test(seal): prove each signature carries its own seal - #218
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The claim was true by construction and untested. SealTest covered a seal on one signature, the multi-signature tests covered revisions without seals, and nothing covered both at once, so a regression would have been silent until somebody opened a file. Two things are asserted, and both were checked against a deliberately wrong document first, since an assertion that cannot fail is not one: One image and one form XObject per signature. A single sealed signature produces one of each, so counting two is counting per revision rather than matching a constant. Two distinct rectangles. Signing twice at the same placement produces "155 250 205 275" both times, so the difference assertion is sensitive to placement rather than trivially true. The filters differ too, DCTDecode for the rendered seal against FlateDecode for the supplied PNG, which shows the second signature carries the caller's image and not a re-render of the certificate. samples/two-seals.pdf ships the same case for readers rather than for the suite. poppler 25.12 reports both valid, the first covering its own revision and the second the whole file.
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Closes the gap noticed while answering a question: the claim that each signature carries an independent seal was true by construction and untested.
SealTestcovered a seal on one signature. The multi-signature tests covered several revisions without seals. Nothing covered both at once, so a regression would have stayed silent until someone opened a file in a reader.What is asserted
One image and one form XObject per signature. Not one pair reused by both.
Two distinct rectangles, neither of them the invisible
0 0 0 0.Different filters,
DCTDecodefor the rendered seal againstFlateDecodefor the supplied PNG, which shows the second signature carries the caller's image rather than a re-render of the certificate.Both signatures then validate, and the report counts two.
Both assertions were checked against a wrong document first
An assertion that cannot fail is not an assertion. Measured before writing them:
images=1 forms=1, so counting two counts per revision rather than matching a constantrectA=[155 250 205 275],rectB=[155 250 205 275], identical, so the difference assertion is sensitive to placement rather than trivially truesamples/two-seals.pdfThe same case shipped for readers rather than for the suite, since the point of this one is visual: the first seal is rendered from the certificate at x 150 / y 240, the second is
src/Resources/img/sign-seal.pngat x 30 / y 60.Verified with poppler
pdfsig25.12:The first covering only its own revision is the expected reading, not a defect: the second signature came after it.
samples/README.mdsays so explicitly, since that line reads like a warning to anyone who has not met incremental signing before.poc/sign-samples.phpregenerates it alongside the others.Verification
composer checkon PHP 8.5 through.docker: green, 136 tests, one more than before.