Tags: rust crypto
Rating:
# SoulCrabber
## Description
Aliens heard of this cool newer language called Rust, and hoped the safety it offers could be used to improve their stream cipher.
```rust
use rand::{Rng,SeedableRng};
use rand::rngs::StdRng;
use std::fs;
use std::io::Write;
fn get_rng() -> StdRng {
let seed = 13371337;
return StdRng::seed_from_u64(seed);
}
fn rand_xor(input : String) -> String {
let mut rng = get_rng();
return input
.chars()
.into_iter()
.map(|c| format!("{:02x}", (c as u8 ^ rng.gen::<u8>())))
.collect::<Vec<String>>()
.join("");
}
fn main() -> std::io::Result<()> {
let flag = fs::read_to_string("flag.txt")?;
let xored = rand_xor(flag);
println!("{}", xored);
let mut file = fs::File::create("out.txt")?;
file.write(xored.as_bytes())?;
Ok(())
}
```
`1b591484db962f7782d1410afa4a388f7930067bcef6df546a57d9f873`
## Solution
Make the `flag.txt` binary by working with `Vec<u8>`:
```rust
use rand::{Rng,SeedableRng};
use rand::rngs::StdRng;
use std::fs;
use std::io::Write;
fn get_rng() -> StdRng {
let seed = 13371337;
return StdRng::seed_from_u64(seed);
}
fn rand_xor(input: Vec<u8>) -> String {
let mut rng = get_rng();
return input
.into_iter()
.map(|c| format!("{:02x}", (c as u8 ^ rng.gen::<u8>())))
.collect::<Vec<String>>()
.join("");
}
fn main() -> std::io::Result<()> {
let flag = fs::read("flag.txt")?;
let xored = rand_xor(flag);
println!("{}", xored);
let mut file = fs::File::create("out.txt")?;
file.write(xored.as_bytes())?;
Ok(())
}
```
Put the binary result in `flag.txt`:
```python
from binascii import unhexlify
open("flag.txt", "wb").write(unhexlify("1b591484db962f7782d1410afa4a388f7930067bcef6df546a57d9f873"))
```
Compile with `cargo`:
- `cargo new`
- Put code in `main.rs`
- Add deppendency in `Cargo.toml`: `rand = "*"`
- `cargo build`
- Move `flag.txt` where the build is and run executable
Get the flag:
```python
from binascii import unhexlify
unhexlify("434854427b6d656d3072795f733466335f6372797074305f6634316c7d")
```
