A CGA based Source Address Authentication Method in IPv6 Access Network(CSA) Guang Yao, Jun Bi and Pingping Lin Tsinghua University APAN26 Queenstown, 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= 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) Im H and I require 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 the CGA 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 Locate the option header Packet Signature Locate Send Process Packet Signature Receive Process Packet addRemove

Address Rewrite Escape the memory copy and option header location Packet Send ProcessReceive Process Packet Rewrite the source address field to the source address Change the source address field to be the 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

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