sreinhardt / tiny_machine

Rust based simple machine emulator challenge

Tiny Machine

Spenser Reinhardt [e-mail]

This challenge is a 4-bit CPU and memory emulator that can be run in a variety of difficulty levels.

• Easy
  • Debug binaries with named symbols
  • Operational error messages returned to user
  • Simplistic final state resolution (input buffer w/ flag -> output buf)
• Medium
  • Optimized and striped symbols
  • Simpler/removing error messages outside of resolution
  • Complex final state dependent on register/memory state
• Hard
  • Release+ optimized and striped symbols
  • Remove all error and debug output (forcing live debugging to determine state)
  • Additional/alternative instructions
  • Altering endianness

Reference material

Getting running

# Install rustup
sudo apt-get install build-essential software-properties-common -y
curl https://sh.rustup.rs -sSf | sh
rustup default nightly
# build and generate md5sum for dns and client binary
cd TinyMachine/
cargo build --release --features ""
#lvl 2 and 3
strip target/release/tiny_machine
md5sum ./target/release/tiny_machine
cp ./target/release/tiny_machine ~/tiny_machine-noflag
# Build executable
cargo build --release --features "real_flag"
cp ./target/release/tiny_machine ~/tiny_machine
# add user
useradd -m -U tinymachine -s /bin/false
# copy binary to directory
sudo cp ./target/release/tiny_machine /home/tinymachine/
sudo chown tinymachine:tinymachine /home/tinymachine/tiny_machine
sudo chmod 540 /home/tinymachine/tiny_machine

• Add systemd service /etc/systemd/system/tinymachine.service

[Unit]
Description=Executes TinyMachine CTF challenge
Wants=network.target
After=network.target

[Service]
User=tinymachine
Group=tinymachine
WorkingDirectory=~
ExecStart=/home/tinymachine/tiny_machine
Restart=always
RestartSec=10

[Install]
WantedBy=multi-user.target

• Start and enable

  sudo systemctl start tinymachine
  sudo systemctl enable tinymachine

300

Title: TinyMachine 1

Is this some sort of small emulator? Who left this thing on!? Sure are a lot of functions, wonder what kind of binary this is?

Try at: 300bcc4101e7955589bde7bdcd9cafe6.bsides.40bytectf.com:12346

Points: 300 Flag: 40ByteCTF{H0w_m4ny_0pc0des_t0_4_tinyM4chine?}

Client build command: cargo build --release --features "lvl1" 300bcc4101e7955589bde7bdcd9cafe6 Server build command: cargo build --release --features "lvl1 real_flag"

400

Title: TinyMachine 2

Look there's another one! This one doesn't seem so friendly... Maybe it has builtin help when running locally?

Try at: bsides.40bytectf.com:45678

Points: 400 Flag: 40ByteCTF{B3_0n3_w1th_th3_bs1d3s!} Client build command: cargo build --release --features "lvl2"; strip target/release/tiny_machine_2 Server build command: cargo build --release --features "lvl2 real_flag"; strip target/release/tiny_machine_2

500

Title: TinyMachine 3

Not again!! Something seems really DIFFerent

Try at: bsides.40bytectf.com:61830

Points: 500 Flag: 40ByteCTF{4r3nt_n3w_4rch1t3cur3s_fun?!} Client build command: cargo build --release --features "lvl3"; strip target/release/tiny_machine_3 Server build command: cargo build --release --features "lvl3 real_flag"; strip target/release/tiny_machine_3