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Jeremy YaoandClaude Opus 5.5
759cfa65f4
* M8: redaction unlinks removed images and forms from inherited and shared resources
Apply Redactions and Remove Hidden Information give a rewritten page its own
pruned /Resources, but the dictionary the page drew through before could still
name the image or form that was removed:
- a /Resources inherited from a /Pages node;
- one resource dictionary object shared by several pages;
- the page's own dictionary, when a form without /Resources drew the image
through it.
A full-rewrite save keeps whatever is still referenced, so the removed image
samples and form text stayed in the saved file while the operation reported
success. Per-page resources (the case fixed in #1099) were not affected.
The interpreter now records the original object behind every XObject it drops
or replaces. After the page loop, each page-tree resource dictionary that still
names one loses that entry unless a page drawing through that dictionary still
draws the name (the same image on another page, or again outside a mark). A
dictionary that loses an entry is replaced by a private copy on its node, so a
dictionary object shared with other nodes is left alone for them. If a page's
use of a name cannot be told (unreadable content, a form that will not decode),
the operation fails closed.
Tests: redacted_xobjects_do_not_survive_through_inherited_or_shared_resources,
an_image_another_page_still_draws_through_the_same_resources_is_kept,
an_image_a_form_drew_through_the_pages_resources_does_not_survive,
a_hidden_layers_image_does_not_survive_through_inherited_resources.
Not covered here: originals named by a form XObject's own /Resources, by an
annotation appearance or by a pattern.
Co-Authored-By: Claude Opus 5.5 <[email protected]>
* M9: a cross-reference entry the reader sets aside is never an unchanged signed object
The reader that judges post-signing changes and the renderer that draws the
page resolve some cross-reference entries differently. A revision appended
after signing could redefine a page's content stream and give the object an
entry the reader sets aside while the renderer follows it:
- an in-use entry at offset 0 (the reader skips it; the renderer fails to read
the object there, rebuilds its index and takes the last definition);
- a second entry for the same object in one section (the reader keeps the
first, the renderer the last).
The classifier compared the signed object with itself, found nothing changed
and reported the signature Valid while the page showed the new content.
pdfcraft-cos now records the entries it does not take at face value
(Document::xref_oddities: offset-0 in-use entries other than object 0,
duplicate entries that differ, reserved cross-reference stream types, and a
hybrid /XRefStm entry that disagrees with the table), and can say whether an
entry locates the object itself (Document::xref_entry_is_exact). What it
resolves is unchanged.
classify_changes treats any such entry added after the signed revision as a
change that is never permitted (page content when the object was a signed page
or its content, other changes otherwise). An object whose content compares
equal at a new place is unchanged only when its entry is exact: where the
reader had to search for the object, another reader may arrive elsewhere.
Tests: a_cross_reference_entry_the_reader_sets_aside_does_not_hide_new_page_content,
a_cross_reference_entry_that_misses_its_object_is_not_an_unchanged_object,
cross_reference_entries_that_are_set_aside_are_recorded,
an_entry_that_misses_its_object_is_found_by_searching_but_is_not_exact.
This closes the two demonstrated triggers and their near variants. It does not
prove that the two parsers agree on every file: other differences in what each
tolerates may remain.
Co-Authored-By: Claude Opus 5.5 <[email protected]>
* M8: Apply Redactions is refused when the page still shows text under a mark
Redaction decides what lies under a mark from the positions its own
interpreter computes, and its verify pass reuses them. Where those differ from
the renderer's, a mark drawn over the text as displayed lies over glyphs the
interpreter places elsewhere, or does not see at all: they stayed in the file
and the operation reported success.
The case the test pins: a font and size set through an ExtGState /Font entry
(`gs`), which the renderer honours and the interpreter does not model. The same
kind of gap was observed for a font a form XObject takes from its caller, for
some predefined CMaps and for a rotated Type 3 font matrix. The standard-14
width error that first showed it is fixed at its root by d0d1ad81.
The engine now asks the renderer, which is what the user saw when placing the
marks. After redaction runs, the result is written as a save would write it
(without the marks' own overlay), its text is extracted, and a glyph still at
least half inside a mark fails the edit with the existing "could not be
verified" error. The edit runs on a copy, so the document is unchanged. A page
whose text cannot be read back fails the same way.
This makes such mismatches fail closed; it does not make those documents
redactable. Teaching the interpreter each of them is separate work.
Test: redaction_is_refused_when_the_page_still_shows_text_under_a_mark (the
line whose font is set by `gs` is refused and left unchanged; the same line set
with `Tf` is redacted).
Co-Authored-By: Claude Opus 5.5 <[email protected]>
---------
Co-authored-by: Claude Opus 5.5 <[email protected]>
pdfcraft-redact
Layer L4 (may use edit): redaction, architecture §11.2.
// Marks are Redact annotations (pdfcraft-annot: Shape::Redact { quads, overlay }).
let marks: Vec<Mark> = marks(&doc); // page, areas (user space), fill, overlay text
let report = apply(&mut doc, None)?; // everything, or Some(&[pages])
clear_marks(&mut doc, None)?; // remove marks without applying
apply removes, under every marked area:
- text: glyphs are cut out of
Tj/TJ/'/"and replaced by aTJdisplacement of the same advance, so the rest of the line keeps its exact position. Widths come from/Widths,/W//DW(composite fonts, embedded CMaps with codespace and CID ranges), Type 3 font matrices, and approximations for the standard 14. A glyph goes when it overlaps an area by more than a fifth of its size (or a point) both ways; zero-size text goes when its origin is inside; - images: fully covered → removed; partly covered → a copy with the covered pixels cleared (8/16-bit and 1/2/4-bit images, image masks; Flate/LZW/RL/A85/AHx). Codecs PdfCraft can't re-encode (DCT, JPX, JBIG2, CCITT) are removed whole (fail-closed); inline images under an area are removed;
- vectors: covered paths are removed; partly covered paths and shadings are clipped so nothing paints inside the areas;
- form XObjects: rewritten recursively into new objects (pages sharing the original keep it);
- annotations whose rectangle overlaps (with their pop-ups), and form fields with a widget under a mark;
- the marks themselves, replaced by boxes in their fill colour (and overlay text) drawn into the
page as a
/PCMark /Redactionstream.
A verification pass re-reads each redacted page and fails the operation if any glyph or inline image is still under an area. Content that can't be decoded makes the operation fail rather than leave it unredacted.
Structure cleanup resolves named MCIDs and indirect content references. Form content references are updated to the cleaned copy; unchanged sibling descriptions remain.
A redacted page that inherits /Resources from the page tree gets them pinned (by reference;
a direct inherited dictionary is made one shared object first) before it is rewritten. The parent's
/Resources is then retired unless another page still inherits it, so it cannot keep a removed
XObject reachable. Pages that aren't redacted are left untouched.
Remove hidden information / Sanitize
let found = sanitize::scan(&doc); // [(Hidden, count)] per category
sanitize::remove_hidden(&mut doc, &[Hidden::Comments])?; // chosen categories
sanitize::sanitize(&mut doc)?; // all of them
Categories: metadata (/Info, XMP), file attachments, comments, form fields (flattened so the
values stay visible), hidden text (render modes 3 and 7, or wholly off the page), hidden layers
(content of off optional-content groups, then the groups), bookmarks, links/actions/JavaScript,
and /PieceInfo private data. Both make the next save a full rewrite.
patterns finds phone numbers, e-mail addresses, credit card numbers (Luhn-checked), US Social
Security numbers and dates for Search & Redact.
codes holds the redaction code sets (U.S. FOIA and U.S. Privacy Act exemptions):
CodeSet::from_id("foia")?.overlay(&["(b)(6)"]) gives the overlay text for the picked codes.
Custom code sets aren't supported yet.
Not yet: pattern locales, struct-tree/alt-text cleanup, metadata and hidden-information sanitising (M8.4), re-encoding of DCT images (they are removed instead).