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From "Michael Klink (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (PDFBOX-4439) Digital signature image is not rendered
Date Sat, 26 Jan 2019 22:27:00 GMT

    [ https://issues.apache.org/jira/browse/PDFBOX-4439?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16753202#comment-16753202

Michael Klink commented on PDFBOX-4439:

This indeed is a left-over of old signature validation result visualization code in Adobe
software (mirrored in Foxit Reader).

*n1* used to be the "layer" activated by Adobe Reader whenever the validity of the signature
was UNKNOWN (yet). In the very first implementations Adobe Reader indeed used the *n1* XObject
contained in the PDF file. Then Adobe discovered that people (surprise, surprise!) could provide
layers for UNKNOWN and INVALID that look like a successful validation and so fake successful
validation; thus, Adobe started using a different XObject (hardcoded in the Reader) instead
of the XObject provided by the PDF.

What you see in Adobe Reader and Foxit Reader now is that hardcoded replacement for the *n1*
layer, not the *n1* XObject you identified in the PDF using the PDFDebugger. It differs not
only in the face but also in an additional shadow of the question mark.

Officially Adobe stopped support for the *n1* layer in Adobe Reader 6 but this only meant
they don't create new signatures with those layers anymore while they still use layers to
display the validation state of a signature if XObjects with those names are used in the underlying
PDF document.

Switching these XObjects off and on and replacing them under the hood is covered by the PDF
specification, it is an historic Adobe gimmick which contradicts a number of current standards.

> Digital signature image is not rendered
> ---------------------------------------
>                 Key: PDFBOX-4439
>                 URL: https://issues.apache.org/jira/browse/PDFBOX-4439
>             Project: PDFBox
>          Issue Type: Bug
>          Components: Rendering
>    Affects Versions: 2.0.13
>            Reporter: simon steiner
>            Priority: Major
>         Attachments: notembedded_pm65.pdf
> java -jar ~/pdf-box-svn/app/target/pdfbox-app-3.0.0-SNAPSHOT.jar  PDFToImage notembedded_pm65.pdf
> Picture of a face is not rendered

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