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Overview of Remote Access

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  1. Overview of Remote Access • Remote Access Management: CHAP • Remote Access:authentication, ACS & RAAS, Concept of AAA • VPN: IPSec, IPSec with IKE, PPTP • Security protocol: • TLS and SSL, SSH, S/HTTP, SET, PGP and others(e.g. S/MIME, PEM)

  2. Remote Access Technology (1) • Dial-up, remote Internet connectivity • Legacy systems • Modem dial-up • ISDN • Contemporary systems • ATM: broadband technology for both backbone, desktop. It loses its popularity to Fast Ethernet, Gigabit Ethernet and is losing ground to fibre ring based on WDMA.

  3. Remote Access Technology (2) • DSL: broadband technology that relies on the exist telephone line. The services can be asymmetric => Speed between upstream & downstream are different • Cable modems: Provide high speed access using existing cableTV infrastructure. It is usually connected all the time. • Wireless computing (mobile phone ,PDAs) => general more and more popular => 802.11 => 802.11b => 802.11g => 802.11a

  4. Remote Access Security Management • Securing enterprise remote connectivity (different ways to authenticate) • Securing external connections (VPNs, SSL, SSH etc..) • Remote access authentication systems (RADIUS and TACACS) • Remote Node authentication (PAP and CHAP) • Remote user management issues • Justification for and the validation of the use of remote computing systems • Hardware and software distribution • User support and remote assistance issues

  5. Remote ID and Authentication Technologies (1) • Password Authentication Protocol (PAP) • A remote security protocol that provides id and authentication of the node attempting to initiate the remote session. • PAP uses a static re-playable password for this. • Use clear text user id or password during communication.

  6. Remote ID and Authentication Technologies (2) • Challenge Handshake Authentication Protocol (CHAP) • Next evolution of PAP: Non-replayable “challenge / response” dialog that verifies the id of the node attempting to initiate the remote session. • CHAP is often used to enable network to network communications and is commonly used by remote access servers and xDSL, ISDN, and cable modems.

  7. Remote ID and Authentication Technologies (3) • Extensible Authentication Protocol (EAP) • Provides a framework to enable many types of authentication techniques to be used during PPP connections. • It allows such things as: • One-time passwords • Token cards • Digital signatures • Biometrics

  8. Remote Access techniques (1) • SLIP - Serial Line Internet Protocol • An older protocol developed in 1984 that allows a computer to use IP over a serial link. • SLIP only provides support for the TCP/IP protocol • does not support error correction or compression. • PPP - Point-to Point protocol • PPP is the newest and most commonly used dial-up protocol. • It includes error correction, data compression, and multi-protocol support (such as IP, IPX and ARAP).

  9. Remote Access techniques (2) • Dial-up and RAS • RAS (Remote Access Service) Server - Performs authentication by comparing the provided credentials with the database of credentials it maintains. • War-dialing - a process used by many attackers to identify remote access modems. • War-driving- a process used by attackers to drive through busy street to identify wireless access points

  10. CHAP: Challenge/Response Authentication (1) client requests a connect (2) server send a random secret key (as the challenge) to the client (3) client encrypts the random key using its own hashed password and transmits the result (as the response) to the server (4) server decrypts the secret using the stored hashed client password and compares it to the original secret key to decide whether to accept the logon Note: Both have the secret key as the common secret (i.e. login password of client). Server does not have a copy of client password, it only has a hashed version of the password.

  11. CHAP: Challenge/Response Authentication

  12. Multiple factors authentication (1) • Something you have (e.g keys, token card) • Something you know (e.g. PIN or password) • Something you are (e.g. biometrics) • 1-factor authentication • involves the party to be authenticated concerned with only one factor (e.g. know something). • 2-factor authentication • involves the party to be authenticated concerned with two factors (e.g. know something, have something, being someone)

  13. Multiple factors authentication - 2 Many e-banking web-site is now considering to use multiple factors authentication to combat attack • The smart card (or token card) actually stored holder’s unique identification. It requires holder to put the card in a reader to get its credentials. Alternatively, holder must use the card to generate a response to a challenge on screen. • Only knowing the user name and password without the card (i.e. lack the 2nd factor authentication) lead to an unsuccessful authentication. • Thus, reduce the risk of accidental release of user name / password to a faked website.

  14. ACS & Remote Access Authentication System (RAAS) • Access control is the way you control who is allowed access to the network server and what services they are allowed to use once they have access. • PPP/SLP/CHAP provide simple but not enough protection, a RASS is required • These systems provide a centralized database, which maintains user lists, passwords, and user profiles. • Authentication, authorization, and accounting (AAA) network security services provide the primary framework through which you set up access control on your router or access server

  15. Common RAAS - 1 • Remote Access Dial-In User Service (RADIUS) • provides a central authentication database for multiple remote access servers and collects accounting information about remote connections • When a user attempts to connect to RAS (e.g. firewall, access servers), s/he will be challenged for a logon name and password • RAS then forward the information to RADIUS server. Note that RAS works as a RADIUS client. • If the credentials are valid, Radius server returns affirmative reply and RAS allows the user in • If these are matched, RADIUS server returns with a rejection. Thus RAS (i.e. RADIUS client) will drop the connection

  16. Common RAAS - 2 Terminal Access Controller Access Control System (TACACS) • provides a way to centrally validate users attempting to gain access to a router or access server • services are maintained in a database on a TACACS server running, typically, on a UNIX workstation • TACACS+ • Additional features including two factors authentication

  17. What is AAA? (1) • AAA is an architectural framework for configuring a set of three independent security functions in a consistent manner. • AAA provides a modular way of performing the following services: • Authentication - Provides the method of identifying users, including login and password dialog, challenge and response, messaging support, and, depending on the security protocol you select, encryption.

  18. What is AAA? (2) • Authorization - Provides the method for remote access control, including one-time authorization or authorization for each service, per-user account list and profile, user group support, and support of IP, IPX, ARA, and Telnet. • Accounting - Provides the method for collecting and sending security server information used for billing, auditing, and reporting, such as user identities, start and stop times, executed commands (such as PPP), number of packets, and number of bytes.

  19. Benefits of using AAA • AAA provides the following benefits: • Increased flexibility and control of access configuration • Scalability • Standardized authentication methods, such as RADIUS, TACACS+, and Kerberos • Multiple backup systems available

  20. Method Lists • A method list is a sequential list that defines the authentication methods used to authenticate a user. • Method lists enable you to designate one or more security protocols to be used for authentication, thus ensuring a backup system for authentication in case the initial method fails.

  21. Typical AAA configuration A typical AAA network configuration that includes four security servers: R1 and R2 are RADIUSservers T1 and T2 are TACACS+servers

  22. AAA process (1) • Suppose the system administrator has defined a method list where R1 will be contacted first for authentication information, then R2, T1, T2, and finally the local username database on the access server itself. • When a remote user attempts to dial in to the network, the network access server (NAS) first queries R1 for authentication information. • If R1 authenticates the user, it issues a PASS response to the network access server (NAS) and the user is allowed to access the network.

  23. AAA process (2) • If R1 returns a FAIL response, the user is denied access and the session is terminated. • If R1 does not respond, then the network access server processes that as an ERROR and queries R2 for authentication information. • This pattern continues through the remaining designated methods until the user is either authenticated or rejected, or until the session is terminated. • If all of the authentication methods return errors, the network access server will process the session as a failure, and the session will be terminated.

  24. Summary : AAA model • Authentication • who are you? • concerns with user identification with password • Authorization • what can you do? what can you access? • access right: student user, root user • concerns with permission • Accounting • what did you do? How long did you use it? How often did you do it. • I access the host xxx with telnet 15 times. • concerns with tracking and logging

  25. Quiz Which is NOT an AAA benefit? a) Scalability b) Automatic installation and configuration c) Flexibility d) Multiple implementation methods provide redundancy

  26. VPN – Virtual Private Networks Two simultaneous techniques to guarantee privacy: 1. Encryption and authentication 2. Tunneling

  27. Private Network • reliable, total control (secure in nature) • proven technology • very expensive, does not meet the need of today’s Internet traffic

  28. What is VPN? - 1 • A Virtual Private Network (VPN) is defined as network connectivity deployed on ashared infrastructure with the same policies and security as a private network • A VPN is an alternative WAN infrastructure that replaces or augments existing private networks.

  29. What is VPN? - 2 • VPN = tunneling + encryption • Tunneling is a method of using an internetwork infrastructure to transfer data for one network over another network. • The tunneling protocol encapsulates the frame in an additional header.

  30. Characteristics of VPN • traffic is encrypted so as to prevent eavesdropping • encryption (use pre-shared key or public keys) • remote site is authenticated, two ways: • user needed to be authenticated • site needed to be authenticated • multiple protocols are supported by VPNs • transparent to users • connection is point-to-point • a unique channel is set up between two end points • multiple channels can exist

  31. Benefits of VPN - 1 • User can have same access to network services while work outside from organization without the requirement for expensive long-distance dial-in (Remote VPN) • Different sites of the organization can be connected together via public networks as if they are connected as a intranet (site-to-site VPN) • without the use of expensive lease line • cost / performance is very good

  32. Benefits of VPN - 2 Summary • Cost Savings • Flexibility • Scalability • Reduced Technology Support • Reduced Equipment Requirement

  33. VPN Classification OSI Layer: Layer 2, Layer 3, Layer 7

  34. VPN Appliance • Three types of VPN appliances • hardware based • speed and security • software based • general-purpose computer (in the form of a software module running as a firewall) • web-based • user use browser (VPN client) and connect to the VPN via SSL (on encryption and user authentication) • require to use software module such as Java virtual machines • limited to certain application supported by Internet browser

  35. VPN Solution Requirements (1) • User Authentication • The solution must verify the VPN client’s identity and restrict VPN access to authorized users only. It must also provide audit and accounting records to show who connected and for how long. • Address Management • The solution must assign a VPN client an address on the intranet and ensure that addresses used on the intranet are kept private.

  36. VPN Solution Requirements (2) • Data Encryption • Data carried on the public network must be rendered unreadable. • Key Management • The solution must generate and refresh encryption keys for the encrypted data.

  37. IPSec (1) • IPSec secures packets at the network layer in a manner that is transparent to the users and also to the protocols that lie above the transport layer. • End-to-end security model that only endpoints of a communication need to the IPSec aware not the transit network devices such as switches and routers. • End-to-end capability can be • Client to client or • Gateway to gateway • It encapsulates IP packets with an additional IP header before sending them across a LAN or the Internet.

  38. IPSec (2) • IPSec is a collection of protocols designed by IETF to provide security for a packet carried by the Internet to ensure: • Confidentiality - IPSec traffic is encrypted. • Authentication - IPSec traffic is digitally signed with the shared encrypted key, so the receiver can verify that the IPSec peer sent it. • Integrity - IPSec traffic contains a cryptographic checksum (message digest) that incorporates the encryption key. The receiver can verify that the packet was not modified in transit.

  39. IPSec (3) • Before IPSec-format packets can be exchanged, both peers must agree on some parameters known as security association(SA) • SA contains information about agreeing on • cryptographic algorithm (DES or 3DES) • Hash algorithm (MD5 or SHA) • Protocol used (AH or ESP) • Authentication method (Kerberos, public key encryption or pre-shared secret) • key expiration time (refresh and regeneration) • Diffie-Hellman group that allows the Oakley protocol to manage the key exchange process.

  40. Format of SAs • A single Security Association (SA) is required between two parties to determine which encryption & authentication algorithm to use. • If a file server has several simultaneous sessions with multiple clients a number of different SAs will be defined, one for each connection via IPSec. • SA is a combination of a destination address, a security protocol, and a unique identificationvalue called a Security Parameter Index (SPI) • SPI is a 32 bit identifier derived from destination host’s IP address and a randomly assigned number. • connectionless IP protocol changed to connection-oriented before security can be applied • Bi-directional (incoming and outgoing) communication requires two Security Associations.

  41. IPSec Framework

  42. IPSec : AH and ESP (1) • IPSec support two main protocols • Authentication Header (AH) : support integrity, authentication • provide anti-replay service • a header in an IP packet contains • cryptographic checksum (similar to message digest) for the contents of the packet • does not provide encryption for the contents of the tunnel, it only provides integrity and authenticity

  43. IPSec : AH and ESP - 2 2. Encapsulating Security Payload (ESP): supports authentication, data integrity, and confidentiality, • define a new header to be inserted into the IP packet • provide privacy for the tunneled packets • two encrypted algorithm are being used: DES, 3DES • AES as the new standard that not yet popular

  44. AH vs. ESP Authentication Header Router A Router B All data in clear text The Authentication Header provides Authentication and Integrity Encapsulating Security Payload Router B Router A Data payload is encrypted The Encapsulating Security Payload provides Encryption, Authentication and Integrity

  45. Why still AH? • Do we still need AH? • No! But AH had been commercially available for a long time, these kinds of products (protocol) still remain in use • it is common for system require less security level and require less system resources (CPU processing power)

  46. Authentication Header (AH) (1) • AH Protocol is designed to authenticate the source host and to ensure integrity of the payload carried by the IP packet • calculate a message digest, using hash function and symmetric key, and insert the digest in the AH • The AH is put in the appropriate location based on the mode (transport or tunnel)

  47. Transport vs. Tunnel Mode (1) AH and ESP can be used in either transport or tunnel modes • Transport mode: IPSec header is added between the IP header and the rest of the packet • Transport mode protects the payload of the packet but leaves the original IP address in the clear. The original IP address is used to route the packet through the Internet. • Transport mode is used between hosts.

  48. Transport vs. Tunnel Mode (2) • Tunnel mode:IPSec header is added in front of the original IP header. • Tunnel mode provides security for the whole original IP packet. The original IP packet is encrypted. • The encrypted packet is encapsulated in another IP packet. The outside IP address denotes the destination tunnel endpoint (original IP address is the host address) • Tunnel mode is commonly used between tunnel gateways

  49. Authentication Header (AH) (2)

  50. Transport vs. Tunnel Mode (AH) • AH is incompatible with NAT because NAT changes the source IP address which breaks the AH header and causes the packets to be rejected by the IPSec peer.