Information authentication is one of the basic information security goals, and it addresses the issues of source corroboration and improper or unauthorized modification of data. More specific, data integrity is the property that the data has not been changed in an unauthorized manner since its creation, transmission or storage. Data origin authentication, or message authentication, is the property whereby a party can be corroborated as a source of the data. Usually, message authentication is achieved by appending an authentication tag or a digital signature to the message. The authentication tag (resp., digital signature) is computed in such a way so that only an entity that is in possession of the secret key can produce it, and it is used by the verifier to determine the authenticity of the message. During this procedure, the message is considered to be an atomic object in the following sense. The verifier needs the complete message in order to check its validity.

Presented with the authentication tag (resp., digital signature) and an incomplete message, the verifier cannot determine whether the presented incomplete message is authentic or not. We consider a more general authentication model, where the verifier is able to check the validity of incomplete messages. In particular, we analyze the cases of erasure-tolerant information authentication and stream authentication. Our model of erasure-tolerant information authentication assumes that a limited number of the message letters can be lost during the transmission. Nevertheless, the verifier should still be able to check the authenticity of the received incomplete message. We provide answers to several fundamental questions in this model (e.g., lower bounds on the deception probability, distance properties, optimal constructions, etc.), and we propose some constructions of erasure-tolerant authentication codes. Streams of data are bit sequences of a finite, but a priori unknown length that a sender sends to one or more recipients, and they occur naturally when on-line processing is required. In this case, the receiver should be able to verify the authenticity of a prefix of the stream, that is, the part of the stream that has been received so far.
We provide efficient and proven secure schemes for both unicast and multicast stream authentication. The security proof of one of the proposed multicast stream authentication schemes assumes that the underlying block cipher is a related-key secure pseudorandom permutation. So, we also study the resistance of AES (Advanced Encryption Standard) to related-key differential attacks.

Goce Jakimoski has received Bachelors and Masters degrees in Electrical Engineering from the Sts. Cyril and Methodius University, Macedonia, in 1995 and 1998 respectively. He has completed a PhD in Computer Science at Florida State University, Tallahassee, Florida in 2006. Goce has worked as an electrical engineer, research assistant, teaching assistant, instructor and postdoctoral fellow. His research interests include cryptography, computer and network security, and he is author or co-author of a number of papers in these areas. His work has been cited more than 200 times, and more than 80 times in 2006. Goce has served as a reviewer for several journals and conferences, and he is on the Program Committee of ICCCN 2007. He is a member of the Phi Kappa Phi and Upsilon Pi Epsilon Honor Societies, the Association for Computing Machinery and the International Association for Cryptologic Research.