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Re: Maximum password length in single-key mode? And, FEATURE REQUEST: be able to use a single password in multi-key mode

debian@xxxxxxx wrote:
> Interactively, 127 bytes - OK (don't want to use that one, I want to use the
> "-p 0" option). How do I find out the limit of mlock()able RAM sizes?

Kernel puts some limit of how much of RAM can be locked. I don't remember
correct limit, but it may be something like half of RAM or something like
that.

There is a potential security hole or Deny-of-service here. non-root users
can can send megs of data to "mount -p 0" and setuid-root mount will mlock()
that RAM.

Next version of loop-AES' util-linux patch will put brakes at 4KB of
passphrase data received through "mount -p 0". Compatible or not, this is a
security issue. It does not make sense to use passphrase longer than few
hundred bytes.

> Does performance go down when I use a
> long password compared to a short password?

Normally no.

> I have not used gpg before, maybe I will use it later on. However, I think
> it's bad to let loop-AES depend on gpg to make the security level higher
> that the security level you could get with a password (a *very* long
> password, as described above).

I prefer not to reinvent the wheel here. gpg implements good symmetric
cipher crypto as well as good public key crypto. If gpg was not used,
a tool had to be written to duplicate that functionality.

> I have been using mcrypt to encrypt a key file (which is my *very* long
> password). Then, I decrypt the key file before it is piped to the losetup
> command. Like this:
> 
> # cat keyfile | mcrypt -d | losetup -p 0 -e aes256 /dev/loop1 /dev/sda1
> # mount /dev/loop1 /mnt/vault

I hope the "losetup -p 0" passphrase is 4094 or less bytes. Otherwise it
will be incompatible with next version loop-AES' losetup and mount.

-- 
Jari Ruusu  1024R/3A220F51 5B 4B F9 BB D3 3F 52 E9  DB 1D EB E3 24 0E A9 DD

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Linux-crypto:  cryptography in and on the Linux system
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