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Posted: 01/05/2009 04:07:29
by Olivier Wallemacq (Basic support level)
Joined: 01/05/2009
Posts: 22

There are 4 signature types available when signing a pdf document (ElPDFSignature.SignatureType )

What are the differences between these options?

Posted: 01/05/2009 05:12:47
by Ken Ivanov (Team)

Thank you for your interest in our products.

Although five signature types are defined, SecureBlackbox currently supports only two of them (stDocument and stMDP). Document signature is a generic signature that just proves the correctness of some revision of the document. MDP (also known as certification signature) also provides means for specifying permissions granted to the users of the document by the author of the document.

A quotation from the PDF reference follows:

A PDF document may contain the following standard types of signatures:
* One or more document (or ordinary) signatures. These signatures appear in signature form fields (see “Signature Fields” on page 695). The signature dictionary corresponding to each signature is the value of the form field (as specified by its V entry). The signature dictionary must contain a ByteRange entry representing a byte range digest, as described above. A signature is validated by recomputing the digest and comparing it with the one stored in the signature.
Note: If a signed document is modified and saved by incremental update (see Section 3.4.5, “Incremental Updates”), the data corresponding to the byte range of the original signature is preserved. Therefore, if the signature is valid, it is possible to recreate the state of the document as it existed at the time of signing.

*At most one MDP (modification detection and prevention) signature (PDF 1.5), also referred to as an author or certifying signature. The signature dictionary of an MDP signature must be the value of a signature field and must contain a ByteRange entry. It may also be referenced from the DocMDP entry in the permissions dictionary (see Section 8.7.3, “Permissions”). The signature dictionary must contain a signature reference dictionary (see Table 8.103) that has a DocMDP transform method. See “DocMDP” on page 731 for information on how these signatures are created and validated.
A signature dictionary for an MDP or ordinary signature may also have a signature reference dictionary with a FieldMDP transform method; see “FieldMDP” on page 736.

Please refer to the PDF reference for more details about the signature types.



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