> For the complete documentation index, see [llms.txt](https://alham-rizvi.gitbook.io/alhamrizvi/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://alham-rizvi.gitbook.io/alhamrizvi/picoctf-writeups/picoctf/web-exploitation/login.md).
# login
### Login PicoCTF Writeup
βAfter getting access to the web page, I only saw a login pagenothing else. So I started Gobuster and found that index.js was available. Then I opened it"
### The file contained the following obfuscated authentication logic:
```javascript
(async()=>{
await new Promise((e=>window.addEventListener("load",e))),
document.querySelector("form").addEventListener("submit",(e=>{
e.preventDefault();
const r={u:"input[name=username]",p:"input[name=password]"},
t={};
for(const e in r)
t[e]=btoa(document.querySelector(r[e]).value).replace(/=/g,"");
return "YWRtaW4"!==t.u
? alert("Incorrect Username")
: "cGljb0NURns1M3J2M3JfNTNydjNyXzUzcnYzcl81M3J2M3JfNTNydjNyfQ"!==t.p
? alert("Incorrect Password")
: void alert(`Correct Password! Your flag is ${atob(t.p)}.`)
}))
})();
```
***
### π Step 3 β Understanding the Logic
Key observations:
* The username and password are encoded using `btoa()` (Base64 encoding).
* Any `=` padding characters are removed using `.replace(/=/g,"")`.
* The encoded values are compared against hardcoded Base64 strings.
* If both values match, the password is decoded using `atob()` and displayed as the flag.
***
### Hardcoded Username (Base64)
```
YWRtaW4
```
Since Base64 requires proper padding, we add `=`:
```
YWRtaW4=
```
Decode it:
```bash
echo YWRtaW4= | base64 -d
```
Result:
```
admin
```
***
### Hardcoded Password (Base64)
```
cGljb0NURns1M3J2M3JfNTNydjNyXzUzcnYzcl81M3J2M3JfNTNydjNyfQ
```
Add padding:
```
cGljb0NURns1M3J2M3JfNTNydjNyXzUzcnYzcl81M3J2M3JfNTNydjNyfQ==
```
Decode it:
```bash
echo cGljb0NURns1M3J2M3JfNTNydjNyXzUzcnYzcl81M3J2M3JfNTNydjNyfQ== | base64 -d
```
Result:
```
picoCTF{53rv3r_53rv3r_53rv3r_53rv3r_53rv3r}
```
π₯ That is the flag.
***
### π― Final Credentials
* **Username:** `admin`
* **Password:** `picoCTF{53rv3r_53rv3r_53rv3r_53rv3r_53rv3r}`
Done
---
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