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AuthoCast: Autonomous Authentication of Mobile Multicast-Senders


Mobile multicast scenarios like IPTV or group conferencing are likely to soon extend into the mobile world: A sportscaster (without support of tradional, AuthoCast Logo expensive broadcasting equipment) may feed its live stream from a sailing regatta to an Internet TV channel. But how to prevent an attacker from hijacking this open Internet channel?

AuthoCast defines a protocol scheme that allows for authentication of mobile Multicast senders. It manages address changes in a secure and cryptographically strong way, preventing the Internet infrastructure and receivers from accepting bogus packets. The concepts of AuthoCast are implemented in the Tree Morphing approach, a mobile Source Specific Multicast (SSM) routing protocol.


Multicast mobility management inherits security risks of multicast and mobility. While the latter effectively instructs network redirects and thereby admits potential vulnerability to theft of service and resource exhaustion attacks, multicast packet replication bears the risk of network assisted amplification for distributed denial of service attacks.

Any mobile multicast solution should therefore carefully secure protocol operations to comply with established IPv6 security standards: A robust, cryptographically strong authentication of signaling is required, which has to proceed without a feedback channel. By this one-way authentication the mobile source, i.e., the owner of the Home Address, has to provide proof of authenticity for the update packets in an autonomously verifiable way.

This can be achieved by using Cryptographically Generated Addresses (CGAs) as defined in RFC 3972. A CGA-protected sender can provide cryptographically strong proof of Home Address (HoA) ownership within a single, self-consistent update packet.


AuthoCast implements mobile multicast source authentication using CGAs. Multicast router states, typically reflecting the nodes Care-of Address (CoA) or group address G, will be extended by (CoA, HoA, G). By choosing the HoA of CGA kind, a sender can provide cryptographically strong proof of HoA ownership within a single, self-consistent update packet.

The protocol follows the principles:

AuthoCast is implemented by combining existing protocol structures, restricting extensions to the minimal. This lightweight approach bears advantages for the protocol robustness and deployment-prospects, as standardized headers and protocols have already been analyzed thoroughly and used in real life scenarios.

Detailed Description & Evaluation

  1. Thomas C. Schmidt, Matthias Wählisch, Olaf Christ, Gabriel Hege
    AuthoCast - A Protocol for Mobile Multicast Sender Authentication
  2. Poster presented at the final competition for the German IT Security Award (sponsored by Horst Görtz Stiftung)
    Autonome Zertifizierung mobiler Multicast-Sender - AuthoCast -
  3. AuthoCast flyer (in German) [Details]


Olaf Christ received the young talents PARS award for the paper "A Light-Weight Implementation Scheme of the Tree Morphing Protocol for Mobile Multicast Sources" [more] presented at the PARS workskshop 2007.