From 1cd71ddffbb51c7d43136d4b00cf09158105ddd5 Mon Sep 17 00:00:00 2001 From: couchot Date: Tue, 13 Oct 2015 09:28:03 +0200 Subject: [PATCH] correction ahmad --- ahmad.tex | 40 +++++++++++----------------------------- 1 file changed, 11 insertions(+), 29 deletions(-) diff --git a/ahmad.tex b/ahmad.tex index f1612a8..0ebbdb5 100644 --- a/ahmad.tex +++ b/ahmad.tex @@ -2,37 +2,19 @@ En étudiant le watermarking, nous avons constaté que très peu de travaux ciblaient les documents PDF qui représentent cependant une part non anecdotique des données échangées en ligne. +Parmi ces travaux, \cite{PD2008} propose la modification du nombre +d'espaces entre les mots ou entre les paragraphes. +Similairement, les auteurs de~\cite{DBLP:journals/sigpro/LeeT10} +ajoutent des caractères invisibles dans le document. +En supprimant ces espaces ou caractères invisibles, la marque s'enlève +facilement. +Dans~\cite{PD2008}, les auteurs modifient de manière imperceptible +le positionnements des caractères. D'autres éléments de postionnement +sont intégrés dans~\cite{WT08}. +Une attaque qui remodifierait aléatoirement de manière faible ces positions + détruirait la marque dans les deux cas. -Several methods of Steganography and Digital Watermarking in PDF and -Text documents have been proposed. In~\cite{PD2008}, a steganographic approach -is presented by hiding information using inter-word and -inter-paragraph spacing in a text. The main disadvantage of this -method is that the hidden message can be destroyed by simply deleting -some spaces between the words in the stego text. In~\cite{PD2008}, -two -different algorithms are proposed which are considered as an -alternative for the original TJ operator method. The TJ operator -displays the text string in a PDF document, allows individual -character positioning and uses character and word spacing parameters -from the text state. The alternative method has less embedding -capacity than the original method. In~\cite{LLGC13} an encryption technique -is proposed by combining the information hiding technique in PDF -documents and the quadratic residue as basis and then apply it to -copyright protection and digital learning. The main drawback of this -method is that the hidden message can be easly removed. In~\cite{DBLP:journals/sigpro/LeeT10}, an -embedding method in source programs using invisible $ASCII$ codes is -proposed. This method is very easy to detect by simply extracting the -modified text from the document, converting it to hexadecimal, -extracting all the inserted invisible $ASCII$ characters, and then, -decoding the embedded message. In~\cite{WT08}, a data hiding in PDF files and -applications by imperceivable modifications of PDF object parameters -is proposed. This method serves to hide data by slight modifications -of the values of various PDF object parameters such as media box and -text matrices. The method is considered to have sufficient -transparency while its main drawback is its very low embedding -capacity. - Substitutive Quantization Index Modulation (QIM) methods were introduced by Chen and Wornell~\cite{CW01}. The Spread Transform Dither Modulation (STDM) is an implementation of this scheme and it has been -- 2.39.5