---
# System prepended metadata

title: Insomini'hack Teaser
tags: [reverse, Write-up]

---

| Name | Categories | Solve |
|------|------------|-------|
|frown | Reverse    |       |
|Unstringify| Reverse |     |



# frown

> How good is your Tetris? Connect, win, and reveal the flag!
> ssh user@frown.insomnihack.ch -p 24
> password: 1nsomn1h4cker

Connect ssh and let's play Tetris game 
![image](https://hackmd.io/_uploads/ryfohPFY6.png)

In the first look, I think we should write an auto-play script
But It takes a long time, while it's have many solves
So guessing time and a little lucky :D 
When played it have flag on the right side. Take it and xor with format flag **INS{**
```
a = 'NIT|~7rXd3isXo6c4Xau7jXau444cfz'
format = 'INS{'

for i in range(len(format)):
    print(ord(format[i]) ^ ord(a[i]), end = ' ')
```
![image](https://hackmd.io/_uploads/HkYnTDKta.png)
Result: 7 7 7 7 
Ohhhhhh Did you see that?? 
We just xor a with 7 and get flag =))) 
```
a = 'NIT|~7rXd3isXo6c4Xau7jXau444cfz'

for i in range(len(a)):
    print(chr(ord(a[i]) ^ 7), end = '')
```
> **Flag**: INS{y0u_c4nt_h1d3_fr0m_fr333da} 


# Unstringify

> Every CTF needs a high-standard strings challenge, find the "correct" flag ! Good luck !
> 
> If your machine is too old you can run the binary with QEMU:
> qemu-x86_64 -cpu max unstringify

Challenge give 1 elf file. Load it into IDA 

```
inv_s_box = (
    0x52, 0x09, 0x6A, 0xD5, 0x30, 0x36, 0xA5, 0x38, 0xBF, 0x40, 0xA3, 0x9E, 0x81, 0xF3, 0xD7, 0xFB,
    0x7C, 0xE3, 0x39, 0x82, 0x9B, 0x2F, 0xFF, 0x87, 0x34, 0x8E, 0x43, 0x44, 0xC4, 0xDE, 0xE9, 0xCB,
    0x54, 0x7B, 0x94, 0x32, 0xA6, 0xC2, 0x23, 0x3D, 0xEE, 0x4C, 0x95, 0x0B, 0x42, 0xFA, 0xC3, 0x4E,
    0x08, 0x2E, 0xA1, 0x66, 0x28, 0xD9, 0x24, 0xB2, 0x76, 0x5B, 0xA2, 0x49, 0x6D, 0x8B, 0xD1, 0x25,
    0x72, 0xF8, 0xF6, 0x64, 0x86, 0x68, 0x98, 0x16, 0xD4, 0xA4, 0x5C, 0xCC, 0x5D, 0x65, 0xB6, 0x92,
    0x6C, 0x70, 0x48, 0x50, 0xFD, 0xED, 0xB9, 0xDA, 0x5E, 0x15, 0x46, 0x57, 0xA7, 0x8D, 0x9D, 0x84,
    0x90, 0xD8, 0xAB, 0x00, 0x8C, 0xBC, 0xD3, 0x0A, 0xF7, 0xE4, 0x58, 0x05, 0xB8, 0xB3, 0x45, 0x06,
    0xD0, 0x2C, 0x1E, 0x8F, 0xCA, 0x3F, 0x0F, 0x02, 0xC1, 0xAF, 0xBD, 0x03, 0x01, 0x13, 0x8A, 0x6B,
    0x3A, 0x91, 0x11, 0x41, 0x4F, 0x67, 0xDC, 0xEA, 0x97, 0xF2, 0xCF, 0xCE, 0xF0, 0xB4, 0xE6, 0x73,
    0x96, 0xAC, 0x74, 0x22, 0xE7, 0xAD, 0x35, 0x85, 0xE2, 0xF9, 0x37, 0xE8, 0x1C, 0x75, 0xDF, 0x6E,
    0x47, 0xF1, 0x1A, 0x71, 0x1D, 0x29, 0xC5, 0x89, 0x6F, 0xB7, 0x62, 0x0E, 0xAA, 0x18, 0xBE, 0x1B,
    0xFC, 0x56, 0x3E, 0x4B, 0xC6, 0xD2, 0x79, 0x20, 0x9A, 0xDB, 0xC0, 0xFE, 0x78, 0xCD, 0x5A, 0xF4,
    0x1F, 0xDD, 0xA8, 0x33, 0x88, 0x07, 0xC7, 0x31, 0xB1, 0x12, 0x10, 0x59, 0x27, 0x80, 0xEC, 0x5F,
    0x60, 0x51, 0x7F, 0xA9, 0x19, 0xB5, 0x4A, 0x0D, 0x2D, 0xE5, 0x7A, 0x9F, 0x93, 0xC9, 0x9C, 0xEF,
    0xA0, 0xE0, 0x3B, 0x4D, 0xAE, 0x2A, 0xF5, 0xB0, 0xC8, 0xEB, 0xBB, 0x3C, 0x83, 0x53, 0x99, 0x61,
    0x17, 0x2B, 0x04, 0x7E, 0xBA, 0x77, 0xD6, 0x26, 0xE1, 0x69, 0x14, 0x63, 0x55, 0x21, 0x0C, 0x7D,
)

def inv_sub_bytes(s):
    for i in range(4):
        for j in range(4):
            s[i][j] = inv_s_box[s[i][j]]

def inv_shift_rows(s):
    s[0][1], s[1][1], s[2][1], s[3][1] = s[3][1], s[0][1], s[1][1], s[2][1]
    s[0][2], s[1][2], s[2][2], s[3][2] = s[2][2], s[3][2], s[0][2], s[1][2]
    s[0][3], s[1][3], s[2][3], s[3][3] = s[1][3], s[2][3], s[3][3], s[0][3]

def add_round_key(s, k):
    for i in range(4):
        for j in range(4):
            s[i][j] ^= k[i][j]

def xtime(x):
    return (((x << 1) ^ 0x1B) & 0xFF) if (x & 0x80) else (x << 1)

def mix_single_column(a):
    t = a[0] ^ a[1] ^ a[2] ^ a[3]
    u = a[0]
    a[0] ^= t ^ xtime(a[0] ^ a[1])
    a[1] ^= t ^ xtime(a[1] ^ a[2])
    a[2] ^= t ^ xtime(a[2] ^ a[3])
    a[3] ^= t ^ xtime(a[3] ^ u)

def mix_columns(s):
    for i in range(4):
        mix_single_column(s[i])

def inv_mix_columns(s):
    for i in range(4):
        u = xtime(xtime(s[i][0] ^ s[i][2]))
        v = xtime(xtime(s[i][1] ^ s[i][3]))
        s[i][0] ^= u
        s[i][1] ^= v
        s[i][2] ^= u
        s[i][3] ^= v

    mix_columns(s)

def bytes2matrix(text):
    return [list(text[i:i+4]) for i in range(0, len(text), 4)]

def matrix2bytes(matrix):
    return bytes(sum(matrix, []))

def xor_bytes(a, b):
    return bytes(i^j for i, j in zip(a, b))

key = [0x0, 0x3, 0x19, 0x5a, 0x5b, 0x0, 0x59, 0x2, 0x0, 0x3, 0x15, 0x1, 0x5c, 0x9, 0x1, 0x5e, 0x42, 0x53, 0xd, 0x16, 0x4d, 0x6, 0x42, 0xd, 0x27, 0x52, 0x42, 0x3a, 0x63, 0xb, 0x54, 0xf]
out = bytes.fromhex('51CC0FBEA0262A146D758930ECFD461C0FA3B4798B62C90668EA03BE2AC7F2C4')

for i in range(2):
    chunk = out[i*16:(i+1)*16]
    chunk = xor_bytes(chunk, key[i*16:(i+1)*16])
    m = bytes2matrix(chunk)
    inv_mix_columns(m)
    inv_sub_bytes(m)
    inv_shift_rows(m)
    print(matrix2bytes(m))
```
> **Flag**: INS{T45k_Sp0n$0r3d_By_G4l4h4d<3}

