test(fuzz): add some libFuzzer targets

.gitignore

@@ -1 +1,4 @@
 /target
+/fuzz/corpus
+/fuzz/artifacts
+/fuzz/coverage

Cargo.toml

@@ -27,7 +27,7 @@ portable = ["aes"]
 std = []
 
 [workspace]
-members = ["xtask"]
+members = ["fuzz", "xtask"]
 
 [dev-dependencies]
 divan = "0.1.0"

fuzz/Cargo.toml

@@ -0,0 +1,27 @@
+[package]
+name = "fuzz"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]
+arbitrary = { version = "1.3.1", features = ["derive"] }
+libfuzzer-sys = "0.4.7"
+lockstitch = { path = ".." }
+
+[[bin]]
+name = "aead"
+path = "fuzz_targets/aead.rs"
+
+[[bin]]
+name = "hash"
+path = "fuzz_targets/hash.rs"
+
+[[bin]]
+name = "new"
+path = "fuzz_targets/new.rs"
+
+[package.metadata]
+cargo-fuzz = true
+
+[package.metadata.release]
+release = false

fuzz/fuzz_targets/aead.rs

@@ -0,0 +1,23 @@
+#![no_main]
+use arbitrary::Arbitrary;
+use libfuzzer_sys::fuzz_target;
+use lockstitch::{Protocol, TAG_LEN};
+
+#[derive(Debug, Arbitrary)]
+struct Input {
+    key: Vec<u8>,
+    nonce: Vec<u8>,
+    ad: Vec<u8>,
+    plaintext: Vec<u8>,
+}
+
+fuzz_target!(|input: Input| {
+    let mut aead = Protocol::new("lockstitch.fuzz.aead");
+    aead.mix(&input.key);
+    aead.mix(&input.nonce);
+    aead.mix(&input.ad);
+
+    let mut ciphertext = input.plaintext.clone();
+    ciphertext.extend_from_slice(&[0u8; TAG_LEN]);
+    aead.seal(&mut ciphertext);
+});

fuzz/fuzz_targets/hash.rs

@@ -0,0 +1,9 @@
+#![no_main]
+use libfuzzer_sys::fuzz_target;
+use lockstitch::Protocol;
+
+fuzz_target!(|data: &[u8]| {
+    let mut hash = Protocol::new("lockstitch.fuzz.hash");
+    hash.mix(data);
+    let _ = hash.derive_array::<32>();
+});

fuzz/fuzz_targets/new.rs

@@ -0,0 +1,11 @@
+#![no_main]
+use std::str;
+
+use libfuzzer_sys::fuzz_target;
+use lockstitch::Protocol;
+
+fuzz_target!(|data: &[u8]| {
+    if let Ok(utf8) = str::from_utf8(data) {
+        let _ = Protocol::new(utf8);
+    }
+});