Rating:
# Just Letters
Misc
## Challenge
Hope you’ve learned the alphabet!
nc misc.2019.chall.actf.co 19600
Author: derekthesnake
https://esolangs.org/wiki/AlphaBeta
## Solution
It is an Esolang with instructions as alphabets.
When we connect to the server, we need to read a flag at memory zero.
Welcome to the AlphaBeta interpreter! The flag is at the start of memory. You get one line:
Let's refer to the C++ interpreter, this is because the provided page is not so detailed.
https://github.com/TryItOnline/alphabeta/blob/master/AB.cpp
I will copy out the relevant instructions which we need to print the flag
#### Instructions
// Set memory pointer to start, then put it
// into Reg3 to be printed out to stdout
if ( Program[Position] == "Y" ) { Register4[Mode] = 0 ;}
if ( Program[Position] == "G" ) { Register1 = Memory[Register4[0]] ;}
if ( Program[Position] == "C" ) { Register3 = Register1 ;}
if ( Program[Position] == "L" ) { cout << char(Register3) ;}
if ( Program[Position] == "S" ) { Register4[Mode] += 1 ;}
So we have YGCLS to print the first char
To print subsequent chars, we can repeat GCLS.
YGCLSGCLSGCLSGCLSGCLSGCLSGCLSGCLSGCLSGCLSGCLSGCLSGCLSGCLSGCLSGCLSGCLSGCLSGCLSGCLSGCLSGCLSGCLSGCLSGCLSGCLSGCLSGCLSGCLSGCLSGCLSGCLSGCLSGCLSGCLS
It works, but it ain't fun and it is a hacky solution.
$ nc misc.2019.chall.actf.co 19600
Welcome to the AlphaBeta interpreter! The flag is at the start of memory. You get one line:
> YGCLSGCLSGCLSGCLSGCLSGCLSGCLSGCLSGCLSGCLSGCLSGCLSGCLSGCLSGCLSGCLSGCLSGCLSGCLSGCLSGCLSGCLSGCLSGCLSGCLSGCLSGCLSGCLSGCLSGCLSGCLSGCLSGCLSGCLSGCLS
actf{esolangs_sure_are_fun!}
---
Alternatively, let's do a loop
// Set position pointer to start at index 1 of YCGLS = C
if ( Program[Position] == "Z" ) { Mode = ( Mode + 1 ) % 2 ;}
if ( Program[Position] == "Y" ) { Register4[Mode] = 0 ;}
if ( Program[Position] == "S" ) { Register4[Mode] += 1 ;}
if ( Program[Position] == "Z" ) { Mode = ( Mode + 1 ) % 2 ;}
// Loop until a null char is reached
if ( Program[Position] == "y" ) { Register2 = 0 ;}
if ( Program[Position] == "O" ) { if ( Register1 != Register2 ) NewPosition = Register4[1];}
We have the payloads...
Effectively, our code will loop and print each char, starting from memory zero, until a null byte is reached
Y # set memory pointer to zero
CGL # print the char at current memory [index 1]
S # increment to next memory pointer
ZYSZ # Loop: setup by making position pointer to index 1
yO # Loop: jump to position pointer of index 1 if current char is not a null byte.
Put to server
$ nc misc.2019.chall.actf.co 19600
Welcome to the AlphaBeta interpreter! The flag is at the start of memory. You get one line:
> YCGLSZYSZyO
actf{esolangs_sure_are_fun!}
## Flag
actf{esolangs_sure_are_fun!}
