Several PDF implementations including MuPDF and Foxit generate their AES-256 encryption keys from predictably weak random state. MuPDF seeds its drand48 generator with only the current epoch in seconds, leaving just 9 bits of entropy, while Foxit also relies on time-based randomness. This allows passwordless decryption of protected PDFs by brute-forcing the small key space.
Background
PDF encryption has evolved through multiple revisions, with revision 6 introducing AES-256 for stronger protection. However, the security of the encryption fundamentally depends on the quality of randomness used to generate keys.
- Source
- Lobsters
- Published
- Oct 29, 2026 at 10:13 AM
- Score
- 7.0 / 10