A CGA based Source Address Authentication Method in IPv6 Access Network(CSA)

Guang Yao, Jun Bi and Pingping LinTsinghua University

APAN26Queenstown, New Zealand

Aug 4, 2008

Outline

• Background of IP Spoofing• Related Work• CSA Mechanism• Evaluation and Experiment

1 Background of IP Spoofing

• Attackers can easily use deliberately or randomly set source address to send packets.

• Such packets can be used in various network attacks, e.g., SYN flooding, Smurf, Man-In-The-Middle.

• When an attacker uses IP spoofing , it will be very hard to trace him.

• According to the observation of CAIDA, there are at least 4000 spoofing attacks per week.

An Example of IP Spoofing Attack

Spoof Source Address=10.10.1.1

Amplified Response

Amplified Response

2 Related Works

• There are three kinds of prevention methods– Filtering on path– End-to-End Authentication– Traceback

• Filtering in the access network belongs to “Filtering on path”. It filters spoofing packets nearest to their source, and limits the damage of these packets to the minimum.

Access Network Mechanisms

• Ingress Filtering– Effective but has coarse granularity

• IP Source Guard– For IPv4 only– Cannot be used in a network without switch

• Signature Based Authentication– Only allow user to have a fixed address– Need PKI to authenticate the identity of user

3 CSA Mechanism

• Outline– Summary of Requirements– Overview of Procedure– New Ideas

Summary of Requirements for A IPv6 Access Network Mechanism

• Host level filtering granularity• Light-weight in both deployment and authentication• Suit All Address Assignment Methods in IPv6

– Stateless Autoconfiguration– DHCP– Manual Configuration– Cryptographically– Private

• Allow an interface to be assigned multiple addresses

Overview of Procedure• Phase1: Address Authorization (5 steps)

(4) Check whether identifier H can use the required

address A

(3) I’m H and Irequire to use address A

(5) Return a “signature seed” for future authentication

(2) An identifier is used to show the

applicant is H

(1) Prepare an address A

Overview of Procedure

• Phase2: Address Authentication

Add Signature

Check Signature and Remove it

Generate Signature based on “signature

seed”

New Ideas

• Phase 1: Address Authorization– Use Host Identifier to achieve host level granularity– Router authorizes the request address based on the

knowledge of address assignment

• Phase 2: Address Authentication– Light-weight signature generation

• Pseudo Random Number Generation– Light-weight signature adding and removal

• Address Rewrite

Host Identifier• Host generates a public key pair first.• For anonymity address owner (DHCP,SAC,CGA,Privacy),

• identifier = hash(Public Key) [Described in CGA]• For any address Assignment mechanism involving manual

configuration, • identifier = hash(Public Key + Share Secret ).

The Share Secret is a bit string allocated to the host with address by network administrator.

• The identifier must appear with the public key and a signature on the whole packet computed by the private key. And the packet must contain a nonce to prevent replay attack.

• Attacker can get the identifier and the public key by sniffer, but cannot generate a correct signature.

Authorization on the Knowledge of Address Assignment

• The knowledge of address assignment:– Manual Configuration: Re-compute the identifier

using the shared secret of the address owner.– SAC/Privacy/CGA: The address has not been

registered by another node. In CGA case, the request address must be a correct CGA address computed on the public key.

– DHCP: The identifier in the request packet must be the one which has been used to apply address from DHCP server. [See next page]

Address Allocation in DHCP Case

Source address set to theCGA identifier

Record the CGA identifier

Record the address allocated.Bind the identifier and the address. DHCP Solicitation

Light-weight Signature Generation

• Signature Generation– Fixed Signature

• Not secure in access network– HMAC

• Mature and secure, but need computation on each packet– Pseudo Random Number (Preference)

• Generate a sequence of signature on the signature seed using a pseudo random number generation algorithm

• Loop:– Get the first signature from the sequence– Add the signature into the packet, send packet– Remove the signature from the sequence

• No computation on packet, fast

Light-weight Signature Adding and Removal

• The position to place signature in the packet– IPSEC Authentication Header– A new option header (e.g. Hop-by-hop)– In source address field and use Address Rewrite

• The signature is used as local address,• The router rewrites it with the authorized address • Save the cost of memory copy and locating header)

Traditional Signature Mechanism

Packet Packet

Locate the option header

Packet

Packet

Signature

Locate

Send Process

Packet

Packet

Signature

Receive Process

Packet

add Remove

Address Rewrite

• Escape the memory copy and option header location

Packet

Send Process Receive Process

Packet

Rewritethe source address fieldto thesource address

Changethe sourceaddressfield to bethe signature

Packet

Mapping table from signature to

address

4 Implement and Experiment

• The host module is implemented as a program on a Linux PC.

• The router module is implemented as an element of Click Router.

• The demo can work with Stateless Autoconfiguration, Manual Configuration and CGA.

• Currently we use pseudo random number signature generation algorithm.

Experiments

Before Deployment After Deployment

Thank You!