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All my valuable data is in VeraCrypt volumes. The (very strong) keys of the volumes are stored in a single KeePass database, which uses a reasonably strong password.

I want to encrypt my backups too, in a way that enables me to restore them, even if I loose all the data on my computer (the VeraCrypt volumes and the KeePass file).

Is it risky to use the same password for the KeePass file and the backups encryption ? If someone cracks my KeePass database, he gets the key for the VeraCrypt volumes (and my data) ; if someone cracks my backups' encryption, he gets my data too.

How could reusing a password in this case lower the security ?

Hey
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The point about not reusing passwords is damage containment. You do not want a breach in one system revealing a password that grants access to other data and systems that would otherwise have remained secure.

If the two usages ultimately protect the same data, then it makes sense to use the same password. Your case is a bit different: the two usages are "cascaded". By encrypting your backups, you are applying an extra encryption layer over that which is already provided by KeePass and VeraCrypt. If your master password is strong, that extra encryption layer is redundant. You could make unencrypted backups.

Arguably, you should make unencrypted backups, in case the encryption system for the backups happens to be weaker than the one used by KeePass. When doing password-based encryption, the password must be processed with a proper password-based key derivation function (see this); KeePass makes an effort and the iteration count can be configured. If the encryption system is not as robust as KeePass in that respect, then it may help the attacker: the attacker will run his dictionary attack on the backup, and once he found the password, he can then apply it to open KeePass and unlock the VeraCrypt modules.

Summary: if you can make sure that the backup encryption system processes the password in a way which is at least as resilient as KeePass to dictionary attacks, then using the same password is harmless. Otherwise, it can be harmful and you should abstain; i.e. encrypt with another, independent password, or don't encrypt backups at all.

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Tom Leek
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  • @YdobEmos if the attacker chooses to go after Veracrypt first, it will take them half as long to crack the Keypass password (compared to normal, if they are the same password). I would suggest increasing the Veracrypt iteration count to the same (PIM 1500). That is if they can even crack it in the first place... – Richie Frame Mar 05 '16 at 01:11