now, there are different levels of implementation available among the different vendors, but ideally the same technology needs to be available to everyone to assure future interoperability in

multivendor networks, including the Internet

At Cisco, IPSec functionality is available in Cisco IOS software releases 11.3T and later Initially, Cisco targeted gateway devices for IPSec, including routers and access servers

• Internet Key Exchange (RFC 2406)—provides:

–Security association management

–Key management

At the IETF, IPSec includes security protocols that provide:

•Data integrity monitoring

•Data, user, and device authentication capabilities

•Data confidentiality, including encryption protocols

There are also Internet Key Exchange (IKE) capabilities that provide security association

management and key management (The RFC numbers are listed here for you to look up on the

IETF web site if you like.)

– Diffie-Hellman

• Negotiates digital certificates

Integrity and Authentication

Encapsulating Security Payload

Confidentiality, Integrity, and Authentication

Encapsulated Security Payload

IPSec Overview: Headers

• Two types: Encapsulated Security Payload

(ESP) and Authentication Header (AH)

– Data integrity-no modification of data in transit

– Origin authentication-identifies where data

originated

– AH does not provide confidentiality; industry

moving toward ESP, which does

IPSec takes an IP packet and adds two headers to it

First, it provides an authentication header, which provides knowledge that a packet originated from a trusted source It also guarantees that if a packet is changed, you know it This is not encryption It just ensures that information is not intercepted, nor has its content changed

The second header is the encapsulated security payload This does the same thing as the

authentication header and also allows you to encrypt the payload

–Outer IP header specifies

IPSec processing destination

–Inner IP header specifies

ultimate packet destination

• Transport mode:

between two hosts

–Header after IP header,

before TCP/UDP header

When you are encrypting information, there are two basic modes you can use The first and most commonly used is the Tunnel Mode This is applied to an IP tunnel between gateway devices It can also be used on remote clients talking to gateways In Tunnel Mode, the original packet is

encrypted Then the IPSec header is added (as we just talked about), along with a second IP header that corresponds to the gateway you want to talk to The flow here goes like this: information goes

to the first gateway, which encodes the payload, puts a new header on, and sends it to the second

gateway The second gateway strips the new header, decrypts the payload, checks the packet for integrity, and forwards it to the destination

Transport Mode happens between two hosts As diagrammed here, the packet header is removed, the payload is encrypted, an IPSec header is added, the first header is reattached, and the packet is forwarded

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Encryption: DES and 3DES

• Widely adopted standard

• Encrypts plain text, which becomes

“cyphertext”

• Triple DES

– The 56 bit DES algorithm run 3 times

– 112-bit triple DES includes 2 keys

– 168- bit triple DES includes 3 keys

• Accomplished on VPN client, server,

router, or firewall

IPSec provides a framework for plugging in and using many different encryption algorithms The most common are Data Encryption Standard, or DES, and Triple DES DES is lighter than Triple DES Triple DES does multiple passes over the packets This can be applied at IPSec termination points on the VPN client, a server, router, or firewall

DES is a symmetric encryption algorithm I use a key on the front-end to encrypt the data, and the same key on the back-end to decipher it to get the original data IPSec lets you re-key the DES key The end points renegotiate the DES key they wish to use So if you want to, you can make a

different key periodically and stump any hackers

As a quick disclaimer, there are export limitations on encryption technology depending upon which technology it is and where you want to send it

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Internet Key Exchange (IKE)

IPSec Next

Ifyou have two end points, the first thing they need to do is agree upon who they are The second thing they do is figure out a series of algorithms for authentication and encryption so they can talk

to each other After that, they start bulk encryption and start passing data back and forth This

process is called the IKE, or Internet Key Exchange negotiation

Once the initial handshake is agreed upon, the endpoints set up a security association that defines the parameters they will use for bulk data transfer That’s the next step, the IPSec step

Part of the initial IKE negotiation commonly uses a Diffie-Hellman algorithm This is the way the end points agree on the encryption key they will use for the bulk data transfer

Credential

Expiration

Subject Name:

“Internet, Organization, Jane Doe”

Expires: 11/30/99 Signed: CA’s Signature

Serial #: 29483756 Public key:

• Binds the subject’s identity with a public key

–Signed by a “trusted” certifying authority

• Identity proved by ability to sign using associated

private key

Digital certificates are analogous to passports or driver’s licenses It is a unique certificate for a

given user or device It contains the kinds of information listed here, including a public key, specific attributes such as a serial number or unique qualifier, an expiration date, and the subject

usage-name A “public key” is stored with the certificate

Layer 2 Tunneling Protocol (L2TP), combines PPTP and L2F

PPP Extensible Authentication Protocol (authentication only, see RFC 2284)

SOCKS protocol

The following are various VPN resources that can provide additional information on VPN’s:http://kubarb.phsx.ukans.edu/~tbird/vpn.html

http://www.usenix.org/publications/login/1999-12/features/harmful.html (requires USENIX membership)

http://www.optonline.com/plweb-cgi/fastweb?getdoc+view1+all002+1093+0++cryptographyhttp://www.ietf.org/html.charters/ipsec-charter.html

http://www.openssh.com/

http://www.uni-erlangen.de/docs/RRZE/dezentral/unix/linux/HOWTOS/mini/VPN-4.htmlhttp://www.xs4all.nl/~freeswan/

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PKI (In a Nutshell)

• PKI, the glue that binds ecommerce

– SSL is a simple, particle example

• Boils down to resolving trust

– Who is really on *both* ends of the pipe?

• Enables remote access

– VPN connectivity, email, extranets, etc.

With VPN’s, there is a big problem with key management PKI or public key infrastructure is the glue that binds all of the pieces of e-commerce together It all comes down to trust and PKI provides the inter-trust relationship needed for people to communicate

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What is PKI?

• A management structure for public keys

– Ok, we both have private/public keys Now what?

– There is more than meets the eye

• public and private encryption keys

• digital certificates

• certificate authorities

• digital signatures

• key-management protocols

PKI is a management structure for public keys We have all of these public and private keys but how

do we manage and track them? When it comes to PKI, the following are some of the key concerns:

•public and private encryption keys

•digital certificates

•certificate authorities

•digital signatures

•key-management protocols

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PKI Issues

• There are a few problems

– Competing standards, or standards still in flux

– Certification of certificate authorities

• Important issue but easy to overlook

– Cross certification between “CA’s”

– Do-it-yourself or outsource?

– User education and/or perception

PKI can get very complex very quickly because the following are some of the key problems that need

to be solved:

Competing standards, or standards still in flux

Certification of certificate authorities

Important issue but easy to overlook

Cross certification between “CA’s”

Do-it-yourself or outsource?

User education and/or perception

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Things to Know

• Most PKI is based upon X.509

– X.509v3 standard targeted CA interoperability – Movement is still slow

• Planning and deployment are critical to

success or failure

• Large scale management isn’t

necessarily a walk in the park

To sum up our brief discussion of PKI, most PKI is based upon X.509 X.509v3 standard targeted

CA interoperability, but movement towards a universal standard is slow

When is comes to PKI, it can be very complicated and may not move too fast Planning and deployment are critical to success or failure Large scale management isn’t necessarily a walk in the park

Now, lets take a look at PGP

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Secure Email

-a Simple Ex-ample

• PGP – A pioneer, still going strong

– PGP started out in 1991 as a way to bring privacy

to a very new, very public communication medium: email.

– PGP at version 2.6.2 became a de-facto standard for email encryption.

– PGP became part of Network Associates, and moved to version 6.0.X.

– PGP is now at version 6.5.8 with new features.

Phillip Zimmermann was the person that brought PGP to the world He wanted to make PGP a free software tool to keep email private, releasing the software in 1991 The United States government viewed this as a violation of the export restrictions for cryptographic software, and made his life pretty tough until the case was dropped in 1996 Though there is now a commercial version of PGP, Phil Zimmermann continues to make it possible to acquire free versions

Because it was free and very hard (at the time) to break, it became very effective in hiding data from anyone There have been many versions of PGP and many restrictions placed on it, as a result The Massachusetts Institute of Technology (MIT) distributes the new PGP and PGPNet version 6.5.8.Network Associates owns the commercial version of PGP, and in concert with MIT, distributes the free version as well