Rating:
# ASIS Cyber Security Contest Finals 2014: CapLow
**Category:** Crypto
**Points:** 75
**Description:**
> Find the flag
> Our new agent encrypt a message like this, let us know what he wanted to say!
> `qvnju181mjziote0zge4mdk0odi4odfmnmnmnmi5zjm2yzy3mq==`
## Write-up
The `==` at the end of the provided ciphertext hints at base64 encoding… But it doesn’t decode to anything useful:
```bash
$ base64 --decode <<< 'qvnju181mjziote0zge4mdk0odi4odfmnmnmnmi5zjm2yzy3mq=='
���_5�<�״����4�ظ���i�h��9��<��
```
It’s a little uncommon for a base64-encoded string to be completely in lowercase like that. Let’s try uppercasing the first few characters:
```bash
$ base64 --decode <<< 'QVNJU181mjziote0zge4mdk0odi4odfmnmnmnmi5zjm2yzy3mq=='
ASIS_5�<�״����4�ظ���i�h��9��<��
```
Aha! That looks like the start of a flag. Let’s continue to uppercase characters one by one, reverting to lowercase only if the change makes the output look worse instead of better. Eventually we end up with `QVNJU181MjZiOTE0ZGE4MDk0ODI4ODFmNmNmNmI5ZjM2YzY3MQ==`:
```bash
$ base64 --decode <<< 'QVNJU181MjZiOTE0ZGE4MDk0ODI4ODFmNmNmNmI5ZjM2YzY3MQ=='
ASIS_526b914da809482881f6cf6b9f36c671
```
The flag is `ASIS_526b914da809482881f6cf6b9f36c671`.
## Other write-ups and resources
* <http://www.mrt-prodz.com/blog/view/2014/10/asis-ctf-finals-2014---caplow-75pts-writeup>
* <https://beagleharrier.wordpress.com/2014/10/13/asis-ctf-finals-2014caplow-writeup/>
