# dyn (rev)
Rust Binary
## Dynamic Analysis
When we run this program, we get the following message:
```thread 'main' panicked at 'assertion failed: `(left == right)`  left: `"./dyn"`, right: `"actf{"`', main.rs:51:5note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace```
It looks like the program checks the command line arguments for the flag. (We see in Ghidra that it does check the last argument).
## In Ghidra
After a bit of reverse engineering, we see suspicious comparison at 0x8d87 to `'_ynourtsd_tet_eh2_bfiasl7cedbda7'`. Unfortunately that's not the right flag. We see a lot of moving single bytes around in memory in advance to that. This indicates that the flag is shuffled before comparison.
## Execute in gdb
Start the program with input `actf{abcdefghijklmnopqrstuvwxyz012345}`. This way we can reconstruct the permutation used by comparing the input position to the shuffled position.
Set a breakpoint to `core::slice::cmp::<impl core::cmp::PartialEq<[B]> for [A]>::eq`
The shuffled input is given in `rdx`. Use this to reconstruct the flag
## Unshuffle the flag```pythonorig     = 'abcdefghijklmnopqrstuvwxyz012345'shuffled = 'fehgbadcnmpojilkvuxwrqts3254zy10'expected = '_ynourtsd_tet_eh2_bfiasl7cedbda7'
print('actf{' + ''.join([expected[shuffled.find(x)] for x in orig]) + '}')```
Output:
	actf{rusty_on_the_details_2fbdb7ac7de}
