CHAPTER 3
118
Syntax
KEY
TYPE
VALUE
EFF
name
(Optional; meaningful only when the value of
V
is 4; PDF 1.6)
The name of the crypt filter
that should be used by default when encrypting embedded file streams; it must corre-
spond to a key in the
CF
dictionary or a standard crypt filter name specified in
This entry is provided by the security handler. (See implementation note 24 in Appendix
embedded file streams that have their own crypt filter specifier. If this entry is not
present, and the embedded file stream does not contain a crypt filter specifier, the
stream should be encrypted using the default stream crypt filter specified by
StmF
.
Unlike strings within the body of the document, those in the encryption
dictionary must be direct objects. The contents of the encryption dictionary are
not
encrypted by the usual methods (the algorithm specified by the
V
entry).
Security handlers are responsible for encrypting any data in the encryption
dictionary that they need to protect.
Note:
Document creators have two choices if the encryption methods and syntax
provided by PDF are not sufficient for their needs: they can provide an alternate se-
curity handler or they can encrypt whole PDF documents themselves, not making
use of PDF security.
3.5.1 General Encryption Algorithm
The following algorithms are used when encrypting data in a PDF file:
•
A proprietary encryption algorithm known as RC4. RC4 is a symmetric stream
cipher: the same algorithm is used for both encryption and decryption, and the
algorithm does not change the length of the data.
Note:
RC4 is a copyrighted, proprietary algorithm of RSA Security, Inc. Adobe
Systems has licensed this algorithm for use in its Acrobat products. Independent
software vendors may be required to license RC4 to develop software that encrypts
or decrypts PDF documents. For further information, visit the RSA Web site at
•
The AES (Advanced Encryption Standard) algorithm (beginning with PDF
1.6). AES is a symmetric block cipher: the same algorithm is used for both en-
cryption and decryption, and the length of the data when encrypted is rounded
up to a multiple of the block size, which is fixed in this implementation to al-