The HKM / HFX cryptosystem is proposed for standardization at the ITU Telecommunication Standardization Sector Study Group 8. It is designed to provide authenticity and confidentiality of FAX messages at a commercial level of security. In addition, the HKM / HFX cryptosystem is designed for unrestricted export.

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Attacks on the HKM/HFX Cryptosystem

With the rapid growth of networked multimedia data systems, copyright protection of proprietary digitized media has gained importance. Inserting a robust and invisible signal that clearly identifies the owner or the recipient is beginning to emerge as the solution. Previous research in the field of watermarking has been successful in inserting a 'static' watermark, which endures ownership rights but is not as robust and tamper-proof as the 'dynamic' watermarks. This paper presents a novel invisible and robust watermarking technique that aims at dynamically inserting the watermark in digital images. Dynamic generation of watermark ensures that whenever the image is viewed, the watermark inserted in the image is different from the previous one providing more security against copyright attacks. This is accomplished by bundling the viewer and the image together, in which the viewer is responsible for embedding the new watermark using the spread spectrum watermarking algorithm every time. We have implemented the proposed scheme and present experimental results.

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Dynamic watermarking of images

The security of transactions flowing across a communications network is of ever increasing importance. In many such circumstances it is important not only to protect the messages from passive interception but also, and often of greater importance, to be able to detect any active attack against messages. An active attack may take the form of an interceptor tampering with the message: altering it, adding information, removing information and so on. While it is almost impossible to prevent an active attack there are many mechanisms to ensure, with a high probability, that such an attack may be detected and hence rendered harmless. The techniques to allow detection and thus audit take many forms of which the most common are normally cryptographically based and depend upon the generation, before transmission of the message, of a check-sum which is then appended to the message. The theory underlying this approach works on the basis that if a would-be fraudster changes any part of the message in any way then the check-sum will no longer be correct and thus the recipient of such message can compute, for himself, the expected check-sum, compare it with that received in the message and if they disagree will know the message has been altered. If on the other hand the expected and received check-sums agree then he knows with a high probability that the message has not been altered. This probability is dependent upon the amount of information within the check-sum (i.e. the longer it is) the lower the probability of an undetected alteration.

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H. J. Beker

Papers

Message authentication and dynamic passwords