this pr can fix #2227 with no doubt.

@stefan6419846
thanks for your analysis

@pilotandy
here is a way to get your test working without calling the to induce the error:

def test_encrypt_stream_dictionary(pdf_file_path):
    user_password = secrets.token_urlsafe(10)

    reader = PdfReader(RESOURCE_ROOT / "cmyk_image.pdf")
    page = reader.pages[0]
    original_image_obj = page["/Resources"]["/XObject"]["/I"]

    writer = PdfWriter()
    writer.add_page(reader.pages[0])
    writer.encrypt(
       user_pass
word=user_password,
       owner_password=None,
       algorithm="RC4-128",
    )
    with open(pdf_file_path, "wb") as output_stream:
        writer.write(output_stream)

    reader = PdfReader(pdf_file_path)
    assert reader.is_encrypted
    assert reader.decrypt(user_password) == PasswordType.OWNER_PASSWORD
    page = reader.pages[0]
    decrypted_image_obj = page["/Resources"]["/XObject"]["/I"]
    assert decrypted_image_obj["/ColorSpace"][3] == original_image_obj["/ColorSpace"][3]

Codecov Report

All modified lines are covered by tests ✅

Comparison is base (ba9491c) 94.36% compared to head (6819b7b) 94.40%.

@@            Coverage Diff             @@
##             main    #2228      +/-   ##
==========================================
+ Coverage   94.36%   94.40%   +0.04%     
==========================================
  Files          43       43              
  Lines        7591     7595       +4     
  Branches     1497     1499       +2     
==========================================
+ Hits         7163     7170       +7     
+ Misses        264      262       -2     
+ Partials      164      163       -1     

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(I've moved/removed a couple of comments from this discussion, as it was not primarily about the PR)

@pilotandy May I move the PDF to https://github.com/py-pdf/sample-files (docs)?

I typically want files to be in the sample-files for two reasons:

1. pypdf repository size: I want to make sure that it is super easy to get pypdf. That includes that the git repository file size should not get too big.
2. sample-files can be used for other projects easily. I hope that the sample-files repository might get used by other PDF libraries and that we create a good re-usable set of test cases

@MartinThoma Here's the PR py-pdf/sample-files#25 for the sample files

Thank you @pilotandy !

If you want,I can add you to https://pypdf.readthedocs.io/en/latest/meta/CONTRIBUTORS.html :-)