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                                               122
      CHAPTER 3                                                                        Syntax



      If revision 4 is specified, the standard security handler supports crypt filters (see
      Section 3.5.4, “Crypt Filters”). The support is limited to the Identity crypt filter
      (see Table 3.23) and crypt filters named StdCF whose dictionaries contain a CFM
      value of V2 or AESV2 and an AuthEvent value of DocOpen.

      Note: Once the document has been opened and decrypted successfully, the applica-
      tion has access to the entire contents of the document. There is nothing inherent in
      PDF encryption that enforces the document permissions specified in the encryption
      dictionary. It is up to the implementors of PDF consumer applications to respect the
      intent of the document creator by restricting user access to an encrypted PDF file ac-
      cording to the permissions contained in the file.

      Note: PDF 1.5 introduces a set of access permissions that do not require the docu-
      ment to be encrypted; see Section 8.7.3, “Permissions.”


      Standard Encryption Dictionary

      Table 3.19 shows the encryption dictionary entries for the standard security
      handler (in addition to those in Table 3.18).

      TABLE 3.19 Additional encryption dictionary entries for the standard security handler
KEY           TYPE      VALUE

R             number (Required) A number specifying which revision of the standard security handler
                     should be used to interpret this dictionary:
                        • 2 if the document is encrypted with a V value less than 2 (see Table 3.18) and
                          does not have any of the access permissions set (by means of the P entry, below)
                          that are designated “Revision 3 or greater” in Table 3.20
                        • 3 if the document is encrypted with a V value of 2 or 3, or has any “Revision 3
                          or greater” access permissions set
                        • 4 if the document is encrypted with a V value of 4
O             string    (Required) A 32-byte string, based on both the owner and user passwords, that is
                        used in computing the encryption key and in determining whether a valid owner
                        password was entered. For more information, see “Encryption Key Algorithm” on
                        page 124 and “Password Algorithms” on page 126.

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