how to decode a base64 string into human readable characters on gnome terminal

Question

I want to decode a base64 encoded string to human readable data, and seeking right encoding for the same.

This is the command that i am trying

echo H4sICJVHi14AA2ZsYWcyLnR4dAAzsvLzdHb193O1Kkktyk3KzLNKLjMp4gIAtRX2oBcAAAA= | base64 -d

Abve outputs to some fuzzy non human readable data.

�G�^flag2.txt3���tv��s�*I-�M�̳J.3)����

Why many characters are missed? How can i read all the characters?

My gnome terminal is set to utf-8. Is there a better / wider encoding ? How do i set that?

Answer 1

Your Base64 encoded data is binary with mixed printable characters and mixed non-printable.

Lets see what it actually contain with hexdump:

<<<'H4sICJVHi14AA2ZsYWcyLnR4dAAzsvLzdHb193O1Kkktyk3KzLNKLjMp4gIAtRX2oBcAAAA=' base64 -d | hexdump -C
00000000  1f 8b 08 08 95 47 8b 5e  00 03 66 6c 61 67 32 2e  |.....G.^..flag2.|
00000010  74 78 74 00 33 b2 f2 f3  74 76 f5 f7 73 b5 2a 49  |txt.3...tv..s.*I|
00000020  2d ca 4d ca cc b3 4a 2e  33 29 e2 02 00 b5 15 f6  |-.M...J.3)......|
00000030  a0 17 00 00 00                                    |.....|
00000035

You can extract valid text with the strings command:

<<<'H4sICJVHi14AA2ZsYWcyLnR4dAAzsvLzdHb193O1Kkktyk3KzLNKLjMp4gIAtRX2oBcAAAA=' base64 -d | strings
flag2.txt
J.3)

Or save it to a bin file:

<<<'H4sICJVHi14AA2ZsYWcyLnR4dAAzsvLzdHb193O1Kkktyk3KzLNKLjMp4gIAtRX2oBcAAAA=' >file.bin base64 -d

Lets check what it is:

file file.bin 
file.bin: gzip compressed data, was "flag2.txt", last modified: Mon Apr  6 15:15:33 2020, from Unix, original size modulo 2^32 23

Since it is a gzip'ed data, lets gunzip it:

<file.bin gunzip
2:NICEONE:termbin:cv4r

Or doing it all in one-line:

<<<'H4sICJVHi14AA2ZsYWcyLnR4dAAzsvLzdHb193O1Kkktyk3KzLNKLjMp4gIAtRX2oBcAAAA=' base64 -d | gunzip
2:NICEONE:termbin:cv4r