Cryptography – Cryptanalysis
Patent
1995-08-28
1997-12-23
Barron, Jr., Gilberto
Cryptography
Cryptanalysis
380 23, H04L 932
Patent
active
057013420
DESCRIPTION:
BRIEF SUMMARY
This invention relates to the security of computer documents and in particular to complex documents, although not exclusively so, and to a means which controls the degree to which the presence of covert information may be reduced or eliminated in documents before transmission external of a secure environment.
BACKGROUND
An ideal way to ensure the security of a computer document, assuming the appropriate integrity of the author, is to have the author create the document on a trusted computer. A trusted computer is designed to prohibit the creation or existence within the document of elements which are not intended by the author to be therein. Should the document created on a trusted computer need to be transmitted externally of the secure environment occupied by the author and the trusted computer, the electronic form of the document can have appended thereto a seal which will indicate, when processed in a particular way, whether the document with which it is uniquely associated has been changed in any way. As long as the document is unaltered, it may then be communicated to its intended recipient, who may view it, on a trusted computer as the case may be.
Complex documents (i.e., documents which contain any non-textural information and/or representational structure) are typically created to communicate information in a form suited to both the writer and the recipient and typically specialised characters and layout will be necessary. Understandably, as long as there exists a likelihood that unauthorised or covert information has been secreted within the document structure and the intended information within the document, that document should not be transmitted externally of the secure environment in which it was created.
A typical example of a complex document comprises text, font selection data, pagination data, page numbering data and many other characteristics unique to the document, the word processing package used to create it and the operating system upon which the package resides. A more complicated document may further comprise purely visual and diagrammatic information (e.g., graphics and bit-map images).
At present there exist very few trusted computer devices which can be used to create documents. These typically have a very limited character set, and are not sufficiently trusted to be used in all situations. Creating a complex document on a trusted device is thus not generally feasible. This severely limits the usefulness of trusted computers in the information exchange arena.
Therefore, there exists a need to devise a method and means for the handling of documents created on untrusted computer devices (which are widely used within secure environments) such that there is an acceptably low probability that such documents, when proposed to be transmitted external of the secure environment, contain unauthorised or covert information.
BRIEF DESCRIPTION OF THE INVENTION
In a broad aspect of the invention, a method of exporting a document from a secure computer environment comprises the steps of: content or form of any covert information contained within said document, a trusted manner, and document, in a trusted manner, external of said secure computer environment. step (c) is replaced by the step: said filtered document a seal which indicates that said document can be communicated external of said secure computer environment. step (b) is replaced by the step: a trusted manner which also conforms to the rule that no pixel of the display is written to more than once for the current portion of the document being displayed. comprising the steps of (a), (b), (d) where step (b) is replaced by the step: a trusted manner which also conforms to the rule that no pixel of the display is written to more than once for the current portion of the document being displayed. comprising the steps of (a), (b), (c) with the following step being performed before step (b): predetermined form of said document is passed to the next step. comprising the steps of (a), (b), (d) with the following step being performed bef
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patent: 5204961 (1993-04-01), Barlow
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O'Brien et al: Richard O'Brien and Clyde Rogers "Developing Applications on LOCK" Proceedings of the 14.sup.th National Computer Security Conference, Washington, D.C., October 1991, pp. 147-156.
Saydjari et al: O. Sami Saydjari, Joseph M. Beckman, and Jeffrey R. Leaman, "LOCK Trek: Navigating Uncharted Space" Proceedings of the IEEE Symposium on Security and Privacy, Oakland, CA, May 1989, pp. 167-175.
Anderson Mark Stephen
Beahan Brendan
Hayman Ken
Nayda Lisa
Pope Michael
Barron Jr. Gilberto
The Commonwealth of Australia of Anzac Park
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