Git Is Good

1 minute to read

We are given a ZIP archive that contains a flag.txt file:

$ ls
flag.txt

$ cat flag.txt
CTFlearn{REDACTED}

But this is not the flag. Looking deeply in the folder, we find a .git directory, so we are into a Git repository (also, the chalenge name pointed this):

$ ls -a
.        ..        .git        flag.txt

We can use git log to show previous commits (which are like snapshots of the project along time):

$ git log
commit d10f77c4e766705ab36c7f31dc47b0c5056666bb (HEAD -> master)  
Author: LaScalaLuke <lascala.luke@gmail.com>
Date:   Sun Oct 30 14:33:18 2016 -0400

    Edited files

commit 195dd65b9f5130d5f8a435c5995159d4d760741b
Author: LaScalaLuke <lascala.luke@gmail.com>
Date:   Sun Oct 30 14:32:44 2016 -0400

    Edited files

commit 6e824db5ef3b0fa2eb2350f63a9f0fdd9cc7b0bf
Author: LaScalaLuke <lascala.luke@gmail.com>
Date:   Sun Oct 30 14:32:11 2016 -0400

    edited files

Using git diff we are able to show the differences between two commits (we must provide some of the first characters of the commit identifiers). This one is interesting:

$ git diff 6e824db5 195dd65b
diff --git a/flag.txt b/flag.txt  
index c5250d0..8684e68 100644
--- a/flag.txt
+++ b/flag.txt
@@ -1 +1 @@
-CTFlearn{REDACTED}
+CTFlearn{protect_your_git}

And there is the flag.