Encrypting - Image color index unchanged

[pilotandy]

When encrypting a PDF with CMYK Indexed color, the colors render incorrectly on the encrypted PDF.
It appears the stream gets encrypted, but the color palette does not, as it is in the dictionary, not the stream of the object.

14 0 obj
<<
/Type/XObject
/Subtype/Image
/Width 576
/Height 229
/BitsPerComponent 8
/ColorSpace [/Indexed/DeviceCMYK 18 <0000001200000011000000100000000f0000000e0000000d0000000c0000000b0000000a00000009000000080000000700000006000000050000000400000003000000020000000100000000>]
/Filter/FlateDecode
/Length 2036
>>
stream
....
endstream
endobj

The output shows the same CMYK values as the input

32 0 obj
<<
/Type /XObject
/Subtype /Image
/Width 576
/Height 229
/BitsPerComponent 8
/ColorSpace [ /Indexed /DeviceCMYK 18 <0000001200000011000000100000000f0000000e0000000d0000000c0000000b0000000a00000009000000080000000700000006000000050000000400000003000000020000000100000000> ]
/Filter /FlateDecode
/Length 2036
>>
stream
...
endstream
endobj

In _encryption.py, starting around line 75, we encrypt the stream, but not the dictionary

elif isinstance(obj, StreamObject):
    obj2 = StreamObject()
    obj2.update(obj)
    obj2.set_data(self.stmCrypt.encrypt(b_(obj._data)))
    obj = obj2

Adding the items of the dictionary, and evaluating them as well

elif isinstance(obj, StreamObject):
    obj2 = StreamObject()
    obj2.update(obj)
    obj2.set_data(self.stmCrypt.encrypt(b_(obj._data)))
    # We're encrypting the stream, consider the dictionary too.
    for key, value in obj.items():
        obj2[key] = self.encrypt_object(value)
    obj = obj2

Now, the CMYK values are encrypted too.

32 0 obj
<<
/Type /XObject
/Subtype /Image
/Width 576
/Height 229
/BitsPerComponent 8
/ColorSpace [ /Indexed /DeviceCMYK 18 <64cda2cefbf39121492b5dfbe74cb864ec4c6101b2675d53c47ae2b5e7591ea3ba6bd2b6bcb1f13eff191f47b9495db796077831f49ac3771b0d0c23eb61418a4df5ddc4945cb16b3b217c86> ]
/Filter /FlateDecode
/Length 2036
>>
stream
....
endstream
endobj

Adobe Acrobat will then decrypt the CMYK color values correctly.

[stefan6419846]

As you apparently managed to identify the root cause and found a fix: Are you willing to submit a PR including a corresponding test ensuring that this indeed is working correctly with the fix employed?

[pubpub-zz]

@exiledkingcc
Can you give your opinion?

[pilotandy]

I’m sorry, I’ve been busy. I can’t use the PDF I found the issue on (it’s not mine), but I can mock something up and create some PRs. It just may take a while.

[exiledkingcc]

a good fix!

[pilotandy]

New PR #2228
still broken though :(