# 4FoldCipher

## Challenge Overview

![](https://3350216265-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2F8aLNxke1qPtepwlrf6VI%2Fuploads%2FeOarLjbfK2vIMBUouxWh%2F4fc%20overview.png?alt=media\&token=a5c757ed-b414-4431-9f54-33af737ea273)

> This crypto challange seems to be weird we look at it at first. The first thing I tried was concatenating all digits and removing `/` to get some binary text. Nothing happened.> ![4fc overview](https://hackmd.io/_uploads/r1NjaFC1gx.png)

### Given ciphertext

> 00 0001 000 101 010 1001 / 011010 1000 01 000 0000 / 0000 010 / 0000 010 000 110 / 00001 01111 11 11111 111 1000 1011 00001 1011 / 0000 010 / 1 1100 111 001 / 0001 000 110

## Steps

### 1. Binary → Morse Code

I noticed a possible Morse pattern where `0 = "."` and `1 = "-"`. The `/` symbols separate words, just like in Morse. After converting:

```
.. ...- ... -.- .-. -..- / .--.-. -... .- ... .... / .... .-. / .... .-. ... --. / ....- .---- -- ----- --- -... -.-- ....- -.-- / .... .-. / - --.. --- ..- / ...- ... --.
```

Using a Morse translator, this gives:

```
IVSKRX@BASHHRHRSG41M0OBY4YHRTZOUVSG
```

### 2. Decrypt the String

After many tries I managed to find the correct decryption method

<figure><img src="https://3350216265-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2F8aLNxke1qPtepwlrf6VI%2Fuploads%2FrS4GIuveevEOpEoDlINW%2Fimg1.png?alt=media&#x26;token=4612b374-1832-4ac1-a332-1926ce509e2a" alt=""><figcaption><p>reverse, atbash cipher</p></figcaption></figure>

&#x20;After many tries, I happened to find that by **Reversing** the string and applying the **Atbash Cipher**, the result becomes:

```
THEFLAGISB4BYL0N14THISISSHZY@CIPHER
```

## Final Flag

```
ictf{B4BYL0N14}
```

*made by k0d*
