The PDF Association started in 2006 as the “PDF/A Competence Center”. The mission was to identify – and thereby establish – a common interpretation of the PDF/A-1 specification. With that accomplished through meetings open to all members, the secondary …“PDF can do THAT?!”
PDF files deliver a complete package of information that defines a document; everything that’s needed to represent the text, graphics and layout that the recipient receives. To most people, PDF is “electronic paper” – the digital expression of a cellul …The only digital document format
What is a “document”? A document is a record of some (typically written) content – a publication, a contract, a statement, a painting – at a moment in time. Until the advent of computers (and scanners), the media typically considered useable for such r …Save the Date: PDF Days Europe 2018, May 14-16, in Berlin
PDF Days Europe is the most popular PDF event of the year. It’s where the PDF industry meets, and where institutional and corporate users come to learn what else PDF could do for them. The first two PDF Days will offer a broad range of educational sessions focussed on current and perennial topics in the world of PDF technology implementation.The Power of the Page
It’s a question that vexes vendors of web-based solutions everywhere: why do people still insist on PDF files? And why does PDF’s mindshare keep going up? “PDF is such antediluvian technology!” they say. “It’s pre-web, are you kidding me? It’s so old-f …
As we reported yesterday, those in the crypto world are well-aware that Google and others have proven that SHA-1, the venerable cryptographic hash function standard, is dead. The consequences, however, are yet to be determined. Somewhere, it is safe to assume, between very very bad and catastrophic.
Among many other potential points of disruption, this recently announced SHA-1 collision attack, as PC World reported, can break code repositories that use the Subversion (SVN) revision control system. To prove the point, it seems, the WebKit browser engine repository became corrupted after someone committed two different PDF files with the same SHA-1 hash to it.
The team responsible for uncovering this vulnerability state on their website, SHAttered.io:
The could have used a variety of different file-types to make this point, but PDF files, of course, contain more information and benefit from more trust.
The PDF specification up through ISO 32000-1 (PDF 1.7) allowed use of SHA-1 for a variety of hashing functions. However, in PDF 2.0, SHA-1 is formally deprecated for use in digital signatures. This means that a PDF 2.0 writer should not use SHA-1 to make a message digest, and a PDF 2.0 reader may reject signatures that still use SHA-1.
Does this mean that PDFs that were signed using the SHA-1 algorithm in the past suddenly become invalid? In principle, it is now proven that the contents of such a PDF can be changed without invalidating the signature. However, the problem only exists in situations where companies didn’t upgrade their document systems to the latest standards.
“For those who are stuck with SHA-1 in their existing repositories of PDF documents, PDF 2.0’s new Document Security Store (DSS) including Validation-Related Information (VRI), as well as a document time-stamp (DTS) signature,” says iText founder Bruno Lowagie. “The document time-stamp signature (subtype ETSI.RFC3161) is an additional signature that should use a more recent hashing algorithm to create the message digest. The procedure of adding a DSS and a document time-stamp should be repeated before the certificate of the last signature that was added expires, or when there are indications that the algorithms that were used, whether the cryptographic hash function or the encryption algorithm, could be jeopardized,” Lowagie said.
PDF developers can test their software – and its response to SHA-1 – in the PDF 2.0 context long before it gets to customers. In January, the PDF Association announced two PDF 2.0 interop workshop events in the UK, and USA, to help PDF developers test their PDF 2.0 files or implementations against others.
The death of SHA-1 makes an excellent case for testing new encryption models and circumstances. Billions of PDF files worldwide rely on secure digital signatures, encryption and other features that use hashing to disambiguate documents. PDF 2.0 is an excellent opportunity to negate this risk for PDF users.