Backup Truecrypt container file

I am confused RE the concerns to backup a Truecrypt container by simply coping the Truecrypt file to another harddrive. I have read that one issue is the fact the original volume and backup copies would use the same key set. Would having more than one file with same encryption key actually make it easier to break the encryption? They are still encrypted.

The second issue I have read about is an attacker could observe the changes between the original and backups. If you copied the original to another drive, what difference would there be between the 2 files.

 

The recommended "secure" procedure to backup TC volumes is in the User´s Manual > How to Backup Securely. Create a new volume and copy the files into it.

 

You will have to decide if you are in a "threat model" where it will make a difference. If you are using file based volumes you can simply copy those to another media (while it is dis-mounted of course) and the encryption is exactly the same as the original. Nothing will be different at all because its an exact replica of the original. Now, the manual describes how over time an adversary can compare the differences (using many multiple copies if you did that) but the manner and methods used would only apply to high risk/high threat scenarios. Is that really you?

For a home user that has an encrypted original volume and a backup on an external drive, there is no fear. That ASSUMPTION is that the adversary walks in your house and grabs the original and the backup at the same time. They are exact replica's so the trail adds NO light to the volume's usage. Do NOT keep multiple copies where the graduated differences can be examined over time. I don't want to discuss the forensics of this but just note its a bad idea to do that.


Robin was correct however that by creating a new volume and spinning off the contents of the original is technically a better solution.

I would say volume size is part of this call. Many file based volumes are 200 meg or less containing important files but not much disk space. It takes seconds to copy a file of 500 meg or less and then completely destroy any previous backups of the original. One especially important consideration is to have "off premises" backups in case of fire/theft.

 

Thanks Palancar, for the detailed explanation; I understand now. I certainly fit your example of a typical home user - no state secrets, simply want to keep my personal date private.