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Encryption

Created by Johan van der Knijff on Jul 15, 2013 · last edited by Johan van der Knijff · on Jul 15, 2013 (view history) · 22 versions

Description

PDF permits the use of encryption as a means of restricting access or (re-)use of content. This may range from documents that can only be opened after providing a password, to disabling specific functionality (e.g. printing, copying content).

Risks

Content may become inaccessible if passwords are not known (even though "cracking" is often technically possible, institutions may not be legally permitted to do this)
Printing / copy restrictions may complicated any future preservation actions

Assessment

The Preflight component of Apache PDFBox (an open source PDF/A validator) is able to detect encryption in a PDF (any PDF, doesn't have to be PDF/A!).

PDF requires password for opening

In Preflight 1.8.0 an open password results in error code 1.0 (syntax error), accompanied by this description:

Syntax error, Error (CryptographyException) while creating security handler for decryption: Error: The supplied password does not match either the owner or user password in the document

In Preflight 2.0.0 only a 'syntax' error message is reported without any indication of anything encryption-related. Reported this as a bug.

PDF requires password for copying document contents

Error code 1.4.2^*^.

PDF requires password for printing

Error code 1.4.2^*^.

PDF requires password to enable text access for screen reader devices for the visually impaired.

Error code 1.4.2^*^.

^*: based on Preflight 1.8.0. In 2.0.0 an error code 1.0 with a 'syntax error' message is produced, but this looks like a bug (see above).

Example files

http://www.opf-labs.org/format-corpus/pdfCabinetOfHorrors/encryption_openpassword.pdf - Requires password to open the file
http://www.opf-labs.org/format-corpus/pdfCabinetOfHorrors/encryption_nocopy.pdf - Requires password to copy document contents
http://www.opf-labs.org/format-corpus/pdfCabinetOfHorrors/encryption_noprinting.pdf - Requires password for printing
http://www.opf-labs.org/format-corpus/pdfCabinetOfHorrors/encryption_notextaccess.pdf - Requires password to enable text access for screen reader devices for the visually impaired

References

References to literature, etc.