[jira] (PDFBOX-5955) Support rare RC4 encryption where R=4, key length < 128 bits

["Tilman Hausherr (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/PDFBOX-5955 ]


    Tilman Hausherr deleted comment on PDFBOX-5955:
    -----------------------------------------

was (Author: tilman):
So that's the solution for now.

> Support rare RC4 encryption where R=4, key length < 128 bits
> ------------------------------------------------------------
>
>                 Key: PDFBOX-5955
>                 URL: https://issues.apache.org/jira/browse/PDFBOX-5955
>             Project: PDFBox
>          Issue Type: Improvement
>          Components: Crypto
>    Affects Versions: 2.0.33, 3.0.4 PDFBox
>            Reporter: Ross Johnson
>            Priority: Major
>             Fix For: 2.0.34, 3.0.5 PDFBox, 4.0.0
>
>         Attachments: R=4, V=4, 40-bit RC4.pdf, R=4, V=4, 48-bit RC4.pdf
>
>
> I've come across some PDFs that open fine in Acrobat, but seemingly no other viewer / parser. Upon further inspection, it seems these PDFs use a rare RC4 encryption scheme where R=4 & V=4, but the key length is given as 40 bits / 5 bytes instead of the normally expected 128 bits / 16 bytes.
> I can't find this behavior explicitly described in the PDF specs, but it seems that Acrobat extends the shorter key to 16 bytes (appending 0x00 bytes) in this situation before the steps described in "Algorithm 1: Encryption of data using the RC4 or AES algorithms".
> I've been able to generate a sample file that demonstrates the issue and uses a 40-bit key. I also made a similar file with a 48-bit key. Note that these files have an empty / blank user password, and Acrobat opens them without a password prompt.



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