New York: Computer scientists at Columbia Engineering have invented FontCode, a new way to embed hidden information in ordinary text by imperceptibly changing, or perturbing, the shapes of fonts in text. FontCode creates font perturbations, using them to encode a message that can later be decoded to recover the message.
The method works with most fonts and most document types. The hidden information will be well maintained even if the document is printed on paper or converted to another file type. The paper will be presented at SIGGRAPH in Vancouver, British Columbia, August 12-16. SIGGRAPH is the annual conference on computer graphics convened by the ACM SIGGRAPH organization.
"While there are obvious applications for espionage, we think FontCode has even more practical uses for companies wanting to prevent document tampering or protect copyrights, and for retailers and artists wanting to embed QR codes and other metadata without altering the look or layout of a document," says Changxi Zheng, associate professor of computer science and the paper's senior author.
It works with common font families, such as Times Roman, Helvetica, and Calibri, and is compatible with most word processing programs, including Word and FrameMaker, as well as image-editing and drawing programs, such as Photoshop and Illustrator. Since each letter can be perturbed, the amount of information conveyed secretly is limited only by the length of the regular text. Information is encoded using minute font perturbations -- changing the stroke width, adjusting the height of ascenders and descenders, or tightening or loosening the curves in serifs and the bowls of letters like o, p, and b.
"Changing any letter, punctuation mark, or symbol into a slightly different form allows you to change the meaning of the document," says Xiao, the paper's lead author. "This hidden information, though not visible to humans, is machine-readable just as barcodes and QR codes are instantly readable by computers. However, unlike barcodes and QR codes, FontCode doesn't mar the visual aesthetics of the printed material, and its presence can remain secret."
Furthermore, FontCode not only embeds but can also encrypt messages. FontCode is not the first technology to hide a message in text -- programs exist to hide messages in PDF and Word files or to resize whitespace to denote a 0 or 1 -- but, the researchers say, it is the first to be document-independent and to retain the secret information even when a document or an image with text (PNG, JPG) is printed or converted to another file type. This means a FrameMaker or Word file can be converted to PDF, or a JPEG can be converted to PNG, all without losing the secret information.
(Source: Materials provided by Columbia University School of Engineering and Applied Science.)