mirror of
https://github.com/michaelrsweet/pdfio.git
synced 2024-11-19 11:58:24 +01:00
18 lines
708 B
Markdown
18 lines
708 B
Markdown
|
Frequently Asked Questions
|
||
|
|
==========================
|
||
|
|
|
||
|
|
Why Don't You Support Writing a PDF File with Encryption?
|
||
|
|
---------------------------------------------------------
|
||
|
|
|
||
|
|
PDF encryption offers very little protection:
|
||
|
|
|
||
|
|
- PDF encryption keys are reused and derived from the user password (padded
|
||
|
|
with a standard base string) and the object numbers in the file.
|
||
|
|
- RC4 encryption (40- and 128-bit) was broken years ago.
|
||
|
|
- AES encryption (128- and 256-bit) is better, but PDF uses Cipher Block
|
||
|
|
Chaining (CBC) which enables attacks that allow the original encryption key
|
||
|
|
to be recovered.
|
||
|
|
|
||
|
|
In addition, PDF usage controls (no print, no copy, etc.) are tied to this
|
||
|
|
encryption, making them trivial to bypass.
|