here's some code... I'm also adding it to our tests as some extra fun.
PDEncryption encryption = doc.getEncryption();
int revision = encryption.getRevision();
if (revision < 5)
{
StandardSecurityHandler standardSecurityHandler = new
StandardSecurityHandler();
int keyLengthInBytes = encryption.getVersion() == 1 ? 5 :
encryption.getLength() / 8;
byte[] computedUserPassword =
standardSecurityHandler.getUserPassword(
ownerpassword.getBytes(Charsets.ISO_8859_1),
encryption.getOwnerKey(),
revision,
keyLengthInBytes);
}
You could also try to use incremental saving. But it is tricky (you need
to set a "breadcrumb trail" to your updated element(s)) and buggy (if
there is a signature and you don't sign yourself).
Tilman
Am 04.01.2018 um 08:26 schrieb Hesham Gneady:
Thanks a lot Tilman .. I will try that 😊
Best regards,
Hesham
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Included Message:
It is possible for older encryption (not AES256): get the source code and have a look at
StandardSecurityHandler.java. There is a segment where "isOwnerPassword()" is called, and
a bit later, "computedPassword"
is calculated by calling getUserPassword(). I tried this by debugging with out
test files and yes I got the user password.
So you could do it by 1) get length, revision and owner key from the
PDEncryption object you get by calling document.getEncryption() 2) check that
revision is smaller then 5, and 3) call getUserPassword().
Tilman
Am 03.01.2018 um 09:29 schrieb Hesham Gneady:
Hello,
I have a PDF file that has an owner password & user password. I'd like
to decrypt it using the owner password, make some modifications to it,
then encrypt it back and save it. I did the first part successfully,
but how can I encrypt it again using the same encryption settings it
had, which I don't actually know? . For example, I know only the owner
password, but not the user password.
Best regards,
Hesham
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