How to Set Up eCryptFS on Linux – The Manual Way

How to set up eCryptFS in Linux will be introduced in this post. We can store encrypted files in one eCryptFS directory, the manual way. The content can be seen only after it is mounted as eCryptFS file system. Otherwise, the users can only see garbled characters in the files.

Note that this tutorial will cover the “manual way” which you may find a little bit different from other tutorials which uses the ecryptfs-setup-private, ecryptfs-mount-private and ecrypt-umount-private tools. The benefit of this method is that you will only need to keep the passphrase only. No ~/.ecryptfs directory is required. And after a directory is mounted, it will not be automatically unmounted after the user session is closed.

Here, we use Fedora 22 as the example platform.

Install eCryptFS tools

First, install utils for ecryptfs:

# dnf install ecryptfs-utils

Add ecryptfs module to Linux Kernel

Load the ecryptfs kernel module:

# modprobe ecryptfs

Mount ecryptfs

If we store encrypted file in /home/zma/.private directory and mount it to /home/zma/private/:

# mount -t ecryptfs /home/zma/.private /home/zma/private

For the first time you mount the ecryptfs directory, it will ask you to set up the encryption as follows.

Select key type to use for newly created files: 
 1) tspi
 2) passphrase
 3) pkcs11-helper
Selection: 2
Passphrase: 
Select cipher: 
 1) aes: blocksize = 16; min keysize = 16; max keysize = 32
 2) blowfish: blocksize = 8; min keysize = 16; max keysize = 56
 3) des3_ede: blocksize = 8; min keysize = 24; max keysize = 24
 4) twofish: blocksize = 16; min keysize = 16; max keysize = 32
 5) cast6: blocksize = 16; min keysize = 16; max keysize = 32
 6) cast5: blocksize = 8; min keysize = 5; max keysize = 16
Selection [aes]: 1
Select key bytes: 
 1) 16
 2) 32
 3) 24
Selection [16]: 2
Enable plaintext passthrough (y/n) [n]: n
Enable filename encryption (y/n) [n]: y
Filename Encryption Key (FNEK) Signature [a-signature-here]: 
Attempting to mount with the following options:
  ecryptfs_unlink_sigs
  ecryptfs_fnek_sig=a-signature-here
  ecryptfs_key_bytes=32
  ecryptfs_cipher=aes
  ecryptfs_sig=a-signature-here
WARNING: Based on the contents of [/root/.ecryptfs/sig-cache.txt],
it looks like you have never mounted with this key 
before. This could mean that you have typed your 
passphrase wrong.

Would you like to proceed with the mount (yes/no)? : yes
Would you like to append sig [a-signature-here] to
[/root/.ecryptfs/sig-cache.txt] 
in order to avoid this warning in the future (yes/no)? : yes
Successfully appended new sig to user sig cache file
Mounted eCryptfs

For the later mounting, it will ask you the info again. You must provide the same choices here to mount the directory correctly. Otherwise, you will see “garbage” content.

To make this easier by not choosing so many options, you may store a command as an alias or a script as follows:

mount -t ecryptfs /home/zma/.private /home/zma/private \
-o key=passphrase,ecryptfs_cipher=aes,ecryptfs_key_bytes=32,ecryptfs_passthrough=n,ecryptfs_enable_filename_crypto=y

The mount process will be like:

# mount -t ecryptfs /home/zma/.private /home/zma/private -o key=passphrase,ecryptfs_cipher=aes,ecryptfs_key_bytes=32,ecryptfs_passthrough=n,ecryptfs_enable_filename_crypto=y
Passphrase: ENTER YOUR PASSPHRASE HERE
Filename Encryption Key (FNEK) Signature [a-signature-here]: 
Attempting to mount with the following options:
  ecryptfs_unlink_sigs
  ecryptfs_fnek_sig=a-signature-here
  ecryptfs_key_bytes=32
  ecryptfs_cipher=aes
  ecryptfs_sig=a-signature-here
Mounted eCryptfs

If you do not want to see the FNEK message anymore, you can add the option ecryptfs_fnek_sig=THE_SIGNATURE_ABOVE with the signature printed to the mount command.

After it is mounted, you can check it:

# df -hT
Filesystem                      Type      Size  Used Avail Use% Mounted on
...
/home/zma/.private              ecryptfs  473G  4.7G  449G   2% /home/zma/private

Then you can read/write from/to files under /home/zma/.private as a normal directory.

Umount ecryptfs

# umount /home/zma/private

Try to less a file under /home/zma/.private. You will only see encrypted binary files.

When you want to read your files, mount this directory again and your files will be back :)

Eric Zhiqiang Ma

Eric is interested in building high-performance and scalable distributed systems and related technologies. The views or opinions expressed here are solely Eric's own and do not necessarily represent those of any third parties.

2 comments:

  1. but…. You make it seem as if this is equivalent to an encrypted home. Unfortunately ALL of that extremely private information sitting in hidden files in your home dir is going to be totally open.

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