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Comment by cduan | Hacker News Reader

It's helpful to understand a little bit of how a PDF file works.

A PDF file stores a sequence of instructions for what do draw on a page. The instructions are commands, such as "write this text here" or "draw a circle there." When you draw black redaction boxes, you are just appending an instruction to the end of the list ("draw a box here"), but most of the time the previous instructions are all still there.

Really, the only way to redact a PDF with certainty, short of manually reading the file itself (yes, PDF files are text-readable; you just have to decompress them) is to rasterize the file to a large image. Otherwise, the instructions for writing the text are all still in the file, and there are any number of ways to extract them (for example, simply by deleting the instruction to draw the redaction box).

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A government document can't (shouldn't) be rasterized because it would loose all the tagging information making it non-accessible in a 508 sense.

It is however trivial for even a non-technically inclined person to remove the text content through Acrobat's content editing pane.

Just as you suggest, things like this seem to be an example of someone in a large organization not quite understanding how the "magic" behind the tools they use work and winding up with results they didn't expect.

I understand that but why would they not just replace the area with text that says [ redacted ] instead of the black box?

Edit: you can pad the redacted box with spaces to keep the formatting consistent.

Perhaps they want to keep the formatting, and don't want pages to reflow after they've already been layed out? The Unicode character "█" works well for this purpose.

I remember a similar story from a few years ago where redacted names where discovered from the length of the redacted characters. Turned out it wasn't too difficult to brute force names and see which ones matched the exact size of the redaction.

They should have used a fixed width font.

Occum's Razor: because "they" did not understand PDF and thought that they were making the text unreadable simply by drawing boxes over it.

From what I have seen in working with the government and the web I think that anigbrowl's comment is spot on. Many people use tools that are designed for the web or the desktop in the same way that they used to use tools designed for print. In this case just slapping a black line over it works in print, and it does not occur to many people that don't fully understand the technology they use that it might not be directly analogous.

A significant portion of my day job involves working with people in government that have a mental model of content distribution that was constructed during the era of print. Its a fun challenge to help people adjust those models to make things more efficient / more informative / less dangerous.

Black boxes look much more secret agent?

Mrs Browl works at a e-discovery company where documents are often redacted depending on which bits are admissible in court; I gather they use TIFF files for exactly the reasons you describe.

I suppose the (extremely limited) redaction features in Acrobat stem from the belief that the document is ultimately destined for printing rather than computer reading.

I have no personal experience and at best perhaps a vague recollection of having read or heard something, but would document images be or in the past have been used also to make discovery as inefficient as permitted for the opposition? Images require a person to analyze, or pre-processing before electronic search and analysis can be performed against them.

OCR is very good nowadays, so that's not so big a problem - and for big lawsuits (eg patent fights) there are literally hundreds of lawyers hired to comb through the vast array of documents deciding whether they're responsive or not.

The pre-processing is largely automated but there's certainly a portion (maybe 5%?) of documents that need to be hand-classified in the database before they get to the lawyers. It an interesting field - lots of money to be made, intense competition for it, relatively simple technology requirements but a legal industry which has been resistant to technology for quite a long time. Autonomy seems to be the leading software company in this space.

I can't speak for their other products but in my experience their enterprise search product is a useless piece of crap.

When you're billing the client $300 an hour to do a job they can't easily take elsewhere, you don't have a lot of incentive to improve efficiency.

I heard once that NSA guidelines are to print out PDFs, redact portions with a marker and then rescan them into new files.

I also work at an e-discovery company and can confirm the use of TIFF files as the court-admissible format for producing any sort of document (especially if it has redactions).

Here is an example of the process to apply redactions to a PDF file (or any sort of electronic document). The document is opened in a third-party native viewer with redaction capabilities (and not in the original application like Arcobat or Office). The end-user draws a black box over the appropriate text using the third-party native viewer. This redaction is saved as a separate layer that can be rendered on top of the native document when viewed in the software, as well as printed out. Finally, when documents need to be produced for court, they are printed out to a TIFF-printer driver, effectively converting them to TIFF and "burning in" the redaction layer. The TIFFs are delivered to the courts and opposing council.

If you open the file in Adobe Acrobat Pro, there's a tool called "TouchUp Object" that lets you literally just click and delete the boxes.

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