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Date: Tue, 23 Jun 2020 23:23:33 +0200
From: Solar Designer <solar@...nwall.com>
To: john-users@...ts.openwall.com
Subject: Re: decryption without original password

Hi Johny,

On Mon, Jun 22, 2020 at 02:50:45PM +0200, Johny Krekan wrote:
> I have tryed Advanced office password breaker. It is product from 
> Elcomsoft which can break 40-bit encryption
> which is used in Word/Excel versions 97/2000. It decrypts document 
> without recovering the actual password. It
> recovers the key which is generated from the password.
> 1. Is doing something like this possible with John on old office documents?

No.  JtR currently only supports passwords, not binary keys.

I can't speak with confidence about third-party software, but you asked
for "thoughts", so here are some:

> more interesting thing:
> I have read on :
> 
> http://lastbit.com/express-recovery.asp
> That they are able to recover the password which was used to protect the 
> document as well as the document
> itself. I assume the key recovery process is similar to Advanced Office 
> password breaker but:
> 2. What method do you think they are using to recover the original 
> password? Regular bruteforce/dictionary?

They might be testing candidate passwords against a previously cracked
40-bit key, which is probably faster once the key is already cracked
anyway, but isn't necessarily faster overall (including the time needed
to crack the 40-bit key).

> They mention that it can happen that they will recover some password 
> that will look quite unusual but will be
> usable to open the file as well as the original passwordd. Is this 
> because the 40 bit key is too short?

You mean "will be able".  Yes, this should be the case.

> 3. What other hash types are vulnerable so it is possible to find 
> password which is much different from
> original but it will allow to decrypt protected resource?

When you're talking about decrypting, you don't literally mean hashes.

Old PDF versions are similar to old Office documents in this respect.

Alexander

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