SECTION 3.5
123
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”
(Required)
A set of flags specifying which operations are permitted when the doc-
ument is opened with user access (see Table 3.20).
P
integer
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
3
Reserved; must be 0.
(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).