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Abstract. Firewalls typically filter network traffic at several different layers. At application layer, filtering is based on various security relevant information encapsulated into protocol messages. The major obstacle for efficient verification of authenticity of messages at application layer is the difficulty of verifying digital signatures without disclosure of content protected by encryption. This is due to a traditional paradigm of generating a digital signature of a message and then encrypting the signature together with the message to preserve confidentiality, integrity, non-repudiation and authenticity. To overcome this limitation, a scheme shall be proposed for enabling signature verification without disclosing the content of messages. To provide maximum efficiency, the scheme is based on digital signcryption.

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Networked and distributed systems have introduced a new significant threat to the availability of data and services: network denial of service attacks. A well known example is the TCP SYN flooding. In general, any statefull handshake protocol is vulnerable to similar attacks. This paper examines the network denial of service in detail and surveys and compares different approaches towards preventing the attacks. As a conclusion, a number of protocol design principles are identified essential in designing network denial of service resistant protocols, and examples provided on applying the principles.

Attaching digital signatures to state update messages in global distributed shared object (DSO) systems is not trivial. If the DSO consists of a number of autonomous local representative that use open, public networks for maintaining the state consistency, allowing a local representative to sign state update messages is not appropriate. More sophisticated schemes are required to prevent unauthorized state updates by malicious local representative or external parties. This paper examines the problem in detail, compares a number of possible solutions, and identifies the most suitable one and demonstrates how the state update messages can be signed using the identified solution.