S E C T I O N H .3
1103
Implementation Notes
22. An option to use an unpublished algorithm was needed because of an ex-
port requirement of the U.S. Department of Commerce. This requirement
no longer exists. Acrobat 7.0 does not use this algorithm to encrypt docu-
ments, although it can decrypt files that are encrypted with the algorithm.
23. Acrobat viewers will fail to open a document encrypted with a
V
value de-
fined in a version of PDF that the viewer does not understand.
24. Security handlers are responsible for protecting the value of
EFF
from
tampering if needed. Acrobat security handlers do not provide this pro-
tection.
25. Acrobat viewers implement this limited mode of printing as “Print As Im-
age,” except on UNIX systems, where this feature is not available.
26. The first element of the
ID
array generally remains the same for a given
document. However, in some situations, Acrobat may regenerate the
ID
array if a new generation of a document is created. Security handlers are
encouraged not to rely on the
ID
in the encryption key computation.
27. In Acrobat 2.0 and 2.1 viewers, the standard security handler uses the
empty string if there is no owner password in step 1 of Algorithm 3.3.
28. In Acrobat 6.0, crypt filter usage is limited to allowing document-level
metadata streams to be left as plaintext in an otherwise encrypted docu-
ment. In Acrobat 7.0, crypt filter usage also includes the ability to encrypt
embedded files while leaving the remainder of the document as plaintext.
29. In Acrobat 6.0 and later, when strings and streams in an encrypted docu-
ment are edited, those streams and strings are encrypted with the
StmF
and
StrF
filters, respectively. In Acrobat 7.0, if the
EFF
entry in the encryp-
tion dictionary is set, embedded files are encrypted with the crypt filter