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Bug report: --custom-range does not support some data/key combinations with improved algo #14

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ncanceill opened this issue Oct 19, 2013 · 2 comments
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@ncanceill
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May be related to #8

Description

When the data is 5 characters (10 bytes, need to test with 11, 12 is ok) or shorter, the improved algo with custom range enabled (and --no-random for embedding) does not find the FlagStr end code.

How to reproduce

  • Use key "abcd" with data "abcd" to get a bad end position
  • Use key "abcd" with data "a" to get an end position not found

For instance:

KEY="abcd"; echo -n "abcd" | ./pdf_hide -vv -o /tmp/test_e.pdf -i -k $KEY --custom-range embed --no-random - /tmp/test.pdf && ./pdf_hide -vv -o /tmp/test_o.pdf -i -k $KEY --custom-range extract /tmp/test_e.pdf
@ncanceill
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The problem happens from various data length depending on the stego-key... this sounds like a deep algorithm flaw.
=(
Investigating...

@ncanceill
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This seems due to the fact that the custom range badly embeds some numerals with value 15: due to the initial value of the operator they are embedded in, the 15 numeral is not found while extracting.
Still investigating...

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