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I have a requirement to zip up some files in Linux with 7zip using AES-256 encryption. The end user will be opening in Windows with 7zip. I'm using the following command:

7za a test.txt -tzip -mem=AES256 -mx9

The problem is that when I open the zip archive in Windows, the Method shows "Deflate" and does not say anything about AES-256.

7zip windows screenshot

How can I (and more importantly the end user) be sure that its using AES-256 as the encryption method?

Here is the doc on how to set the encryption method, which I believe I've set correctly.

Linux 7za version:

me@myhost~> 7za -version

7-Zip (A) [64] 9.20  Copyright (c) 1999-2010 Igor Pavlov  2010-11-18
p7zip Version 9.20 (locale=en_US.UTF-8,Utf16=on,HugeFiles=on,4 CPUs)

The Linux host is SLES 11 SP2, and for Windows I'm on Windows 7.

share|improve this question
Did you mean to use a password? – Ignacio Vazquez-Abrams Jan 28 '13 at 13:47
ah! yes I did mean to use a password. I've been testing, testing, testing, and mistakenly left that option out. Adding back in -pmypassword to the command did the trick and I can see AE-256 Deflate when opened in Windows. Can you post as an answer and I'll accept? – Banjer Jan 28 '13 at 14:00
up vote 10 down vote accepted

7-Zip will refuse to encrypt the data unless you provide a password, since it won't know what key you want to encrypt it with:

7za a test.txt -tzip -mem=AES256 -mx9 -pmypassword
share|improve this answer
Thanks. I had to add -pmypassword to the command. – Banjer Jan 28 '13 at 14:06

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