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Chapter 8. Interactive Features > Digital Signatures

8.7. Digital Signatures

A digital signature (PDF 1.3) can be used to authenticate the identity of a user and the document's contents. It stores information about the signer and the state of the document when it was signed. The signature may be purely mathematical, such as a public/private-key encrypted document digest, or it may be a biometric form of identification, such as a handwritten signature, fingerprint, or retinal scan. The specific form of authentication used is implemented by a plug-in signature handler. Third-party handler writers are encouraged to register their handler names with Adobe; see Appendix E.

Signature information is contained in a signature dictionary, whose entries are listed in Table 8.98. Signature handlers can use or omit those entries that are marked optional in the table but are encouraged to use them in a standard way if they are used at all. In addition, signature handlers may add private entries of their own. To avoid name duplication, it is suggested that the keys for all such private entries be prefixed with the registered handler name followed by a period (.).


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