How real is the threat of aiding cryptanalysis through copying TrueCrypt Containers?

Here is a quote from Leo's website + Truecrypt website:
http://ask-leo.com/can_i_or_should_i_use_truecrypt_for_my_backups.html


"...Truecrypt warns that users should NEVER create volumes/backup volumes by copying the container file. Apparently, since the two volumes use the same master key, it "aids cryptanalysis"

"...Never create a new TrueCrypt volume by cloning an existing TrueCrypt volume. Always use the TrueCrypt Volume Creation Wizard to create a new TrueCrypt volume. If you clone a volume and then start using both this volume and its clone in a way that both eventually contain different data, then you might aid cryptanalysis (both volumes will share a single key set). This is especially critical when the volume contains a hidden volume. See also the chapter How to Back Up Securely."



Now assuming you have a strong password or keyfile, the likihood of your truecrypt container or volume being cracked is very unlikely.

Now, if you were to not follow TrueCrypt advice and copied TrueCrypt containers regularly, would this be a significant threat to your data? Or would it still be virtually impossible to crack your TrueCrypt containers? I mean what if you made 100 copies, does it make any difference?

 

The key here is the bold part. If you make backup to a volume you never modify, there is no danger. But if you backup one encrypted volume and then start modifying the original one, this makes cryptanalysis easier. Suppose that you create a hidden volume, backup the entire encrypted partition/file and then modify something inside hidden volume. If someone compares it with the backup, the hidden volume will be revealed.

 

Well I am currently not using hidden volumes so that is not a primary concern for me.

The only thing I am concerned about is the security of my encrypted containers and the implications of duplicating and copying them for backup purposes.

Example: let's say I have a container called Work.tc. One of the simplest way to backup my container is to copy it to a different drive (Let's call this E: Drive).

E:\Backup\Work9-01-2009.tc
E:\Backup\Work10-01-2009.tc
E:\Backup\Work11-01-2009.tc
E:\Backup\Work12-01-2009.tc


Now, we already know that it is virtually impossible to crack my TrueCrypt container that has a strong password or passkey.

Now the question is, does copying the encrypted container regularly make it easier for my TrueCrypt container/s to be cracked?

*I will not be modifying the copied backup containers in E: drive although of course, I will be continually using my original container Work.tc

After re-reading your response, I think you have already answered my question and that copying and duplicating your TrueCrypt containers in and of itself, does not compromise the security of your TrueCrypt Containers Unless you modify both containers?

Is this correct?


Example, Let's say I make 1000 copies of Work.tc, so as long as I do not modify any of the 1000 copies I will be protected against this threat, correct?

 

I wanted to know the same thing, so didn't want to start a new thread.

I basically have HDD1 with 3 TC containers. I want to make a backup of the files in those containers on HDD2. HDD2 is a new hdd.

Instead of going through the format/make container/password settings again, I was thinking of just copying the 3 containers from HDD1 to HDD2.

They will eventually have different data added to each of the containers at different times, and all will be mounted at the same time as well.

Will this be a problem, that all 6 containers mounted at same time, with 3 being duplicates?

I don't use hidden volumes, and I am going to create the new containers using the same password/Enc algorithm anyway.
Would there be at all any problems, not just security wise, but technically/compatibility/stability wise, having 2 HDD's with duplicate containers on them, all mounted at once?



thanks.

 

I have made extra copies of TC containers before. Just to have another copy. But my question is, even if it would somehow aid in cryptoanalysis, what does that really mean? That someone who has some really special knowledge can figure out that the volumes are not exactly the same?? So what? I am confused as to what difference any of this makes.

And here is question number 2. Who is likely to even have such an advanced knowledge that they could make such a comparison?? Can anyone here at Wilders do something like this? I have never made it a secret that I do not know much so that is why I am asking. But I am just having a hard time understanding that there is really any need for concern.

 

For this attack to be successful, I believe that an adversary needs to know the plaintext contents of one of the two identically encrypted containers in order to potentially determine the contents of the other (see paragraph III.B here).

 

FYI -- Another approach is to re-encrypt an existing container, which results in a different underlying encryption key being used (e.g., PGP Desktop has this feature, and I’m guessing that TrueCrypt does as well).

 

But my main point of the question was, is this necessary for what I'm doing.
I don't have hidden volumes, and if I create new containers, I will be using the same password as the current containers anyway.

My real query is, does having duplicates with the same encryption algorithm/key/password make decryption of the containers some how easier? I'm pretty sure though that this isn't the case.

So probably my main concern, is having 3 containers and 3 identical containers on a separate HDD all mounted at once, and whether this causes any stability between windows and TC or makes it more prone to errors or corruption.

 

If you are simply backing up your containers by duplicating them, then I fail to see that it increases the risk profile. The issue, as I understand it, occurs when you have two identically encrypted files (i.e., using the same underlying encryption key) and an adversary somehow discovers or knows the plaintext content of one of them. In this case, the adversary may be able to use that insight to more easily determine the plaintext contents of the other file (see post #6).

I don’t use TrueCrypt (i.e., I prefer PGP Desktop), but I suspect that as long as Windows sees each container as a unique volume, then it should work well.

You may wish to run CHKDSK on the virtual volumes occasionally as part of your routine maintenance.

 

I frequently back up my containers by copying them, and I have multiple copies stored on my backup drives. Sometimes I mount more than one at a time, and I don't see why this would cause any stability problems whatsoever. Every mounted container is a separate entitity, regardless of its origin. The keys are not shared or compared in any way.

The only real risk is that you might get mixed up by their identical-appearing contents and end up working on the wrong volume.

Also, I consider the risks of "aiding cryptanalysis" to be quite minor, although there's really no way to tell. Perhaps an experienced cryptographer would be able to answer that question properly, but the rest of us can only guess. Of course, I don't expect to have my computer impounded and subjected to an intensive professional analysis, as I merely use TC to protect my sensitive data in the event my computer is stolen in a burglary. Your threat model might be different.

 

The risk here is from two things:

1. The big danger is if you have hidden volumes. (And you said you don't.)

2. If you change the password on one, you potentially leave the others vulnerable to access with the old password if it was not wiped. The most current versions of TC have addressed this in a manner that makes that possibility very remote.

For your purposes, I see no inherent danger in cloning. The TC documentation sometimes errs on the side of caution without proper context. But, better that than the alternative.

 

Thanks, I guess I'll just go ahead and copy the containers to the second hdd then.
The original containers will have everyday files saved to them, where I will only backup only some of those files to the duplicate containers, so eventually they will differ in content, so I didn't think it would be necessary to go through the whole container creation process again, since all of the same settings and password would be chosen again anyway.

Yes, it does get a bit messy with over 6 containers all mounted at the same time, including the physical HDD's. But I will have named all the mounted containers different names, so it will make it slightly easier.

This is basically the same reason I'm using TC.
I don't think I'm being watched by any secret agents or the government, well I hope not




thanks again