How to untar...

[commodore]

I'd like to see what's in the diagnostic logs of a Huawei B535 router. It exports a ZIP file which contains one folder (/var). The folder contains one file: diagnose_enc.tar. I can unpack this from the ZIP. However, if I double-click this file in Total Commander, all I get is "Error in packed file ... !".

Is there anything else that needs to be set up in order for tar (un)packing to work in TotalCmd?

Unless the issue might be elsewhere - namely if I use "tar -xvf diagnose_enc.tar" in command prompt, I also get an error: "tar: Error opening archive: Unrecognized archive format".

[nsp]

If you have a format error also on command line, this probably mean that your tar file is probably compessed gzip, bzip2,..... The first advise is to find what is the file format. You can use trid .
Renanme the extension to match the best guessed format tgz, tar.bzip2,... Normally 7zip should be able to decompress at least to the next step. Using total7zip plugin should probably help to decompress inside TC once renamed...

You can also give a try to bsdtar from libarchive project on github. (msvc compilded artifact)
--Edited

[commodore]

Trid reports:
98.1% (.PGC) PGN (Portable Gaming Notation) Compressed format (1000/1)
1.8% (.DBF) Sybase iAnywhere database files (19/3)

Could it also be possible it's some sort of Huawei proprietary encryption (so that "only they" can open it)?

[Dalai]

Is there anything else that needs to be set up in order for tar (un)packing to work in TotalCmd?

No, there's nothing to do since TC can work with .tar archives out of the box. However, the archive is highly likely to be encrypted, obfuscated or a proprietary archive format if it contains sensitive data. I'm not saying this is the case, but it's possible.

Have you tried opening or extracting it with 7-zip?

[Horst.Epp]

I guess the _enc part of the file name means it is encrypted.

[nsp]

As guessed by @Horst.Epp, the tar file is probably encoded. You can ask directly to huawei support if it is possible to decompress the file and if you can get the proprietary pgm. You can also ask if it is possible to access your router with an ssh console and get raw log files if not encoded.