RE: [pdf-devel] Encryption filters

[Leonard Rosenthol]

Just remember that normal PDF encryption does NOT use "Crypt Filters",
but instead simply encrypts all strings and streams.   "Crypt Filters"
are only ever used as Identity, in the case of unencrypted metadata, or
on embedded files (for a secure envelope).  Not that other options
aren't supported - but those are the only cases where Acrobat will
create them.

Leonard

-----Original Message-----
From: address@hidden
[mailto:address@hidden On Behalf Of David
Vazquez
Sent: Monday, July 28, 2008 5:22 AM
To: address@hidden
Cc: address@hidden
Subject: Re: [pdf-devel] Encryption filters


address@hidden writes:

> Could you please write down a summary of all the needed parameters
> for both filters?

Of course :)

In the encryptation dictionary, both filters involves the use of
following parameters:

  - The entry V specifies the type of algorithm to be used. It should
    be 4 in order to security handler will define the behaviour.

  - CF is a dictionary whose keys and values are crypt filter names
    and crypt filter dictionaries respectively.
  
  - StmF is the name of the crypt filter to encrypt streams by
    default. (the crypt filter should be a CF key entry)

  - StrF, idem for string.

A crypt filter dictionary contains (amongst others) a key named CFM,
whose value could be one of three:
   - None
   - V2 (for RC4/ARC4)
   - AESV2 (for AES)

Finally in filter dictionarity we found a key `name' which let us
declare what crypt filter we want use. It is the name of a crypt
filter defined in CF.

I think it's all! :)