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Complex document security
| Details |
Inventors: Anderson, Mark Stephen; Yesberg, John Desborough; Pope, Michael; Nayda, Lisa; Hayman, Ken; Beahan, Brendan;
Assignee: The Commonwealth of Australia of Anzac Park (Canberra, AU)
Primary Examiner: Barron, Jr.; Gilberto
Assistant Examiner:
Attorney, Agent or Firm: Baker, Maxham, Jester & Meador
A method and means to control the degree to which the presence of covert information may be reduced, eliminated or corrupted in documents created on a computer device (particularly complex documents) before the document is transmitted outside a secure environment in which the document is created. The process of handling a document in a secure environment comprises the preferred step of displaying the document or a predetermined portion thereof in a manner which 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. Preferably the method includes the steps of creating a document, transforming the document into an intermediate form by defining the content and structure of the document using a predetermined set of document describers, applying the intermediate form of the document to at least one filter adapted to eliminate or corrupt the content and form of any covert information contained within the intermediate form of the document followed by the previously described step of displaying the document in the manner described above. |
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DETAILED DESCRIPTION OF THE INVENTION When a document is created and verified visually by its author it is preferable to have some means which provides an assurance that a message displayed on an untrusted computer device is the same message input to that device by the user.
It is therefore imperative that the contents and/or the format of the message is not changed by the untrusted device's hardware or untrusted software and this type of security is provided, for the purposes of the present invention, by what will be referred to as a trusted path device.
As discussed previously, trusted computer devices do not currently support all the functionality of an untrusted computer device.
A trusted path device can assist in overcoming this difficulty since it is located between the untrusted computer device input and its untrusted display.
The trusted path device is also limited in the range of characters and formatting with which it can work but allows the user to be confident that the message input to the device is the same as the message which is displayed.
Having visually verified a message or document using a trusted path device, it is of advantage to seal that same message so as to prevent any unauthorised tampering with the document.
This can be achieved using a suitable message sealing and/or encryption device.
In the first instance, a means to allow the message to be appended or associated with a message classification and/or a digital signature (seal) is usually part of the trusted path device, and, in the second instance, such a sealed message may or may not be encrypted with a separate encryption device and key.
There still exist, however, many circumstances where it is desirable to use variations of untrusted computer devices, trusted path devices and trusted encryption devices so that messages, of various types (e.
g.
, plain text message and complex documents) and security classifications, can pass outside of a secure environment.
One such circumstance arises when a complex document is created on an untrusted computer device, for example a letter containing both text having a particular font, and a bit mapped image
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I/O Systems 
