On Apr 23, 2010, at 19:19 , Peter Stuge wrote: > Martin Paljak wrote: >> Most of the PDF attacks AFAIK make use of stuff in PDF that should >> not be there. Like JavaScript or .exe-s :) >> >> I'm not 100% sure but the PDF format that is used for long-term >> archival, PDF/A [1], should not have at least some of the problems. > > Unless the signature is made on some canonical representation of the > output from the PostScript program, rather than the source, it's not > really possible to know if the signature was for the particular > rasterized image that will be rendered by a distinct interpretation > of the PS program. > > Host filesystem I/O is supported in PostScript, but at least not > mentioned to be removed in PDF/A on Wikipedia. PDF/A requires all > fonts to be embedded in the file, which at least for TrueType means > that there is yet another layer where the recipient is to some degree > executing code (kerning instructions) from the sender. > > Dunno.. Are signed PDFs what govts are using? Seems risky.
The thing with legally binding signatures is that they function in a legal system, which includes in addition to technical mechanisms also related organizational and policy regulations. Yes, the best way to be more assured is to use ASCII text files and RTF and other similar "easy to read" formats, but not using them does not make fraud legal. Fraudsters are regularly prosecuted and the same way would your neat trick "after 30 days start to display €1000000 instead of €9.90 in this PDF" be classified as fraudulent by almost any technical expert and thus not valid in court (where the legality of contracts is usually tested). I'm not a lawyer but those who are have "calmed" me down to not be entirely paranoid either about digitally signed contracts (which I've probably signed in hundreds for now, incl. deals with "valuable" (at least for me) stuff) in both PDF as well as MS word format. They won't automagically start a nuclear war or kill me when I accidentally sign a "I want to be dead" fraudulent PDF. But I've also said that trust in government provided eID can only exist if there is trust for "the system". If you don't trust the legal system or the government or some other parts of "the system", none of the technical stuff can help you gain it. Not even the (usually theoretical) zero knowledge and zero trust systems. I would not "sign a deal" for a revolution with government provided eID or encrypt my terrorist plans with it, for the same trust reasons. -- Martin Paljak http://martin.paljak.pri.ee +3725156495 _______________________________________________ opensc-devel mailing list opensc-devel@lists.opensc-project.org http://www.opensc-project.org/mailman/listinfo/opensc-devel
