Applications of IPSec

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					          IPSec




IPSec.1           CEENet ‘2000 - Understanding and using Remote Access and VPN services
          Applications of IPSec

          •   IPSec provides the capability to secure
              communications across a LAN, across private
              and public WANs, and across the Internet.
              Examples of its use include:
          •   Secure branch office connectivity over the
              Internet
          •   Secure remote access over the Internet




IPSec.2                CEENet ‘2000 - Understanding and using Remote Access and VPN services
          IPSec Explained


          With thanks to William Stallings and,




IPSec.3                CEENet ‘2000 - Understanding and using Remote Access and VPN services
          Applications of IPSec

          •   Establishment of extranet and intranet
              connectivity with partners
          •   Enhancement of electronic commerce security
          •   encrypt or authenticate all traffic at the IP level




IPSec.4                 CEENet ‘2000 - Understanding and using Remote Access and VPN services
          Applications of IPSec


          •   Using IPSec all distributed applications can be
              secured,
              – Remote logon,
              – client/server,
              – e-mail,
              – file transfer,
              – Web access
              – etc.
IPSec.5                CEENet ‘2000 - Understanding and using Remote Access and VPN services
          Applications of IPSec




IPSec.6         CEENet ‘2000 - Understanding and using Remote Access and VPN services
          Where can IPSec be used


          •   These protocols can operate in
              – networking devices,
                 • such as a router or firewall
              – or they may operate directly on the workstation or
                server.




IPSec.7                CEENet ‘2000 - Understanding and using Remote Access and VPN services
          How can IPSec be used


          •   Secure Communications between devices
              – Workstation to Workstation
              – Protection against data changes
                 • Accidental or Intentional
              – Contents can be hidden
          •   Secure communicatoins through IPSec tunnels




IPSec.8                CEENet ‘2000 - Understanding and using Remote Access and VPN services
          Benefits of IPSec


          •   The benefits of IPSec include:
              – Strong security that can be applied to all traffic
                crossing the perimeter.
              – Transparent to applications.
              – No need to change software on a user or server
                system
                 • When IPSec is implemented in a router or firewall



IPSec.9                CEENet ‘2000 - Understanding and using Remote Access and VPN services
           Benefits of IPSec


           •   The benefits of IPSec include:
               – IPSec can be transparent to end users.
               – There is no need to train users on security
                 mechanisms
               – PSec can provide security for individual




IPSec.10                CEENet ‘2000 - Understanding and using Remote Access and VPN services
           Is IPSec the Right Choice?


           •   For transport level (personal) services IPSec
               must be a part of the network code deployed on
               all participating platforms.
           •   Individual protocols may implement their own
               security:
                – E-Mail: PGP
                – Web: SSL
                – E-Commerce: SET
                – Etc.
           •   As a tunnel protocol it is available to all services
               on the network.
IPSec.11                CEENet ‘2000 - Understanding and using Remote Access and VPN services
           The Scope of IPSec


           •   IPSec provides three main facilities
               – An authentication-only function,
                   • Referred to as Authentication Header (AH)
               – Acombined authentication/ encryption function
                   • Called Encapsulating Security Payload (ESP)
               – A key exchange function.
                   • IKE (ISAKMP / Oakley)


IPSec.12                 CEENet ‘2000 - Understanding and using Remote Access and VPN services
           The Scope of IPSec


           •   Both authentication and encryption are generally
               desired,
               – (1) assure that unauthorized users do not penetrate the
                 virtual private network
               – (2) assure that eavesdroppers on the Internet cannot read
                 messages sent over the virtual private network.

           •   Because both features are generally desirable,
               most implementations are likely to use ESP
               rather than AH.


IPSec.13                 CEENet ‘2000 - Understanding and using Remote Access and VPN services
           Security Associations (SA)


           •   Used for both the authentication (AH) and
               confidentiality (ESP)
           •   A one-way relationship between a sender and a
               receiver that affords security services to the
               traffic carried on it.
               – If a peer relationship is needed, for two-way
                 secure exchange, then two security associations
                 are required.
           •   Security services are afforded to an SA for the
               use of AH or ESP, but not both.
IPSec.14                CEENet ‘2000 - Understanding and using Remote Access and VPN services
           Security Associations (SA)


           •   Each SA is uniquely identified by three
               parameters:
               – Security Parameters Index (SPI)
               – IP destination address
               – Security protocol identifier




IPSec.15                CEENet ‘2000 - Understanding and using Remote Access and VPN services
           Security Associations (SA)


           •   Security Parameters Index (SPI)
               – The SPI is a bit string assigned to the SA that has
                 local significance only.
               – The SPI is carried in AH and ESP headers to
                 enable the receiving system to select the SA
                 under which a received packet will be processed.




IPSec.16                CEENet ‘2000 - Understanding and using Remote Access and VPN services
           Security Associations (SA)


           •   IP destination address
               – The IP address of the destination endpoint of the
                 SA
                  • May be an end-user system
                  • Or, a network system such as a firewall or router.
               – Currently, only unicast addresses are allowed



IPSec.17                CEENet ‘2000 - Understanding and using Remote Access and VPN services
           Security Associations (SA)


           •   Security Protocol Identifier
               – Indicates which IPSec protocol is in use on the SA
                   • AH (Authentication only)
                   • ESP (complete encryption and possibly
                    Authentication)




IPSec.18                CEENet ‘2000 - Understanding and using Remote Access and VPN services
           Security Associations (SA)

           •   For any IP packet, the security association is
               uniquely identified by
           •   the destination address
           •   SPI in the enclosed extension header
               (AH or ESP).




IPSec.19                CEENet ‘2000 - Understanding and using Remote Access and VPN services
           Security Associations (SA)


           •   IPSec includes a security association database
           •   The database defines the parameters associated
               with each SA




IPSec.20               CEENet ‘2000 - Understanding and using Remote Access and VPN services
           Security Associations (SA)


           •   Each SA is defined by (contains):
               – Sequence number counter
               – Sequence counter overflow
               – Anti-replay window
               – AH information
               – ESP information
               – Lifetime of this security association
               – IPSec protocol mode
               – Path MTU

IPSec.21                  CEENet ‘2000 - Understanding and using Remote Access and VPN services
           Security Associations (SA)

           •   Sequence number counter
               – A 32-bit value used to generate the sequence
                 number field in AH or ESP headers
           •   Sequence counter overflow
               – A flag indicating whether overflow of the sequence
                 number counter should generate an auditable
                 event and prevent further transmission of packets
                 on this SA
           •   Anti-replay window
               – Used to determine whether an inbound AH or ESP
                 packet is a replay, by defining a sliding window
                 within which the sequence number must fall
IPSec.22                CEENet ‘2000 - Understanding and using Remote Access and VPN services
           Security Associations (SA)


           •   AH information
               – Authentication algorithm, keys, key lifetimes, and
                 related parameters being used with AH
           •   ESP information
               – Encryption and authentication algorithm, keys,
                 initialization values, key lifetimes, and related
                 parameters being used with ESP
           •   IPSec protocol mode
               – Tunnel, transport, or wildcard (required for all
                 implementations)
IPSec.23                CEENet ‘2000 - Understanding and using Remote Access and VPN services
           Security Associations (SA)


           •   Lifetime of this security association
               – A time interval or byte count after which an SA
                 must be replaced with a new SA (and new SPI) or
                 terminated, plus an indication of which of these
                 actions should occur
           •   Path MTU
               – Any observed path maximum transmission unit
                 (maximum size of a packet that can be transmitted
                 without fragmentation) and aging variables
                 (required for all implementations)
IPSec.24                CEENet ‘2000 - Understanding and using Remote Access and VPN services
           Security Associations (SA)


           •   The key management mechanism that is used to
               distribute keys is coupled to the authentication
               and privacy mechanisms only by way of the
               Security Parameters Index.
           •   Therefore, authentication and privacy are
               specified independent of any specific key
               management mechanism.




IPSec.25                CEENet ‘2000 - Understanding and using Remote Access and VPN services
           Authentication Header (AH)


           •   Provides support for data integrity and
               authentication of IP packets
           •   Ensures that content changes of a packet in
               transit can be detected
           •   Enables an end system or network device to
               authenticate the user or application and filter
               traffic accordingly
           •   Prevents the address spoofing attacks
           •   Guards against the replay attack

IPSec.26                CEENet ‘2000 - Understanding and using Remote Access and VPN services
           IPSec Authentication Header




IPSec.27         CEENet ‘2000 - Understanding and using Remote Access and VPN services
           Authentication Header (AH)

           •   Authentication is based on the use of a Message
               Authentication Code (MAC)
           •   The two parties must share a secret key.
           •   Uses the following elements to guarantee data
               integrity
               – Payload length
               – SPI
               – Sequence number
               – Integrity Check Value (ICV) or Message
                 Authentication Code (MAC)
IPSec.28                CEENet ‘2000 - Understanding and using Remote Access and VPN services
           Anti-Replay Service


           •   A replay attack is one in which an attacker
               obtains a copy of an authenticated packet and
               later transmits it to the intended destination.
           •   The receipt of duplicate, authenticated IP packets
               may disrupt service in some way or may have
               some other undesired consequence.
           •   The Sequence Number field is designed to thwart
               such attacks.



IPSec.29                CEENet ‘2000 - Understanding and using Remote Access and VPN services
           Anti-Replay Service

           •   When a new SA is established, the sender initializes a sequence
               number counter to 0

           •   Each time that a packet is sent on this SA, the sender increments
               the counter and places the value in the Sequence Number field

                – Thus, the first value to be used is 1
           •   If anti-replay is enabled (the default), the sender must not allow
               the sequence number to cycle past 232 – 1 back to zero

                – Otherwise, there would be multiple valid packets with the same
                  sequence number

           •   If the limit of 232 – 1 is reached, the sender should terminate this
               SA, and negotiate a new SA with a new key



IPSec.30                    CEENet ‘2000 - Understanding and using Remote Access and VPN services
           Anti-Replay Service

           •   Because IP is a connectionless, unreliable
               service, the protocol does not guarantee that
               packets will be delivered in order and does not
               guarantee that all packets will be delivered
           •   Therefore, the IPSec authentication document
               dictates that the receiver should implement a
               window of size W, with a default of W = 64
           •   The protocol describes means to determine that a
               sequence number is correct in respect to it's
               position in or above the window


IPSec.31                CEENet ‘2000 - Understanding and using Remote Access and VPN services
           Message Authentication Code

           •   Uses an algorithm known as HMAC
           •   HMAC takes as input a portion of the message and a secret
               key and produces a MAC as output
           •   This MAC value is stored in the Authentication Data field of
               the AH header
           •   The calculation takes place over the entire enclosed TCP
               segment plus the authentication header
           •   When this IP packet is received at the destination, the same
               calculation is performed using the same key
               – If the calculated MAC equals the value of the received MAC,
                  then the packet is assumed to be authentic


IPSec.32                  CEENet ‘2000 - Understanding and using Remote Access and VPN services
           Message Authentication Code

           •   The authentication data field is calculated over:
               – IP header fields that either do not change in transit
                 (immutable) or that are predictable in value upon
                 arrival at the endpoint for the AH SA
               – The AH header other than the Authentication Data
                 field
               – The entire upper-level protocol data, which is
                 assumed to be immutable in transit (for instance, a
                 TCP segment or an inner IP packet in tunnel
                 mode)

IPSec.33                 CEENet ‘2000 - Understanding and using Remote Access and VPN services
           Message Authentication Code


           •   For IPv4, examples of immutable fields are
               – Internet Header Length
               – Source Address.
           •   An example of a mutable but predictable field is
               the Destination Address




IPSec.34                CEENet ‘2000 - Understanding and using Remote Access and VPN services
           Encapsulating Security
           Payload (ESP)

           •   Provides confidentiality service, including
               – message contents and limited traffic flow
                 confidentiality
               – As an optional feature, ESP can also provide a
                 authentication services like AH




IPSec.35                CEENet ‘2000 - Understanding and using Remote Access and VPN services
           IPSec ESP Format




IPSec.36         CEENet ‘2000 - Understanding and using Remote Access and VPN services
           Encapsulating Security
           Payload (ESP)

           •   Security Prameters Index (32bits)
           •   Sequence Number (32 bits)
           •   Payload Data (variable)
           •   Padding (0–255 bytes)
           •   Pad Length (8 bits)
           •   Next Header (8 bits)
           •   Authentication Data (variable


IPSec.37                CEENet ‘2000 - Understanding and using Remote Access and VPN services
           Encapsulating Security
           Payload (ESP)

           •   Security Prameters Index (32bits)
               – Identifies a security association
           •   Sequence Number (32 bits)
               – A monotonically increasing counter value.
           •   Payload Data (variable)
               – A transport-level segment (transport mode) or IP
                 packet (tunnel mode) that is protected by
                 encryption.


IPSec.38                CEENet ‘2000 - Understanding and using Remote Access and VPN services
           Encapsulating Security
           Payload (ESP)

           •   Padding (0–255 bytes)
               – Extra bytes that may be required if the encryption
                 algorithm requires the plaintext to be a multiple of
                 some number of octets
           •   Pad Length (8 bits)
               – Indicates the number of pad bytes immediately
                 preceding this field




IPSec.39                CEENet ‘2000 - Understanding and using Remote Access and VPN services
           Encapsulating Security
           Payload (ESP)

           •   Next Header (8 bits)
               – Identifies the type of data contained in the payload
                 data field by identifying the first header in that
                 payload (for example, an upper-layer protocol
                 such as TCP)
           •   Authentication Data (variable)
               – A variable-length field (must be an integral
                 number of 32-bit words) that contains the integrity
                 check value computed over the ESP packet minus
                 the Authentication Data field
IPSec.40                CEENet ‘2000 - Understanding and using Remote Access and VPN services
           Encryption and Authentication
           Algorithms

           •   The Payload Data, Padding, Pad Length, and Next
               Header fields are encrypted by the ESP service.
           •   The current IPSec specification dictates that a
               compliant implementation must support the Data
               Encryption Standard (DES).




IPSec.41               CEENet ‘2000 - Understanding and using Remote Access and VPN services
           Encryption and Authentication
           Algorithms

           •   A number of other algorithms have been
               assigned identifiers and could, therefore, be used
               for encryption;
           •   These include
                – Three-key Triple DES
                – RC5
                – International Data Encryption Algorithm (IDEA)
                – Three-key Triple IDEA
                – CAST
                – Blowfish
IPSec.42                CEENet ‘2000 - Understanding and using Remote Access and VPN services
           Transport and Tunnel Modes


           •   AH and ESP each support two modes of use
               –Transport mode
               –Tunnel mode




IPSec.43               CEENet ‘2000 - Understanding and using Remote Access and VPN services
           Transport and Tunnel Modes

                                         Orig IP
                                 IPv4    Header       TCP               Data


                                                   Original IP Packet


                                                      Authenticated
                                                            Encrypted

                              Orig IP    ESP                                    ESP ESP
                       IPv4   Header      Hdr      TCP           Data           Trlr Auth

                                                     Transport Mode


                                                         Authenticated
                                                             Encrypted

                        New IP     ESP     Orig IP                                   ESP ESP
                IPv4    Header     Hdr     Header         TCP            Data        Trlr Auth

                                                      Tunnel Mode




IPSec.44          CEENet ‘2000 - Understanding and using Remote Access and VPN services
           Transport Mode

           •   Provides protection primarily for upper-layer
               protocols.
               – Extends to the payload of an IP packet.
                  • TCP
                  • UDP
                  • (ICMP), etc.
                                                   Authenticated
                                                        Encrypted

                               Orig IP   ESP                             ESP ESP
                        IPv4   Header    Hdr    TCP           Data       Trlr Auth

                                                  Transport Mode




IPSec.45                 CEENet ‘2000 - Understanding and using Remote Access and VPN services
           Transport Mode

           •   Typically used for end-to-end communication
               between two hosts
               – for example, between a workstation and a server,
                 or between two servers
           •   When a host runs AH or ESP over IPv4, the
               payload is the data that normally follows the IP
               header
                                                  Authenticated
                                                       Encrypted

                              Orig IP   ESP                             ESP ESP
                       IPv4   Header    Hdr    TCP           Data       Trlr Auth

                                                 Transport Mode




IPSec.46                CEENet ‘2000 - Understanding and using Remote Access and VPN services
           Transport Mode


           •   ESP in transport mode encrypts and optionally
               authenticates the IP payload but not the IP header
           •   AH in transport mode authenticates the IP
               payload and selected portions of the IP header


                                                  Authenticated
                                                       Encrypted

                              Orig IP   ESP                             ESP ESP
                       IPv4   Header    Hdr    TCP           Data       Trlr Auth

                                                 Transport Mode




IPSec.47                CEENet ‘2000 - Understanding and using Remote Access and VPN services
           Transport Mode


           •   As an example, consider a Telnet session within
               an ESP packet in transport mode
               – The IP header would contain 51 in the Next
                 Header field
               – In the ESP header, the Next Header field would be
                 6 for TCP
               – Within the TCP header, Telnet would be identified
                 as port 23



IPSec.48               CEENet ‘2000 - Understanding and using Remote Access and VPN services
           Transport Mode


           •   Transport mode operation may be summarized
               for ESP as follows:
               – At the source, the block of data consisting of the
                 ESP trailer plus the entire transport-layer segment
                 is encrypted
               – The plaintext of this block is replaced with its
                 ciphertext to form the IP packet for transmission
               – Authentication is added if this option is selected

IPSec.49                CEENet ‘2000 - Understanding and using Remote Access and VPN services
           Transport Mode


            – The packet is then routed to the destination
            – Each intermediate router needs to examine and
              process the IP header plus any plaintext IP
              extension headers but will not need to examine
              the ciphertext
            – The destination node examines and processes the
              IP header plus any plaintext IP extension headers




IPSec.50            CEENet ‘2000 - Understanding and using Remote Access and VPN services
           Transport Mode



            – Then, on the basis of the SPI in the ESP header,
              the destination node decrypts the remainder of the
              packet to recover the plaintext transport-layer
              segment
            – This process is similar for AH, however the
              payload (upper layer protocol) is not encrypted




IPSec.51             CEENet ‘2000 - Understanding and using Remote Access and VPN services
           Tunnel Mode


           •   Tunnel mode encapsulates an entire IP packet
               within an IP packet to ensure that no part of the
               original packet is changed as it is moved through
               a network
           •   The entire original, or inner, packet travels
               through a tunnel from one point of an IP network
               to another
               – No routers along the way need to examine the
                 inner IP header                             Authenticated
                                                                 Encrypted

                                 New IP    ESP    Orig IP                              ESP ESP
                          IPv4   Header    Hdr    Header      TCP            Data      Trlr Auth

                                                            Tunnel Mode
IPSec.52                CEENet ‘2000 - Understanding and using Remote Access and VPN services
           Tunnel Mode


           •   Tunnel mode is used when one or both ends of
               an SA is a security gateway, such as a firewall or
               router that implements IPSec, etc.




                                                             Authenticated
                                                                 Encrypted

                                 New IP    ESP    Orig IP                              ESP ESP
                          IPv4   Header    Hdr    Header      TCP            Data      Trlr Auth

                                                            Tunnel Mode
IPSec.53                CEENet ‘2000 - Understanding and using Remote Access and VPN services
           Tunnel Mode


           •   With tunnel mode, a number of hosts on networks
               behind firewalls may engage in secure
               communications without implementing IPSec.
           •   The unprotected packets generated by such
               hosts are tunneled through external networks
           •   These paths use SAs set up by the IPSec process
               in the firewall or secure router at the boundary of
               the local network
                                                             Authenticated
                                                                 Encrypted

                                 New IP    ESP    Orig IP                              ESP ESP
                          IPv4   Header    Hdr    Header      TCP            Data      Trlr Auth

                                                            Tunnel Mode
IPSec.54                CEENet ‘2000 - Understanding and using Remote Access and VPN services
           Tunnel Mode


           •   Transport mode is suitable for protecting
               connections between hosts that support the ESP
               feature




                                                            Authenticated
                                                                Encrypted

                                New IP    ESP    Orig IP                              ESP ESP
                         IPv4   Header    Hdr    Header      TCP            Data      Trlr Auth

                                                           Tunnel Mode
IPSec.55               CEENet ‘2000 - Understanding and using Remote Access and VPN services
           Tunnel Mode

           •   Tunnel mode is useful in a configuration that
               includes a firewall or other sort of security
               gateway that protects a trusted network from
               external networks
               – Encryption occurs only between an external host
                 and the security gateway or between two security
                 gateways
               – This setup relieves hosts on the internal network
                 of the processing burden of encryption and
                 simplifies the key distribution task by reducing the
                 number of needed keys

IPSec.56                CEENet ‘2000 - Understanding and using Remote Access and VPN services
           Transport and Tunnel Modes




IPSec.57         CEENet ‘2000 - Understanding and using Remote Access and VPN services
           Tunnel Mode

           •   The user system prepares an inner IP packet with
               a destination address of the target host on the
               internal LAN.
               – For a Telnet session, this packet would be a TCP
                 packet with the original SYN flag set with a
                 destination port set to 23.
           •   This entire IP packet is prefixed by an ESP
               header; then the packet and ESP trailer are
               encrypted and Authentication Data may be added.



IPSec.58                CEENet ‘2000 - Understanding and using Remote Access and VPN services
           Tunnel Mode

           •   The Next Header field of the ESP header would be
               decimal 4 for IP-in-IP, indicating that the entire
               original IP packet is contained as the ìpayload
           •   The resulting block is encapsulated with a new IP
               header whose destination address is the firewall
               – This forms the outer IP packet
               – The Next Header field for this IP packet is 50 for
                 ESP




IPSec.59                CEENet ‘2000 - Understanding and using Remote Access and VPN services
           Tunnel Mode


           •   The outer packet is routed to the destination
               firewall.
               – Each intermediate router needs to examine and
                 process the outer IP header plus any outer IP
                 extension headers but does not need to examine
                 the ciphertext.




IPSec.60                CEENet ‘2000 - Understanding and using Remote Access and VPN services
           Tunnel Mode


           •   The destination firewall examines and processes
               the outer IP header plus any outer IP extension
               headers
               – On the basis of the SPI in the ESP header, the
                 gateway decrypts the remainder of the packet to
                 recover the plaintext inner IP packet
           •   This inner packet (tunnel contents) is then
               transmitted on the internal network



IPSec.61                CEENet ‘2000 - Understanding and using Remote Access and VPN services
           Tunnel Mode


           •   The inner packet is routed through zero or more
               routers in the internal network to the destination
               host
               – The receiver would have no indication that the
                 packet had been encapsulated and protected by
                 the tunnel between the user system and the
                 gateway.
               – It would see the packet as a request to start a
                 Telnet session and would respond back with a
                 TCP SYN / ACK

IPSec.62                CEENet ‘2000 - Understanding and using Remote Access and VPN services
           Tunnel Mode


           •   The return packet would go back to the gateway.
           •   The gateway would encapsulate that packet into
               an IPSec packet and transport it back to the user
               system through this tunnel, etc




IPSec.63                CEENet ‘2000 - Understanding and using Remote Access and VPN services
           Key Management

           •   Manual: Configures each system with its own
               keys and with the keys of other communicating
               systems.
                – This is practical for small, relatively static
                  environments.




IPSec.64                CEENet ‘2000 - Understanding and using Remote Access and VPN services
           Key Management

           •   Automated: Enables on-demand creation of keys
               for SAs and facilitates the use of keys in a large
               distributed system with an evolving
               configuration.
                – An automated system is the most flexible…
                – But requires more effort to configure and requires
                  more software, so smaller installations are likely to
                  opt for manual key management.




IPSec.65                 CEENet ‘2000 - Understanding and using Remote Access and VPN services
           Key Management


           •   Default automated key management protocol for
               IPSec is referred to as Internet Key Exchange
               (IKE)
           •   IKE provides a standardized method for
               dynamically authenticating IPSec peers,
               negotiating security services, and generating
               shared keys




IPSec.66                CEENet ‘2000 - Understanding and using Remote Access and VPN services
           Key Management


           •   IKE has evolved from many different protocols
               and can be thought of as having two distinct
               capabilities
               – ISAKMP (Key Management)
               – Oakley (Key Distribution)




IPSec.67               CEENet ‘2000 - Understanding and using Remote Access and VPN services
           Key Management


           •   ISAKMP (Pronounced Ice-Uh-Kamp)
               – provides a framework for Internet key
                 management
               – provides the specific protocol support, including
                 formats, for negotiation of security attributes
               – Does not dictate a specific key exchange
                 algorithm
                  • Consists of a set of message types that enable the
                    use of a variety of key exchange algorithms.


IPSec.68                CEENet ‘2000 - Understanding and using Remote Access and VPN services
           Key Management

           •   The actual key exchange mechanism in IKE is
               derived from Oakley
           •   Plus several other key exchange protocols that
               had been proposed for IPSec
           •   Key exchange is based on the use of the Diffie
               Hellman algorithm
               – But provides added security
               – In particular, Diffie-Hellman alone does not authenticate the
                 two users that are exchanging keys, making the protocol
                 vulnerable to impersonation
               – IKE includes mechanisms to authenticate the users

IPSec.69                  CEENet ‘2000 - Understanding and using Remote Access and VPN services
           Public Key Certificates


           •   An important element of IPSec key management
               is the use of public key certificates
           •   A public key certificate is provided by a trusted
               Certificate Authority (CA) to authenticate a user's
               public key
           •   The essential steps include…




IPSec.70                CEENet ‘2000 - Understanding and using Remote Access and VPN services
           Public Key Certificates


           •   Step 1
               – Client software creates a pair of keys, one public
                 and one private
               – The client prepares an unsigned certificate that
                 includes a user ID and the user's public key
               – The client then sends the unsigned certificate to a
                 CA in a secure manner




IPSec.71                CEENet ‘2000 - Understanding and using Remote Access and VPN services
           Public Key Certificates


           •   Step 2
               – A CA creates a signature by calculating the hash
                 code of the unsigned certificate and encrypting the
                 hash code with the CA's private key
                  • The encrypted hash code is the signature
               – The CA attaches the signature to the unsigned
                 certificate and returns the now signed certificate to
                 the client



IPSec.72                CEENet ‘2000 - Understanding and using Remote Access and VPN services
           Public Key Certificates


           •   Step 3
               – The client may send its signed certificate to any
                 other user
               – That user may verify that the certificate is valid by
                  • Calculating the hash code of the certificate (not
                    including the signature)
                  • Decrypting the signature using the CA's public key
                  • Comparing the hash code to the decrypted
                    signature.


IPSec.73                CEENet ‘2000 - Understanding and using Remote Access and VPN services
           Public Key Certificates

           •   If all users subscribe to the same CA, then there
               is a common trust of that CA
           •   User certificates can be placed in the directory
               for access by all users.
           •   Or a user can transmit his or her certificate
               directly to other users.
               – In either case, once B is in possession of A's
                 certificate, B has confidence that messages it
                 encrypts with A's public key will be secure from
                 eavesdropping and that messages signed with A's
                 private key are unforgeable
IPSec.74                CEENet ‘2000 - Understanding and using Remote Access and VPN services
           Public Key Certificates


           •   If there is a large community of users, it may not
               be practical for all users to subscribe to the same
               CA
           •   Because it is the CA that signs certificates, each
               participating user must have a copy of the CA's
               own public key to verify signatures
           •   This public key must be provided to each user in
               an absolutely secure



IPSec.75                CEENet ‘2000 - Understanding and using Remote Access and VPN services
           Recommended Web Sites


           •   The IPSec Working Group of the IETF. Charter for
               the group and latest RFCs and Internet Drafts for
               IPSec:
               – http://ietf.org/html.charters/ipsec-charter.html
           •   IPSec Resources: List of companies
               implementing IPSec, implementa-tion survey, and
               other useful material:
               – http://web.mit.edu/tytso/www/ipsec/index.html

IPSec.76                 CEENet ‘2000 - Understanding and using Remote Access and VPN services

				
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