2020.06.19 zh3r0

zh3r0 2020 Crypto - gboad maddy

CTF writeup: Gboard's alternate symbols get promoted to ciphertext in zh3r0 CTF 2020's gboad maddy. Map them to letters, apply ROT13 and infer the missing characters.

Event
zh3r0
Category
crypto
Topic
Crypto
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gboad maddy

Description

Plain text
You see this everyday if you use android.

?<³|⁰([{⁰|Pf¹&<=f{³&f"{P)

Author : Finch

In the challenge text above, P stands for %.

Hint

Plain text
len(flag)=28

Someone pointed out after the ctf

They we small accent symbols on gboard
HMMMMMMMMMMMMMMMMMMMMMM

Gboard keyboard with each long-press symbol shown above its corresponding letter key

Substituting the accent symbols for the letter, we can get

Plain text
"?<³|⁰([{⁰|Pf¹&<=f{³&f"{P)" 
mu3e0{to0eq_1gur_o3g_xoq}

rot13 of which produces

Plain text
zh3r0{gb0rd_1the_b3t_kbd}

Since the length of the flag was mentioned to be 28 characters, one has to fill out the possible missing characters :\

zh3r0{gb0rd_1s_the_b3st_kbd}