Download challenges: Neuland CTF Repository

*Part 1: aynaq{o4f3
Part 2: ..--.- -.... ....- ..--.- .---- ..... ..--.- -. --- --... ..--.- ....- ..--.-
Part 3: M05DcllwNzFvbn0= *

We get three parts of the flag encrypted/encoded by different methods. The first part of the message appears to represent ** nland{**. The fact that

The flag is `nland{b4s3_64_15_NO7_4_3NCrYp71on}`

MD5: e10adc3949ba59abbe56e057f20f883e

SHA1: 5baa61e4c9b93f3f0682250b6cf8331b7ee68fd8

LM: 598DDCE2660D3193AAD3B435B51404EE

Flag format: nland{<MD5>_<SHA1>_<LM>} in all lowercase

The flag can be generated by brute forcing three different hashing algorithms. A hash is a digital fingerprint that uses a hash function to map data of any length to a shorter, fixed-length value. In IT security, these hashes are mostly one-way functions and offer collision resistance, making it easy to calculate a hash but almost impossible to conclude the original string. Therefore, an efficient way to decrypt the hashes is a dictionary attack, where frequently used words are hashed with the respective hashing algorithm and compared with the original. Tools like hashcat make this process easy. We download a dictionary like rockyou.txt and use it as input for hashcat. The command looks like the following:

```
hashcat.exe -a 0 -m 0 hash.txt rockyou.txt
hashcat.exe -a 0 -m 100 hash.txt rockyou.txt
hashcat.exe -a 0 -m 3000 hash.txt rockyou.txt
```

The hash.txt file contains the hash value to be decrypted. We use the parameter *-a* to determine the dictionary mode, *-m* stands for the hash algorithm.

The flag is `nland{123456_password_qwerty}`

*Can you read my message without the private key?*

```
c: 24795976732186127960014008753803478286219924961358994925564930277505139413283367757656447224830225064133651246343035441112407129772003927463166449052456907513
e: 65537
n: 67037366790941822378007197878613492487588187468048328737227273255156041659689092651657208107757810805499108569166854436320366276808520739379431210884782583791
```

The title already reveals that it is about the cryptographic method RSA. Since n only has 158 digits, we have a good chance of finding the two factors, q and p, needed to calculate the private key. FactorDB is an online collection of prime numbers which fortunately stores our fully factored n. The private key d can be calculated with `inverse(e) % (p-1) * (q-1)`

. With the private key, the ciphertext c can be decrypted with the equation `M = pow(C , d) % n`

.

*Python script:*

```
from Crypto.Util.number import *
p = 7796601204626807
q = 8598280844627430267706791405975187760390046230909096659417881790296619284204527797467017995321195814866230752519838250409205362581256112387913
n = 67037366790941822378007197878613492487588187468048328737227273255156041659689092651657208107757810805499108569166854436320366276808520739379431210884782583791
c = 24795976732186127960014008753803478286219924961358994925564930277505139413283367757656447224830225064133651246343035441112407129772003927463166449052456907513
e = 65537
d = inverse(e,(p-1)*(q-1))
m = pow(c,d,p*q)
print("Message: ", long_to_bytes(m))
```

The flag is `nland{ROll1n9_your_Own_r54}`

*Santa has a message for you.
(Flag format nland{<message>} in all lowercase)*

An LED-illuminated Christmas tree is provided to solve the task, which regularly changes its colors. After looking at it for a while, the following features become apparent:

- 6 different colors (green, yellow, blue, light blue, pink, red)
- The 6th color is displayed longer
- After 18 colors, the Christmas tree shuts down and starts again from the beginning

With this information, we can create the following pattern:

green | yellow | yellow | blue | green | yellow | yellow | blue |

red | blue | light blue | pink | red | blue | light blue | pink |

light blue | pink | green | red | light blue | pink | green | red |

A quick Google search shows that only a few cryptographic algorithms use colors as a form of representation. One of them is Hexahue, which uses the same colors.

Enter the color combination into an online decoder and get the word ho.

The flag is `nland{hoho}`