Glossary / AES Encryption
What Is AES Encryption in PDFs?
AES (Advanced Encryption Standard) is a symmetric block cipher that serves as the recommended encryption method for PDF documents. Introduced in PDF 1.6 with 128-bit keys and extended to 256-bit keys in PDF 2.0, AES provides strong, standards-based security as specified in ISO 32000-2.
How AES works in PDFs
AES operates in Cipher Block Chaining (CBC) mode within PDFs. Each PDF object is encrypted with a unique initialization vector (IV) and a key derived from the document's master encryption key and the object number. AES-256 uses a 256-bit key, making brute-force attacks computationally infeasible with current technology.
Why AES replaced RC4
AES was adopted by NIST in 2001 after a rigorous public evaluation process. Unlike RC4, AES has no known practical attacks against properly implemented versions. The ISO 32000-2 (PDF 2.0) standard deprecates RC4 entirely and mandates AES for new encrypted documents.
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