From: Dennis E. Hamilton <email@example.com>
To: 'Dr. R. O Stapf' <firstname.lastname@example.org>; email@example.com
Sent: Tuesday, 16 October 2012, 14:34
Subject: RE: [libreoffice-users] Re: how to crack a PW in LO?
It is important to separate the use of passwords to set
protections from use of a password to encrypt the document.
Only "Save with Password" provides cryptographic security
of the document.
The "Save with Password" encryption is difficult to attack.
The password is usually the weakest point and the password
may fall to a variety of attacks that use pre-computed
dictionaries of SHA1 digests and other brute-force
techniques. It is also possible that an attack may break
the encryption without discovering the password itself.
All of these attacks are believed to required great effort.
In general, one should expect that a password used in
"Save with Password" is not discoverable unless it is
carelessly chosen or heavily reused.
The harder the password is to attack, the harder it is
to recover, of course.
In contrast, all of the protection settings are insecure.
The protections are trivial to remove. It can be done
by any knowledgeable user with a Zip utility and an XML
editor. It is not necessary to know the password to
remove the protection. However, all passwords used in
making protection settings should be considered compromised.
That is because the document stores an SHA1 or other unsalted
hash in "plain view" in the document. These hashes are
cracked with ease using conventional systems. A password
used to set a protection should not be used for any
more-private purpose. In particular, if the same passwords
are used for protections on unencrypted documents and for
saving with password (encryption), the encryption can be
broken directly using the SHA1 digest from the protection
Protection settings are on spreadsheet fields and sheets.
There are protection settings on text as well. The
protection against altering change-tracking and the
protection for keeping a document read-only are all of
this kind. The protection is useful for avoiding mistaken
It is easy for all of these protections to be removed, the
document altered, and the protections restored with the
very same unlocking password without ever having to
know the password.
A digital signature can prevent the document from undetected
alterations, but that doesn't work for turnaround documents
where some alterations are meant to be allowed.
There is more explanation of the use and risk of protections,
and their removal, here:
A proposal for more-reliable security of protection passwords
(but not the protections themselves) is before the
OASIS ODF TC:
From: Dr. R. O Stapf [mailto:firstname.lastname@example.org]
Sent: Tuesday, October 16, 2012 06:30
Subject: Re: [libreoffice-users] Re: how to crack a PW in LO?
you are perfectly right about this!!!
On 16.10.2012 22:22, Andrew Douglas Pitonyak wrote:
Unless you have a lot of time to kill (days, weeks, months, etc), you are much better off not
forgetting your password.
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