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PDF and Cryptography: Securing the Document

How does PDF encryption actually work? A deep dive into AES, public keys, and digital certificates within the PDF standard.

A PDF file wrapped in chains with a digital key

PDF and Cryptography: Securing the Document

We click “Protect with Password,” but what is actually happening under the hood? The PDF specification includes robust cryptographic features to ensure confidentiality and integrity.

1. Encryption Algorithms

  • RC4 (Legacy): Old PDFs used RC4 (40-bit). This is now easily broken.
  • AES-256 (Modern): The current standard (PDF 2.0). It uses the Advanced Encryption Standard with a 256-bit key. It is effectively unbreakable with current computing power.

2. Public Key Infrastructure (PKI)

Instead of a shared password, you can encrypt a PDF for a specific recipient using their Public Key.

  • Only the person with the matching Private Key (on their smart card or USB token) can open it.
  • This is used heavily in government and military communications.

3. Digital Signatures

Cryptography isn’t just about hiding data; it’s about proving it hasn’t changed. A digital signature creates a hash of the document content. If a single pixel changes, the hash changes, and the signature is invalidated.

Conclusion

PDF security is enterprise-grade. When configured correctly, it is one of the most secure ways to transmit information.

Crypto-ready. MergeCanvas supports AES-256 encryption and digital signing out of the box.