PAdES PDF is a set of restrictions and extensions to PDF and ISO 32000-1 making it suitable for advanced electronic signature. Its name stands for PDF advanced electronic signature.
While PDF and ISO 32000-1 present a framework to electronically sign documents, PAdES PDF signature defines accurate profiles for the use of the advanced electronic signature under the Directive 1999/93/EC of the EU.
The PAdES format
By default, the e-signature is always embedded within the signed PDF document, which is only human-readable. It is not thus suitable in case the data has to be read by a computer as well. PAdES does not support parallel signing and it requires a PDF software to sign and verify an e-signature.
An important advantage is that electronically signed documents remain valid for long periods of time, even if the underlying cryptographic algorithms are broken. At any time in the future, in spite of technological and other advances, it would be possible to validate the document to confirm that the signature was valid at the time it was signed – a concept known as Long-Term Validation (LTV).
Documents signed electronically in PAdES format can be used or stored for many years or even decades so that at any time in the future, despite any possible technological improvements, it should be possible to validate the document in order to confirm that the signature was valid at the time when it was signed, concept known as “Long-Term Validation” (LTV).
This is an additional format to the other two electronic signatures developed by ETSI, both recognized by the EU and suitable for applications that do not involve a person’s reading of the document such as advanced electronic signature for files CMS (CAdES) and the advanced electronic signature for XML (XAdES).
For documents in PDF format, the signature data is incorporated directly into the signed document, allowing the contents of the PDF file to be copied, stored and distributed as a simple electronic file. The signature can also have a visual representation of an input field, as you might also have in a printed document.
A significant advantage of the PAdES PDF is that it is deployed by a widely recognized software. No development or customization of specialized software is required.
PAdES PDF profiles
The following list briefly defines the profiles defined by PAdES (ETSI TS 102 778):
- PAdES Basic. Basic profile that meets the requirements specified in ISO 32000-1.
- PAdES-BES Profile (Enhaced). This profile specifies an advanced PDF signature based on CAdES-BES and incorporates option of including a timestamp (CADES-T).
- EPES Profile (Enhaced). This profile specifies an advanced PDF signature based on CAdES-EPES. It is the PAdES-BES Profile by adding a signature policy identifier and optionally a reference to the type of commitment.
- PAdES-LTV Profile (Long Term). It’s the long-lived signature format. This profile allows you to extend the validity of signatures in PDF format indefinitely. It can be used in conjunction with other PAdEs profiles. This profile is used to ensure validation many years after the completion of the signature. That is, it guarantees long-term validation.