muddy

muddy is a literal string obfuscation library, designed to provide an easy way of avoiding simple static binary analysis tools such as strings or YARA rules. It functions by encrypting texts at build time, and embedding an in-place decrypter that is evaluated at runtime.

Usage & Examples

// examples/simple.rs
use muddy::muddy;

let non_obfuscated = "notsupersecret9001";
let obfuscated = muddy!("supersecret42");
println!("{}", non_obfuscated);
println!("{}", obfuscated);

Compile this example and grep the binary for obfuscated:

cargo b --example simple

strings ./target/debug/examples/simple | grep obfuscated
Only the second nonobfuscated line should appear.

muddy primarily provides the exported muddy!() and muddy_unchecked!(), macros, which each take a literal text as input, encrypt it at buildtime, and generate an in-place decrypter which is evaluated to the plaintext &'static str at runtime.

By default, these macros will encrypt literal strings with the chacha20poly1305 implementation and embed the key inside the binary.

Runtime-provided decryption

If the env argument is provided to the macro invocation, the deobfuscation key will not be embedded into the binary. Instead, it will be generated at buildtime and must be provided at runtime.

use muddy::muddy;

let obfuscated = muddy!(env, "supersecret42");
println!("{}", obfuscated);

Running cargo b will print out MUDDY='<SOME_KEY>' to stderr.

This env will then need to be set at runtime, otherwise the program will panic: MUDDY='<SOME_KEY>' cargo r

You may also set your own key identifiers: muddy!(env = "MY_KEY_NAME", "supersecret42")

muddy_unchecked!()

The difference between muddy!() and muddy_unchecked!() is that the muddy!() macro checks that the macro invocation is not evaluated multiple times. Opt for muddy_unchecked!() if you can uphold this guarantee.

use muddy::muddy_unchecked;

fn f() -> &'static str {
  muddy!(env, "supersecret1")
}

fn f2() -> &'static str {
  muddy_unchecked!(env, "supersecret42")
}

fn f3() -> &'static str {
  muddy_unchecked!(env, "supersecret9001")
}

for _ in 0..2 {
  println!("{}", f()); // <----- fine, since `muddy!()` provides checks against multiple evaluations
}

for _ in 0..2 {
  println!("{}", f2()); // <---- panics at the second evaluation
}

for _ in 0..2 {
  std::thread::spawn(|| {
    println!("{}", f3()); // <-  panics at the second evaluation
  });
}

Alternatively:

use muddy::muddy_unchecked;

// only evaluated once
let plaintext = muddy_unchecked!("supersecret1337");
for _ in 0..2 {
  println!("{}", plaintext); // <--- fine
}

for _ in 0..2 {
  std::thread::spawn(move || {
    println!("{}", plaintext); // <- also fine
  });
}

Note on obfuscation and encryption

This crate does not provide any form of real encryption. It only makes the task of understanding strings in your binary more difficult. Obfuscation is not security.

This crate also does not obfuscate any debug symbols you may have. Profile settings such as

# inside Cargo.toml

[profile]
strip = true
panic = "abort"
# ...

and more can be found in the cargo reference.

Macro expansion

To check what this macro expands to:

• install cargo expand
• run: cargo expand -p muddy --example simple

Unstable API

This crate is still very much a work-in-progress. Expect breaking changes between minor releases.

Migrating from previous versions

Previous versions of this crate provided obfuscation for static strings. This behavior may be achieved with the current API by using a once_cell::Lazy:

use once_cell::sync::Lazy;
use muddy::muddy_unchecked;

static MY_STRING: Lazy<&'static str> = Lazy::new(|| muddy_unchecked!("some text"));

Next steps:

• check proc macro testing suites

Disclaimer

This library is developed with the sole intention of providing a tool to challenge and educate cybersecurity professionals. It is not intended for any malicious or unlawful activities. The creators and contributors of this library do not endorse, encourage, or support the use of this tool for any illegal purposes.

Shoutouts

• thanks to @blastrock for his advice on muddy v0.3.0

Similar/related projects

• cryptify
• litcrypt
• include-crypt-bytes
• obfstr
• Interesting related article by vrls.ws

License

Dual-licensed under Apache 2.0 and MIT terms.