ISSN : 1796-203X
Volume : 2    Issue : 5    Date : July 2007

Watermarks and Text Transformations in Visual Document Authentication
Igor Fischer and Thorsten Herfet
Page(s): 44-53
Full Text:
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Integrity of digital documents is a very important issue if they are to be legally binding. Common
solutions, like digital signatures or message authentication codes, are based on cryptography and
require computers or similar hardware to be produced. They can be trusted only as long as the
employed hardware can be trusted. We present a complementary scheme for document
authentication in untrusted environment. The scheme combines visual authentication, human-
recognizable watermarks, and image transformations, and is suitable also for larger text document.
Because it relies on visual cryptography, it requires practically no computational power on the
receiver side. To prevent potential attackers from obtaining signatures without author’s knowledge,
we propose using a simple challenge-response protocol.

Index Terms
visual authentication, digital documents, watermarks, text deformations, CAPTCHA