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                                               730
         CHAPTER 8                                                         Interactive Features




                     TABLE 8.103 Entries in a signature reference dictionary
KEY                    TYPE          VALUE

Type                   name          (Optional) The type of PDF object that this dictionary describes; if
                                     present, must be SigRef for a signature reference dictionary.

TransformMethod        name          (Required) The name of the transform method (see Section 8.7.1,
                                     “Transform Methods”) that guides the object digest computation or
                                     modification analysis that takes place when the signature is validat-
                                     ed. Valid values are:
                                        DocMDP       Used to detect modifications to a document relative
                                                     to a signature field that is signed by the originator of
                                                     a document; see “DocMDP” on page 731.
                                        UR           Used to detect modifications to a document that
                                                     would invalidate a signature in a rights-enabled doc-
                                                     ument; see “UR” on page 733.
                                        FieldMDP     Used to detect modifications to a list of form fields
                                                     specified in TransformParams; see “FieldMDP” on
                                                     page 736.
                                        Identity     Used when signing a single object, which is specified
                                                     by the value of Data in the signature reference dic-
                                                     tionary (see Table 8.103). This transform method
                                                     supports signing of FDF files. See “Identity” on page
                                                     737 for details.

TransformParams        dictionary    (Optional) A dictionary specifying transform parameters (variable
                                     data) for the transform method specified by TransformMethod.
                                     Each method except Identity takes its own set of parameters. See
                                     each of the sections specified above for details on the individual
                                     transform parameter dictionaries

Data                   (various)     (Required when TransformMethod is FieldMDP or Identity) An indi-
                                     rect reference to the object in the document over which the digest
                                     was computed or upon which the object modification analysis
                                     should be performed. For transform methods other than FieldMDP
                                     and Identity, this object is implicitly defined.

DigestMethod           name          (Optional) A name identifying the algorithm to be used when com-
                                     puting the digest. Valid values are MD5 and SHA1. (See implemen-
                                     tation note 144 in Appendix H.) Default value: MD5.

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