8

I had a question. Im trying to backup and encrypt files, but using the more recent aes256 or aes512 encryption.

1) I heard 7z defaults to aes128, I want to use the best one (aes256... i think?), how do i do it?

Here is my command:

cd /mnt/MyBackupHardDrive ;

7z a MyFullComputerBackup-AES256.7z -t7z -m0=lzma2:d1024m -mx=9 -aoa -mfb=64 -md=32m -ms=on /home/MyHomeDirectory

2) Does this automatically encrypt the filenames too?

Thanks for any help you can offer!

15

It is possible to get AES 256 encryption with 7z and make the archive and filenames only visible with the use of a passphrase. I note that the vital 'passphrase' option is missing from your own command line.

An example, for which I have borrowed liberally from the man pages:

7z a \
  -t7z -m0=lzma2 -mx=9 -mfb=64 \
  -md=32m -ms=on -mhe=on -p'eat_my_shorts' \
   archive.7z dir1

A slightly more secure method is to actually leave the -p field blank, then 7z will prompt you to type a password before actually creating the archive.

Explanation:

Here is an explanation for those not well versed in the 7z command line:

a                   Add (dir1 to archive.7z)
-t7z                Use a 7z archive
-m0=lzma2           Use lzma2 method
-mx=9               Use the '9' level of compression = Ultra
-mfb=64             Use number of fast bytes for LZMA = 64
-md=32m             Use a dictionary size = 32 megabytes
-ms=on              Solid archive = on
-mhe=on             7z format only : enables or disables archive header encryption
-p{Password}        Add a password

Testing the archive:

The subsequent archive can be tested with the command 7z l -slt archive.7z which I demonstrate below:

andrew@illium~/test$ 7z l -slt archive.7z

7-Zip [64] 16.02 : Copyright (c) 1999-2016 Igor Pavlov : 2016-05-21
p7zip Version 16.02 (locale=en_US.UTF-8,Utf16=on,HugeFiles=on,64 bits,8 CPUs x64)

Scanning the drive for archives:
1 file, 12919 bytes (13 KiB)

Listing archive: archive.7z


Enter password (will not be echoed):   <-------------
--
Path = archive.7z
Type = 7z
Physical Size = 12919
Headers Size = 247
Method = LZMA2:14 7zAES
Solid = -
Blocks = 1

----------
Path = dir1
Size = 0
Packed Size = 0
Modified = 2017-06-23 14:10:59
Attributes = D_ drwxr-xr-x
CRC = 
Encrypted = -
Method = 
Block = 

Path = dir1/200px-Aum_calligraphy.svg.png
Size = 12663
Packed Size = 12672
Modified = 2015-05-06 07:29:23
Attributes = A_ -rw-r--r--
CRC = 77BD9922
Encrypted = +                    <-------------
Method = LZMA2:14 7zAES:19       <-------------
Block = 0

andrew@illium~/test$ 

Note the call for a password as well as the notation that gives the encryption as 7zAES:19 aka AES-256 (I have arrowed these points for the sake of clarity).

Caveats:

  1. Note that in the man pages there is a specific warning against using 7z for archival purposes under Linux:

    DO NOT USE the 7-zip format for backup purpose on Linux/Unix because :
    - 7-zip does not store the owner/group of the file.
    
  2. Note as well some limitations and work arounds given in the man pages in regards to the backing up of directories under Linux....

  • Thanks so much. Perfect Explanation, thanks! So... 7zaes19 = aes256, you are awesome!!!!!!!! This is axactly whet I wented! – WubiUbuntu980 Unity7 Refugee Jun 23 '17 at 4:41
  • 1
    @WubiUbuntu1980 Great news! Have a read of the man pages regarding backing up directories on Linux systems though, there are a few traps... – andrew.46 Jun 23 '17 at 4:42
  • Much appreciated honestly your explanation was perfect. Have a good day – WubiUbuntu980 Unity7 Refugee Jun 23 '17 at 4:44

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