climb_the_hill

climb the HILL

Author : Ragul N S

Flag: CTF{y0u_h4ve_cl1m6ed_the_h1ll_here_1s_y0ur_fl4g}

Problem Statement

>increasing altitude...
>z3{ryu0kdhhxwuph__oin4}{h5cn78y6a{obebxbh932j
>6 24 11
>12 13 10
>20 17 15
Flag format: CTF{...}

Proposed difficulty level: Easy

Solution

We can get a hint from the Description and the name of the Challenge that it is Hill Cipher.

The basic idea behind the Encryption Scheme is :

• Select alphabet containting N letters.

Letter	a	b	c	d	e	f	g	h	i	j	k	l	m	n	o	p	q	r	s	t	u	v	w	x	y	z	0	1	2	3	4	5	6	7	8	9	{	}	_
Number	0	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16	17	18	19	20	21	22	23	24	25	26	27	28	29	30	31	32	33	34	35	36	37	38

• Use an n x n invertible matrix (modulo N) (where N is the total number of letters in the alphabet) as the key.
• Multiply each block of n plaintext letter numbers mapped to the respective letters with it.

The Decryption Scheme is :

• Select the same alphabet containting N letters. (In this challenge we have to guess the alphabet map from the ciphertext)
• Find the inverse of the given key matrix.
• Use the inverted n x n matrix (modulo N) as the key.
• Multiply each block of n ciphertext letter numbers mapped to the respective letters with it.

The encrypt.py file has the code for converting the plaintext into the cipher text and the decrypt.py has the code for converting cipher text to plain text. The key and the values for plaintext and ciphertext are hardcoded in the program.