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                                                     123
         SECTION 3.5                                                                   Encryption



KEY               TYPE      VALUE

U                 string    (Required) A 32-byte string, based on the user password, that is used in determin-
                            ing whether to prompt the user for a password and, if so, whether a valid user or
                            owner password was entered. For more information, see “Password Algorithms”
                            on page 126.

P                 integer   (Required) A set of flags specifying which operations are permitted when the doc-
                            ument is opened with user access (see Table 3.20).

EncryptMetadata   boolean (Optional; meaningful only when the value of V is 4; PDF 1.5) Indicates whether
                          the document-level metadata stream (see Section 10.2.2, “Metadata Streams”) is
                          to be encrypted. Applications should respect this value.
                            Default value: true.

         The values of the O and U entries in this dictionary are used to determine
         whether a password entered when the document is opened is the correct owner
         password, user password, or neither.

         The value of the P entry is an unsigned 32-bit integer containing a set of flags
         specifying which access permissions should be granted when the document is
         opened with user access. Table 3.20 shows the meanings of these flags. Bit
         positions within the flag word are numbered from 1 (low-order) to 32 (high-
         order). A 1 bit in any position enables the corresponding access permission.
         Which bits are meaningful, and in some cases how they are interpreted, depends
         on the security handler’s revision number (specified in the encryption
         dictionary’s R entry).

         Note: PDF integer objects are represented internally in signed twos-complement
         form. Since all the reserved high-order flag bits in the encryption dictionary’s P val-
         ue are required to be 1, the value must be specified as a negative integer. For exam-
         ple, assuming revision 2 of the security handler, the value -44 permits printing and
         copying but disallows modifying the contents and annotations.

                                    TABLE 3.20 User access permissions
         BIT POSITION         MEANING

         1–2                  Reserved; must be 0.

         3                    (Revision 2) Print the document.
                              (Revision 3 or greater) Print the document (possibly not at the high-
                              est quality level, depending on whether bit 12 is also set).

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