Abstract: A steganographic technique using pdf files to carry secret data is proposed.Data are embedded into the control sequences in a TeX source file to slightly modify inter-word spaces in the text.Appropriate coding schemes may be applied.The coded TeX file is then compiled and converted to generate a stego-pdf file, which is convenient to be disseminated over the Internet.In reception, jpg images are obtained from the pdf document, and the hidden data are extracted by detecting the spaces between words.Data security is determined by the ability of reliably detecting small difference in space widths, size of the document file in terms of the amount of data to be embedded, and the encryption and coding techniques used.

Key words: text steganography, document image, security, information hiding, TeX