tests: add fuzzing of secret key

fuzz/.gitignore

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+target
+corpus
+artifacts
+coverage

fuzz/Cargo.toml

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+[package]
+name = "tari_crypto-fuzz"
+version = "0.0.0"
+publish = false
+edition = "2018"
+
+[package.metadata]
+cargo-fuzz = true
+
+[dependencies]
+libfuzzer-sys = "0.4"
+
+[dependencies.tari_crypto]
+path = ".."
+
+# Prevent this from interfering with workspaces
+[workspace]
+members = ["."]
+
+[profile.release]
+debug = 1
+
+[[bin]]
+name = "keys"
+path = "fuzz_targets/keys.rs"
+test = false
+doc = false

fuzz/fuzz_targets/keys.rs

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+#![no_main]
+
+use libfuzzer_sys::fuzz_target;
+use tari_crypto::ristretto::RistrettoSecretKey;
+use tari_crypto::tari_utilities::ByteArray;
+
+fuzz_target!(|data: &[u8]| {
+
+    if data.len() < 32 {
+        return;
+    }
+    match RistrettoSecretKey::from_bytes(&data[0..32]) {
+        Ok(r) => {
+            // WIP: this should fail because we do a mod.
+            // We should implement from_bytes_canonical
+            assert_eq!(&r.to_vec(), &data[0..32]);
+        }
+        Err(e) => {
+            // This is unlikely to fail
+            todo!()
+        }
+    }
+
+});